From Devek site:

Early 928 transmissions often experience 1st/2nd synchro degradation and wear out after clutch action becomes partial, and clutchless shifts become the norm. The pain lodges in the transmission, but the fault is in the clutch master cylinder, which is hidden behind the brake vacuum booster. Cars over 100,000 miles have normally had clutch and slave cylinder changes, but no master cylinder changes because of the difficulty of accessing the master cylinder. The trick is pulling the vacuum booster, made easy (after brake master cylinder removal) by fully compressing the brake booster spring and trapping the plunger on the engine bay side, removing the four nuts and disconnecting brake pedal linkage in the driver's footwell. Then the clutch master cylinder is easy to change; don't forget to replace the fluid supply line between the cylinder and the brake reservoir, for it will be another 7-8 years before anyone removes the vacuum booster again!

Question:

If one were to change out the clutch master would this correct the sycro problem or just prevent it from getting worse? Currently first to second shifts are tricky as are downshifts from third to second and second to first. I would like to avoid a rebuild for a while if possible.

Mitch Johnson
83/928S US 54250 miles
Black 5 speed

 

My gut feel is that the #2 syncro problem will always get worse. Making sure that the clutch system is in proper working order is good but the only way to prevent wear in #2 syncro is not to shift into 2nd gear or double clutch the rest of your life (that won't happen, 2nd gear is too much fun!). I replaced my #2 synchro because I too had the noisy 2nd gear shift problem and did not adjust anything in the clutch system and the difference was remarkable. Shifting into 2nd is quiet as a church mouse. Good Luck!

 

I concur with Paul. The synchro is only going to get worse. You can alleviate the symptoms with good clutch, hydralics, and synchro soothing tranny fluid but the synchro will never be as good as it is today.

I'm running Redline 75-90NS in my 5spd and noticed an immediate improvement over the tired stock fluid. I've also bled the clutch really well and shortened the shifter. For now, it's sliding in/out of 2nd real well. You may find that fresh brake/clutch fluid and a good bleed will tune up your shifts. Your clutch disks could be worn and slipping. At 54k miles you shouldn't be having much trouble with synchros unless the tranny has been ham-fisted all it's life. Give these options a shot and let us know how it turns out.

 

Complete rebuild - $1450 Vertex.com

 

Correction- vertexauto.com

 

Difficult shifting can be caused by:

Clutch hydraulics. You can start by bleeding the system completely. One trick is to unbolt the slave cylinder - don't disconnect the line, but you may have to remove the clamp on the metal line - and push the operating rod firmly to the bottom of the cylinder. Replace and bleed normally.
If you do need to replace/rebuild the master cylinder, one way is to pull/replace the master cylinder guts from inside the car.

Clutch adjustment. The dual-plate clutch must be properly adjusted to fully release. This is done by adjusting the three centering adjustments that center the floating intermediate plate between the flywheel and the the pressure plate.

Many owners have reported improved shifting by changing to RedLine or Sweptco oil.

At the cost to rebuild the transmission, it pays to try everything else first.

 

I went through this whole deal with the Bastard...started with replacing the fluid and then checking the throw on the slave....ended up replacing the entire clutch pack (my car had sintered metal disks from Callaway) and all 5 syncros with the slider and dog teeth for 2nd gear.

I have Swepco in the box now, but I may switch to a synthetic.

Proper clutch alignment is critical....misalignment here makes the syncros wear very quickly. I think mine had 60,000 miles on it and 2nd was pretty shot. The freakin' sintered metal disks and improper adjustment did not help one bit.

I think shifting an early 928 is always going to be notchy...

BTW...I'm back on the stock clutch now with no slippage. The twin disk is very strong....torque wise.

 

I concur that the second and third syncro's wear quickly. The only solution is to replace the syncro's. I know where that can be done for under $1000. <img border="0" alt="[bigbye]" title="" src="graemlins/xyxwave.gif" />

 

And that would be...?

 

Interesting that the only problems I have are downshifting from 2nd into 1st. I cannot get the car back into 1st over 10mph. Double clutching doesn't help. Going into and down from all other gears works fine, so now I'm hoping that a rework of the clutch and hydraulics might solve my problem.

 

KB - Downshifting into 1st gear is usually not a good idea. It puts lots of stress on #1 syncro (unless you are double clutching) and when the clutch is engaged, lots of stress on the driveline. In my opinion 1st gear should only be used for acceleration from a dead stop, nothing else. My trans. protests loudly if I even think about selecting 1st gear from anything but a dead stop.

 

Agreed, 1st can usually be avoided except from a dead stop. That's what I do anyway. But, It seems like I should be able to get into 1st from 10mph. 20 or 30 I can understand, but 10???

 

Mitch

The answer to your question is no. A dragging clutch because of a release problem, master cylinder, slave, binding pilot bearing, cease pilot bearing, worn of broken clutch spring, will not discriminate and effect only one or two gears. In your case first and second. It will affect all of the gears. Yes, a clutch release problem or speed shifting will over work the synchronizer prematurely wearing them in turn causing hard grinding, up and down shifts. Just save for a rebuilt.

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

 

May replies and I thank you all, for the record let's see if I have it correct.

Clutch hydralics may or may not be at fault.

Clutch adjustment should help (assuming it is slipping, which I dont "feel", 3rd-5th no problems at all).

Redline 75W90NS appears to be a solid option.

A rebuild is in my future.

Ok I will check/adjust the clutch and chenge to the good oil. In the meantime I will go from 1st to 3rd and enjoy my shark for a while then rebuild.

Anyone know of a 6-speed for these beasts?

Steve C. Do I understand that the information provided on the Devek site on this topic is unreliable?

Thanks for the input everyone, you are all great!

 

Mitch, I have been researching te 6-sped option but have had no luck. My question was could the C5 transaxle of the current model Corvette be wedged into the 928? I was looking for exterior dimensions for the gearbox and such but could not find any. A NEW C5 6-peed is cheaper than having my 83 5-speed rebuilt. Let me know if you find out any info.