Vibration - Polyurethane Motor Mounts vs Rubber

[Hallboss]

Trying to troubleshoot a vibration in my 302 that occurs at about 1,700 rpm and higher. I replaced the OEM type motor mounts with the polyurethane Lick Creek mounts from Duff. Has anyone noticed more vibration feel when changing out the OEM rubber motor mounts with the polyurethane?

The vibration occurs when revving the engine while stationary and also can feel it when cruising freeway speeds. Lower RPMs is fine.

 

[widowmaker77]

I’ve never used those motor mounts but I have read in other forums where people say they do. It stands to reason in my mind since poly is harder than rubber they wouldn’t dampen the vibration from the engine like rubber does. Maybe someone else will chime in that’s actually used the poly mounts.also just to be on the safe side, check your harmonic balancer to be sure it’s not trying to come apart

 

[DirtDonk]

Give us some more information please.
Was the engine running fine and perfectly smooth, then you replaced the mounts? Or is this part of an overall rebuild and you’re just now firing the engine up?

 

[Hallboss]

Give us some more information please.
Was the engine running fine and perfectly smooth, then you replaced the mounts? Or is this part of an overall rebuild and you’re just now firing the engine up?

Yes, was running fine and way smoother than it is now. Motor is solid with good hp/torque. The only thing I can think of is those damn motor mounts. Checked timing, spark plugs, and EFI is reading everything is good. With the vibration happening during rev/stationary, definitely eliminates the running gear.

I will check the harmonic tomorrow.

Just wondering if anybody else is running the polyurethanes and experienced a change in vibrations.

 

[Madgyver]

I welded up my stock engine mounts when the rubber separated causing issues with pump pulley and electric fan.
no issues with vibrations.

 

[Broncobowsher]

Historically, poly is more rigid than rubber. The engine probably always had a vibration, the rubber mounts ate the vibration and you didn't get it. Now the more rigid poly is passing the vibration through. There is a little give, not as much as rubber but more than solid.

 

[73azbronco]

Yes, was running fine and way smoother than it is now. Motor is solid with good hp/torque. The only thing I can think of is those damn motor mounts. Checked timing, spark plugs, and EFI is reading everything is good. With the vibration happening during rev/stationary, definitely eliminates the running gear.

I will check the harmonic tomorrow.

Just wondering if anybody else is running the polyurethanes and experienced a change in vibrations.

are you really sure it's sitting down on the mounts, and is tight? I have historically had trouble getting ford bronco engines to sit right and it required a crow bar and muscle to push them to where we had full contact with mounts and it was level.

How is tranny mount?? How are u joints?

 

[Hallboss]

Historically, poly is more rigid than rubber. The engine probably always had a vibration, the rubber mounts ate the vibration and you didn't get it. Now the more rigid poly is passing the vibration through. There is a little give, not as much as rubber but more than solid.

What I was assuming as well. Couple hundred dollars for the polys, but will probable get new rubber ones and dump the polys.

 

[Hallboss]

are you really sure it's sitting down on the mounts, and is tight? I have historically had trouble getting ford bronco engines to sit right and it required a crow bar and muscle to push them to where we had full contact with mounts and it was level.

How is tranny mount?? How are u joints?

they are tight, but the vibration is noticeable now when just revving it and not moving. Thanks for the suggestions

 

[m_m70]

Have you tried removing the belts to see if it's one o the accessories? I had a fan that started to vibrate at around 2k rpm's. Easy and free test.

Haven't heard of anyone having vibration issues just from new poly mounts. Guessing you don't have the old ones still to swap back to test your theory??

 

[Hallboss]

Have you tried removing the belts to see if it's one o the accessories? I had a fan that started to vibrate at around 2k rpm's. Easy and free test.

Haven't heard of anyone having vibration issues just from new poly mounts. Guessing you don't have the old ones still to swap back to test your theory??

Definitely will do that with the belts. I also have the old mounts, but might just buy new OEM style mounts. The Duff's are poly and listed as "heavy duty" so not sure if that makes a difference in the poly density. Project for next weekend! Thx

 

[nvrstuk]

The only poly engine mounts I've ever physically handle were MUCH stiffer than rubber and then would transfer more vibration.

When you replace those with OEM rubber ones make sure you get the mts that have the large rivets built in so if they ever split/separate the rivets keep the mounts from separating into two pcs and potentially allow the engine to rotate and cause any issues...

 

[toddz69]

Trying to troubleshoot a vibration in my 302 that occurs at about 1,700 rpm and higher. I replaced the OEM type motor mounts with the polyurethane Lick Creek mounts from Duff. Has anyone noticed more vibration feel when changing out the OEM rubber motor mounts with the polyurethane?

The vibration occurs when revving the engine while stationary and also can feel it when cruising freeway speeds. Lower RPMs is fine.

I ran rubber mounts for decades and switched to WH poly units about 15 years ago. There is slightly more vibration with the poly units but I'd characterize it as negligible. I'd say I notice it only because I've driven my truck for decades with both types and I'm pretty sensitive to NVH differences. I don't find the difference to be disconcerting or objectionable. What you're experiencing seems to be something else, imo.

Todd Z.

 

[nvrstuk]

You replaced the mtr mts, ANY other work done on ANY thing while replacing the mounts?? Asking because just replacing mtr mts to replace them isn't common and are usually done when "other" work is done, so I'm guessing that something else was done to the engine/drivetrain and so mtr mts were replaced then????? Maybe not but we don't know so just asking...

Might check your harmonic balancer to see what kind of condition it's in also. Flexplate/flywheel, etc bolts all tight, etc, etc?

Also, not being nosey, where in "PNW"?

 

[pcf_mark]

Take a flashlight and carefully check if the mounts bottomed or touching the frame or anything. Sometimes they squish or are too thin and the metal edge make contact with outer metal and transfer the vibration. Also look around sometimes a 1/8" thinner mount makes something else make contact transferring vibration - like exhaust or valve covers.

 

[Hallboss]

I ran rubber mounts for decades and switched to WH poly units about 15 years ago. There is slightly more vibration with the poly units but I'd characterize it as negligible. I'd say I notice it only because I've driven my truck for decades with both types and I'm pretty sensitive to NVH differences. I don't find the difference to be disconcerting or objectionable. What you're experiencing seems to be something else, imo.

Todd Z.

Thanks for this info. I was able to isolate the main vibration while underway, which was not from the mounts. There is still more vibration with the poly units, but I’d agree that its not awful. Still it’s more vibration than I want. Will be ordering new rubber mounts.

You replaced the mtr mts, ANY other work done on ANY thing while replacing the mounts?? Asking because just replacing mtr mts to replace them isn't common and are usually done when "other" work is done, so I'm guessing that something else was done to the engine/drivetrain and so mtr mts were replaced then????? Maybe not but we don't know so just asking...

Might check your harmonic balancer to see what kind of condition it's in also. Flexplate/flywheel, etc bolts all tight, etc, etc?

Also, not being nosey, where in "PNW"?

No, I replaced the mounts because I could see the rubber on the passenger side looked like it was separating. I decided to just change them, but after searching I found the Lick Creek ones sold by Duff. I thought they would be better than OEM style, but didn’t even think about the “heavy duty” polyurethane vs OEM rubber vibration dampening. The mounts are built great, just pissed that I have more vibration now.

I’m in the SW Washington area.

Thanks to all that commented - the major vibration while underway was a smoked U-joint. Appreciate everyone’s troubleshooting suggestions.

 

[nvrstuk]

....but ujoints don't vibrate when stopped... think that threw us off a bit.

Glad you got it figured out!

 

[Hallboss]

....but ujoints don't vibrate when stopped... think that threw us off a bit.

Glad you got it figured out!

Roger that, but I had noticeably more vibes both stationary and moving. Thanks... was just the combination of the new motor mount install and timing of the rear u-joint deciding to go at the same time. I did get the info I wanted on the polyurethanes. I'm not mud bogging this thing or rock crawling, so going back to the rubber mounts. Street comfort for me is better. Hopefully this helps others when considering changing over to the polys, might save them $250 with purchase and shipping cost.

 

[nvrstuk]

Good info for all for sure. Even tho I run enough HP to warrant them I use stock mounts to keep overall height to a minimum also. I already have my engine lowered 3/8"