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Old 09-11-2008, 03:13 PM   #1
jhargis
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Default Feeler: Developing a reinforcement for the 5mt case



Here's my idea: Creating a steel reinforcement that ties into the bolts of the front bearing cradle/bulkhead to the bolts at the rear bearing cradle section of the transmission. The above image shows the 3 main weaknesses in the case that I am targeting. This would be in the form of a 1/4" steel plate reinforcement (many times thicker than what is in the picture) which would be on the passenger side of the transmission using 4130 steel stand-offs welded to the plate to space the plate just above the high section of the case webbing. Subaru added quite a bit of reinforcement to the "spine" of the case that runs along the top in the newer 8 bolt cases. I've added an additional plate reinforcement in that area just above the front bearing cradle. The idea here is to keep the 1st-5th section of the transmission "square" under heavy loads. While case distortion is probably not the primary cause of gear failure, it is often thought of as a possible contributing factor, especially in high horsepower applications. Reinforcing the case is a basically matter of having a better foundation for your gearbox.

I've also sourced better-than-factory hardware. The factory bolts do not carry standard identification markings on them, but given the factory torque specs and other characteristics, I'm about 99% sure that they are zinc-finish class 8.8 metric cap screws... This is actually pretty weak stuff. I'm looking at class 10.9 hardware to replace the less expensive and weaker factory bolts. This will result in more rigid hardware that is capable of using higher bolt torque specs to keep the case halves really well clamped together.

Question is: Before I go through the proper channels to become a vendor, would anybody be interested in this sort of thing? If I made a jig and built these myself, I could probably keep it in the $100-$150 range per unit for a selling price... Pehaps a good suppliment to a new or upgrade gearset, and judgeing by the amount of space available under the car, it *might* even be installable without transmission removal.

*This post edited 9/15/08 to reflect updates in product developement*
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Last edited by jhargis; 09-24-2008 at 03:31 PM.
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Old 09-11-2008, 03:22 PM   #2
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I'd give it a look. I'm not picturing the design in my head, but I guess that's why you're making it and not me At one time I had though about ratchet strapping that mutha together
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Old 09-11-2008, 04:16 PM   #3
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Because of the nature of the long input shaft that extends over the front differential, that input shaft is thought to flex quite a bit under load. To make matters worse, the case is fairly weak in comparison to a lot of other transmission designs. Any lack of rigidity or speration of the 2 halves of the front bearing cradle (the forward "bulkhead" of the case) could indeed allow the entire bearing to change it's orientation very very slightly to accomodate the flex in the input shaft. This same front bulkhead also holds the front pinion shaft and bearing... and a pinion geas tends to generate a lot of pressure and side-load on their bearing as it tries to push itself off of the ring gear on the diff. Strengthening this section of the transmission case seems like it could only help.

Here's my logic... I think there's not enough clamping force and enough stability in that front bulkhead:
A) Seems like quite a few instances of bearing failure (my factory transmission included) reported here on nasioc were decribed where the entire bearing with it's outer race, starts spinning in the case. With enough force holding that outer race in the case, ther is no where for the race to spin and roller bearings generally fail catastrophically jettisoning their components and shavings all over the inside of the transmission. In the 5mt, the whole outer race can often spin if the bearing fails, which *MAY* be a sign that there is insufficient support around the input shaft bearings.
B) Why would subaru put so much attention into an entirely different front bulkhead design using steel as the material of choice? This requires an extra step in casting, added steps in manufacturing and different tooling... all of which are very costly over the course of an entire manufacing run. An extra few hundred dollars per unit does not sound like much, but it's astronomical as a whole when you have to built 10,000 or 20,000+ units of something.

I work in manufacturing quality control, and in my experience with a few different companies, 2 things happen with near perfect certainty. 1) Most companies only reinforce existing designs incrementally as much as they have to in order to keep production cost effective (hence the stregnthening tweaks here and there we see in the 5mt over the years). In fact, if the product is unneccesarily strong, companies will often cost-cut by using less material (making the part weaker). 2) They do not generally put a heck of a lot of effort into completely redisgning a part or product (the 6mt) unless costs incurred from failure rates are predicted to exceed the cost of a complete redesign and related retooling. Subaru knew the 5mt would not handle the USDM STi's power and weight reliably enough to be cost effective on the warranty side of the deal, so they made an entirely new transmission. Subaru changed 5mt case design and added some reinforcement in the case castings in 1998 with a new 8 bolt bell-housing and added webbing in the case (IIRC), but I don't think they stregnthened it enough to really take care of case flex, I do think they added just enough to illeviate some of the warranty problems.

Last edited by jhargis; 09-16-2008 at 02:49 AM.
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Old 09-11-2008, 04:44 PM   #4
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Old VW's had problems with the crank case splitting behind I think it was cylinder #3 when they were made to make well over stock power. They'd weld additional webbing into the case to re-enforce and prevent cracking. I wonder if something similiar could be done here. The problem I see, is you run the risk of distorting the case if you weld or bolt anything to it.

Has anyone actually quantified how stiff the factory case is?

It's going to be interesting to see the 09 5MT case because they're adding 40hp. If they don't do something, you know there's going to be problems.
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Old 09-11-2008, 05:58 PM   #5
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The case isn't the issue, we've done the research and it's come down to a matter of material and design of the gears that is causing the failure.

-Dylan @ DS1
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Old 09-11-2008, 09:19 PM   #6
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Originally Posted by MasterKwan View Post
Old VW's had problems with the crank case splitting behind I think it was cylinder #3 when they were made to make well over stock power. They'd weld additional webbing into the case to re-enforce and prevent cracking. I wonder if something similiar could be done here. The problem I see, is you run the risk of distorting the case if you weld or bolt anything to it.

Has anyone actually quantified how stiff the factory case is?

It's going to be interesting to see the 09 5MT case because they're adding 40hp. If they don't do something, you know there's going to be problems.
Well, I was originally thinking it would be quite useful to weld in some extra webbing... Which I could do quite easily with my TIG... And since I have the weaker 4 bolt case from a 97 STi, I might still do that to mine when I replace the clutch in the next 10k miles or so,

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Originally Posted by DS1 Motorsports View Post
The case isn't the issue, we've done the research and it's come down to a matter of material and design of the gears that is causing the failure.

-Dylan @ DS1
http://forums.nasioc.com/forums/showthread.php?t=986710

No doubt, the gears could use some extra material. PPG, mfactory and some other aftermarket sets are just so beefy that they can probably have a much greater tolerance for seperation between the teeth. So most of the research I've found on here seems to point at shaft flex being the major culprit... But for there to be a huge amount of shaft deflection, the entire bearing would probably have to move just a tiny bit with the shaft. In other words, if the shaft is flexing enough and the bearing is not changing it's position relative to the centerline of the shaft at all, then it seems like bearing failure would probably be a more common occurance as that front input shaft bearing is not at all well suited to loads applied at an angle (just a standard open bearing with flat rollers and no integral inner race). This type of bearing would eat itself quickly if the journal machined into the input shaft where to align itself with a bowed and flexing input shaft (which is exactly what it would since it is part of the input shaft).

I'm also very curious to see exactly what part of the case was measured. My degree is in metrology so, this kind of thing really interests me. For example if they were measuring deflection of the case from outside of the case by looking for changes in width or outside dimensions, flex in the areas around the bearings might not even show up. Tweaking that front input shaft bearing by only a couple of degrees probably wouldn't show up as measurable distortion anywhere on the outside of the case, but a couple of degrees would probably be enough to accomodate A LOT of seperation between drive and driven gears, espcially 2nd and 3rd sitting closer to the middle of the shaft. Everybody seems to have wiped their hands and called the notion of case flex a myth except Subaru themselves, just look at the 6mt case man... why in the world would they go through so much trouble to make the 6mt case so much more substantial in webbing, and why would the front bulkhead section that houses the front bearings be so wildly stronger? I mean its a steel bulkhead the size of the 45lb. weighs you see at the gym compared to a dinky aluminum section that is split across it's face held together with 3 bolts... that's not even comparable, and not very cheap either.

Am I being completely ilogical in saying that if shaft flex in between 2 bearings is in issue then those bearings are probably not staying perfectly in place as well? I never said that case flex is the MAIN issue here. But maybe it's a contributing cause, and if a $100ish reinforcement could potentially get rid of a contributing cause, wouldn't it be worth it?

Dylan, I have much respect, and perhaps you could help me out on this one... Short of the thread I just posted is there any data or source that you know of that once and for all laid the case flex theory to rest? Maybe I'm beating a dead horse, but you never know if the horse is really dead unless there is obvious evidence or a bullet hole.

Last edited by jhargis; 09-12-2008 at 12:13 PM.
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Old 09-11-2008, 11:40 PM   #7
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I'm not saying the case doesn't flex, just saying that the gear deflection created isn't strong enough to flex it as far as one would think.

I agree with you on the fact if bearing deflection was as much as you say bearing failure would be a lot more common simply from the stress placed on them.

Don't give FHI credit for the 6mt, Porsche designed the 6mt not FHI, the design is based on the standard Porsche 6mt with minor changes to fit the Subaru line up. The front plate isn't steel, it's cast iron and as we know not exactly the world's best structural metal

I do appreciate the idea of bettering the 5mt simply out of weight savings and drive train loss but with the gears that are available now the number one failure I see now is transfer case gears.

-Dylan @ DS1
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Old 09-12-2008, 12:23 AM   #8
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Ahhhh... I remember reading that somewhere, I completely forgot Porsche is said to have a hand in the 6mt... Figures. Cast iron it is, you'd know that better than I would, so I'll trust you there. Nonetheless, a thick solid one-piece section of cast iron is still wildly stronger than a thinner longitudinally split aluminum section.

Funny you should mention transfer case gears... I was just looking at that and it wouldn't knock my socks off to learn that there is some case distortion involved there. If I remember my 5mt's insides correctly, that output shaft back there is cradled by 1 conical roller bearing which is in-turn seated in a not so beefy rear section of the transmission at the back... and nothing distorts the shape of things like a wedge. I was thinking that was a somewhat weak looking design. Not sure if gear separation is an issue there, but I have an idea for that too. But then again, distortion of the rear section could be non-existent and the problem is small gears. Any insight?

Here's where I'm coming from on this reinforcement idea: It's not going to save everybody's transmission from the immanent destruction that comes with just plain abusive driving... I don't think that case distortion is the main or even secondary failure factor. I think it's maybe the 3rd reason down the list behind 1) just plain small gear teeth on a high power high traction platform and 2) Really long input shaft that twists and flexes under the stresses incurred when gear teeth are trying to push apart (wedge shapes) and torsional stresses found in a long unsupported section of twisting input shaft.

However, I think that holding the 1st-5th gear section square and using better than factory hardware would help. It could be great for decent drivers with reasonable power levels that just want a little extra insurance, LGT/RA gear users that want that cherry on top, or hard-core PPG and M-Factory users that keep the 5mt for weight reduction and heck, why not reinforce the case that is holding your $2500-5000 gearset together? Plus I think it will be installable without removing the transmission... It gets a little tight toward the back where the trans tunnel tapers in, but I think there's enough room to get new bolts in and clear a torque wrench for proper torque spec.

I need to look at material, welding gas, welding wire costs and labor time per unit to build, but I think I could keep the price well worth it while keeping it worth my time. Would I as a consumer consider the reinforcement for $500? Hell no, but if I can keep it down around $100, I'd buy it as a WRX owner. I have the undoubtedly weaker 4 bolt case, so I'm definitely making one for my car either way... but I have an 8-bolt transmission laying around upon which I could prototype the part for 02-07 WRX transmissions. Maybe the LGT and '08+ WRX transmissions have the same case dimensions and bolt pattern in that spot too, but I'm not sure.

Last edited by jhargis; 09-12-2008 at 12:51 AM.
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Old 09-12-2008, 07:48 AM   #9
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Put me on the list for one; it can only help.
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Old 09-12-2008, 09:05 AM   #10
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Quote:
Originally Posted by jhargis View Post
Hell no, but if I can keep it down around $100, I'd buy it as a WRX owner.

You said the magic words... If there was some reinforcing that bolted up without dropping the trans, and was under $200 including some high grade bolts, it would be a no brainer!
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Old 09-12-2008, 10:31 AM   #11
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Awesome... good to hear some positive feedback.

Basically, if I can drum up enough support, I'll get a jig going, source some better-than-factory bolts, and go through the proper channels to become a nasioc vendor.

To be fair and give myself enough time to do this right, I'm kinda aiming to have the design down and start building them in the next 3 months.

*AGAIN: I want to be honest here: I don't want people to think this will single handedly save their transmission. This reinforcement is meant as a supplimental stregnthening device, not a do-all end-all upgrade*

The 5mt has some limiting design issues like fairly narrow spacing from input to output shaft (gear centerline spacing) that limits how large the gears can physically be. It also has a longitudinally split case that probably could use some improvement. The point of this reinforcement is simply to maximize the possibilities of the 5mt and provide some reinforcement where it can most likely be used, at the front and rear bearing cradle sections.


Anybody else have any interest?

Last edited by jhargis; 09-12-2008 at 10:47 AM.
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Old 09-12-2008, 12:24 PM   #12
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I was thinking that was a somewhat weak looking design. Not sure if gear separation is an issue there, but I have an idea for that too. But then again, distortion of the rear section could be non-existent and the problem is small gears. Any insight?

However, I think that holding the 1st-5th gear section square and using better than factory hardware would help. It could be great for decent drivers with reasonable power levels that just want a little extra insurance, LGT/RA gear users that want that cherry on top, or hard-core PPG and M-Factory users that keep the 5mt for weight reduction and heck, why not reinforce the case that is holding your $2500-5000 gearset together? Plus I think it will be installable without removing the transmission... It gets a little tight toward the back where the trans tunnel tapers in, but I think there's enough room to get new bolts in and clear a torque wrench for proper torque spec.

but if I can keep it down around $100, I'd buy it as a WRX owner.
The transfer case is a nightmare of a design aka big open cavities, small bearings, big loads

Keeping that center section square would probably have to involve using the bell housing bolts as a reference in order to prevent twist?

If you can get this done for $100 I'd be willing to pick one up for testing.

-Dylan
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Old 09-12-2008, 12:42 PM   #13
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I don't know what kind of flex the transmission might exhibit due to torsional stress, but for the center section I'd be mainly concerned with keeping that trasfer shaft with the concical bearing in place... If I had to venture a guess on the highest likelyhood of transfer case distortion, I'd reckon it's in that area. I was thinking about 1 of 2 options for the rear of the transfer case:

Option 1 - Send me the entire center and rear sections of the trans case and I can TIG weld in additional webbing and then send it back. TIG can be set for fairly shollow penetration without distorting or warping any parts of the case, and aluminum sheds heat very quickly, so I wouldn't be worried about distortion one bit. Additionally, all of the transfer case bolts thread into aluminum, which isn't ideal. Those bolt holes could be drilled out and either helicoiled or I could installed really tough steel thread inserts to allow for higher bolt torque specs. I bet you could easily add another 20ft/lb to those bolts without any damage or distortion to the case itself IF those bolts were threading into steel. More bolt torque = less sliding of the 2 mated surfaces from stresses in the case as well as thermal expansion (we all know aluminum is a thermal expansion monster).

Option2 - A Steel structure that ties into the bolts at the front of the center section and the rear of the center section which then wraps around the back side just under the ouput shaft with a large diameter bolt than can be tightened to press against and reinforce the back side of the case, or it could thread into a threaded aluminum bung welded to the rear section... Triangles make things stronger so if I shape the reinforcement just right, this would likely increase torsional rigidity and reduce bowing of the rear section where that conical transfer shaft bearing is... I can't imagine that a 1/4" thick span of cast aluminum can hold that bearing in place under heavy load... for god's sake, the average guy can readily snap a 1/8" piece of extruded aluminum flat bar by hand.

I suppose I could fab a cage that surrounds the entire transmission and ties all of the sections together... Our gearboxes are so far forward that there's tons of space to work with... But that's a lot more fab work and material than a simple reinforcement plate or rear reinforcement structure.

I have a great little Esab TIG machine in my garage (the "shop" as my frieds refer to it) and I can mill aluminum flat bar into contoured shapes on my end mill, so I'll probably be up for work if a customer would be willing to send me the case and wait for a few days worth of turnaround time to have addition webbing welded in.

My normal day job has been all kinds of busy this year, but it looks like business will be hitting a big slow down, so I'll probably have more free time on my hands to do this kinda stuff on the side. I figure that I may have the opportunity to be another resource to the subie community, get myself a vendor account and make a buck without shafting folks. As one guy with tools I already own, I can do small production run items like this for a very low initial start-up cost and I've got almost no overhead to worry about... everybody comes out happy.

Last edited by jhargis; 09-12-2008 at 01:10 PM.
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Old 09-12-2008, 01:26 PM   #14
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Tig welding the stock case sucks, it's the cheapest most porous piece of aluminum you'll ever see.

On top of that warping the case becomes a huge issue not because of the welder but because of the heat needed to weld crappy/dirty aluminum.

I think the cage thing might work but clearence in the tunnel might be an issue.

-Dylan @ DS1
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Old 09-12-2008, 02:00 PM   #15
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Well, you speak of a lot of wasted space inside. Maybe one could develop an internal cage, maybe something that doesn't need much more than a little drilling. The engineering would have to be rather precise and function for any variances there might be from case to case. However, you eliminate the space issue for the tunnel. This may also include some outer hardware as well to ensure good, sturdy mounting through the case and sealing.
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Old 09-12-2008, 02:48 PM   #16
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Tig welding the stock case sucks, it's the cheapest most porous piece of aluminum you'll ever see.
Hmmm. Strange. I've welded forged and extruded aluminum to cast aluminum before quite successfully with either TIG or MIG... The cliche: A really good TIG guy can put some aluminum down on a coke can without making holes. It would have to be really terrible stuff to not be able to set a good weld on it... Maybe MIG would be a better option then? I've found it to be less sensitive to surface prep and material conditions. If the quality of the casting is really so bad that a half decent welder can't make it work as you suggest, then I'd say case reinforcement is not just a novel idea, I'd say it's a neccesity. The design is questionable enough, and if the material is actually porous and weak, then the steel reinforcement becomes a hands down decision for me.

Back Road Runner: Good thinking, but while there is some space in there, that center transfer case has some internal webbing and blocked off areas that would make an internal structure pretty much impossible... However, I think I'd have at least an inch of clearance even around the tightest area at the very back of the transmission where my propsed transfer reinforcement would go... I'll have to get under my car after work and see what it looks like back there, but I think there's just enough space for me to work with.

Last edited by jhargis; 09-12-2008 at 02:55 PM.
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Old 09-12-2008, 03:07 PM   #17
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It's the worst aluminum I've ever had to weld
What I think makes it so bad is you can never really clean all the gear lube out of the pores in the aluminum.

The internal thing sounds interesting, kinda like a billet main cap for a sbc.

-Dylan
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Old 09-12-2008, 03:11 PM   #18
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good for you man keep working on it if you think it will help. This is just like what Buschur was trying or is trying to do, fix what is breaking instead of fixing the whole thing (waiting for a 3rd gear ).

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Old 09-12-2008, 03:33 PM   #19
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The cliche: A really good TIG guy can put some aluminum down on a coke can without making holes.
I have a friend who has cut a 24 pack of cans out so the cans can be laid out as a sheet, he then welded all the seems to make one big sheet. Cool thing is, it is what got him his current job at Vision Fabrication, that was almost 10 years ago.
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Old 09-12-2008, 03:37 PM   #20
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good for you man keep working on it if you think it will help. This is just like what Buschur was trying or is trying to do, fix what is breaking instead of fixing the whole thing (waiting for a 3rd gear ).
^^^ Well, that's sort of what I'm trying to accomplish here... Reinforcing the case is probably not going to keep gears from shattering after somebody repeatedly murders the clutch pedal shifting with a puck-type clutch and big turbo. It's sort of a secondary modification. For somebody to buy it, they'd have to be looking at the big picture as a case reinforcement is just a good way make the transmission's foundation a bit stronger... I'd classify this as a supporting mod of sorts.

Basically, it's probably a good inexpensive way to keep everything together and maybe even improve longevity of the transmission... The less the bearings move around, the better... And if this translates even a little bit into a stiffer envelope for the front input shaft bearing, and especially that heavily loaded pinion shaft, it may be able to marginally decrease gear tooth seperation... And when you're talking tolerances in the thousands of an inch or less, a little bit can go a long way. Especially for those who are investing a lot of $$$ into an aftermarket gearset, a case reinforcement might be the "cherry on top" to really complete the package.

Just learned I've got a 3 day weekend
So I'll probably start with a mock-up in the next couple of days. It's super convenient to have that spare trans laying around, so I can get the ground work laid right away.

Last edited by jhargis; 09-12-2008 at 03:51 PM.
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Old 09-12-2008, 03:43 PM   #21
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Quote:
Originally Posted by flstffxe View Post
I have a friend who has cut a 24 pack of cans out so the cans can be laid out as a sheet, he then welded all the seems to make one big sheet. Cool thing is, it is what got him his current job at Vision Fabrication, that was almost 10 years ago.
HAHA, please tell me he then wrote his resume in sharpie on the sheet that he fabbed... You couldn't possibly get better resume "paper" then that for a welder .
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Old 09-13-2008, 03:40 PM   #22
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Time to get down to some good ol' engineering.

The factory bolts do not have standard grade markings on them, so I'm not sure exactly what rating they carry. Torque specs are dead-on consistent with metric class 8.8 (equivalent to US grade 5 bolts). So I'll go with that.

I've sourced some good class 10.9 (metric equivalent to grade 8) bolts in the lengths that I'll need. I think this would be a good upgrade in fastener strength.

This would raise bolt torque values to:
8mm bolts: 22 ft./lbs (up from 18 ft./lb.)
10mm bolts: 45 ft./lbs (up from 29 ft./lb.)

Last edited by jhargis; 09-13-2008 at 04:04 PM.
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Old 09-13-2008, 04:11 PM   #23
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If you build it, they will come...

Of course if its in and around $100's
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Old 09-14-2008, 08:12 PM   #24
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Another interesting tidbit: There is an alarming amount of wiggle room in the bolt holes... I found that I can machine down a 7/16 grade 8 bolt just slightly to fit a bit more snugly than the factory 10mm bolts... This results in a bolt that is 1/25 (.04) of an inch larger in diameter... Doesn't sound like much, but the difference is quite visible when they are side by side. The modified 7/16 bolt would be about 10% wider than the factory hardware, AND there is a pretty good chance I could find these in these in grade 9 (aerospace fasteners).

Might not mean much of a difference at below 400whp over the class 10.9 bolts that would come with the reinforcement, but I could possibly add this as an option for a little more money if anybody is interested... Probably would add another $20 to the final price. But for those guys looking for big power through after-market gears, thicker hardware could be very good to keep everything tied together.

I never really thought about looking at bolt grades... but the class 8.8 factory bolts are just a tiny tiny bit stronger than US grade 5 (basically equivalent). While the 8.8's are wildly cheaper ($2-3 less per bolt than 10.9) and easier to source, for those of you that don't know bolt grades, class 8.8 bolts are not by any means a good choice for this type of application... Factory bolts would have a yield strength around 90,000psi where the class 10.9 bolts are up in the 130,000psi range, so that's a pretty big difference. Even with sources in large quantities, for Subaru to be able to save $10-15 per transmission, I can see why they went with the 8.8 cap screws. $10 is a lot of money when you build thousands of them.

Last edited by jhargis; 09-14-2008 at 10:57 PM.
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Old 09-15-2008, 10:00 AM   #25
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I'd be interested in a little reinforcement for the trans case. Good luck
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