Transmission mount advice.

Sub03

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Hi everyone.

After spending a year chasing a cyclic vibration noise in my '77 Aspen (5.2 magnum/a904) in the 1800-2000 rpm area, I discovered the problem was a little dent in the power steering pump pulley. Replaced pump pulley and crank pulley and the Aspen was smooth again.

Hoping to get rid of a slight driveline vibration in 35-45 mph and 75 mph++, I replaced U-joints and transmission mount on it yesterday.
The vibration issue is gone, but now I hear a mid range rpm noise through the floor. I'm sure the cheap (Westar) trans mount from Rockauto is the source of my problem. Engine running strong and smooth, no misfiring.

Googled the problem and found several Jeep forums stating aftermarket trans mount is crap with rubber being too hard, and OEM is the only way to go.
Comfort is my goal here, so I prefer rubber mounts and not poly.

Has any of you guys or girls any experience with this? What brand should I buy?
 

volare 1977

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The last couple i bought were NOS mopar ones but they are getting hard to find and expensive when you do find them. The quality in the rubber nowadays is crap especially india and china so that doesn`t leave many choices.
 

Mikes5thAve

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Rubber still ages so the only real benefit to nos is the better metal bracket. The one I used was an anchor one and it wasn't made perfectly straight.
 

Aspen500

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After building my car, I had the cyclic resonant type of vibration also, around 45 mph and up. Tried this, that and the other thing with little to no change. Going by the vibration frequency, I knew it was related to the drivetrain. As a last ditch effort, I replaced the poly trans mount with a stock style I got at Carquest next door to work, they actually had it in stock(!), and,,,,,,,,,,,,vibration gone. When the stiff poly bushing transmitted normal driveline vibration to the body and the hertz of the vibration matched the resonant frequency of the body, it caused a very annoying resonance and vibration. Got to the point where I didn't even want to drive the car at more than city speeds.

IIRC, the mount was made in India but it's been in there almost 10 years and seems fine yet. Guess India crap is better than China crap, but not by much.
 

Sub03

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Thank you for responding guys.

After building my car, I had the cyclic resonant type of vibration also, around 45 mph and up.

Yeah, I saw your post in this thread from three years ago:
Unfortunately the thread died out without any conclusion from the thread starter.

My vibration is definitely rpm related and not prop shaft/wheels.

I found som mounts at Mancini racing and Summit racing. The prices being a bit higher makes me think they could be of better quality. But then again I don't know, and it's a pain and time consuming to order and ship to Norway if they are crap too...

So I was hoping someone who changed their tranny mount lately would chime in with what brand they used and if it turned out OK.
 

volare 1977

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Theory sounds good but I never had any issues with any NOS rubber mounts I have used. I will take them over the junk out there nowadays. I buy them any time I see them at a decent price.
 

BudW

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Urethane (or Polyurethane) for engine/transmission mounts are only for racers.
For street use, only use rubber, or the noise/vibration will bug the dickens out of you.


Actually, for racing, I might consider the Left engine mount being Urethane (or solid), but leaving the Right side and transmission mounts rubber. The other two mounts will not lose any power transfer and will prevent breakage and reduce vibrations.
Either that or directly tie the engine to the chassis:
BB Motor Plate Ft.png

BB Trans Motor Plate.jpg


I wouldn't be surprised there is only one or two people manufacturing our (rubber) mounts - then companies putting their sticker on the box.

Rubber will go bad over time - but I think the high/low temperatures our cars see, as well as oil/coolant and other contaminates also does a number on it as well (oil will cause rubber to deteriorate pretty quick). I would not have any worry about using a new but old rubber mount.

The only thing that might make a transmission mount hard to find is some FMJ mounts have an extra (welded on) exhaust mounting bracket - which might finding the correct mount hard to find. About ten years ago (or so), I bought a few transmission mount inserts - so I could reuse my existing metal transmission mount frame:
Trans Mount Insert.png

I have yet to install an insert, but have heard from friends they can either be easy to install, or a royal pain (mainly getting the old metal shell removed). Now transmission mounts, in general, I have replaced a bunch of in my life - but some of the transmission mounts specific to a few FMJ's are getting hard to find.
BudW
 

Aspen500

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The spool mounts (technically insulators) on our cars have very little movement to begin with as compared to pancake mounts, provided they're in good condition. I'm talking both engine and trans. Even if the engine and trans internals were balanced to perfection, there's still a vibration caused by the firing pulses. One reason so many FWD (and even some RWD) cars with a 4 cyl vibrate so frigging bad at idle when in gear. Firing pulses equal the resonant frequency of the car, or steering column, or whatever and they vibrate something awful. If you look at the engine, it seems to be sitting almost still but inside the car you'd swear there's a 2 lb weight attached to the flex plate. Ford Focus comes to mind. Feels like sitting in a giant vibrator. No, I don't mean THAT kind of vibrator :)
 

Mikes5thAve

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Mine is anchor brand and like I said other then the sleeve through it being on a slight angle I've never had any problem with it.
 

M_Body_Coupe

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Hmm...now you guys have me second guessing my plans!

So the engine mounts I currently have are in very good condition...NOS stuff when I put the 360 motor in the car some years ago, and very little wear & tear since (summer only driving, about 6K total).

However, because the build is pretty healthy, the motor does vibrate a good amount and my thinking was that before I see the NOS rubber get all torn to pieces with the stouter stroker build, I should just upgrade to the POLY inserts, which is what I picked up and it's ready to go!

So how significant of a change have you guys felt going from a rubber to poly engine bushings?

I already have the poly trans bushing, no complaints there. If anything I always felt that stiffening up the driveline was the better direction to pursue when it came to performance applications. After all, I'd rather have the power going to the wheels than being spent twisting the powertrain instead...although how big of an impact that has is hard/impossible (???) to tell.

Maybe pursue BudW's suggestion to replace just the LEFT mount?
 

BudW

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I am going by my experience. your experience will be different. Also, I'm not exactly what the intention of your car is.
My extensive racing history is it is OK to have one solid (or welded up) engine mount (the Left one) but when you try to go solid (or welded) on both engine mounts that you (we, in this case) will experience breakage (K-frame, the ears on block, etc.) over time. This was before urethane mounts were available - so can't comment much there in regards to racing.
After breaking the mounting ears off of two different 340 blocks (4 speed), among other breaking other things, we had to do something different.

Urethane for engine mounts (and control arm bushings) is to "harsh" for me for daily street usage. The passenger side mount doesn't give much problems (rubber breakage) nor has the stress of the Left side. so I suspect having Right side rubber and Left solid or urethane might be a good combination.
For us, we had a welded up Left side mount and rubber for Right side/transmission and breakage dropped drastically.

The transmission mount has always been a source of NVH (Noise, Vibration, Harshness) for Chrysler during the '70's-'80's - and I have seen numerous TSB (Technical Service Bulletins) over the years. I suspect a urethane mount for transmission will also produce NVH - but don't have any experience with that (urethane for transmission) with Chrysler products.
If this is for a race car or on a performance car driven seldom/for short distances, I don't think NVH will matter to the driver.

I plan on using rubber for all three mounts for my big block FMJ's

On a side note, Chrysler did have an option for the older (non-spool mounts) cars, which might apply here. It was a (good sized, 1/4" thick, maybe) cable that attached from K-frame to engine ear mount bolt that was always loose (not tensioned) when engine was in all but WOT conditions. When in WOT, the cable held the engine in place and not the rubber. The (6 to 8" long, I can't remember) cable had two round eyelets on both sides and the cable was welded onto the eyelets. I have seen cables with a plastic wrap and other cables without (on factory cars). I haven't seen this on spool type mounts - because (I suspect) the engine will not go anywhere if the rubber breaks.
It wouldn't be too hard to fabricate a cable (or chain, or whatever) to use as a torque limiter if wanted. It be better for daily driving than using all urethane mounts.
BudW
 

SlantSixSullivan

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I bought the Anchor brand mount and can't say I'm happy with it. Haven't driven the car yet, but I did inspect the mount prior to installing it, and I'm glad I did because the sleeve that goes through the rubber insert was too small on the ID and needed drilled (9/16) for my bolt to fit. I absolutely had to get the tranny hung that day, to make room in the garage for my brothers car that needed fixed. As I drilled roughly 75% of the way through the sleeve, the rubber spun out of the mount and made the rest of the job harder. I put it all together loose just to get the car out of the way. It will not be staying like that. I may try my luck with the same brand, or may go urethane
 

Aspen500

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As I mentioned, when I had the urethane trans spool installed, the resonant vibration was unbearable at anything over 50 mph, or lower if in 2nd gear. When the frequency of the vibration (from firing pulses) matches the resonant frequency of the body, the whole thing has a cyclic vibration. It may not bother some people, but I couldn't stand to drive the car at anything over city speeds. My experience only.

It's the same reason the manufacturer's hang heavy rubber mounted weights on things like the trans, exhaust system, rear differential, etc. It's to reduce the harmonic vibrations and resonance by changing the resonant frequency of either the drivetrain part or the body itself. As an auto tech, I've run into situations where the complaint is resonance, drone or high frequency vibration and then found the factory weight had fallen off. Amazing how much difference it can make.
 

M_Body_Coupe

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Aspen500 brings up an excellent point about those weights that you'll occasionally find here and there, that by all accounts seems to just "weigh the darn thing down"...LOL!

I moved to a poly transmission mount when I built my coupe. I also removed the trangle (or half-doughnut shaped) weight that was attached to the tailshaft housing. It wasn't so much because I was trying to shave some weight off, rather I was putting an X-pipe exhaust in place and that spot was the best-fitting spot to place the X-pipe section in.

Anyways, I also have this high-speed resonance, you can easily tell that is precisely what it is as well. Subsequently I put the re-installation of something to damped that vibration with on my To-Do list. If anything at best it may help/cure it, at worst it does absolutely nothing and all it had cost me was some time to implement.

Here is what that setup looks like right now:

trans_mount.jpg


trans_mount2.jpg
 

Duke5A

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Had the Schumacher poly mounts with the 360 and never had any complaints. I agree using rubber, but if you can't find goods then no bug deal. Use what you can get.
 

Aspen500

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I'm not so sure poly engine mounts will cause the resonance due to what and where they are attaching. A poly trans mount will cause resonance as it transmits through the crossmember directly to the floor of the car instead of a heavy k-frame bolted to subframe rails.
 
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