RSAErick

I knew that there was SOME grinding when power-shifting (shifting quickly) from 2nd to 3rd at near red-line, but apparently the "spectators" at yesterday's track event were horrified by the sound. <img border="0" title="" alt="[Eek!]" src="eek.gif" />

I slowed down my shifting, which prevented the grinding. Obviously this is an acceptable solution to the problem, but now I'm concerned.

Am I about to lose my transmission? Is this an indication that the syncros are shot?

Out of curiosity, how many miles/km have others got out of their transmissions before a rebuild was necessary? What were the indications?

Thanks.
Erick

Jeff Curtis

Two things here, the viscosity of the gear lube you're using plays a part, and the possibility you have a LWF is an issue as well.

You see, between shifts, especially if you have a LWF, the internals in the transmission tend to slow down rapidly, due to the lack of rotational mass, understand how the viscosity and type of lube you're using can add to the overall picture.

While a gear lube change may NOT be in order...as I don't believe there's a valid "thinnner" solution that would assist in curing this issue, a LWF will always cause this type of "knick" when engaging say third from second and so forth...usually on the upshift, although I notice issues when I want to downshift from fifth to third. <img border="0" title="" alt="[Eek!]" src="eek.gif" />

Of course, the other possibility is internal parts wear, which would normally cause this type of issue...live with it -or- invest the "BIG bucks". <img border="0" title="" alt="[Wink]" src="wink.gif" />

Dave R.

Jeff,
The flywheel is on the motor side of the clutch, not the transmission side, right? If that's true, then wouldn't the flywheel have zero effect on how quickly the transmission spins down while the clutch is disengaged?

Rich W

Erick,

My transmission refused to go into 2nd gear a little over a year after I bought the car. Bad synchro. Don't know how it happened, but I stopped any semblance of "power shifting" after that.

Recently replaced the 2/3, 3/4 synchros with steel racing synchros. World of difference.

My advice: stop "power shifting" and let the synchros do their work. Otherwise, you'll be looking at a rather expensive repair.

RSAErick

Okay, I'm quiting the power-shifting cold turkey.

But now Rich, you've got me curious about the steel syncros... what is the "world of difference" that you refer to? And how much would it cost to upgrade to the steel syncros, and what is the downside (besides cost)?

Thanks.
Erick

Jeff Curtis

Dave, to answer your question, that would be a YES.

BUT, the engine slows rapidly, causing the dreaded stalling some of us experience (me?? ...no more!) and there is some assumed drag on the whole drivetrain.

SO, you are accurate and my "theory" may be a little "off kilter" but I thought I'd give it a whirr!

Truthfully, neither the 915 or G-50 were designed for any type of "spirited" shifting...it's just not supposed to happen.

It seemed I have more trouble with 3rd once I installed my LWF.

Dave R.

Jeff,
OK.
Isn't this a great excuse to rebuild your G50 and see what's inside? After all, you've already done the body & engine, why stop now? <img border="0" title="" alt="[Wink]" src="wink.gif" />

<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />
-Dave
'90 C2

Jeff Curtis

Sure is a good excuse, but I'm waiting for "grindage" first...and don't want to see THAT anytime soon!! <img border="0" title="" alt="[Eek!]" src="eek.gif" />

Bill Gregory

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"><strong>BUT, the engine slows rapidly, causing the dreaded stalling some of us experience (me?? ...no more!) </strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Jeff,

Did you complete the modification to the idle stabilizer? Sounds like you did and it works? Same procedure as posted on the 993 board? Or did the Cyntex chip fix it? Gee, full of questions this morning....

Kevin

Erick

On my RSA there was a update on the '93s with the shift rod tension adjuster. It was updated to a rolling ball mount versus a ecentric stud. When your have your car shut off, is it tough to get into reverse? Try to adjust the shift rod. Do you have access to the manuals? Email me if you don't. It is also common to bend the shift forks from heavy handed shifting.

Jim Michaels

My understanding is that 911s don't like to be "power" or speed shifted. If the slightest hesitation in neutral going up from 2nd to 3rd cures the grind, then this may not be abnormal; at least from my limited experience. But if you have to hesitate in neutral for a full second to prevent grinding, something probably needs attending to. If it's just DE, you don't need to be jamming the gear lever up and down anyway; or be near redline for that matter. Be just a little gentle and save your car a lot.

tonytaylor

The quality of the shift from 2nd to 3rd deteriated after I fitted a LWF and has been getting worse of late to the extent that at the last trackday there was sometimes no gears in the box at all on 2nd to 3rd and problems shifting down 3rd to 2nd were occuring.
I have had the transmission oil changed and the clutch bled (apparantly), and so far road use shows a big improvement, but I won`t know if the problem has been resolved or a rebuild will be needed soon until a few track miles have been done.
Changing fluids frequently appears to be cheaper than a tranny rebuild !

DJF1

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by tonytaylor:
<strong>The quality of the shift from 2nd to 3rd deteriated after I fitted a LWF and has been getting worse of late to the extent that at the last trackday there was sometimes no gears in the box at all on 2nd to 3rd and problems shifting down 3rd to 2nd were occuring.
I have had the transmission oil changed and the clutch bled (apparantly), and so far road use shows a big improvement, but I won`t know if the problem has been resolved or a rebuild will be needed soon until a few track miles have been done.
Changing fluids frequently appears to be cheaper than a tranny rebuild !</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">That is very interesting! You are the first one describing a puzzling problem I have too... On my last race I was facing problems with the box getting very mussy and after a few laps I temporarily would loose all gears! After a cool down drive back to the pits as I would pull in the box would work normally again. I took off all the underside trays and cooling helped a bit but still there was a problem. No problems also with worn linkages or gear oil as this was fresh I might add...I called my mechanic and he said that he does not think its a box problem, but he will investigate the clutch and slave cylinder.

If you find anything new please post it.

Thanks again! <img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />

tonytaylor

Danny J,

I thought the problem I was having was temperature related as it worsened throughout the day and throughout individual lapping sessions

J richard

You cant force a shift in a factory 911 box and expect it to last long, 915 or G50. The little nicks you get on upshift will just get bigger and bigger as the damage gets worse. I found this out the hard way on one of my early cars. On the street the answer is slow down and don't force it, On the track I tend to use a modified double clutch on the upshift. Just enough of a release of the clutch as you slide through neutral to match the gearset prior to moving the lever into the next gear. It sounds more dangerous than it is and once you get it down as habbit you can complete the shift faster than ramming it in gear, but it slides in like butter. I've always refered to it as "power shifting". Basically it's the reverse of your heal toe downshift double clutch, but since you are already at revs you don't need the throttle blip, just modulate the pedal. I have also found that the gear oil viscosity does affect the ability of the syncros to do their job. Seems almost like they loose the "stickyness" of the syncro to the cone of the gearset and the gear passes straight through to the next one, or not at all. The factory had all sorts of transmission oil coolers/pumps on their racecars for this, obviously they needed it. Running Swepco has helped some of my cars, others didn't make any difference.