VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc 1936 Master differential

Another thing to check for is a washer that was left in place when disassembled.

Oh, okay now I got it. I think I have the thicker ones as well and will try to find so I can measure them.

Dave

No luck on 323198. I did find one labeled 328198 but it must be mislabeled since it measures .460.

Dave

I still haven't been able to get back to it, but will sometime today. I have a whole stack of 328198 here now. It seems to be too thick. After measuring things quickly with a caliper, and comparing to some genuine GM gears and bearings, it seems likely that the carrier casting is mis-machined. I hope not. It is the best one I have, and I have spent a lot of time cleaning up the inside.

Hopefully I just made some kind of mistake test-fitting the pinion, but it sure looks like that washer is going to have to be thinner than what GM normally supplied.

Ok i reassembled it again and with no shims (except the 328198 backing washer). The manual sates that the bottom of the pinion should be level to the bottom of the teeth of the ring gear.

http://chevy.oldcarmanualproject.com/shop/1938/38csm093.html

This is what I am seeing:



I am sort of at a loss for how to measure that, but it looks to be sticking out at least .060. No extra washers or shims, only a 328198 (.190) in this picture. I did not re-run the contact pattern this time, but it was unusable before, and this pinion protrusion looks about the same.

I am guessing I need to get a machinist to cut a 328198 down to about .100, and then shim it back up, Any ideas?

I am now wondering if that "3360" mark is 3.360 inches (with a pinion setting tool, as used on some newer vehicles).

EDIT... I need to find a better way to measure this.. maybe in the morning.

It wont help your problem but I can't find 323198 in any of my Chevrolet books maybe that is a Pontiac number? I could also be I am going blind...

Dave

It's probably a typo-part number is 328198 grp5.460

Yes, it was a typo, and I made it several times. Sorry about that. I have gone back and corrected the posts. Thanks!

This cannot possibly need a shim pack as thin as I originally thought. It would pull the pinion tight against the rear bearing. I now think the number on the face of the gear is the actual depth, and am trying to find someone local who can measure it accurately.

I checked with several shops that build axles today, nobody has the pinion setting tool. I took it to a machinist friend, and we measured it as well as we were able without the fixture. I do believe the mark on the front of the gear refers to a distance. If that is true, then using a 323198 washer plus the only 2 shims I have (they measure .016 each), the pinion is still too deep in the carrier, and needs .022 more shim.

We measured from the flats with the bearing caps removed. If the carrier bearing bores are not perfectly centered, that potential error is not accounted for. This should get it close enough to check the pattern and make slight adjustments if necessary.

Dave39MD, you have a PM about shims.

I have had shims for a few days now, but haven't had a lot of time to work on it. The end of shimming has to be close though, so I thought I would ask about the next part now....

The next things to do will be tightening the big nut on the pinion bearing and riveting the pinion to the driveshaft.

I assume that nut needs to be really tight before staking. How do you do it? There just isn't any good place to grab it with a vise.

Then there is the pin. IIRC the manual says something like "use a steel pin and peen over both sides". How would you get the first head started?

I do have a rivet I bought with my last box of Filling Station parts. It was not listed for 1936, only 1930-33, but maybe it would be OK if cut off to the correct length? How do you guys do this?

Then, how tight should the splines be? It is fairly tight, but not super tight. I was considering putting a little Loctite in there when I assemble it for the final time. I just noticed the Pontiac manual says that a little looseness in the spline allows for bending of the torque tube. Chevrolet did not mention that and it is literally the same torque tube as 1936 Chevrolet Master except for 1/2" difference in length. I also don't see why the tube would be bending unless the torque ball was horribly misadjusted.

I recall that on later models, Chevrolet had a press fit on the pinion requiring a puller to remove. Any harm in making it really tight on a 1936?

It is spring and I am finally working on this again.

I never got back here to say so, but I did get the pinion shimmed properly last fall. It wasn't easy. With the new shims (Thank you Dave39MD!) I was initially not able to get anything close to a usable pattern. One thing that became clear was that the pinion was longer (thicker) than it was supposed to be, and the instructions in the factory manuals weren't going to work.

I bought a pinion setting tool on ebay. It is a Hinckley-Myers tool intended for 1930s Buicks. It has a depth micrometer built into a fixture that clamps in where the carrier bearings go.

The trouble is, the Buick tool was based on the idea that you start at a specific setting on the tool, and the markings on the pinion tell you how many thousandths to shim in or out from default. There are 2 reasons that is a problem. The first is since the Chevrolet/Pontiac rear axle was not intended to be set this way, there is no default measurement in the shop manual(s) for the Hinckley-Myers tool. The second is that my aftermarket pinion was not marked plus or minus in thousandths, as GM might have done with a Buick. It was marked with the actual distance from the pinion face to the center of the carrier bearings.

I took the Hinckley Myers tool to a machinist friend, who took measurements. He verified that the tool and it's checking fixture were still accurate, and then he measured the "default" dimension with the micrometer set at zero.

With a little math it was no big deal to figure out what the micrometer should read when the pinion was set to the dimension it was marked. I was finally able to get an acceptable pattern, not perfect, but OK. I don't recall what the actual shim stack was, but it was thicker than Chevrolet's default by quite a bit. The ring gear wants to run at .007 backlash. Both the pinion shimming and the ring gear backlash adjustments were extremely sensitive, and it was quite difficult to hit the magic spot that gave an acceptable pattern.

And now I have a couple of questions...

Firstly, How do you tighten the big staking nut that holds the front pinion bearing to the pinion? The shop manual (1938) has you doing it before riveting the pinion on. Were they clamping the spline? It seems like that would cause damage.

Secondly, what do you use to rivet the pinion to the driveshaft? I see the Filling Station doesn't stock a rivet in 5/16" for this. I am guessing it is just a piece of steel 5/16" steel dowel, as the shop manual (1938) mentions riveting it on both ends. I have a 5/16" hot rolled steel dowel here. How much metal should be sticking out each end before you start hammering?

Thanks for any hints.

http://chevy.oldcarmanualproject.com/shop/1938/38csm086.html

When I rebuilt the rear in my 32 I used a common nail. I left about 1/8" sticking out before hammering and after 19 years it's still in there. It does need to be a snug fit thru the bore.

Thanks, I'll try with about 1/8" and see how it goes.

I looked through my rear end parts and found some rivets a little larger than 5/16 , 11/32. I have flat head and round head, do you think they might be right for what you are doing?

Dave

I don't know but I will check tonight or tomorrow. I have not had time to work on it today yet. Thank you!

These turn out to be actually 5/16". I just measured the hole. I think (hope) I have it covered as I have some 5/16 steel dowel here. I am going to start with 1/8" sticking up based on what m006840 said, and also what Chistech said over on the AACA forums.

Thanks for looking!