Early 911 Driveline Issue - Can Anyone Help?

[t6dpilot]

I have a new to me 1971 911 that is experiencing play in the driveline. I will explain it and see if anyone has any ideas.

This occurs more pronounced in the higher gears (3 - 5), but still is noticeable in the two lower gears. Basically, it feels that when you go from either a tension loaded driveline in decel or accel mode to the other (i.e. let off the gas while in the same gear after accelerating or accelerating after letting the car coast), there is a "clunk" for lack of a better word that comes from the differential area (?). The clutch is good, so it is not that.

I had a shop take a look at it for assessment, but did not dismantle the differential. They stated that when you held one wheel stationary, the other wheel could rotate freely about 70 degrees. When you rotated them in opposite directions, there was also play, but I cannot remember how much. They felt that it was what he called the "spider gear" in the differential and it was probably worn.

Does anyone have any experience with this and is this something I can disassemble, check out, and repair myself. I have pretty decent mechanical skills, but no manuals other than Wayne's 101 Projects. Any help/opinions would be appreciated.

BTW, I am going to take it to my early 911 specialist and have him look at it as well. Thanks!

[Kelly Bell]

CV joints?

[t6dpilot]

Kelly,

If I remember correctly your CV joints would be bad if you heard a whine upon acceleration or deceleration, correct? Once the driveline is under load, it works just great. It is when you transition the load from decel to accel or vice versa.

Anybody else have any ideas? I will eventually track it down - I just wanted some opinions to narrow my troubleshooting. Thanks.

[Grady Clay]

Scott,

I would get under the 911 and put a wrench on all 16 CV joint bolts. The clunk can be just before one comes loose and does serious damage.

That said; the usual culprit is a rubber center clutch disc having come partially apart. Is there any sign of the clutch not completely releasing and grinds into gear?

Spider gears and differential/ring gear issues are very rare. Is there anything unusual on your transmission drain plug magnet?

BTW, do you know if your transmission has the simplified differential update? This might be a good excuse to look.

Best,
Grady

[t6dpilot]

Grady,

Thanks for the ideas. I will try the CV bolts to see what is going on there. The clutch is seems fine with good engage and release points and does not grind going into any gears (except first if you rush it into gear from neutral when you are at a full stop). The PPI shop did a transmission fluid tranfusion and did not note any abnormalities with the drain plug. Finally, I do not know whether the transmission has the simplified differential update.

[RetroSC]

What about motor mounts?

[t6dpilot]

Motor mounts are old, but still tight. I tested them with a jack and the motor and chassis moves exactly at the same time. I do have new mounts, but have not installed them yet.

Any other ideas...?

[Early_S_Man]

Scott,

CV joints with worn ball bearings and races can exhibit what I call a mild 'Lurch-Clunk' behavior -- even if all of the bolts are tight. If you find all 16 CV bolts tight ... I suggest an easy test in 1st gear:

1. Get up to about 15 - 20 mph and hold your speed constant for about five seconds with light throttle.

2. Back off the throttle slightly ... just enough that vehicle's inertia is no longer being maintained by engine thrust. If, after a noticeable time delay [0.5 - 1.5 seconds] there is a perceptable lurch and then a mild clunk or thump, then lightly apply throttle again and see if there is another time delayed lurch-clunk?

If this test produces the precise results I stated, then I believe you CV joints and axles need to be removed for disassembly, cleaning, and evaluation. Sometimes a repack with a premium moly grease such as Valvoline SynPower Synthetic Grease with moly #985 or #986 is all the is needed, but if there is discoloration and pitting of the races and ball bearings as shown in the two articles, then there is no other choice -- replace the joint!

The following articles are a good reference for Lobro CV joints:

http://volksweb.relitech.com/cvjoints.htm

http://www.type2.com/bartnik/cvjoints.htm

CV joint disassembly

[t6dpilot]

Warren,

I do believe that we have hit the jackpot with your description! I think that is exactly what I am experiencing. In any gear, I need to remove or apply throttle very gingerly to avoid a "lurch/clunk" as you describe. It actually happens more in the higher gears, but I will try it in first tonight.

So, my first course of action is to disassemble the CV joints and axles. I will check out the article links that you sent and go from there. Sounds like a great project for the winter. Thanks for your help and I will let you know how it goes.

[Kelly Bell]

Good luck!