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Old 04-27-2001, 05:44 PM   #1
Jazz95
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Question Third gear grinding

Ever since I bought my subie, I've been experiencing a grind while downshfting into thrid gear. At first i thought it was me, but then I realized that it only happens when I'm doing more than 40 mph and put it in third. Is there a quick fix for this? Or will it cost me a new tranny?

Jazz95
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Old 04-27-2001, 06:22 PM   #2
T-WReX 2.5RS
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i think that is considered a factory defect. check with your subaru dealer.

tony.
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Old 04-27-2001, 06:39 PM   #3
pottsie350
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Sounds like the third gear synchro may be bad, does it grind more if you shift into third faster? or does it grind the same no matter what speed you shove it into third?
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Old 04-27-2001, 06:51 PM   #4
TimStevens
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A little rev-matching and double-clutching can do wonders for an aging tranny...

-tim
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Old 04-27-2001, 11:20 PM   #5
jhuang76
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Jazz95, following what TimStevens mentioned, do you double clutch when you downshift into 3rd. The fact that you mentioned this occurs more often at a higher speed seems (coupled with it occuring in only while downshifting) makes me believe (I apologize ahead of time if I'm wrong) that you may not be properly double clutching.

FYI, the proper way to minimize syncro damage (and grinding) while downshifting is:
1) disengage clutch and shift into neutral
2) engage clutch and rev the engine until your engine is a little above the correct "engaging" rpm of the lower gear.
3) disengage clutch and shift into lower gear. The shifter should almost feel like it's being "sucked" into gear. This is how a good shift should feel like.
4) if needed, rev your engine again to match speed and release clutch (if matched really well, I'd just dump the clutch and go).

Joe
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Old 04-28-2001, 06:53 AM   #6
neuromancer
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Jhuang,

This is probably a dumb question, but what is the correct enganging RPM for a gear. I tought myself standard, and always did it by feel, I guess.
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Old 04-28-2001, 03:18 PM   #7
pottsie350
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Might be time for a synchronizer. You aren't running synthetic gear lube by any chance? If you are you should run one of the gear lubes that is designed for synchronized trannys. Another possibility, since you say it does it over 40, is that there is not enough freeplay between some of the other gears, and the 3rd gear cog is being drug along with the next gear simply by friction, and the friction from the synchro isn't enough get the gear up /down to the correct speed.

If you aren't using synthetic and you want it fixed then it sounds like a rebuild is in order. But don't do it just on account of my advice. Let a tranny mechanic listen to it. Or practice double clutching and live with it
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Old 04-28-2001, 10:55 PM   #8
jhuang76
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The correct engaging RPM is really complicated. You could calculate it based on the gear ratios AND your current RPM BUT, in real life, if you're braking, that changes things, the engine is decelerating, again, screwing things up.

For example: 4th gear is 1.088:1 and 3rd gear is 1.448:1 (for a 00 RS).

If you're in 4th at 2000 RPM (engine), then your tranny output shaft is at roughly 1838 RPM (2000/1.088). Now if you tried to shift into 3rd, AND assuming your wheels/tranny output is at the exact same speed, then your engine must be at 2662 RPM (1838*1.448). In other words, you will need to rev your engine (and the layshaft) to about 2700 before you should engage 3rd gear, or else the syncros will do the work.

As you can see, the percent change will stay the same ( x * 1.448 / 1.088 ) where x is your 4th gear rpm. BUT, the higner the absolute value of the RPM, the larger the gap. IE, at 4000 RPM in 4th gear, you'll need to rev to 5324 or 1324 RPM more!

BUT, on the other hand, if you're braking really hard, the time it takes to double clutch, your wheels/tranny output also slowed down SO you don't need to rev as much to match perfectly! SO - 1324 jump is only needed if you're on a level ground AND not braking (ie. coasting to a stop light that just turned green).

You should as an experience racer for this, but from my limited race experience, this is the reason why I like to downshift really quickly (when I'm braking hard). I'm literally pumping and dumping my clutch as fast as possible whem I'm running down my gears. I've developed a decent rhythm (again, dependent on the gear I'm in - almost a semi stab up high like 4th and 5th to a full stab going from 3rd to 2nd).

Thanks to ColinL, here is a website with all the gear ratio http://home.kscable.com/lockes/colin/imp_gears.htm

Hope this helps. If anybody sees and error, please let me know.

Thanks,

Joe
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Old 04-28-2001, 11:21 PM   #9
jhuang76
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Jazz95, please think that I'm implying you're doing anything wrong by not double-clutching. In fact, on good syncros, you should never have to do it (heck, that's what syncros are designed to do)! The real fix is to have the tranny checked out by a professional. I'm just offering a quick fix if you will that'll at least stop the grinding (for now).

Joe
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Old 04-29-2001, 12:59 AM   #10
Jazz95
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Yes, it happens no matter how slow or fast I shift the gears. Double clutching huh? Well, I've been practicing, but I don't quite have it down yet. I start the process a little too late sometimes. But thanks for the info, I'll put it to good use.
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