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Polyurethane engine and transmission mounts

Polyurethane Engine and Transmission Mounts by PolyPro

Polyurethane Engine and Transmission Mounts

Engine and transmission mounts hold the powertrain to the body or subframe, carry its weight and damp the vibration and torque reaction it produces. This section covers engine mounts, gearbox mounts, differential mounts and damper crankshaft pulleys. PolyPro casts them from polyurethane in its own moulds, for passenger cars, commercial vehicles and special machinery. The rest of the suspension and driveline range sits in the PolyPro catalogue.

 

What Engine and Transmission Mounts Are and How They Work

An engine mount is a flexible element between the powertrain bracket and the body or subframe. It carries the weight of the engine and gearbox, holds the assembly in its designed position and isolates the shell from the vibration produced by combustion pulses and rotating masses. Its second job is to absorb torque reaction: under acceleration and braking the engine tries to rotate about its own axis, and the mounts are what stop it from shifting.

In most layouts the powertrain rests on three or four points, and each mount works in its own direction: one mainly in compression, the others in shear and torsion. Transmission mounts — the gearbox mount and the differential mount — also take drive thrust and the shock that comes with load changes. The damper crankshaft pulley sits apart: it absorbs torsional vibration of the shaft itself and carries no weight.

 

Signs of Worn Engine and Transmission Mounts

Mount wear builds up slowly, so the driver gets used to the new vibration level and notices the fault late. The flexible element hardens, cracks or separates from the metal sleeve, the assembly sags, and the load moves onto the neighbouring mounting points.

  • vibration at idle that carries into the steering wheel and gear lever
  • a dull knock when pulling away, braking or changing gear
  • the powertrain lurching or jumping when the throttle is snapped open
  • cracks, delamination or torn-out chunks in the flexible element
  • the assembly sitting low: misaligned pulleys and stretched hoses
  • oil traces or fluid leaking from a hydraulic mount

Check on a lift: prise each mounting point with a bar to feel the play, then have someone load the engine briefly in gear — movement of a few millimetres means the flexible element is finished. Look at the brackets too, since cracked metal follows a collapsed mount.

 

Polyurethane or Rubber in Engine Mounts

Factory mounts are made from a rubber compound tuned first of all for comfort: it is soft and absorbs high-frequency vibration well, but it ages faster from heat, oil and ozone, and after a few seasons it takes a permanent set and sags. Polyurethane is denser, far more resistant to oil, fuel and temperature swings, deforms less under steady load and keeps the height of the mounting point through its service life.

In practice a polyurethane mount lets the powertrain move less: driveshaft angles stay where they should, gear changes feel cleaner and the lurch when the throttle is released disappears. The trade-off is slightly more vibration reaching the shell — barely noticeable on commercial vehicles and machinery, more of a question on a passenger car, where it depends on the durometer chosen. The Shore value is listed on each product page.

 

How to Choose Engine and Transmission Mounts

Selection starts from the assembly and its fitting dimensions, not from the vehicle name: mounts that look identical often differ in height, sleeve diameter and bolt spacing. There are four things to check.

By Assembly Type

Work out which element has actually failed. The mount under the engine carries the weight and the torque reaction — that is the engine mount. A gearbox mount works mainly in shear and takes the jolts of gear changes, so a collapsed one shows up as a knock when shifting rather than as idle vibration. Behind the rear axle or transfer case sits the differential mount, which absorbs driveline shock. The damper crankshaft pulley is separate again: it controls torsional vibration of the shaft and is not a mount at all. Replacing the wrong part will not remove the vibration.

By Fitting Dimensions

Remove the old mount and measure it before ordering: overall body size or outer sleeve diameter, height of the flexible section, stud diameter and length, centre-to-centre spacing of the fixing holes and the inner bush bore. Compare those figures with the product page. If the old part has broken up and there is nothing left to measure, work from the bracket and the seat in the body. For rare machinery PolyPro makes a mount to a drawing, a sample or a worn part, from one piece up. Check left and right mounts separately, as they often differ in height and seat angle.

By Durometer

Durometer is chosen for the duty cycle, not on the principle that harder is always better. A car used daily in town takes the softer option, so comfort is kept and no extra vibration is fed into the shell. A truck, a bus, special machinery or an engine with higher torque needs a denser polyurethane, otherwise the assembly shifts under drive and loads the driveshafts. The Shore value is listed on each product page — go by that figure, because the colour of the part says nothing about hardness. Keep the same grade across all mounting points, which matters most on a vehicle used in a mixed duty cycle.

By Operating Conditions

Take account of how the vehicle is used. Constant contact with oil and fuel, high under-bonnet temperatures, road salt and rough ground shorten the life of rubber mounts far faster than smooth tarmac does. On machines that pull away loaded, tow a trailer or run on unmade roads it makes sense to move to polyurethane at every mounting point at once: one new mount alongside three worn ones takes the bulk of the load and will not last. If the assembly is already out, changing all the mounts in one go saves a second strip-down. It is worth checking the brackets as well, because metal often cracks after a mount collapses.

Why Engine and Transmission Mounts Are Bought from PolyPro — Retail and Wholesale

PolyPro is the manufacturer, not a reseller: its own moulds, its own casting shop, dimensional control on site and sales without intermediaries. That means an engine mount reaches you without a chain of mark-ups, and its dimensions follow the drawing rather than the batch. The products carry a warranty. Retail is by the piece: you can order a single mount for one mounting point instead of a set. Non-standard parts are made to a drawing, a sample or a worn part, also from one piece up.

Wholesale is set up for workshops, parts shops, fleets and resellers. The partner programme gives bonuses on turnover or on the size of a single order, access to prices and stock levels, and shipment under the partner's own brand. International shipping is available.

 

Frequently Asked Questions

What is the difference between an engine mount and an engine cushion? 

They are the same part: mount is the term used in manufacturer catalogues, while cushion or pillow is the workshop name. This section brings together every flexible mounting point of the powertrain and driveline: engine mounts, gearbox mounts, differential mounts and damper crankshaft pulleys.

How many mounts hold the powertrain? 

It depends on the layout. On most passenger cars with a transverse engine there are three or four points for the engine and gearbox together, rear-wheel-drive layouts add a differential mount, and trucks and machinery use more points. Check the mounting diagram for the specific assembly.

Do all the mounts have to be replaced at once? 

Technically one can be replaced on its own, but a new mount next to worn ones takes the larger share of the load and gives up sooner. If the mileage is the same at every point, it is more sensible to replace the set, so the assembly sits square and vibration does not move from one mount to the next.

Can polyurethane replace a hydraulic mount? 

A polyurethane mount has no fluid chamber, so it works as a plain flexible element: it holds the assembly more precisely and cannot leak, but it damps high-frequency vibration differently from a hydraulic unit. On commercial vehicles and in hard service the swap makes sense; on a passenger car a softer grade is chosen.

How can mounts be checked without a lift? 

Put the vehicle on the handbrake, select a gear and briefly raise the revs while watching the engine. Visible shifting or jumping of the assembly, a knock, or parts touching the body mean the flexible element has failed. Then inspect the mounts for cracks and for any fluid leak.

Which durometer should be chosen? 

The Shore value is listed on each product page. For daily town driving the softer option is normal; for goods vehicles, special machinery and engines with higher torque a denser grade is used. Go by the duty cycle and the mass of the assembly rather than by the colour of the part.

Is it possible to buy a single mount rather than a set? 

Yes, retail is by the piece, so one mount can be ordered for one mounting point. If the item you need is not in stock, PolyPro makes it to a drawing, a sample or a worn part, also from one piece up. The products carry a warranty, and international shipping is available.

What are the terms for workshops, parts shops and fleets? 

Wholesale is available to workshops, parts shops, fleets and resellers. The partner programme gives bonuses on turnover or on the size of a single order, access to prices and stock levels, and shipment under the partner's brand. Terms are agreed individually.