Top shift transmission.

Randy1944

Randy1944

Senior Member
I got great advice earlier and would like to get more opinions. I have bought the Van Pelt book on these transmissions. I have a stock 39 pickup with a top shift transmission that pops out of gear on occasion. I have bought what appears to be a late forties top shift transmission that is in pieces. The cluster gear has a broken tooth. I have decided to rebuild this transmission into a unit that I can use as a backup for my 39 pickup, that has a closed drive shaft. I have found that I need to find a Main Shaft Bearing Retainer #78-7085 B. Then I need to replace the Main Output Shaft #7061, to convert this transmission into one that will work on my closed drive shaft. Then I will need another Main Cluster Gear to replace damaged one. Am I better with used parts or new parts? I expect to buy new bearings and other worn items but am concerned with the meshing of new and old parts. Thanks for advice and especially help with sources for used parts if I go that way.
 
Randy1944 said:
I got great advice earlier and would like to get more opinions. I have bought the Van Pelt book on these transmissions. I have a stock 39 pickup with a top shift transmission that pops out of gear on occasion. I have bought what appears to be a late forties top shift transmission that is in pieces. The cluster gear has a broken tooth. I have decided to rebuild this transmission into a unit that I can use as a backup for my 39 pickup, that has a closed drive shaft. I have found that I need to find a Main Shaft Bearing Retainer #78-7085 B. Then I need to replace the Main Output Shaft #7061, to convert this transmission into one that will work on my closed drive shaft. Then I will need another Main Cluster Gear to replace damaged one. Am I better with used parts or new parts? I expect to buy new bearings and other worn items but am concerned with the meshing of new and old parts. Thanks for advice and especially help with sources for used parts if I go that way.
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Randy ..... Not a thing wrong with SELECT used gears, especially if you purchase pieces from someone like Mac VanPelt that absolutely knows this stuff backwards and forward. Even SOME "SELECT" bearings are a better choice than some of the trash bearings that are being offered today, even when talking about name-brand bearings. This is reason enough to speak and deal with someone like Mac VP when buying trans components.

Coop


.
 
I run used clusters and main shafts that are in great shape in my transmission rebuilds. If you carefully sift through gears and pick out the best there are no issues. NOS gears are very expensive. I agree with V8Coopman.
 
If it pops out of second gear, then there are some things to consider:

1) It is usually a case where worn parts and loose clearances cause this to happen. It is very common!

2) I've not found a single rebuilder that will guarantee their transmissions WON'T pop out of second gear on deceleration (especially from higher RPMs). Most will hem and haw a bit if you specifically ask. ;)

So, it is kind of up to you to see if you can round up the best parts, set the clearances on the tighter side, etc..

3) Things I do: I have Charlie/NY re-bush my second gear to the specific main-shaft I will be using in the transmission. This is to get a slight "drag fitment" on the bushing. I've found that used gears and even NOS ones can be quite loose on the mainshaft.

4) Main shaft: I try to find NOS main shafts (or really nice used ones) - as any wear on the front bearing snout introduces a lot of play into the mix. Lots of guys don't mic the snout to see the wear - I always do. I also put the transmission input and main shafts in my lathe and see how much side deflection I get (with the caged roller I'm planning on using). Sometimes I swap things out to achieve the least amount of deflection where they meet in the middle. Of course, this requires that you have multiple sets to work with. ;)

5) Mainshaft Caged Roller Bearings: I try to find NOS originals or the best used ones possible. Last time I checked, all the repop ones were not up to the quality of the originals. One big issue is with the hardening of the "cages" - the repops I saw did not have hardened cages like the originals - big issue for me!

6) Main Cluster Shaft: All the repops I have seen use inferior materials, are not hard enough and are .001 undersize. If VanPelt has any NOS ones, I'd sure use them. Or, he might have really good used ones. You can turn them over 180 degrees to put the worn side on the bottom - this does help with used ones.

7) Main shaft stack-up end-play: I setup my thrust washers and the resulting stack-up end-play to be about .0025. I never allow it to be over .004. Usually, this requires screwing around with thrust washer combinations, or surface grinding them to exact clearances or surface grinding the back of the 2nd gear to achieve the tight clearances. The tighter the stack-up thrust, the better.

These are the basics, hope this helps!
B&S
 
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Jake dalka said:
How bout starting by checking the condition of the detent springs and parts of your current transmission…..
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That is a temporary band aid. Popping out of gear is an indication of other problems. Those springs alone can't hold the gears in mesh.
 
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Bored & Stroked: Your post about clearances and dimensional sizes raises a question.

Where does one go to find out the original sizes of the transmission main shaft gear and other critical sizes?

Thanks, Jim
 
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