88950 Transmission Rebuild Question

[LegionPiper]

Hi folks,

There is plenty of documentation on the actual process of rebuilding the unit.
However, I am wondering whether anyone treats the gaskets while applying them ?

The Docs just state to clean the area, put the gasket on the surface, and then mate them.

Does anyone put sealers etc on as well ???

Also, since all bolts traverse through the casting itself to the inside, does anyone apply thread sealer ???

How about the bearing surfaces ? Anything there ??

Thanks

[sturmtyger380]

I just rebuilt a M37 transmission and used aircraft sealer on all gaskets and bolts. After I filled it i still had leakage from the front lower bearing.

I had to take the input shaft off so I could get the bottom bearing cover off. The gasket was still good but just not sealing well. Since the front lower was leaking I decided to do the back one also.

I used some of the expanding Permatex the Right Stuff - Gasket Maker. It expands so don't use too much. I put some on both the body and bearing cover and reassembled.

So far no leaks.

http://www.permatex.com/products-2/prod ... ker-detail

[ashyers]

I like Loctite 515 anaerobic flange sealant. Easy to use, easy to clean up, no chunks in the oil, and easy to remove if you have to crack things open again !

I'm curious to know how the rebuild goes. I have not done the M37's transmission yet, but may soon. Take notes of any "tricks"!

Andy

[LegionPiper]

Sure thing Andy.
I am taking pictures and notes along the way.

I did discover that my particular model is quite early, so the correct manual was the M37 Restoration Guide ( TM 9-8031-2 /T 019-75—A-100 ) My Reverse forks are on the reverse idler gear shaft as opposed to the Transmission Cover Assembly.

The Tool required to back the shaft out must be quite the engineering marvel.

For that part, we tapped a piece of 1/8 " steel, slid it into the slot in the shaft, and backed the shaft out using this home-made puller.
More news later.

[T. Highway]

Please share pictures of the home made puller and special tools that you made to do this rebuild.

Bert

[LegionPiper]

Hi Bert,
You bet !
I have another spare that I'll be using to fix the existing Transmission that's in the truck right now.
The Tools that I built were crude, but gave me ideas on what would work better.
I'll post the pics of those tools shortly.

Quick question, I have two 88950 castings.
The tops look identical in every aspect except one.
The first has 6 caps, one on each end of the Shift Rails to remove them.
The other only has 3, on the end opposite the Shift Tower.

I haven't found any manuals that contain a top like this ??

The only approach I can figure to remove the rails is to use a Bolt & Long Sleeve set against the inside of the cover to back them out through the single hole...

Anyone ever come across this ?

[Elwood]

Aside from the shift rail holes, those two castings don't look identical. The shift towers are slightly different in shape, and the horizontal edges along the front have some differences. Could the cover without the through holes for the rails be from a different New Process transmission?

[MSeriesRebuild]

We had similar situations back in the early days. Soon learned that gaskets must be of the proper thickness or leaks will happen. You just can not pull a gasket out of the kit and install with the assumption it is the correct thickness of material. Bearing retainers all over the unit can be an issue; best way is to check the fit of all retainers either with a feeler gauge or marking compound on the ones where a feeler gauge can't be used. After bearings are installed and seated fully, hold the bearing retainer tightly against the snap ring on the ball bearings, measure the gap between the retainer and the case at several locations around the circumference and go with a gasket thickness approx. .006" thicker than the gap; gasket must compress. Absolutely use a premium gasket sealer, we prefer anaerobic. If bolt threads are not sealed really well, oil will find its way past the threads. We use sealer designed for threads on hydraulic fittings with a good result. Put a small amount of sealer in the hole threads, then apply to bolt threads, this insures sealer is on the threads all the way through the hole. May not appear right away, but after a couple of weeks you will have a seeping, dripping mess if bolts are not sealed. Tightening a retainer that does not have enough gasket thickness under it will often result in cracked retainers also. Bolts don't have to be extremely tight if the job is done properly; most retainer bolts are 5/16"x18 thread pitch. Use split lock washers and SAE flat washers where space will allow for better distribution of tensioning, grade 8 hardened washers are the best option. The proper torque for the 5/16 course thread bolts is 180 in. lbs. Recheck torque several times waiting a few minutes between successive torque applications. This gives a chance for the gasket to compress and any excess sealant to squeeze out. Pay attention to the bolt length; choose a length that will reach all the way through the case, and be flush or very close on the inside when installation is complete. If bolts that are too short are used leaving a cavity in the bolt holes where oil can puddle or stand inside the case, they will be far more likely to be the source of a drip that shows up outside around bolts. Pay attention to the inside of the case surface; many of these old castings are very porous. Oil will actually seep through the porous casting. We coat ours inside with a couple of good coats of epoxy primer and paint the outside making sure all areas are covered completely; allow it to cure well before oil is put in. Glyptol is also a good high quality interior coating that works very well. Another likely leak source is around the outer case of oil seals. In most of these older gear boxes, you will see that others have been very wreckless when removing oil seals. This results in scratches and many times deep gouges in the retainer castings where seal pullers have been used carelessly. If you don't fill these areas with a 2-part epoxy and sand the seal bore back smooth, oil will find its way between the seal case and its cast bore after a few days. Added insurance here, apply anaerobic sealer in the retainer seal bore before pressing the seal into place, applying sealant in the bore will fill any minor low spot imperfections left in the seal bores as the seal is pressed in. Many times leaks here will be blamed on what is thought to be a leak from the seal lip when that is not the problem at all. Lastly, check those yoke seal mating surfaces, any wear grooves, rust pitting, etc., will not allow a new seal to do its job. Older yoke surfaces most often are not machined to a smooth enough finish for today's precision seal lip material to mate well enough. It is common practice for us to install a redi-sleeve on all yokes, even if they look decent. These are polished stainless steel; that have a really nice precision finish and will not cause rust issues later. I always apply a thin coat of anaerobic before pressing the redi-sleeve onto the yoke, as with seals, this will fill minor imperfections as the sleeve is pressed into place. When yokes are installed onto the splined shaft, apply a nice bead of silicone on the washer before slipping it on the shaft. This forces sealant around the shaft splines when the nut is torqued into place preventing oil from passing between the splined shaft and yoke, and dripping around the nut. Cleaning well, close inspection, paying attention to detail, and following the above guidelines has paid off well for us in building leak free gear boxes.

[LegionPiper]

Hi there Charles,
thanks so much for the detailed reply, you have no idea how much I appreciate it !
I really do want a no-leak Case once we're done, so I'll revisit the Screws and check clearance on the gaskets.
I'll also look for a redi-sleeve for the Yoke.

Say one more question sir, I started the process of preparing the plate for removal in the cab and discovered that I don't have a NP420 in the truck at all. ( I suspect the original was removed when the previous owner pulled the Winch out )
From looking at the tower, it looks like a NP 435, or at least the tower does.

Does the NP435 fit perfectly onto the Truck or would modifications have been made to the frame / drive-train to make it fit ?

Thanks again,
Derek

[MSeriesRebuild]

Hi there Charles,
thanks so much for the detailed reply, you have no idea how much I appreciate it !
I really do want a no-leak Case once we're done, so I'll revisit the Screws and check clearance on the gaskets.
I'll also look for a redi-sleeve for the Yoke.

Say one more question sir, I started the process of preparing the plate for removal in the cab and discovered that I don't have a NP420 in the truck at all. ( I suspect the original was removed when the previous owner pulled the Winch out )
From looking at the tower, it looks like a NP 435, or at least the tower does.

Does the NP435 fit perfectly onto the Truck or would modifications have been made to the frame / drive-train to make it fit ?

Thanks again,
Derek

This is an impossible question, 435 transmissions were used by various manufacturer's. Different variations in design are common, such as input shaft lengths, diameters, spline count, etc. There was also numerous differences in the case in relation to mounting ear placement, among other case differences. I can't say I have ever seen a 435 that was a direct fit into an M37 application. You would need to determine for sure if that is what you have. The top assembly used on the 420 and the 435 are very similar, I would suggest looking a little closer at what you have.

[LegionPiper]

Thanks Charles !
I'll clean it up prior to removal and inspect it further and take pictures as well.

There was nothing obvious under the truck to suggest that major changes were made.
However, once the grease and dirt is removed ....

[MSeriesRebuild]

Thanks Charles !
I'll clean it up prior to removal and inspect it further and take pictures as well.

There was nothing obvious under the truck to suggest that major changes were made.
However, once the grease and dirt is removed ....

My guess is you do have a 420, if you post detailed pictures after clean up, should be able to tell you I think.

[LegionPiper]

Hi Charles,
I tracked the Redi-Sleeve down to Timken.

How did you determine the size and shape that is needed ?
Is there a part number to order them from a local Bearing Supply Company ?

Thanks

[MSeriesRebuild]

Hi Charles,
I tracked the Redi-Sleeve down to Timken.

How did you determine the size and shape that is needed ?
Is there a part number to order them from a local Bearing Supply Company ?

Thanks

Part# 99212. NAPA offers these from the SKF line, Speedi-Sleeve, Same number for Timken, Redi-Sleeve. We have used many of both brands, equal quality. I don't prefer 1 over the other. Ordering on line from some sources could be import parts, be careful. Many of these are not true to size, could end up being too tight or too loose.

[Elwood]

Hi Charles,
I tracked the Redi-Sleeve down to Timken.

How did you determine the size and shape that is needed ?
Is there a part number to order them from a local Bearing Supply Company ?

Thanks

This might help: http://www.timken.com/EN-US/products/se ... s/7707.pdf

Page 6 gives a basic overview of Redi-Sleeves. Page 130 is the catalog of the individual Redi-Sleeve part numbers, including size ranges.

Redi-Sleeves are available through most auto parts stores, eBay, Amazon, rockauto.com, Finditparts.com, etc.