How different is B1gearbox?

[jim lee]

I have the pre-B1 1953 version of the M37 and I was wondering how different the B1 gearbox is to what I have now. Would it bolt up and work?

-jim lee

[m-37Bruce]

I think it's non syncro, pre- B-1 and synchronized for the B-1? Double-clutch for us, simple shift for the B-1 folks. I don't think they are interchangeable either? (I've been wrong before )

[mike_l]

Bruce is right, internally they are not interchangeable. However, the late (B1 style) will bolt up to the engine and mount in the truck the same as the early transmission. I'm running a B1 transmission in my '54 now without any problems.

[topellis]

From what I understand the two transmissions are interchangeable as assemblies but the internal parts do not interchange between the two. I am pretty sure that the gears that are Syncro is the same for both earlier and later ones. (between 1st and 2nd) I rebuilt my earlier version one 8 or so years ago and I remember that the synchronizer itself was difficult to locate as were some calibrated (thickness) snap rings you used to set the amount of play in the main gear assembly. I have heard it said that the later B1 transmission would not fail as the earlier ones would on the main shaft where the snapring groove is and that made them more desirable.

Mark

[jimmy_stikx]

Both are synch'ed through 3-4th, 1-3rd aren't. As far as I've read, the ratios are the same. Everything else has been stated.

[Chris P]

How can you tell, from the outside, which one is installed on a truck?

[MSeriesRebuild]

A little bit of accurate info in this thread, a bunch of it however is not correct.

Synchronization is with 3rd and 4th gear in either unit, only 1st and 2nd is non-synchro. This is true of both early and late units. It is true that the later NP420 units used in B-1 trucks is a vastly improved trans, because of 2 issues. The mainshaft design and the shift tower design. The mainshaft is far heavier in the 420, and has a snap ring that holds 2nd gear in addition to the earlier single snap ring design in which a single small ring held everything on the mainshaft forward of 1st gear. The addition of the much heavier shaft and the double snap ring design greatly cuts down on mainshaft failures which are fairly common in the early style units.

The shift tower design is different in that the stub ball has an alignment slot on both sides of the ball and is removable from the tower on the outside. The early box stub ball had only a single groove on the right side. Once a relatively small amount of wear became prevalent in the shift ball / tower area, shifting becomes really sloppy, especially going into reverse.

Most internal parts are not interchangeable, however a few are. No problem at all changing the whole box, either fits like a glove.

Someone ask how the early is externally recognizable from the later 420; on the early unit, simply look at the shift tower, the stub shaft / ball assembly is not removable to the outside. It can only be removed from the inner side of the top cover, AFTER all the shift rail mechanism has been removed. The 420 has a retainer on top of the ball which with a quarter turn counter clockwise will lift out allowing the stub ball and spring to lift straight out the top of the tower.

[Chris P]

Thanks Charles!