The Stovebolt Site Forums The Shop Area Driveline 1955 GMC Hydramatic Flexplate Question

I have a 1955 GMC 100 2nd Series 248 L6 4.1L with a 4speed Hydramatic transmission. I'm in need of a good/working condition 139 tooth Flexplate. I have a six volt starter to go with it. My current flexplate has a lot of worn out teeth so I'm looking for a replacement. Flexplate has 18 holes that is used to bolt to the torus cover and also has a rubber seal around it. My question is, can these worn out teeth some how have some welding done to them to fix the grinding noise when trying to start it up? Or can another year or engine size flexplate be used in it's place? If so, would anyone have info on where to find one? Thanks a lot in advance for any info.

AL

Contact FATSCO transmission parts in New Jersey. If they don't have the part they probably know where to find one. I've been doing business with them for 30-something years on vintage transmission stuff.

http://www.fatsco.net/contact-us.html

Jerry

I did not realize that the 1955 GMC 100 2nd Series trucks were still six volts.
Chevrolet switched to 12 volts in 1955 2nd Series trucks.
1929 - 1954 Chevrolet Master Parts and Accessories Catalog shows the flywheel below:
Truck Automatic Transmission - Flywheel and Fluid Coupling illustration
I think both GMC & Chevrolet flywheels are the same.
The crankshaft bolts hole pattern probably are different.
They both have 139 teeth.

Welding then machining the gear teeth would be tricky because of the pitch or angle of the teeth.
They have to match the starter gear teeth.

I know the Chevrolet flywheels are hard to come by because they were a one year & three month production in 1954-55 1st series .

GMC production fairs a little better 1953 - 1955 2nd series.
So it should not be as hard to find one.

Call http://www.restorationhydramatics.com/ talk to Gene in Cali.
Or http://nwtparts.com/ ask for John.
Or here might be one on eBay do not know if it is 139 tooth.
This ONE is 12 volt 168 tooth

If you can find the GMC part number that would be helpful?

Since the H-M flywheels are so scarce and expensive, I wonder if anyone has tried machining the teeth off and installing a shrink-fit gear from a standard shift flywheel? It should be a fairly simple operation for somebody with a big lathe. I'll bet a brake drum lathe would work if some careful measuring was done.
Jerry

Hotrod,

Thank you for the Fatsco link. I will give them a call on Monday.

Jorb,

Thank you as well for the links provided. As far as the part number, the only info I was able to find was same numbers from the link you provided showing the parts of the hydramatic. I will give those places a call on Monday.



AL

I think the replaceable ring gear trick was tried by a guy on the old gmc truck site and it turned out to be a fail. I don't know the details but do recall he considered it a nice try but nope project.

That makes it an interesting challenge! Anybody got a junk flywheel to practice on?
Jerry

I've got at least one spare 1954 Chevrolet H-M 6v flywheels, but none is available for experimentation or practice.

Jorb,

I've been looking around for a part number for the flywheel but no luck. I've taken some pictures of my current Hydramatic flywheel. I've tried to find information to see if the Chevy & GMC flywheels are interchangeable, but not luck yet.

tclederman,

Could you PM me? I would like to see a picture of your Chevy Hydramtic flywheel and see it the crankshaft bolt holes are lined up differently.

AL

AL,

Here is one side of the flywheel. I'll see if I can find a photo of the other side.

Post a link to a photo of your flywheel.

additional photos of flywheel (near bottom of page)

By the way, the 1953 GMC Hydra-Matic flywheel is different from the 1954 Chevrolet truck flywheel. I'll see if I can find a photo of a 1953 GMC H-M flywheel.

There would be no point in butchering up a good one, but if anybody has replaced a flywheel for bad starter gear teeth, I'd love to have it for experimenting. With an accurate lathe and a tool post grinder for the final diameter machining, I can't really see why a separate ring gear couldn't be fitted. Once the gear is in place and running true, a few TIG welds would assure it stays put.
Jerry

The 1954 Hydramatic Spec. sheet says the H-M flywheel is heavy pressed steel with teeth cut in outer edge and hardened.
(Bottom LH side of page, under Fluid Coupling)
There are two areas were they have been known to leak, connection at crankshaft and outer rubber seal at torus connection.

I sent an e-mail to Jerry to see if by any chance he still had his failed flywheel. I directed him to this thread or if he contacts me, I will pass on what I find out. The ring gear should be well outside the sealed area of the torus housing. I know the ring gear was too thick also that came on a manual transmission flywheel so it will have to be thinned.

tclederman,

Thanks for the link to the pics of the flywheel.
Here is a link to some pics of my flywheel.
https://www.dropbox.com/sh/2fom5i25tbz15rn/AABwOG05voewOM2wLsU3bYyoa?dl=0

What do you guys think? The six bolt hole pattern does
look the same to me. My flywheel does not have the three extra holes as the Chevy HM flywheel.
Would it matter at all? Everything else seems to be the same, but I need all of your opinions.
Thanks again for all your help.

Those teeth look rough all the way around, like they have been run against a 12 volt starter gear. If the bolt spacing is the same on the Chevy flywheel and the torus bolts up the same, I see no reason not to do the swap, but be aware that it's possible the Chevy has an oddball spacing on at least one bolt to keep from mis-aligning the ignition timing ball. I'm not sure if that's the case on the GMC.
Jerry

There is another thing I noticed between the GMC and the Chevrolet H-M Flywheels.
This Picture of the GMC flywheel, shows a rubber crankshaft seal.
This Picture of the Chevrolet flywheel, shows no oil seal groove for a rubber oil seal at crankshaft.
I think I read somewhere Chevrolet used a paper gasket at the crankshaft. Not sure about this.

Those extra holes in the Chevrolet flywheel I believe are for the dowel pins that are in the end of the Chevrolet crankshaft.
Best to stay with the GMC flywheel that is intended to be used with the GMC crankshaft.

I'm in the process of looking for the part number of the flywheel and I'll post the part number. I'll call those places you posted in the morrning. Any updates on flywheels please let me know.

A.R

A.R.

Part numbers and some casting numbers are here. (this info might have been posted above)

The 6v/12v 139/168 teeth flywheels are poorly/confusingly delineated in that Master Parts Catalog (for 1955 1st and 2nd, 1/2 ton vs larger trucks).
Assume that 1955-2nd Chevrolet trucks are 12v with 168 teeth.

Here are the part numbers (no casting nos):
8615574 - 168 teeth
8615138 - 139 teeth (corrected number- thanks)

I see the part number as 8615138. I take all HM GMC flywheels from 53-55.5 were interchangeable?

A.R.

I doubt that "all HM GMC flywheels from 53-55.5 were interchangeable" - I think the 1953 GMC flywheel might have been different from later GMC flywheels. Maybe someone will post info from a GMC parts catalog/manual? A GMC parts catalog/manual would help to confirm if/when Chevrolet and GMC flywheels were the same.

Also, it is possible that late 1955 (Blue Chip) GMCs might have been 6v?

(Sorry - my GMC documentation is inaccessible)

As to whether there was a paper gasket used on the Chevrolet HM flywheel at the crankshaft connection.
I guess the answer is NO.
Read under Flywheel installation 1 thru 7
Number 2 says to use a sealer Goodyear Pliabond #3 on the flywheel and crankshaft flange. (This looks to apply to the manual flywheel also.)
Number 5 says to torque bolts to 50-60 ft lb.
Number 7 says on automatic, Run out should not exceed .005
Continued Next page If it exceeds .005, replace flywheel.
Look at fig. 74..Possible leak points. Below under "Diagnosis of oil leaks" its says Insufficient sealer.

So, Chevrolet used a sealer between crank and flywheel.
GMC used a rubber o-ring seal. Look for number 45 arrow in illustrantion 1 and illustration 2
GMC Fluid leak Chart & fig. 54 "Possible Cause" Damaged Seal

I called Northwest Transmission Parts and they are looking into finding the flywheel. I gave them the part number for reference too.

I think about why Chevy would use a sealer between the crank and flywheel and GMC would use an 0-ring seal. I know both methods work, but wouldn't it be cost effective to adopt one method for both divisions?

A.R.

It would have been more cost-effective to share engines between car lines like Ford did, but Chevy, Buick, Pontiac, Cadillac, Olds, and GMC all used very different engines for many years. Sometimes efficiency is trumped by brand rivalry, even in the same company. Why don't all the US military services wear the same uniforms?
Jerry

Just be clear the part # 8615138 is the part number for the Chevrolet H-M Flywheel not the GMC flywheel.


"ten-hut" At ease
.

Ok guys, sorry for the long delay but I have an update on the flywheel. I had called Northwest Transmissions Parts in Ohio. They did not have a hydramatic flywheel at all. But they told me they had their own machine shop, and if I send them my flywheel, they would have no problem rebuilding the worn out teeth. They had the flywheel for about two an a half weeks before shipping it back to me. It looks great! All the teeth were repaired back to original and provided the seals as well.

These were the before pictures.
https://www.dropbox.com/sh/2fom5i25tbz15rn/AABwOG05voewOM2wLsU3bYyoa?dl=0

These are the after pictures.
https://www.dropbox.com/sh/y4bn81a4ip9qjhm/AAA4b0UuB4xDGvIhw6wrzU0na?dl=0


I'll be installing in the next day or two, so I'll give you guys an update on how it goes.

What do you guys think?

Those restored flywheel teeth look like brand new flywheel teeth.
It looks like Northwest Transmissions Parts knows how to restore badly chewed up Hydra-Matic flywheel teeth.
It would be interesting to see how they restored the teeth.
Just out of curiosity, what was the restoration cost?
Must of been a lot less than a complete replacement flywheel. (If you can find one)
Just one piece of advice, I think those restored flywheel teeth deserve some new starter teeth too.

I just might have my backup flywheel restored at Northwest Transmissions Parts also.
One of the 18 bolts was snapped off by the previous owner.

Jorb,

I concur, it would be interesting to see how they restored all the teeth on the flywheel. They have a full machine shop so I can imagine the welding and precise machine equipment they have to get my flywheel back to OEM status.
The cost was not too bad at all. The flywheel repair was $225 and I also purchased the front and rear flywheel o-ring seals together for $29.00. They told me it would cost anywhere from $125 to $425, depending on how much work needed to be done. I was happy to pay up to $425 considering I just could not find a flywheel anywhere. But to be quoted for $225, I was even happier to pay it!
I also agree, the flywheel teeth deserve new starter teeth, and it got it as well. I also sent my 6V hydramatic starter to be repaired at SouthEast Chevy down in Apopka, Florida(Could not find a replacement anywhere). They did a great job on the starter as well!
If you decide to send your backup flywheel to Northwest Transmissions Parts, I'm sure you'll be happy with their work.

A.R.

Ok guys, sorry for the long delay in response. But here's the update for my flywheel.

Installed the re-surfaced flywheel and transmission. Also installed the newly rebuilt 6v starter. Let me say it sounds great when it's being cranked over to start. No more hearing the teeth grind up against the worn out flywheel teeth. Northwest Transmissions did a great job restoring the worn out flywheel teeth.

A.R.