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Question: C1 Engine Mounts and Clutch Chatter


Aug 26, 2014
United States
I have a '62 with a 383 stroker (just got it running last week) and Tremec TKO 600 5-speed, with standard front engine mounts and the supplied Tremec rear mount. Over the three years I have owned this car I've evolved from a 327 and Muncie 4 speed, to an upgraded 327/ 320 HP with the Tremec. I installed a resurfaced 11" flywheel and I installed new front rubber mounts three years ago. Since I've owned the car I have used three different clutch discs (10 1/2" and 11", all street quality) and have experienced bad clutch chatter, especially in reverse. The chatter has not gone away with any of my engine / transmission / clutch plate iterations. Note that this chatter occurs at idle speed and lessens at higher engine speed.

When I test-drove the 383 with the hood off last week I noticed a pronounced movement (rotation) of the engine that corresponds with the chatter that shakes the entire car. It's worst in reverse and also in first gear when starting up an incline. But I also get very minor chatter when downshifting. No engine movement / no chatter.

I've thought about temporarily making solid front mounts to see if the problem goes away, but I know that's not a solution. I've considered shortening the sleeve inside the existing mounts so I can squeeze them down tighter. I've looked for poly replacement mounts and cannot find them. I've also considered installing a rack-and-pinion system so I can use side engine mounts.

Before I go to extremes, I wanted to see if any of you experts have any other suggestions on minimizing the chatter. While driving with the hood off I see a definite correlation between engine movement and shaking. Therefore I conclude that I need to tighten up the engine mounting in some way.

In the past two summers I have put about 2000 miles on the car each year. When I installed the stoker this winter the flywheel looked like brand new. Do I simply need to get some mileage on the clutch and flywheel in order to reduce the bite between the clutch plate and flywheel? Any suggestions or advice from your own experiences will be appreciated.
The fact that you are still experiencing this problem with different engines and transmissions seems to eliminate most of the normal culprits. You are putting enough miles on it to wear the new off of the friction parts but I wouldn't expect them to be the problem anyway since you haven't seen any burn marks on the flywheel or abnormal wear. With the motor mounts in good shape and properly torqued I'd look for a common denominator. Are you using the same bellhousing with both engine/trans combos?

If so, check to see if the transmission mounting surface is parallel with the engine mounting surface and that the transmission hole center is in alignment with the crankshaft centerline. You may have an alignment problem between the engine and trans. I was reading a while back in one of the magazines where they checked several bellhousings and the factory ones were almost always right on the money but they found several aftermarket ones that needed machining or aligning with offset dowels.

I have used two early 60s aluminum bell housings with my setups. Both have the starter mounted to the bell housing. The '62 bell housing was the first to be used with the Tremec, and I did not go to the trouble to center it. I had trouble all that summer with vibration in the engine / transmission, so I learned my lesson.

I centered the '60 bell housing each of the last two winters, to both the 327 and the 383, using offset dowels. I am well within Tremec's tolerance for alignment.

In 2015 and 2016 I ran an 11" flywheel and pressure plate with an 11" clutch disc. I had some problems with gear clash going into first and reverse, in addition to the chatter. So for 2017 I installed a 10.5" disc in the same setup as an experiment. The gear clash is gone now. The chatter is the same.

I've put over 300 miles on the new setup and plan to keep wearing the friction parts in. My next experiment may be to shorten the motor mount sleeves so I can torque the rubber down tighter. The chatter is most irritating in reverse at idle speed, and when downshifting.

I'm also going to check the motor mount bolts to make sure they are not too long (and bottoming on the threads). I replaced the rubber three years ago, but the sleeves and bolts are the same since I bought the car in 2014.
I've been looking for specs on those motor mount bolts and sleeves. I'm not sure if the rubber is as hard today on the cushions as it was originally or not. Could be that it just needs more crush. I'll keep looking. I bought new ones from GM in the early '70s for mine and reused the original hardware. I never had a chatter problem even with a 3.36 rear gear that required a little slipping of the clutch to get rolling with the Duntov cam in the 270 horse.

Another thought. Has your car been lowered? That would change the drive shaft angle.

Thanks for helping sort this out, Tom. The car is not lowered. The rear-end is a 3.36 posi installed this winter. It was an open 3.36 prior. With this rear-end and the 5 speed I got 18 mpg on my last fill-up, with mostly country road driving. I'm really happy with that and will eventually get to the root of the chatter problem. It doesn't sound like a common problem.
I found the bolt length from a non GM source that says 7/16 20 by 3 1/2 " . Torque specs are 25 to 35 LBS. FT. I'd go for the maximum. I'm still looking for the sleeve length. If I can't find it I can disassemble mine to measure it. Mine are unquestionably original. I need to remove the water pump to rebuild it anyway.

Tom, I really appreciate your research on this. Since we have a gloomy day in northern Ohio I plan to work on the mounts today. I'll get to the root of the chatter eventually. I'm enjoying this stroker as much as my speed shop (Koffel's) said I would.
Dave B

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