Polyurethane Motor Mount Bushing Fabrication - 2000 Endeavor

[Ted DuPuis]

My motor mounts are original and toast (Freightliner XC chassis, Cat 3126B engine). While they aren't literally falling apart, they are sagging and allowing a lot more flex and motion of the engine than I would like. This is especially the case under certain transients where the torque goes from the engine driving the bus to the bus driving the engine, especially downshifts.

One of the motor mounts was bad enough that I could spin the bottom puck and it had around 1/8" clearance, and that's probably a good portion of it.

Although this is unconventional, I decided to make polyurethane bushings for it. These aren't used in most (any?) production vehicles because of the increased transmission of NVH (noise/vibration/harshness). I think in this case it will be a net benefit. In my previous experience, replacing worn rubber bushings that are allowing more flex than original with polyurethane ends up reducing vibrations some, and replacing the "bad" vibrations (caused by the engine not being controlled) with the "good" vibrations (the nice visceral sensation of a good-running diesel Cat, in this case).

I chose a 70A Durometer (relatively soft) polyurethane. Aftermarket motor mounts can be anything from 60A-95A from what I've seen. The worse the inherent vibration characteristics of the engine (for example an in-line 4) the softer you want. An I6 is naturally balanced, and although diesels have significant torque pulses, it's a pleasant vibration to me.

We'll see if I'm right or not. If I'm wrong, it's not too hard to buy new rubber ones from Freightliner and throw them in.

[Skip426]

I'm in the process of searching for upgrades for these same mounts.

In the case of the engine/transmission mounts , I'm sure they are sagged enough to allow the retaining washer to contact the frame when the engine is under load.

[Ted DuPuis]

Originally Posted by Skip426

I'm in the process of searching for upgrades for these same mounts.

In the case of the engine/transmission mounts , I'm sure they are sagged enough to allow the retaining washer to contact the frame when the engine is under load.

Skip, you're looking at exactly what I'm looking at, and I have observed the same sag.

I've got enough polyurethane leftover to make another set I think if you end up wanting to copy my results or can tell you where I bought it from. The stock mounts are normal Lord mounts. Hopefully will finish up and test drive sometime this week.

I've already got the forward (front of engine, rear of bus) mounts fabbed and in, they're looking good.

[Skip426]

Ted , I had contacted a company about upgraded mounts , but , unfortunately lost the link to a hard drive failure.

I'll dig around and see if I kept the company web address written in my old school note book .

[Rob_M]

Try Prothane and Energy suspension. They both list universal bushings by size.

[Ted DuPuis]

Originally Posted by Rob_M

Try Prothane and Energy suspension. They both list universal bushings by size.

I didn't check Prothane, but I did check Energy Suspension - they had nothing big enough for what was needed.

I've got one motor mount about finished fabrication wise. Have to finish a few other details and then I can get that in and make the other one.

[Rob_M]

Originally Posted by Ted DuPuis

I didn't check Prothane, but I did check Energy Suspension - they had nothing big enough for what was needed.



I've got one motor mount about finished fabrication wise. Have to finish a few other details and then I can get that in and make the other one.

Prothane probably won’t either then.

What did you cut the poly with? Those will last forever and I doubt you’ll notice any difference driving it compared to rubber. These big 6cyl Diesels are smoooooth.

[Ted DuPuis]

Originally Posted by Rob_M

Prothane probably won’t either then.

What did you cut the poly with? Those will last forever and I doubt you’ll notice any difference driving it compared to rubber. These big 6cyl Diesels are smoooooth.

I'm expecting it will overall be smoother than the dead rubber mounts would. We'll see how it works out.

I've been cutting the poly with my horizontal band saw to make the pucks, and then hole saws to cut the center holes for the bushings/bolts. The key I find is having the band saw set up with both a faster blade speed and a very slow rate on the arm coming down.

[Ted DuPuis]

I got all 4 engine mounts replaced and installed. We’ll have to see how this works once I run the engine and can test drive it, but it all went together more or less as expected.

I’m also working on my generator mount upgrade (air springs, not poly) so I need to finish that before I drive it.

[Ted DuPuis]

I managed to test drive the bus yesterday with the poly motor mounts. It was only a short drive (figure around 20 miles) and I was looking at a bunch of other things at the same time as I've done a lot of work on this (see my other threads - turbo upgrade, some changes to the cooling system, air spring isolators for the generator...). However, I can say that these poly mounts are working exactly as I had hoped they would.

First thing that I noticed was how much I didn't notice that the engine was running compared to the rubber mounts. Not that the engine was vibration free, but I wasn't getting the rattling of things in the RV that had come with the engine running especially at idle before. I attribute this to the fact that the engine is actually being held in place now, and probably moreso that now the motor mounts aren't contacting the frame as seems to be the normal with the stock rubbers as they sag some. Given that the poly shouldn't sag, I don't foresee this being an issue going forward.

On the road, I felt the engine was a bit "growlier" than before. Note that I also was driving with a new turbo, so how much of that was potential sound transmitted to the body from the mounts vs. the turbo changing the exhaust note is hard to say. Probably more of the latter. But what was definitely the motor mounts was smoother overall operation, especially during gear shifts. Again, the engine is now being held in place more solidly, so during changes in torque the engine isn't flopping around and allowing clunks.

The 70A durometer seems to be perfect. I don't see any benefit from going harder. 60A may isolate the engine even better at idle and I doubt would have any significant impact on movement during gear changes.

But, to Skip and others, I definitely believe this is the way to go and wouldn't change a thing based on my initial test drive. After I put some more miles on this I'll report back on future thoughts. However this is absolutely better than my worn stock motor mounts in every conceivable way, and I think that it's also better than new stock mounts would've been.

[Ted DuPuis]

We just got back from an 11-day, 3500 mile trip in the bus. This provided a good opportunity to test the motor mounts under many conditions.

Our impressions (I say our because my wife chimed in with her thoughts as well) are very positive. Undoubtedly the engine and the bus overall are smoother all around. You do notice when the engine is running, but the RV interior and dishes are no longer rattling like we had before. My wife was the one who noticed the dishes no longer rattling, I had just noticed the overall quieter operation.

My wife is a good test of whether something I've done has really improved smoothness. She said a bunch of times on the trip that she couldn't believe how much smoother the bus was, especially during shifts which tended to be more jarring before. The bus can still have jarring shifts (especially downshifts under engine braking), but the overall operation is much smoother.

We'll see how long the mounts last, but polyurethane tends to last longer than rubber (I've never replaced anything polyurethane, I've replaced a lot of rubber bushings/mounts), so I'm not expecting any longevity issues.

[Rob_M]

Originally Posted by Ted DuPuis

We just got back from an 11-day, 3500 mile trip in the bus. This provided a good opportunity to test the motor mounts under many conditions.

Our impressions (I say our because my wife chimed in with her thoughts as well) are very positive. Undoubtedly the engine and the bus overall are smoother all around. You do notice when the engine is running, but the RV interior and dishes are no longer rattling like we had before. My wife was the one who noticed the dishes no longer rattling, I had just noticed the overall quieter operation.

My wife is a good test of whether something I've done has really improved smoothness. She said a bunch of times on the trip that she couldn't believe how much smoother the bus was, especially during shifts which tended to be more jarring before. The bus can still have jarring shifts (especially downshifts under engine braking), but the overall operation is much smoother.

We'll see how long the mounts last, but polyurethane tends to last longer than rubber (I've never replaced anything polyurethane, I've replaced a lot of rubber bushings/mounts), so I'm not expecting any longevity issues.

Good job! Those mounts will probably outlive the bus.

My wife is also the one that notices ride characteristics. She’s also my speed monitor lol.

[Ted DuPuis]

Originally Posted by Rob_M

Good job! Those mounts will probably outlive the bus.

My wife is also the one that notices ride characteristics. She’s also my speed monitor lol.

I agree, I think these should outlive the bus, at least live longer than we're likely to keep it.

One thing my wife said on this trip was that she can't believe how much better riding and driving this thing is now vs. when we bought it, and her perspective has been 100% as a passenger. It's just been chipping away at things little by little. I'm sure my cousin's 2020 Dutch Star still is nicer riding and driving, but it cost a lot more, and I think mine would win in a drag race.

[Skip426]

Ted, I ment to ask when you posted about completing your install ; was there an easy way to change the transmission mounts ( rear engine )?

I didn't spent a great deal of time looking at them, but they appeared more complex than the front of the engine.