The Stovebolt Site Forums The Shop Area Driveline 54 half ton hydramatic transmission troubles

I have a couple concerns with my drivetrain, I’ve gone through and completed a new U joint replacement along with all the replacement engine and transmission mounts are new.

First thing is, now that I have replaced all the three engine transmission mounting points I seem to get a nasty vibration at 40-45 mph. Prior to changing out the three engine-tranny front mounts, the three mount points were hardly there especially the front transmission mount. Also there was a lot less drivetrain vibration as well. I did not replace the Okie bushing and did not find any large amounts of play in the driveshaft in the bushing. Which makes me wonder if it could have something to do with the transmission. It’s dual range functionality works quite well except for the kickdown needs to be adjusted so it will function.

Second thing is when I move the selector down to 1-2 the transmission and engine seems to labor quite a lot until I move it back to the 1-3 selection and then it functions normal again, has anyone experienced this condition?

AnyHelp would be appreciated thank you

What is your engine serial number?
What is the code on the engine ID plate on the transmission?

They were matched at the factory, to assure satisfactory alignment.

Those transmissions are very sensitive to throttle pressure adjustments, which also controls the kickdown. The rod from the carburetor to the transmission serves as both throttle pressure and kickdown. Also find a copy of the service manual and do a band adjustment. The front and rear bands are critical to good performance, and an out of adjustment band could be responsible for the problems in the 1-2 shifter position.
Jerry

I have a fresh transmission ready to install so really have no experience with a pristine condition transmission operation. The transmission that was in the truck before I tore it down for restoration acted similar to what you described in 1-2. It would all but drag the engine down. I did have a transmission shop (with the owner being of the age that he was well versed in the H-M transmission) check it over and adjust it before it was installed. I also let him drive it for it's maiden flight. I was led to accept that 1-2 was for tromping it trying to get out of a mud bog or some similar scenario. The throttle pressure adjustment as mentioned is critical. a quarter turn seems like it can be the difference between running all gears within 15 feet and not downshifting when slowing down for a corner. Had to "sneak up on it".

Vibration? that is tough. What U-joint did you use. I know the front half is H-M only. The back half is common with manual transmission u-joint. Did you put a manual transmission u-joint in it by chance? The rear mount is just a rubber isolator in a plate that is sandwiched in a bracket that bolts to trans tailhousing. Maybe take it loose and see if it helps take driveline out of a bind? Have to assume that alignment to engine is still the same as you would be using same adapter plate and dowel pin alignment. Are you sure front mounts are correct and that it has not somehow turned into a more "solid" motor mount? Loosen each bolt a quarter turn to see if improves?

My advice may be crap. But I am sure it will draw better troubleshooting technique suggestions if it is.

Greg H brings up a good point about the front mounts. There needs to be a gap between the metal parts where the rubber goes between. This is done by how snug you tighten two of the bolts. The castle nuts on these two bolts are held into position by cotter pins. Too often these fasteners are either not serviceable or lost and replaced by the wrong fastener type and over tightened which squishes the rubber so far that the metal parts come into contact, giving you a solid metal mount. This will loosen the fillings in your teeth in some cases.
The Factory Manual does a poor job of explaining the process of adjustment as well as how the parts go together in my opinion.
I am still waiting for Hotrod Lincoln to apply his Tennessee engineering skills into coming up with a simpler front mount design which does not require any brain cells to rub together to install.
Carl

As I mentioned, the Hydramatic, there are two rubber mounts at the front of the transmission all but disintegrated, but once I replace them this vibration started. So are you saying I need to loosen the bolts for the rubber sandwich? Could that solve the problem since it was never the two mounting pads there when I first got the truck?

Front of the transmission was all but unsupported I’m not sure how many years prior to me buying the truck, how important are these two rubber pads at the front of the transmission and if I loosen them hopefully that could be a solution, any thoughts?

There are two mounts one on either side of the "bellhousing" They are two part each. A part that wraps around the top of the crossmember and a part that goes in from the underside. The front motor mount that Carl talks of is under the engine timing gear cover under a "metal box" to keep oil from destructing the rubber parts. There is actually a fourth mount although it is more of a stabilizer than a mount that is on the rear of the transmission. It bolts to the tailhousing and it attached to the rear crossmember but has a rubber isolator sandwiched in.

I am with you on all the different locations of the four mounts, was not aware there was a unique HM timing gear (area)
front mount. Never have seen an option at any of the supply shops that offer such a mount for HM set ups.

If there is such a supplier can you let men know who that would be?

Also maybe I need to tune the tightness the front (engine) and tranny tail piece mounts. The center (bell housing) mount has that
sleeves between the 2 pieces of rubber that kind of prevents you from over tightening.

Everything is nice and secure for the first time in I don't how many years, maybe too secure.

Thanks Todd

I was not clear. The front mount should be the same. (the one under the timing cover)

So can you tell me if I am to adjust the front motor mount adjustment is it the two inner bolts or the two outer bolts, please let me know thanks 1 million

I am not aware of any adjustment to any of the motor mounts.
Once the bolts are tightened down, that is all that needs to be done.
This applies to both the manual and auto trans. equipped trucks.

1954 Chevrolet Truck Shop Manual
Engine Mounting
Page 1
Page 2

The vibration issue is a process of a elimination.
The first thing to check is to see if the engine serial numbers on the flywheel rear housing matches
the engine serial numbers on the machined boss, located to the rear of the distributor. Read number 18. & Flywheel Housing HERE and Attached Photos

The flywheel front and rear housings compromise a matched set.
Far left and far right parts in this Illustration. Group no. 0.683 Part of Housing Assembly

It is possible the reason why you didn't feel the vibration until you replaced the motor mounts,
could be because the engine and tranny wasn't line-up correctly to begin with. Read this POST to gain more insight
It was shaking all along but you did feel it because the engine & tranny were loose at their mounting points.

More on engine block and HM tranny Alignment and how to fix the problem if the engine serial numbers don't match.
54 shop manual calls it Face Runout and Bore Runout.
Flywheel Housing Alignment check
Page 2
Page 3

xfiles

You may be right about the old motor mounts, they were all worn out or nonexistent