Explod-y clutch or explod-y tranny?

[Pazuzu]

I have one or the other in my SC.

Driving at lunch. Stopped at light. Person tries to bump me to squeeze by, so I hop into gear a bit forcefully to move a foot or two. Let out the clutch fast under revs and got a good sized BANG (thought she hit me...). Turns out it was something in the drive train letting go.

I have no motion in any gear including reverse.
I just did the rear suspension, my first assumption was a CV joint let go because I messed with them, but it doesn't appear to be the case from my very cursory check on the side of the road.
Tranny in gear or not, clutch engaged or not, there's a "rocks in the washing machine" sound. It varies slightly in volume and "anger" with the clutch, but not enough to make me think there's much to that.
With the tranny in gear and the clutch out, that sounds increases in speed based on which gear I choose (so, 3rd is a faster sound than 1st).

Clutch was due for some work, it's about 75K on a replaced clutch. Based on the paperwork that came with the car, it was replaced with a SPRING CENTERED clutch (from the part number). I cannot fully assume that there really is a spring centered clutch in there just because of a shop receipt from 15 years ago.

I had zero sounds or warning in the three blocks before this happened. Car is a heavy use daily driver, if there was something building up over the past few weeks or days I would have noticed. No change in drivability before this, no sounds, no nothing.

I will pull the engine and tranny this week, but if there's any tests I can do before then, or if this is classic for one or the other exploding, then I would love some advice.

[rusnak]

I'm hoping for you that it's just a clutch failure. Or maybe something weird with the pressure plate. If it's shifting, and the car can be pushed in neutral but not in gear, then perhaps the tranny is ok. I hope so.

[gtc]

I once had a CV break free from it's axle, and it failed in a similar fashion. The splines on the end of the axle shaft had rusted out, and the whole CV assembly was spinning freely. Or rather, the axle was spinning freely within the CV. Everything was still "together" so I couldn't see anything wrong until I jacked up the car and noticed that one of the axles wasn't turning when I rotated the rear wheel.

[Jetjockey]

My first ideas would be to check the clutch fork and clutch fork shaft. I am not sure about the 915 but the G50 has a viewing window covered by a plastic plug high on the left side of tranny. The rubber disks had a history of self destructing but not the case if yours is really a spring centered disk..

[rusnak]

The problem is that is shifts, which would suggest that the clutch, TO fork, TO bearing, and pilot bearing are good. That leaves the main shaft and intermediate, which would be bad.

[Tigerrat]

Wow sorry to hear. Your diagnosis sounds thorough but heck if I know what to conclude from it. Hopefully it's just the clutch. You are getting your share of mechanicing in these days. Good luck. Ken

[landrover88]

I t might look like this

[Pazuzu]

Originally Posted by rusnak

I'm hoping for you that it's just a clutch failure.

Tell me about it...a blown CV is Hopeful Thought #1, a blown clutch is a distant Hopeful Thought #2, any tranny damage is Geeze My Life sucks Thought #3...

If it's shifting, and the car can be pushed in neutral but not in gear, then perhaps the tranny is ok.

I didn't even think to try moving it in gear, but it moved freely in neutral, and made no noises when pushed around the parking lot (which might negate the CV joint )

Originally Posted by gtc

I once had a CV break free from it's axle, and it failed in a similar fashion.

I'll have it in the air tonight and the axles will be the first things checked. I've had a CV blow catastrophically in my old off-roading truck, and it made a similar "marbles" sound afterwards, but I had a load on the engine when in gear. I cannot remember if the engine load changed much if at all when the tranny was in gear.

Originally Posted by Tigerrat

Wow sorry to hear. Your diagnosis sounds thorough but heck if I know what to conclude from it. Hopefully it's just the clutch. You are getting your share of mechanicing in these days. Good luck. Ken

Hey, can I borrow your engine yoke? Oh, wait...dammit!

[Tigerrat]

Well the yoke can get in the way if you are working on the clutch. If you have heat exchangers you can set it on a furniture dolly like I did. If you have headers of some sort you may have to improvise. Let's hope for CV's.

[Pazuzu]

Weeee!!!

CV bolts backed out. 5 were completely loose on the passenger side hub, the 6th was mangled when it finally let go. Doesn't seem to have hurt the hub flange.

Did some research here, found that it's not unheard of even among the elders here to have this happen. I have all new bolts and schorr washers on order (for both sides, all around). At least 4 of the bolts are fine enough right now, maybe 5, so I can get it buttoned back up for now. It'll let me limp to work and back for the next 2 days, after which I can properly fix things.

[Grady Clay]

Here is THE thread:
Reconstructing Constant Velocity (CV) Joints

While long, it is worth studying completely.

Glad it is this 'easy' fix.

Best,
Grady

[Pazuzu]

Yeah, that thread came up about 45 times in my search last night.

When I took everything apart the other weekend, there were no moon plates nor schorr (or any, for that matter) washers. I think between replicating that, probably not torquing to 40 ft-lbs instead of 30, having grease in there, yadda yadda yadda contributed to this.

There seems to be an ancient gasket on each flange, really stuck on there (another gasket fell off when I took them apart, so they were doubled up in there). I'll remove that as well. do a proper degreasing of all of the surfaces, and it should be fine after that.

It was fortunate that it was the hub end, so it didn't whip around and damage anything, there's some real horror pictures on here of loose axles tearing hell out of stuff.

[Pazuzu]

Oh, and before you ask Grady, my axles have the heavier machined plate attached to the boots, not the thin tin/sheet metal covers. I don't think I need the moon plates in this case, I got the impression that they were to distribute the force on the covers so they don't warp.

[Grady Clay]

Mike,

The purpose of the ‘moon plates’ was to have a surface of intermediate hardness between the soft mild steel of the tin boot cover and the extremely hard Schnorr washer teeth.
The Schnorr washer teeth even make an impression in the ‘moon plates’.
The pressures are so great when torque to spec (33 ft-lbs) that the bolt head or Schnorr washer actually causes ‘plastic flow’ of the mild steel under the head or washer.

No one has posted (measured) hardness of the thick boot covers you have.
My ‘scratch test’ indicates that they too are mild steel.
If it were my 911, I would add the ‘moon’ washers, new Schnorr washers and new class 12.9 M8 bolts of the appropriate length (1½ threads through the flange).
(Do not use single flat washers. The purpose of the 2-hole ‘moon plate’ is one bolt acts as an ‘anti-spin’ locking device for the other.)

These type 923 100 mm CV joints with M8 bolts seem to be adequate for the 2-liter type 923 ’76 912E (which they were designed for).
With a 3-liter 911, they seem to come loose too often for my taste.
I think the small CV joints and lack of safety hardware was the result of the ‘bean counters’ overruling the engineers.

In your situation, I suspect the double gasket preventing proper metal-to-metal contact between the CV joint and the stub axle flange was the (proximate cause) culprit.

For safety sake, I recommend you re-do all four CV joints.

Here is a good solution for getting the CV joint on the flange without contaminating the surfaces with grease.

Best,
Grady