marky mark

Has anyone noticed a vibration after installing a poly trans mount? This is on a '69 427/390 4 speed. The vibration comes in around 1800 rpm and lasts until about 2300 rpm.

It kind of feels like an engine vibration and also can feel it through the shifter handle. Does it whether moving or stopped or with clutch in or clutch out, in gear or in neutral. Did not seem to notice it before.

Isn't the transmission still rotating via the input shaft whether the clutch and/or gears are engaged? That seems like a basic question but I really don't know the answer.

During some exhaust work I had done they removed the exhaust hanger that goes between the tranny & it's mount which was stock (rubber insert). This caused a shifter obstruction so they shimmed it with a few washers. I took it back as I still wasn't happy with the shifter and also to check overall transmission height, etc.

As a solution they removed the old mount and shims and replaced it with the poly style mount. Somewhere I read these might be a bit taller than the stock mounts,not sure about that, not that it matters. This solved the shifter obstruction and everything else seems fine also.

One tranny mechanic I spoke with advised against using a poly mount. The engine mounts are still the stock style (rubber inserts). He suggested using poly mounts on the engine and a stock mount on the tranny, so a snot to put too much stress on the tranny.

Guess the only way to know for sure (where the vibration is coming from) is to replace everything with the stock set-up and exhaust hanger, which I don't need anymore.

Anyone have any experience with this issue? Also, is it a bad idea to use a poly tranny mount and/or while using stock style engine mounts?

Any help/opinions appreciated!!

Regards and thanks, Mark

MEGALADON

Replace it with a stock one, if you notice a change, its your mount,
if not, its not your mount. I never heard of a problem like that with
a poly mount. Even my engine has poly mounts. good luck

GTR1999

The last engine/ tranny I installed I used poly mounts in both locations. I had a problem getting a tranny mount that was the same height as the original,Energy suspensions mount didn't fit. Once I get the correct mount I didn't notice anything different. The car has about 2,000 miles on it now.
Gary

GTR1999

The last engine/ tranny I installed I used poly mounts in both locations. I had a problem getting a tranny mount that was the same height as the original,Energy suspensions mount didn't fit. Once I got the correct mount I didn't notice anything different. The car has about 2,000 miles on it now.
Gary

Twin_Turbo

it's not the mount material, it's the size. I've noticed that the poly mounts are taller than stock rubber ones leading to all kinds of problems like problems with the shifter linkage and also vibration due to improper drive shaft angles. The way to eliminate it is to shim the pinion mount on the diff to the proper angle.

marky mark

Twin Turbo, the height issue was a concern of mine but would it be an issue when you standing still just revving the motor?

Other thought were a flywheel/clutch balance issue or perhaps the harmonic balancer going bad. Just seemed to notice after the tran mount was installed.

Guess advice on going back to the stock set-up is the best solution.

Another project that creates more trouble. I could write a book on these experiences!

Thanks, Mark

exdrag77

I use the ES mount kit with no problem and no unusual vibrations. If you notice something after installing ply, it could be that there is a problem that didn't show with stock but since the poly is stiff, now is letting you know something's wrong in the trans or engine.

marky mark

That is a very good point that I haven't considered. Good observation!

Thanks, Mark

Fevre

I would not use a poly trans mount with stock rubber type motor mounts, the rubber mounts will allow the eng to move more than the poly trans will let the trans move and may cause the trans case to flex and possibly crack. You can use poly motor mounts with a rubber trans mount.

Larry B.

I replaced the differential nose mount with a poly mount when I had the diff out and it transmitted a lot of vibration into the car so I switched back to rubber.. vibration gone. I would think that the trans mount would do the same thing. Also I replaced the trans mount with one from Autozone (UGH) and it crushed down within a few days so the shifter linkage wouldn't clear the cross member. I have had one fron the last detain in there for a couple of years... no problems.

joe78

I have a 78 vette with a tci streefighter they do not want you to use poly mts.

CGGorman

I've got Energy poly engine mounts and Prothane poly tranny mount (it's ~1/8" shorter than Energy's). No vibration here. Though, I'm also running a TKO-600. Not exactly apples to apples, but throwing my experience in the pile anyway. My bellhousing is aligned within .003" TIR in ALL directions, if that matters.

exdrag77

Poly isn't stiff enough to break aluminum so I wouldn't worry about that one. The mount will rip in half before trans damage would occur!

ZD75blue

Whats the stock height of the transmission mount?

Sounds like something that requires measuring before purchasing... Given that every motor mount I've seen thats non GM/FOMOCO/Mopar has looked like some foreign guy carved it out of a hunk of rubber with a plastic spork.

marky mark

Fevre, that's what I thought. I'm now hearing a clicking noise underneath the car (staionary or moving). Might be the exhaust pipe is touching something or possibly related to trans mount issue.

I didn't have my bellhousing (stock one) aligned or checked.

With all this good info and obvious changes I'm experiencing I'm going to have it switched back to stock, including the exhaust hanger.

Only other thing I added to this recent rebuid was a roller bearing style pilot bearing. I have heard these may cause problems if alignment isn't right.

My guess is my tranny is sitting up too high now. It's times like these I wish I had access to a lift!

Thanks for all the replies!!

Regards, Mark

stingr69

Marky,
The gears in the tranny are not turning if the car is stopped and in gear with the clutch released. If it still vibrates, it is not from inside the tranny.

-Mark.

marky mark

So the tranny input shaft is not turning when the clutch is not engaged and/or the car is in neutral?

Thanks for the input.

Mark

Fevre

With the clutch in no, with the tranny in neutral and clutch out yes it does turn.

CGGorman

Additionally, with the pedal depressed (clutch dis-engaged) the crankshaft is spinning and the input shaft of the tranny likely isn't, BUT the pilot bushing/bearing IS. With the tranny in neutral and pedal released (clutch engaged), the pilot bearing is stationary in relation to the input shaft. If there is a problem with the pilot bearing, it may be more pronounced with the clutch disengaged.

stingr69

Exactly. The output shaft and synchros are always tied to the driveshaft while the input shaft, cluster gear and reduction gears are all turning away with the clutch disk.

If you push down on the clutch pedal while stationary, the disk will tend to release the reduction gears from the engine but it can still rotate some. Once you put it in any gear, all the gears are locked to the driveshaft so if the driveshaft is not turning, nothing inside the gearbox is turning.

Trannys are kind of tough to visualize if you have not already played around inside one before.

-Mark.