911F1

I just purchased a 1995 C2 and I'm starting to notice when I shift into 3rd I feel a slight thud feeling through the shift ****. Its not grinding and goes into gear ok. The car doesn't vibrate from it or do anything strange. It feels like something is tapping the gear right before it engages. Its worst during warm up and gets slightly better when everything is up to temp. Now here's the strangest part of all. When I shift it lightning quick no matter the RPM it goes right in with out the slight thud.
Could this be a synchro going bad? Thanks for input!

IainM

could be the wrong weight oil in the tranny. Or it could just be the way it is. Mine is quite knarly for the first few shifts 1-2-3 until things warm up. Once hot everything is silky smooth.

911F1

I just changed the tranny fluid today to Mobil 1 75w 90 Synthetic LS. Going for a nice drive tomorrow and warm it up. I'll report back. Thanks for you input.

pp000830

I have a theory, for the synchronizers to work the gear lubricant needs to provide just the proper amount of lubricity to protect the components but not so much as to diminish the friction in the synchronizer to the point where it does not consistently function. Since the friction rings in the syncros acts like clutches permanently in the transition state, temperature, speed, gear oil condition and degree of wear on the clutch rings in the syncro can all profoundly influence feel. Also as the friction rings in the synchros become worn the area of proper function becomes smaller and even slight variations in the above items can cause the feel to fall outside of what is acceptable to a driver.
I believe this is why transmissions can exhibit a notch feeling as a transmission ages.
Just one man's theory from my personal experiences over the years.
Andy

911F1

I changed the transmission fluid and drove around to get things warmed up. The shifting felt better but I still notice the notch going into third.

What is the single most mod people have done to smooth out shifting?
RS motor mounts, golden rod shift linkage, short shiifter, stiffer tranny mount etc... I know this might not be the solution. But I can try to rule out drivetrain slop. Thanks

mpruden

I have a similar symptom and have done new fluid, motor mounts, shift bushings (the 2 nylon ones and the 4 black rubber ones). While all were worth the relative little effort and did improve things, I still have the issue.

I plan on a re-gear in the next few years to freshen things up. Until then, I'll just wait an extra second when selecting gears, especially when cold. I'm not drag racing anyone in a 993 anyway.

Macca

Spot on. The OPs symptoms are a sign of failing syncho. Common on 2/3rd. I have just been through this exercise. Notchy for years but worked ok on the road bu after a season of track days much worse to the point with hot gear box on track wouldnt easily go into 3rd first try. I waited to long and needed $2200 USD of parts and a similar labour bill to rectify (replaced synchros on 1-2-3-4-5 plus cones 2/3 and guide 2/3). Synco rings inside material significantly worn and deposited onto dear collars. Luckily machine shop polished them off the chrome collars without need for new gear sets (very expensive). My advise - if you are noticing it now on the road then get it done before you take a chunk out of the brass synchro ring like I did getting p*ssed off with it on track and forcing it into gear!

heres some pics: the last two are the collars after being cleaned up!

911F1

I installed the RS mounts last weekend and changed the tranny fluid out again. I used Motul (MotylGear 75w 90). The car feels much better. When its all warmed up I don't even notice any syncro issues. When its cold its noticeable sightly. What 993 doesn't have a problem when cold though. I'm very happy with the results. I really can't say enough about the MotylGear fluid. I think it made a huge difference. I also changed out the brake fluid as well. Put in Motul 600 dot 5. Bled the brakes and clutch. Wow! The clutch pedal feels so smooth. I think this helped my gear changes as well. A little routine maintenance and tender loving care go pretty far. Thanks for everyone who chimed in.

Ed Hughes

Mine doesn't have a problem when cold....

chaoscreature

They way you describe the issue sounds a bit like shift linkage to me.
Have you pulled the skinny sheet metal belly pan off yet and made sure all the little shifter bits look proper and feel tight?

mpruden

Just an update to the OP experiencing the thud on a 2-3 shift. Try yet another gear lube before you tear into the gearbox.

Based on my research, my 130k mile car has classic minor synchro wear on 1-2 and 2-3. I've done 2 gear oil changes in the past year. As of yesterday, I think I found the winner with Mobilube PTX.

Seems every gearbox is a bit different. Try the popular fills (Delvac, Redline, etc) until you find the right match for your gearbox. I can tell you mine was horrendous when I bought it. The Redline NS blend improved things, but the Mobilube PTX feels great, even cold. I'd say it's taken 65% of the notchiness out of the gearbox when cold, and 90% when warm. Shifting in all gears is much smoother, especially the 2-3 shift.

It's expensive, so you may want to try the cheaper usual suspects first. ($36 a liter at my local dealership).

hkspwrsche

http://www.suncoastparts.com/product/00004320420L.html

interesting