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Engine mount vibration


WPVT

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The engine vibration that I am experiencing with my 1954 C-1-B6 pickup seems excessive to me. The engine runs pretty smooth, but it seems like too much engine vibration is being transmitted to the frame and thence to the steering wheel and cab.  I've read everything on this forum relating to motor mounts. Mine don't look that bad, but they are undoubtedly old. 

So in the interest of experimentation, I loosened all of the mounts, front and rear. I jacked up the engine about an inch and started the truck. Much smoother, of course. True "floating power". I'm going to take the truck for a spin tomorrow with the engine mounts loosened to see if that is an improvement over when they're tightened. My theory being that it will give the engine a little more freedom to vibrate, without that transmitting to the frame.  (All the bolts are in place, so I won't lose the engine.) 

 

If I decide that I need new rear motor mounts, I have quite a puzzle ahead. The lower rear rubber mounts aren't a problem but the upper rear rubber donuts won't come out without first lifting out the steel washer/spacer and that's going to require more clearance than seems to be easily available.  I'm not ready to take extreme measures unless I can be sure there will be a significant benefit. 

 

Has anyone replaced the rear mounts without pulling the engine and been pleased with the results ?

Edited by WPVT
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  • WPVT changed the title to Engine mount vibration
21 minutes ago, wallytoo said:

do the smaller trucks have rubber rear mounts?

 

unlike this for my 1.5-ton?  and these are actually bellhousing mounts, as the rear/middle of the motor has no mounts.

 

P7122176.jpg

Small trucks have the same mounts you do. They are between the brackets that hang from the frame and mount vertically to the bell housing

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36 minutes ago, WPVT said:

They are rubber mounts.

 

oh, you have a c-series.  not used to seeing those on the forum yet.  clearly different mounting, and perhaps why nobody has answered - a lot of us are b-series and earlier owners.

Edited by wallytoo
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C- series pickups use rear cross member donut style mounts...same as say a p15.

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I don't want to sound like a broken record but...

 

If you are concerned with vibration then you need to replace all of the rubber mounts for the engine, transmission and cab, especially if their age is unknown...there are ways to quantify rubber hardness, but I found that I should be able to press my thumbnail into the rubber to distort its surface on isolation bushings such as a motor mount...if I can't do that, then the rubber has hardened and is in a state of degradation, requiring replacement

 

When I replaced the 55yr old motor, transmission and cab mounts on the '49, it helped dampen vibration significantly.  Transmission mounts were replaced by supporting the transmission and removing the mount brackets from the bell housing when more clearance was needed to remove the old rubber.  Old rubber was pancaked, hard as chinese calculus, and transferred carbon whenever I held them.  But it still had a small vibration going over 50mph, which I attributed to being a 1-ton work truck over 55 yrs old with an engine that probably not perfectly balanced, and the vibration did not change after 10k miles.  So I figured that was part of that old beast's character, it's way of hollering at me WHARS THE FIRE :cool:

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Thanks everyone. I just completed replacing the rear engine mounts on a C-1. It took about two hours work, but 2 weeks of research. I learned some very important basic principles about this mount design that I'd like to pass along. The C series mounts are a little different than the B series, but the basics apply nonetheless.

The mounts use a rubber donut and steel washer on top that the engine rests on. Then comes the frame. Then comes either another rubber donut (C-series) or a rubber washer (B series) followed by a steel washer. Running through these is a long, fine threaded bolt, and a tubular spacer that determines the distance between the washers once the nut is tightened. The tubular spacer is integral with the upper steel washer, making a tee shaped assembly. That's unfortunate when it comes to disassembly, since there isn't room to lift out the tee assembly from above in one piece. 

 

Here's what I did to disassemble and remove the old mount. I removed the lower nut from the bolt. On mine the nut is 11/16 and the bolt head above is 5/8. Then I removed the steel washer and the lower rubber donut. Using a Dremel and a cut-off wheel I cut as much as I could off from the tubular spacer...about 1". Then I jacked up the engine about an inch or so and after lifting the bolt up through and removing it was just able to slide the upper rubber donut and the washer/spacer assembly out sideways. I put the tubular spacer in a vise and cut the washer off flush. My new assembly consists of the two steel washers, top and bottom, separated by a loose tubular steel spacer that I made and  cut to a very precise length. That length is critical. Now I could insert the spacer from below when re-assembling everything.

 

There's been a lot of postings regarding the hardness and dimensions of the mounts that are currently available. Also the fact that the B series used only a rubber washer on the bottom yet suppliers only sell a lower thick rubber donut. Those things don't really matter. What matters is understanding the principle behind the original mount design. The engine rests on a steel washer, which rests on a rubber donut, which rests on the frame. Underneath, there is a rubber donut or a rubber washer...either will work. The bolt that passes through this sandwich has a tubular spacer that prevents the assembly from being tightened beyond a certain point. THE most important point is that the spacer has to be a precise length that will prevent the rubber from being clamped tightly. The engine weight rests on the upper rubber donut, and the lower donut or washer is NOT brought up tight against the frame. There is intentionally a small gap left there. The lower mount fastening will prevent the engine from spinning over, but it's not supposed to be tight. Tighten it up, and the engine vibration will shake the whole truck. Leave it loose, and it does its job and prevents engine vibration from being transmitted to the frame and cab. 

 

I would recommend replacing the mounts to anybody with an old truck and old mounts. If you do it as outlined above, the difference is like night and day. I hope this post proves helpful.

Edited by WPVT
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6 hours ago, JBNeal said:

Transmission mounts were replaced by supporting the transmission and removing the mount brackets from the bell housing when more clearance was needed to remove the old rubber. 

 

transmission mounts?  again, as i noted earlier, the larger trucks do not have a rubber mount at the bellhousing/frame interface.  it is a solid steel connection.  the only rubber is at the front of the motor, where it mounts to the front crossmember.  no rubber to the rear of that, at all.  surprisingly little vibration (none noticeable) with this setup.   very long rear driveshaft for my "152".

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