Engine Mounts, P15; Caution

[Sam Buchanan]

3 hours ago, soth122003 said:

Hey Sam,

You might try and remove the lower mount. It's an easy task and when I changed my mounts I also did not have a lower mount. So when I changed mine I did not install the lower mount. I think the only reason for the lower mount is to reduce vibes transmitted by the mount bolt to the frame.

 

Joe Lee

 

Joe, I think by having the bolts loose enough to not compress the mounts I've accomplished pretty much the same thing as leaving out the bottom mount. But it might be worth a try.

[Sam Buchanan]

Just got off the phone with Berbaum, was told the mounts I received were from stock they received about a year and a half ago. I asked if they had gotten any feedback about too-firm mounts or if any other mounts were available and the answer to both inquiries was "No".

[desoto1939]

I had the clutch and pressure plate replaced on my 39 Desoto and also motor mounts at the trans and front and still had some vibrations. We had to replace the original vibration dampener which was part of the lower crank pully. After replacing the dampener then the vibrations went away.  Just another thought to your issue.

 

Also when we put on some rear motor mount they were red in color and we determined that they were also too hard so when with all black rubber ones.

 

Rich Hartung

Desoto1939@aol.com

[Cold Blue]

Sam - someone posted that the front motor mount may be the problem. I replaced my front mount (the old one was a folded piece of radiator hose!!) with a new one. The rubber on the new mount was quite hard. It had the mounting bolts moulded into it, captured by the rubber, and I could not induce any movement of the bolts, as you maybe could do with soft rubber. For sure it did not pass the fingernail test. Replacing the front mount did not produce any vibrations at all; the 6 banger runs as smooth as a kitten. With that said, somehow I believe that something other than the new rear mounts is causing the vibes? Could something on the motor be touching the car frame or body? Or maybe the new mounts raised the rear of the engine enough that the drive shaft alignment is off now? Just for the heck of it, I might jack the rear wheels off the ground, start 'Ole Bessy", put her in gear, get under the car and feel around for the source of the vibes.

[Sam Buchanan]

1 hour ago, Cold Blue said:

Sam - someone posted that the front motor mount may be the problem. I replaced my front mount (the old one was a folded piece of radiator hose!!) with a new one. The rubber on the new mount was quite hard. It had the mounting bolts moulded into it, captured by the rubber, and I could not induce any movement of the bolts, as you maybe could do with soft rubber. For sure it did not pass the fingernail test. Replacing the front mount did not produce any vibrations at all; the 6 banger runs as smooth as a kitten. With that said, somehow I believe that something other than the new rear mounts is causing the vibes? Could something on the motor be touching the car frame or body? Or maybe the new mounts raised the rear of the engine enough that the drive shaft alignment is off now? Just for the heck of it, I might jack the rear wheels off the ground, start 'Ole Bessy", put her in gear, get under the car and feel around for the source of the vibes.

 

I've looked for any places where exhaust or drivetrain could be touching the car. Keep in mind the ONLY thing that changed other than the mounts is the bellhousing is riding maybe 3/8" higher than before (probably where it would have been with the mounts it came with out the factory). The driveshaft is not a problem--at 45mph I disengaged the clutch, allowed the engine to go to idle, and the vibes went away even though road speed hadn't changed. That eliminates the driveshaft. Getting Ole Bessy started and feeling under the car (nawww...don't think I'll be doing that!) won't do any good, I've reduced the vibes except in mid-rpm range by removing all compression of the mounts. 

 

Please keep in mind this engine ran VERY smoothly with the old mounts, never noticed any issues until the mounts were changed. Lots of ideas have been presented as to what is now wrong (driveshaft, damper, interference) but EVERYTHING points to the new rear mounts being too hard. I looked at the front mount and it still has rubber in place (but why would that have changed overnight when the rear mounts were changed??).

 

A very experienced member of the forum has stated that there are new mounts out there that are too firm. I'm convinced I got a set of them.

 

I'll drive the car as is and don't intend to mess with this any more unless someone finds mounts that are soft enough to convince me to pull the transmission again. All the suggestions and feedback is certainly appreciated even though the root issue still exists.

 

One bright spot is the transmission leak that started this whole process is FIXED.

Edited August 16, 2019 by Sam Buchanan

[Frank Elder]

As stated the hard mounts have raised the height if the motor possibly changing your pinion angle. probably not your problem, but softer mounts would compress more giving you the correct angle and not transfer vibration from the engine.........maybe consider shaving these hard mounts until they match the pinion angle and maybe it won't  vibrate as much until you find the ones you need ?

Just a WAG nothing else...lol.

[Sam Buchanan]

Frank, the new mounts have restored the angle to what it should be with new mounts...... 

 

I'm a bit perplexed as to why there seems to be a resistance by folks accepting......that these mounts are just too firm.....simple as that.

 

Softer mounts (lower modulus of elasticity) wouldn't ride lower, they would just absorb vibration instead of transmitting it. 

 

But I do appreciate the efforts to find a smoking gun.

Edited August 17, 2019 by Sam Buchanan

[Frank Elder]

Gotcha, my last question.....Are you a purist and it " must " be stock mounts and nothing else, or are you open to other avenues ? And my saying purist is not an insult it takes all kinds to make our cars what they are.

[Sam Buchanan]

1 hour ago, Frank Elder said:

Gotcha, my last question.....Are you a purist and it " must " be stock mounts and nothing else, or are you open to other avenues ? And my saying purist is not an insult it takes all kinds to make our cars what they are.

 

Frank, definitely not a purist, my car has been modified to make it as reliable as I can (electric fuel pump, alternator, etc) because its purpose is to be driven. Just got back from the 22 mile trip to the airport. 

 

The mounts are a closed chapter as far I am concerned......I ain't pulling that transmission again anytime soon! The purpose of this thread is to inform those who are yet to consider changing mounts and let them know there are things to consider. I close my part of this thread with the following scan from the Service Manual:

 

The mounts I have don't have a white stripe......and they sure aren't pliable........but......they do transmit vibration.......

 

Edited August 17, 2019 by Sam Buchanan

[Frank Elder]

[Cold Blue]

19 hours ago, Sam Buchanan said:

 

I've looked for any places where exhaust or drivetrain could be touching the car. Keep in mind the ONLY thing that changed other than the mounts is the bellhousing is riding maybe 3/8" higher than before (probably where it would have been with the mounts it came with out the factory). The driveshaft is not a problem--at 45mph I disengaged the clutch, allowed the engine to go to idle, and the vibes went away even though road speed hadn't changed. That eliminates the driveshaft. Getting Ole Bessy started and feeling under the car (nawww...don't think I'll be doing that!) won't do any good, I've reduced the vibes except in mid-rpm range by removing all compression of the mounts. 

 

Please keep in mind this engine ran VERY smoothly with the old mounts, never noticed any issues until the mounts were changed. Lots of ideas have been presented as to what is now wrong (driveshaft, damper, interference) but EVERYTHING points to the new rear mounts being too hard. I looked at the front mount and it still has rubber in place (but why would that have changed overnight when the rear mounts were changed??).

 

A very experienced member of the forum has stated that there are new mounts out there that are too firm. I'm convinced I got a set of them.

 

I'll drive the car as is and don't intend to mess with this any more unless someone finds mounts that are soft enough to convince me to pull the transmission again. All the suggestions and feedback is certainly appreciated even though the root issue still exists.

 

One bright spot is the transmission leak that started this whole process is FIXED.

Sam - glad the leak is fixed!!! When I find some soft mounts I will do what you did and grid the shallow groove so the oil drains out properly. I now think you are right - mounts that are too hard are the problem. I am going to order some mounts that I found on the Web and see if they pass the fingernail test. The ones I found are not too expensive, so if they are too hard, big deal. I will let you know if they appear to be good mounts. Congrats!!

[kencombs]

I've noted some later model mounts are molded with cavities that reduce cross section of the mount rubber.  Maybe drill some holes in the mount to soften?

 

Look at this site for info:

https://www.avproductsinc.com/center-bonded/two-piece-mounts.html

Note that in each size they offer three different durometer mounts.\

 

It would be nice to know the specs on yours.

 

Maybe the reason the original type isn't provided by vendors is that they are buying stock items from somewhere similar to the ones I linked.  And have Ordered the wrong spec.

[Eneto-55]

54 minutes ago, kencombs said:

I've noted some later model mounts are molded with cavities that reduce cross section of the mount rubber.  Maybe drill some holes in the mount to soften?

 

That's what I was trying to get at with my comment last Wednesday evening, but not sure I was clear enough on what I meant.

 

I have some white rubber 'donuts' about the right size & shape that I picked up on the bargain table at the local hardware store.  (They used to have $5.00 bag sales - what ever you could get into the bag.  Now they upped it to $10.00, and it's hardly worthwhile anymore.)

Anyway, these white rubber ones have a triangle cast into it, with the number '12' inside the triangle.  I had wondered if that was a hardness rating, but I couldn't find any such thing in an on-line search.  They are pretty soft and bendable.  Would white rubber hold up as well as black rubber?  Is there a real difference in the composition?  Some say that the stuff they add to rubber that makes it black greatly increases its strength.

[Sam Buchanan]

2 hours ago, kencombs said:

I've noted some later model mounts are molded with cavities that reduce cross section of the mount rubber.  Maybe drill some holes in the mount to soften?

 

Look at this site for info:

https://www.avproductsinc.com/center-bonded/two-piece-mounts.html

Note that in each size they offer three different durometer mounts.\

 

It would be nice to know the specs on yours.

 

Maybe the reason the original type isn't provided by vendors is that they are buying stock items from somewhere similar to the ones I linked.  And have Ordered the wrong spec.

 

Drilling the holes is a reasonable idea.

 

Now......who wants to do the prototype work (buying several sets and removing and reinstalling the transmission several times for road tests until the right combination of holes is found)? 

 

I'm convinced an undesirable spec is being used to manufacture our mounts. That spec may work ok in other applications.

Edited August 17, 2019 by Sam Buchanan

[kencombs]

1 hour ago, Sam Buchanan said:

 

 

 

I'm convinced an undesirable spec is being used to manufacture our mounts. That spec may work ok in other applications.

 

I'd bet they reseller just ordered the wrong spec from the catalog, and the right one exists, if we could just find the right manufacturer's catalog.

[Dodgeb4ya]

I bet no one today really knows or cares a lot about the correct type and firmness of the rubber used on an old flat head engine mount.?

If most people don't bitch than all is good for the seller and re-pop fab man.

Edited August 17, 2019 by Dodgeb4ya

[Sam Buchanan]

46 minutes ago, Dodgeb4ya said:

I bet no one today really knows or cares a lot about the correct type and firmness of the rubber used on an old flat head engine mount.?

If most people don't bitch than all is good for the seller and re-pop fab man.

 

I suspect that pretty much sums it up.   

Edited August 18, 2019 by Sam Buchanan

[RobertKB]

Very interesting thread. I have an identical problem in my '51 Dodge D39 business coupe. Loosening the pressure on the bolts holding the mounts has helped but still some vibration. Like you, when I depress the clutch at speed the vibration disappears. I'm hoping that with more miles and lots of heat down there that the mounts will soften up. Right now, even though there is some vibration, the car is certainly driveable.

[kencombs]

23 hours ago, Sam Buchanan said:

 

Drilling the holes is a reasonable idea.

 

Now......who wants to do the prototype work (buying several sets and removing and reinstalling the transmission several times for road tests until the right combination of holes is found)? 

 

I'm convinced an undesirable spec is being used to manufacture our mounts. That spec may work ok in other applications.

stumbled across this pic while searching for something else

 

  I wonder if that company is still around.  At least, I feel more confident of the 'holes' suggestion.

[Sam Buchanan]

4 hours ago, kencombs said:

stumbled across this pic while searching for something else

 

  I wonder if that company is still around.  At least, I feel more confident of the 'holes' suggestion.

 

I ran across a different photo of those mounts back when I was shopping for mine but moved on since they were listed for Chryslers. But without knowing the density of the rubber and how much weight is supported by the mounts I don't know if this is of much value to P15 owners. I couldn't find this company in Mr. Google's search.

[Furylee2]

On 8/18/2019 at 4:19 PM, kencombs said:

stumbled across this pic while searching for something else

 

  I wonder if that company is still around.  At least, I feel more confident of the 'holes' suggestion.

I just bought these at a swap meet in March for $10. He had two sets, wish I picked up both. I can tell you, they pass the finger nail test.

[Sam Buchanan]

Well...lookee what I found.....was poking around on the Rock Auto site for a couple of items and found some transmission mounts listed under the 1954 Plymouth section (my car is a '48 and no mounts listed for that year). Matter of fact they had two sources for upper mounts from which to choose. And.....one of the mounts was only $2.45 instead of the $12 I paid "the other place". 

 

Hey, why not order a pair and see what they look like? Here they are:

 

 

 

And they do a passable job of passing the thumbnail test! These were made in India and appear to be rubber instead of the hard stuff my other new mounts are made of. Now...if someone wants to volunteer to pull the transmission out of my car we'll pop these puppies in and see if Smoothness returns. 

 

(I've had ponderings about whether or not the bellhousing could be wedged up enough with the tranny in place to swap out the mounts....it would be very tight but might work.....)

Edited August 29, 2019 by Sam Buchanan

[Eneto-55]

If you have had the center floorboard panel out, you might be able to get enough room by pulling that out.  But if it's not been out for decades, then bolts will probably twist off.

[Sam Buchanan]

18 minutes ago, Eneto-55 said:

If you have had the center floorboard panel out, you might be able to get enough room by pulling that out.  But if it's not been out for decades, then bolts will probably twist off.

 

Oh its been out....about five times.....   

[soth122003]

You know Sam, you could probably pull the floor and jack up on side of the tranny at a time and change them out easily. I know the right side is a breeze but the left side might give you some trouble. just a thought and I would probably only take about 20 minutes per side.

 

Joe Lee