Clutch chatter = weakening diff mount

[Zed Head]

I fabbed up a crude snubber for the front of my R-200 differential, since I knew that the diff mount was showing signs of end-of-life (visible debonding when pried on with a screwdriver off the car), and found that it eliminated a bad clutch chatter problem that I was having. I assume that the weakening original rubber diff mount was allowing the front of the diff to bounce up and down at low acceleration levels, causing the clutch to stick and slip, ie chatter.

Just putting this out there for anyone that may be having a clutch chatter problem. Something to look at. My clutch and pressure plate are brand-new, properly installed and broken in, but still chattered if I tried to leave a light or stop sign slowly.

The snubber I made is fairly solid and positions a urethane bump stop about 1/16 inch above the diff at rest. In action, the diff rises up and contacts it, stopping the bouncing (my guess, not actually seen in action).

The R/T mount or similar would probably have the same effect.

[jmortensen]

It probably wasn't clutch chatter. I suspect the front of the diff was lifting when you put power to it and the driveshaft U-joints were binding, creating the vibration you felt. Congrats on fixing it though.

[Zed Head]

It pulled away fine if you left quickly, the faster the better. It was the attempts to drive slow and smooth that gave the "chatter." I did not resurface the flywheel (should have pointed that out), so the weak diff mount might have been multiplying the effect.

Either way, if someone has a similar "chattering" issue, wherever it's coming from, the diff mount might be part of the problem. That was my basic point. Just trying to add something I haven't seen described before.

Anyway, thanks for reading, and the alternative view. I should have taken a video (I recently saw one here or over at Hybridz) to try to nail down what was happening.

[oldhemi]

Good info!!! Thanks for the time to put it out here. JM is prolly right on where the noise is coming from. I would have suspected a new install to be the new clutch components!

[tlorber]

Good to know. I have a similar problem-although my mount looks fairly new. Do you have any pictures of your solution?

[Arne]

As I noted in the RT-mount thread, when I installed the RT-mount as a limit strap replacement (using the stock lower mount and upper poly bumpstop) the difference in the amount of lash in my drivetrain was startling. My car is much easier to drive and shift smoothly now. And my lower diff mount was only ~5000 miles old, in a car with a bone-stock L24. I highly recommend the RT-mount in this config to anyone who drives their car regularly.

[nahurry]

i too left my lower diff mount in place with the r/t mount. so much smoother now!

[tlorber]

Arne,

Can you direct me to that past "RT-mount" thread? I was under the car this weekend looking at that rubber strap-that thing looks worthless since there is so much slack in it. If there is a means of providing more support, I guess now is the time to do it since I have the rear suspension apart.

[Zed Head]

Good to know. I have a similar problem-although my mount looks fairly new. Do you have any pictures of your solution?

I used the word crude and tried to direct attention to the R/T mount because my fix is rough and has only been on the car for a week. My car is essentially my own little experimental test ground to play with, and a reason to get greasy, tear things up, put them back together then go drive around.

The new "diff arrester" is a piece of 1/8 x 1 1/2 inch steel that has been twisted and drilled to use the large arrester strap mounting bolts (the ones with the 22 mm heads) to hold it in place. The snubber is a 1 1/2 inch diameter bump stop from Energy Suspension, mounted in the middle of the metal strap, that has been trimmed down to barely touch the top of the diff. It may be susceptible to metal fatigue though so I really can't recommend it unless you feel comfortable with taking a chance and like to crawl around under your car to check it out regularly.

Full acknowledgment - I did read Arne's post about using the R/T mount as a snubber, along with hundreds of other diff mount ideas, and that fed some of my thinking. The two other popular ideas with the tabs and the bolt or the L-shaped bracket are essentially snubbers also.

One other odd finding - I tried to preload the snubber a little bit (more is better right?) by adding a thick washer under it and levering the mounting bolts in, and found that it transmitted a loud drumming noise in to the car at takeoff. So I went back to the original tiny air gap (about a metal ruler's thickness) and things have been very tight with no added noise or vibration.

I've also noticed that we pay a lot of attention to the diff nose rising but that there is very little space for the diff nose to drop before the mount hits solid metal. The stock setup allows the nose to rise a lot but gives a hard landing on the way back down. One more thing to think about.

Sorry for the excess words. I like to write.

[Arne]

Arne,

Can you direct me to that past "RT-mount" thread? I was under the car this weekend looking at that rubber strap-that thing looks worthless since there is so much slack in it. If there is a means of providing more support, I guess now is the time to do it since I have the rear suspension apart.

Previous was a Group Buy thread. I don't know if Dave has any left now.

http://www.classiczcars.com/forums/showthread.php?t=36463

[Zed Head]

this just came up today on hybridz - http://forums.hybridz.org/showthread.php?t=127993&page=7

[GreenZZZ]

Replacing the bushings at the back of the transmission really helped my ride.... Just FYI...