OK...now what? Spent $, still clunks before load

[bigchillcar]

Here's the deal...I've been trying to run down a concern for months and months. It's a 'clunk' and let me descibe it:

If I tap or blip (quick tap) the throttle, I feel what I interpret to be 'play' before loading takes place. Letting off of the throttle and then tapping it again and it clunks just before it loads. It can do it in any gear. It reminds me of slop I've felt in worn driveshaft/u-joint combos in old Jeep CJ's. Maybe I'm unrealistic...if you hit the gas in your car, does it load immediately and 'go' without this travel play the instant before load?

What I have done:
I found wear and torn boots in my old cv's, so I replaced both rear axles with bolt-in Lobros. I still have this problem, although I feel the drivetrain has improved. I've checked the motor and tranny mounts for tightness...they are, although I don't know how old they are. Could they look basically ok, but cause this problem?

New guesses: Could it be the clutch and or flywheel? I've heard people talk about 'clutch shudder', but I'm not sure we're describing the same thing. Could it be worn differential (R&P)? Could it be the engine to tranny connection bolts? I haven't checked to see if they're loose, so I guess I could look up proper torque and check? I'm so close to the problem now that maybe I can't see the forest for the trees. Rant over. HELP!
Ryan

[oldE]

Ryan,
I would re-check the motor and transmission mounts. Can you see any signs of movement anywhere when you're under the car? How about movement felt through the shifter? Failing that, check your rear suspension for play in tha swing-arm bushings, torsion bar end bushings and all other mountings and adjustments. Problems there might also be indicated through unusal tire wear.
Last, have you changed the transmission oil recently? If so, were there any nasty bits in evidence on the plug? With the car in gear and one wheel blocked to keep it from turning, rotate the other wheel back and forth to feel how much play there is in the differential and the pinion
Good luck.
Les

[bigchillcar]

oldE,
No, I can't seem to find anything loose that could be moving while underneath. I can sort of feel this through the gear shift, though if I hold the shifter while blipping throttle. You could be right - the mounts may look and seem fine, trouble is I had a friend observe while I throttled the engine up to speed and he said the engine didn't seem to move.

These various bushings probably could stand a change. But since it only does it while not under load, I don't know...

I haven't changed the tranny fluid in about a year. Checked the level a few weeeks ago and it was full. It's a daily driver for 10-12k miles per year.

I haven't tried blocking a single wheel, but putting it into 4th gear, with both wheels off of the ground, it has and still does seem like more play than should be there, even with the new axles. I've heard you should have some, but I'm not sure how much is toom much in this case.
Ryan

[bigchillcar]

Anyone ever had to actually replace their worn differential in a 915? What was it doing? Was it fine under load, but buck a little until loaded? I really need help here...there really are few knowledgable people in my state.
Ryan

[Thomas Owen]

You may want to give one of the tranny rebuilders a call (John Walker, Gary Fairbanks) because it sounds to me like something internal. Maybe they can give you a test or two to perform.
Good luck,

[bigchillcar]

Thomas,
Yes, I'm starting to think you're right. It would probably be much easier to try and describe over the phone. I had at least thought of maybe pm'ing John Walker, he's been helpful in the past.
Ryan

[tiorio]

Sounds real familiar.

Broken clutch spring or destroyed rubber center on clutch disc depending on what your car has. Yes you have to drop the motor to check it out but it easily eliminates another possible problem from the list!

Good luck!

[bigchillcar]

bump. any new ideas?

[Dan Owens]

Ryan,

When you replaced the rear axle boots did you rebuild the axles or put in new ones?

[bigchillcar]

Todd,
Did you have these symptoms, then? Does the clutch spring assist in maintaining engaging the clutch? I'll pull my manuals. I keep reading about 'clutch shudder' in past threads, but can't decide if it's what I've got.
Ryan

[bigchillcar]

Dan,
Brand new bolt-in replacement axles...it wasn't that much more to pay and Pelican's price seemed to have dropped quite a bit on this item. I re-checked their bolts last night...fine and torqued to 34 ft/lbs. as m8's should. I can't quit thinking differential now...I would think worn ring and pinion gears would have slack until under load.
Ryan

[Eugene at Pelican Parts]

I would be concerned about my differential too. Do you hear any droning while you drive? You should pull it out and examine the ring gear. Careful... it's heavy. Do you have limited slip (actually, were they even offered back then)? Unfortunately the pinion gear is machined onto the output shaft. If you see wear, a good option may be to swap for a rebuilt 915.

[bigchillcar]

Wong,
Good point, I don't think I really do hear droning and you'd expect to hear it, wouldn't you? I've got to run out for a minute...I'll listen again for that specifically.
Ryan

[bigchillcar]

Getting delayed, will have to listen for it later in the day...
Ryan

[tiorio]

Originally posted by bigchillcar
Todd,
Did you have these symptoms, then? Does the clutch spring assist in maintaining engaging the clutch? I'll pull my manuals. I keep reading about 'clutch shudder' in past threads, but can't decide if it's what I've got.
Ryan

Ah yes, I had the same symptoms and looked in all the same places for the problem. A tech mentioned that it sounded like I had blown the rubber center of my clutch and he was right. I also remembered back to when I had broken the springs ON THE CLUTCH PLATE on a VW and it was the same feeling/symptoms.

I don't think it's shudder because that really is like a shudder, not a single clunk. I also was a bit vague, I don't think it's the helper spring, but it could be either:

The rubber center on your clutch disc if that model year has same...

-or-

The springs on the clutch disc itself if you don't have the rubber center disc.

Hoping that makes more sense!

[buttjoint]

Be fore you rip and tear, pm john walker, he's the man! JIM

[emcon5]

Mine did the same thing. The culprit:



Somewhere along the line, a PO replaced my "Exploding rubber centered 911SC clutch®" with an earlier version of a rubber dampened clutch, from a 2.7 IIRC.

This version of clutch has a rubber damper in the center, with 3 metal tabs (you can kind of see them in the right and lower circular holes). The triangular cutouts are probably anchors for the rubber center. Well, the rubber center was long gone by the time I replaced the clutch, and the 3 tabs were free to rotate almost 120° freely, before they hit the triangular stops.

"Klunk"

You may be able to see rubber residue on top of the transaxle, it will come out the inspection hole at 12:00.

Hope this helps,

Tom

[bigchillcar]

tiorio, buttjoint and emcon5,
you guys just might be on the money...i had already taken the liberty of pm'ing JW and read his reply just before seeing your three. He says similarly:

how about the trans mount hitting the sway bar? there's usually a sign, like rust dust. also, the spring plate bushings wear out. jw

I need to check into this...sounds like a motor drop. If this is the problem, I wonder how long I have to take action before it's 'demanded' of me?
Ryan

[buttjoint]

I don't belive you will have to drop the engine if JW is correct, and he probably is. JIM

[bigchillcar]

buttjoint,
the spring plate bushings are internal with the clutch assembly...i'd need to drop engine/tranny assembly to open and get to them.
Ryan