Shopping Cart
Your cart is empty.

Browse Categories
JEEP Model, Year, and Engine We currently ONLY SUPPORT those vehicles listed below. Grand Cherokee: No Products

Ultra-Flex Rubber vs. Classic Polyurethane
Which is Better?
Some swear by rubber motor mounts. Others prefer the feel of polyurethane.

Here are some considerations:
  • Daily driver (lean toward rubber) or trailer queen (lean toward Polyurethane) or daily driver and weekend adventurer (it's a personal choice).
  • Sporty feel (Polyurethane) or cushion comfort (Rubber).
  • Engine finely tuned (Polyurethane works) or old and tuned in a fog (Rubber).
  • Driveline survived a few drops (Rubber) or pristene (Polyurethane)?
  • Hot and dry (Polyurethane) or cold and wet (it's a personal choice).
More Specific Advice:
  • 4 cylinder engines: Rubber is better.
  • Wrangler 4.2 or 4.0: Both work well, it's a personal choice.
  • XJs and MJs (all engines): Rubber is better.



Durometer (Shore A Scale)
70 Shore-A
89 Shore-A

Vibration Dampening

Oxidation Resistance

Petrochemical Resistance*

Temperature Rating**
-60 to 185 (F)
-30 to 185 (F)

Heat Aging Resistance
Very Good

Tensile Strength
Very Good

Weather Resistance

* Based on amount of bushing exposed in motor mount when installed on vehicle.
** Nominal performance retained within this range. Does not indicate failure outside this range.  
What's the dog say? Around here, the Brown Dog's word is law. And since we're in the heat of the desert southwest, we run Classic Polyurethane motor mounts. (Our 2.5L Wrangler YJ is our daily-driver and our weekend trail rig.) The Brown Dog likes the more secure feeling of knowing what's going on under the hood.  About half of the 2.5s cannot tolerate polyurethane due to the vibration nature of the engine.  XJs, with the unibody design, are better with rubber.
Designed to minimize vibration transfer. Whether you select Ultra-Flex rubber or Classic polyurethane, we strongly urge following all installation tips to take full advantage of the vibration reduction inherent in our design.

Particularly important installation tips include:

- Do NOT over-tighten through-bolts. Even slightly over-tightening these bolts defeats the vibration transfer reduction designed into Brown Dog mounts.

- Inspecting and/or changing transmission mount when changing motor mounts. It's practically impossible to inspect a transmission mount until the cross member/transfer case skid is dropped and the transmission mount nuts removed. Since we recommend loosening the transfer mount bolts prior to raising the engine (using a block of wood and jack under the oil pan), most customers change the transmission mount when they change motor mounts.

- If you have any questions, not sure how to approach something, not sure if it looks right, or not sure if a vibration is 'normal,' call us. Our phone is forwarded 24/7 for technical assistance.
Still unsure?
Give us a call, 866-401-3877 or email