I’ve dropped my transmission and I’m addressing the mount, which I’m pretty sure is original to the car. The rubber is intact and feels soft/pliable (having never felt a new one, I don’t know if soft is bad, I am getting lots of vibration). I’ve read about filling the mount with polyurethane to reduce vibration and improve overall function of the mount.
Question, is this a better option than an OEM Porsche mount? They are not cheap for sure, but I’m ok paying if they perform better. If polyurethane DIY performs the same then I’ll save the money. Ultimately I want the best solution to reduce vibration as much as I can.
Thanks in advance.
OEM Transmission Mount vs DIY polyurethane
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Tom
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For what it's worth, I never got vibration as a function of a worn tranny mount. How's your clutch and TT?
I DID get shattered CV joints more than once, which seems to be a function of the tranny moving side-to-side more than intended. In my case, I had installed a new mount when I had the tranny rebuilt, and it was noticeably firmer in terms of tranny movement. With the old mount, the tranny felt like it was just hanging there on a rubber hook -- you could move it side to side with very little effort. The new factory mount firmed it up noticeably, but the 3L motor still ended up breaking CV joints. So I filled it with 60A urethane from McMaster and have not had a problem since.
The firmer the mount, the more noise and vibration it transmits, so I opted for the 60A. Lots of folks use the 80A, but I have no rear seat, which amplifies the noises back there and didn't want to push it with the 80A. See the comparison I did below. I briefly tried a 'semi-solid' mount and hated it for a street car -- it amplified every vibration, squeak, gear, tick, whir, etc. to super loud levels in the cabin. Fine for an all-out race car, but I couldn't stand it in my street car. (It's for sale if anyone wants it...
)
Also be sure to check the mount for cracks. When they get old and the tranny starts moving side to side, the mounts can develop crack, which allows the tranny to swing back and forth even more. I welded mine up, and then boxed them in with an additional metal side, since the factory C-shape is vulnerable to pulling apart and cracking.
I DID get shattered CV joints more than once, which seems to be a function of the tranny moving side-to-side more than intended. In my case, I had installed a new mount when I had the tranny rebuilt, and it was noticeably firmer in terms of tranny movement. With the old mount, the tranny felt like it was just hanging there on a rubber hook -- you could move it side to side with very little effort. The new factory mount firmed it up noticeably, but the 3L motor still ended up breaking CV joints. So I filled it with 60A urethane from McMaster and have not had a problem since.
The firmer the mount, the more noise and vibration it transmits, so I opted for the 60A. Lots of folks use the 80A, but I have no rear seat, which amplifies the noises back there and didn't want to push it with the 80A. See the comparison I did below. I briefly tried a 'semi-solid' mount and hated it for a street car -- it amplified every vibration, squeak, gear, tick, whir, etc. to super loud levels in the cabin. Fine for an all-out race car, but I couldn't stand it in my street car. (It's for sale if anyone wants it...
)Also be sure to check the mount for cracks. When they get old and the tranny starts moving side to side, the mounts can develop crack, which allows the tranny to swing back and forth even more. I welded mine up, and then boxed them in with an additional metal side, since the factory C-shape is vulnerable to pulling apart and cracking.
- cracked-mounts.gif (503.1 KiB) Viewed 256 times
- boxed-mounts.gif (398.38 KiB) Viewed 256 times
I was also feeling a faint “wobble” at different speeds. Difficult to describe, almost felt like an axle was bent slightly. Coupled that with the vibration I thought I’d start with transmission mount. Already have new OEM hydraulic motor mounts.
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Tom
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A million years ago, I was feeling a wobble in my steering wheel, and it felt like the rear end was wandering on its own while cruising in a straight line. This was in a 2nd gen RX7. After tearing half the rear end apart, I finally realized one of the rear tires had like 10 pounds of air. Filled it up and all was better. (Well, not entirely, it went flat again and I had to replace it, but you get the point.
) I'd be inclined to jack up the rear and take a good look at all the rear suspension points with a tire iron in hand (a-la Edd China....)No harm done doing the tranny mount, but my old one was super bad (tranny felt like it was hanging from an exhaust donut) and the only thing I ever noticed were broken CV joints.
Thanks for the feedback Tom.
Interestingly I dont feel anything at the steering wheel, which is awesome. I feel it in the back of the car, the whole car. My logic was maybe the tranny was “swinging” to freely. But like most things, I’m just guessing lol
Interestingly I dont feel anything at the steering wheel, which is awesome. I feel it in the back of the car, the whole car. My logic was maybe the tranny was “swinging” to freely. But like most things, I’m just guessing lol
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Zirconocene
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I did the DIY polyurethane thing on my transmission mount. I never got good before/after since there were so many other issues going on (badly timed balance shaft belt) but the car felt solid all the way through once I get everything timed correctly. Taping things up appropriately was the most finicky thing about the process. Lots of folks recommend silicones from McMaster Carr but there are significantly less expensive options out there, with more degrees of freedom on the hardness you want.
ETA: The one thing I will say that is a tenuous connection is that I used to feel the same kind of thing you're describing, but on the front end of my 928. In that case it was an issue with the steering rack mounts. I don't know if there is something analogous on the back end of the 944 that might result in the same feeling but it might be worth looking at some of the other suspension components back there, apart from the trans mount.
Cheers
ETA: The one thing I will say that is a tenuous connection is that I used to feel the same kind of thing you're describing, but on the front end of my 928. In that case it was an issue with the steering rack mounts. I don't know if there is something analogous on the back end of the 944 that might result in the same feeling but it might be worth looking at some of the other suspension components back there, apart from the trans mount.
Cheers
Cheers
1990 928 GT
1990 928 S4
1991 944 S2
1993 968
2002 911 C2
1990 928 GT
1990 928 S4
1991 944 S2
1993 968
2002 911 C2
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ROB III
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The primary reason I changed the mount is knowing what happens to elastomers over time, reading about the issue from RL before the TIME OF CARPOKES, and none of our cars are spring chickens anymore. I'd also changed the engine mounts with new OEM's due to age of the original ones. I bought a new rear mount and used the 60A from McMaster and bought new brackets I found on Ebay. Its not solid and I thought the basic mount would survive longer with the added support. I feel the rear end is more stable and I get the sense there is less movement from the rear in transitions. It was also a good excuse to buy some LONG extensions for my ratchet(s).
Do people generally just fill their old mount with urethane or buy a new one and fill that? My trans is flapping in the breeze and the new motor is not going to help that. Was just about to buy a semi-solid mount but Im not keen on the noise, its bad enough without the rear carpet in.
Can I ask what your symptoms are?Bergerac wrote: ↑Tue Mar 26, 2024 11:00 pm Do people generally just fill their old mount with urethane or buy a new one and fill that? My trans is flapping in the breeze and the new motor is not going to help that. Was just about to buy a semi-solid mount but Im not keen on the noise, its bad enough without the rear carpet in.
I have new motor mounts, which helped a lot, but I’m still experiencing some vibration and “wobble” feeling. I’m hoping it’s as simple as addressing the transmission mount, which I’m sure it’s original to the car.
No particular symptoms apart from maybe a bit of jerkyness at part throttle. When I have the car on the hoist you can move the tranaxle a couple of inches side to side with just one hand.