OK, you can laugh at me all you want but I just want to make sure that what I'm doing is not bad for my tranny/brakes. I do a lot of driving especially on streets, and usually I go 40-60mph. when I hit a stop, I put it on neutral and just brake...sometimes I downshift, but most of the time I dont 'cause its a gas killer. My friend said that since, the WRX is AWD, that I should downshift when I'm slowing down. Is this true or can I just put it neutral and hit the brakes. Please help me!!:(

PS: my car is a 5spd

I don't think it matters either way. Sometimes I will downshift if I think I will be taking off again before I come to a stop. Otherwise I will just brake and take it out of gear as I come to a stop. I usually like to keep it in gear just in case I need to dodge some idiot. In the snow I would suggest not engine braking (or downshifting) just because you can lock the wheels up without ABS to help you and you can slide out of control if you don't know what you are doing.

I don't think you are neccessarily harming your tranny or brakes.. what I can tell you thought is that you are using up your brake pads more. By putting the car in neutral you are relying solely on the brakes to slow it down and eventually stop it, where as if you lift off and leave it in gear (not necessarily downshift) some of the braking is done by the engine. :)

engines and transmissions, are for accelerating

Brakes are for decelerating

PERIOD

the only reason to downshift is to be ready

with the correct gear, to begin accelerating again (usually after the apex)


engine braking, causes unneccesary engine and transmission wear

and when cornering, can also cause unwanted weight shfits

that may, cause you tires to exceed their friction circle and give you unwanted oversteer


Brake pads and rotors are cheap, compared to engines and transmission work

I don't know.. when I'm driving on the street I don't normally try to take the best line around corners and try to hit the apex..just a bit hard with all the traffic and stuff..

and also.. the manual says that is it advisable to help braking by doing some engine braking when driving.. presumably on the streets and not on some racetrack.. :)

With the crappy 8:1 compression ratio (with the turbo kicked in then it's 16:1 at a max boost of 1 atm) of the WRX you won't really get all that much engine braking anyway. I'm with the guy who said replace the brake pads instead of the engine. I always went from high gears to neutral when coasting to a stop in my old car, and the front pads were good after 70k miles. Engine braking is for guys in big diesel trucks coming off of mountains IMO :)

BTW check out www.howstuffworks.com and search for "manual transmission" for an explanation of one. It will really help you understand what is or isn't good for it.

Corn-Picker

<i>"With the crappy 8:1 compression ratio (with the turbo kicked in then it's 16:1 at a max boost of 1 atm)"</i>

How do you figure that? Compression is a set variable, you can't change it... you can only change the pressure at which the air within the cylinder is before the valve closes and the piston compress it.

8, I think he meant to say:
When the boost kicks in it creates power similar to 16:1..

8, you are right in saying the compression ratio can't change, but if you force twice as much air/fuel into the same volume (the cylinder when compressed is constant volume becasue the pistion is all the way up (TDC) and the valves are closed), the pressure will change, creating more power, because you are compressing a greater quanity of the mixture in that same volume, creating a larger explosion, exerting more force down on the piston for the power stroke.

That is why people with turbos, nitrous, or superchargers strive for lower compression. You can force more air/fuel mix into the cylinder, and much faster rate than N/A, so it creates more power than a car with less boost and higher compression. This is also why a good exhaust, and intake are important together (and not just one or the other). You need to be able to complete all 4 engine cycles as fast as possible to create the most power. If you have a bunch of boost and a small exhaust, you can't get the exhaust out as fast is the air is moving into the cylinder, which is bad, or the oppostite with a bad intake and a good exhaust like sucking through a straw. It is important to match the system.

Also: I think you had a typo 8:
How do you figure that? Compression is a set variable, you can't change it... you can only change the pressure at which the air within the cylinder is before the valve closes and the piston compress it.
You can't change the pressure of the air in the cylinder when a value is open, because it is not being compressed, pressure in the cylinder is escaping through the open valve. The piston is moving down or up while the valve is opening (int = piston down, exh = piston up), so you have a volume change and an air/fuel mixture change at the same time. Cylinder pressure will varry with these changes, but will increase like crazy once the valves close on the power stroke.

Try doing a compression check and watch the gauge through the engine cycles. It is pretty neat to see.

And back on topic now:
O, and don't worry about not downshifting. Not a big deal. I tend to do it a bit since I live in the Boston area (my brakes are 35K miles old, and look new). I am not going fast enough to really hurt the drivetrain, so I do lots of 3rd-2nd downs.

Paul G.

paultg - We'll have to get into a discussion elsewhere sometime. I have a feeling we both know what we're saying, and they're both true, but that we can't quite connect on the thoughts. :)

You're all saying that rolling in neutral isn't bad for your car? Then why do you need a flatbed to tow the darn thing?

bemani has a point

The center diff. will be ruined ifone set of wheels is rolling and the other set is not. Most companies won't tow your vehicle with all wheels on the ground, but I think it says in the owners manual towing behind say an RV with all wheels on the ground and car in neutral is O.K.

Paul G.

that's only for the automatic transmission (towing with all 4 wheels on ground). subaru says manual has to be towed on a flat bed.

With the USDM's smaller-than-the-rest-of-the-world's brake rotors I would tend to take it easy on the brakes during repeated hauling down from high speed. Smaller rotors heat soak quicker and a hot rotor is easier to warp, especially sitting at a stop light. Replacing rotors is costly and annoying.

With the WRX's relatively fragile transmission I would tend to take it easy on sharp downshifts and double-clutch whenever practical.

What this all translates to is a mellower approach to red lights and stop signs. If I am vying for position at a light I will do the late braking thing, otherwise I'll start slowing a little earlier and brake more gradually, thowing in a downshift or two.

--scott

Well, you have a good point then, I am not sure, but I know it is a center diff. issue (at least I think, more than a tranny issue), and I know the owners manual does not tell you downshifting when slowing down with a manual transmission is required.

If you get a chance, maybe call a dealer and ask. I would like to know.

Paul G.

Frank_M
I seem to remember reading "your" words of wisdom in a book titled Going Faster- Mastering The Art Of Race Driving-The Skip Barber Racing School by Carl Lopez

Are we required to paraphrase now? Maybe he actually learned somethign from reading a book. Try it sometime.:rolleyes:

actually never read that book..but heard a lot of good things about it


I've ben living by that rule for years..probably first read it in a Tech Q&A letter in R&T Mag

back in H.S. (which is a lot longer ago, than I like to think):(

CAUTION to anyone who read this:

"that's only for the automatic transmission (towing with all 4 wheels on ground). subaru says manual has to be towed on a flat bed."

This statement is WRONG and backwards. If you tow a vehicle with a A/T with any wheels on the ground you are causing the A/T parts to rotate without any means of lubrication because the A/T pump is not being powered by the engine. If you tow a vehicle with a M/T with all 4 wheels on the ground it is the same as coasting. Paultg is correct that towing a M/T with 2 wheels on the ground will over-work the center diff. viscous couple.

Went to the car and got my owners manual:
'99 Impreza Manual states the following:
-------------------------------------------------------------------------------
Towing with the front wheels raised off the ground (8-15):
Never tow a manual transmission AWD vehicle with the front wheels raised off the ground while the rear wheels are on the ground. This will cause the vehicle to spin away due to the operation or deterioration of the viscous coupling (aka: Center diff..).

CAUTION:
When transmission failure occurs, transport your vehicle on a flat bed truck.
-------------------------------------------------------------------------------
Towing with all wheels on the ground (page 8-16):
Never turn the ignition switch to the "LOCK" position while the vehicle is being towed because the steering wheel and the direction of the wheels will be locked.
Remember that the brake booster and the power steering do not function when the engine is not running. Because the engine is turned off, it will take greater effort to operate the brake pedal and the steering wheel.

CAUTION:
When transmission failure occurs, transport your vehicle on a flat bed truck.
For AWD vehicles or FWD vehicles with automatic transmission, the traveling speed must be limited to less than 20 MPH (30 km/h) and the traveling distance to be less than 31 miles (50 Km). For greater speeds and distances, transport your cehicle on a flat bed truck.
For Outback models, be sure to use fledxible cable for towing purpose and wrap the towing cable with cloth to prevent damage to the bumper.
--------------------------------------------------------------------------------
So, it does not say you can't tow an AWD/FWD automatic with the front wheels off the gound, which I found interesting. I think the auto tranny cars have electonic AWD, not mechanical viscous couplings.

So, in conclusion, it is O.K. to coast in neutral with a manual transmission AWD vehicle . You can also tow your manual transmission AWD vehicle with all four wheels on the ground, or all four wheels on a flat bed.

Paul G.

I found this towing thing kind of interesting, so I went to take a look at the 2002 Impreza/OBS manual I have.

Basically, the same thing Paul has written, now on pages 9-15 to 9-20, except this warning:

"Never tow AWD vehicles (both AT and MT) with the front wheels raised off the ground while the rear wheels are on the ground, or with the rear wheels raised off the ground while the front wheels are on the ground. This will cause the vehicle to spin away due to the operation or deterioration of the center differential". [9-15 - 9-16]

So, there you have it.

-Ray

LOL when all else fails RTFM*
Good job on the research guys.
PS if you are not 100% sure of your facts, say so or don't say anything, some people may take your bad info and ruin their car.
just my 44.297 Lira
















* Read The F___Ing Manual

I'm not sure if anyone's interested, but this is what I found in my Haynes manual(Subaru - Legacy 1990 thru 1998):
Towing:
Warning: Before towing models eqqipped with an automatic transaxle, the vehicle must be placed in front wheel drive mode. This is done by inserting a spare fuse into the FWD connector inside the engine compartment (see illustration). [I don't have a scanner] If this isn't done, damage to the transfer clutch may occur.
The vehicle can be towed with all four wheels on the ground, as long as speeds do not exceed 20 mph and the distance is not over six miles. (0-13)


Now I checked under my hood after reading that, and I actually paid attention to the little fuse box - next to the passenger strut tower - marked FWD. I looked for an explination in the manual, but I found nothing. Does anyone else know about the proper application of this disabling circuit?

Do the newer models still have this feature?


Regards,
Chuck.

If you're coasting on all four wheels, your diff is not working hard.
The [center] diff takes a difference in relative wheel speed [between front and back], and creates a reaction torque in proportion to that speed difference to bring the two pairs to the same speed. When the speeds are the same, then the reaction goes away, and the diff is benign.
If you tow with 2 wheels off the ground, the diff will be unable to bring the two pairs of wheels to the same speed (since two are rolling, and two are stopped), so instead the diff will just be heating up as it continually fails to match wheel speeds. That's the bad part.
4 wheels rolling at same speed = fine.
4 wheels rolling at vastly different speeds* for a long time = not fine.

I think I may be reiterating, but thats my summary.

Sopps

*Cornering and mild wheel slip do not count as "vastly different speeds" -- that's what the diff is for.