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The transmission mount is the most overlooked part of a driveline upgrade. People spend thousands on a built trans and a billet converter, then bolt it to a torn, oil-soaked factory rubber mount and wonder why the shifter rattles and the driveshaft angle is off. On a stock-power daily, the soft rubber factory mount is fine. The moment you add torque, sticky tires, or a stall converter, that mount becomes the weak link — it lets the powertrain rock under load, which changes pinion angle and beats up the rest of the driveline.
There are three material choices, and the right one depends entirely on how the truck or car gets used. There is no single "best" — there is best for your build.
The Three Mount Types
| Type | Best For | NVH (vibration into cabin) | Durability Under Torque |
|---|---|---|---|
| OEM Rubber | Stock to mild builds, daily drivers | Lowest (smoothest) | Tears under high torque, soaks up oil |
| Polyurethane | Street/strip, towing, 400-700 hp | Moderate (some buzz) | Excellent — the sweet spot |
| Solid / Billet Aluminum | Drag, race-only, heavy stall | High (transmits everything) | Bulletproof but harsh |
For 90 percent of street-driven performance builds, polyurethane is the answer. It controls powertrain movement far better than rubber, lasts longer, resists oil, and still keeps enough cabin comfort that you can live with it on the road.
Durometer — The Number That Matters
Polyurethane mounts are rated on the Shore A durometer scale — higher number means harder material, which means firmer control but more vibration. You will see two common grades:
- ~80A durometer: the streetable poly choice. Noticeably firmer than rubber, controls movement well, still daily-able. Start here.
- ~95A durometer: race-oriented. Very firm, transmits more vibration and gear whine. For dedicated strip cars or heavy stall setups.
If you have to ask, buy the 80A. The 95A is for people who already know they want it and accept the buzz.
Recommended Mounts By Use Case
Energy Suspension Poly Mount — The Street/Strip Default
Energy Suspension makes hyper-flex polyurethane transmission mounts for most popular GM and Ford platforms in the streetable durometer range. They are oil-resistant, hold the powertrain steady under hard shifts, and are priced sanely. This is the mount we reach for first on a 500-700 hp street build.
Check Energy Suspension poly mounts
Prothane Motor/Trans Mount — Budget Poly
Prothane is the other major polyurethane brand and usually a touch cheaper. Quality is good, fitment is solid on common platforms, and they offer the same firmer-than-rubber control. A fine choice if Energy Suspension is out of stock for your application.
Check Prothane mounts
Heavy-Duty Rubber Mount — For Tow Rigs That Stay Comfortable
If your build is a towing truck and you value a quiet cabin over the last bit of pinion-angle control, a heavy-duty reinforced rubber mount (often with an interlocked steel insert so it cannot separate if the rubber tears) is the smart middle ground. You get most of the durability of poly without the buzz.
Browse HD transmission mounts
Solid Billet Aluminum Mount — Race Only
Solid aluminum mounts eliminate all powertrain movement, which is what you want when launching a heavy stall converter on slicks and protecting driveshaft geometry. The price is brutal NVH — you will feel and hear the entire driveline. Do not put one in a daily.
Check solid billet mounts
What Kills a Transmission Mount
- Oil and ATF contamination. Rubber swells and rots when soaked in a leaking transmission or engine. Fix the leak; this is why poly wins on a leaky build.
- High torque rocking. Each hard shift and launch torques the powertrain. Soft rubber tears at the bond line.
- Wrong pinion angle. A collapsed mount drops the tailshaft and changes driveline angle, which causes vibration and U-joint wear — people chase the wrong part for months.
- Age. Twenty-year-old rubber is hard and cracked regardless of miles. If you are in there, replace it.
Quick check: have a helper brake-torque the trans (foot on brake, light throttle in drive and reverse) while you watch the mount. If the powertrain visibly lifts or the rubber splits open, it is shot.
Building a Transmission? Get the Hard Parts Too
A mount is the easy part. gearboxinsider.com stocks the billet converters, shift kits, HD frictions, and seal kits that go into a real performance build. Same-day ship before 2pm Eastern, free shipping on every order.
Shop Gearbox Insider →FAQ
Will a polyurethane mount make my car shake?
You will feel more idle vibration and a little gear whine versus rubber, especially at the 95A durometer. At 80A on a street build, most people stop noticing within a week.
Do I need to upgrade the motor mounts too?
If you are controlling powertrain movement, yes — matching poly motor mounts make a bigger difference than the trans mount alone. A loose engine still rocks the whole assembly.
Can I reuse the old mount bolts?
Inspect them. If the threads are clean and they are not stretched, yes, torqued to spec. If they were oil-soaked and rusty, replace them — cheap insurance on a part that holds your transmission up.