EastEnd944

After replacing both cv axles on my 1988 944 NA, I have found myself breaking axle after axle, and every time it breaks it is the same axle on the same side. It is always the passenger side axle, and the joint that connects to the transmission. After breaking an axle I did a transmission swap (unrelated reasons) and still I continue to be able to drive the car for a short while, and then the CV joint breaks. What can cause this?

fwb42

Sounds like a bad transmission mount.

ddombrowski

What kind of axles are you using? I've heard bad things about some of the commonly available rebuild units.

Also, like the other poster said, check the trans mounts.

V2Rocket

+1 trans mount
the 85.5+ mount is a floppy banana-hammock which lets the trans sway over an inch side to side...
see here for illustrated "fix" instructions.

https://rennlist.com/forums/944-turb...ion-mount.html

Dougs951S

You can replace the mount without removing the trans. Just support it with a jack and undo it from the crossbrace. Then undo the two 17mm bolts holding the brace to the frame and lower the trans juuust enough to wiggle the brace free.

Van

And, how are your engine mounts?

EastEnd944

The transmission hanger mount is in good condition (at least from what I can tell), however I have been using non oem, cheaper axles, Although I wouldn't understand why one axle would consistently last but the other side would break? As for the engine mounts, I'm not quite sure what condition they are in, but how could they affect that one axle?

MAGK944

Van has a point. The engine through to the transaxle is one solid lump and if the engine mounts are toast, the trans will move with the engine. I guess as the engine torque is transmitted one way it could compress and misalign only one axle and cause it to prematurely fail. Long shot but if your engine mounts are worn, why not replace them and eliminate the possible cause of your axle problem. Or at least check them:

Van

The engine and transmission are a solid assembly, bolted together through the torque tube. The crankshaft (and driveshaft) rotation, when looking at the front of the car, is clockwise. This means the inertia of revving the engine and/or accelerating will twist the engine/transmission in such a fashion to lift the passenger side up a little bit if the mount is broken.

This movement may be causing the axle on one side to be compressed or extended beyond it's physical extents, and thus it breaks.

You know, I just had another thought... have the rear wheel bearings ever been changed? If so, look at the large nuts on the outside of the stub axle (under the wheel center cap). Do they look like they're in the same place on the threads? If not, I wonder if one side's stub axle has an inner wheel bearing race left on it... This would prevent the stub axle from sitting in the right place in the control arm, which would make the gap the axle fits in a little too small, causing the axle to bottom out in compression, which might lead to the same axle always braking in rapid succession.

85euro928

Hey guys,
Thanks for the input and links. The OP is my son and to be honest this problem has been driving us nuts.
We haven't changed the wheel bearings but we will check to see if they were and if someone left the race on the axle. If not, reading through the thread and the links I'm thinking we're gonna to change out the MM's to Meyle units, rehab the trans mount with urethane, and then fab a bar like 95ONE did to reduce the lateral transmission movement. Hopefully this will work.

V2Rocket

^^the urethane-fill trick almost entirely negates the need for the "trans brace" ala 95ONE...it really locks it in place.

85euro928

Yea but at this point the insurance company has flat bedded the car home four times in the last 3 months so I'm thinking belt and suspenders.

V2Rocket

bw993

I would highly recommend going with OEM CV axles and avoiding the cheap EMPI axles. I have solid engine mounts and a solid transmission mount on my 951 and never had a problem with axles, until I decide to swap out my original stock axles with EMPI axles as preventive maintenance. I broke both EMPI axles in less than 1 month. I went back to OEM axles and it's been 12 months of track events with no issues.

Just my experience.

85euro928

Yea I'm sorry we got rid of the original axles as the joints were just barely making a clicking noise and could have probably just been re-greased and flipped. The aftermarket axles have a warranty so the broken one will be returned and replaced, if any break again my plan is to rebuild the joint with OE.