The Stovebolt Site Forums The Shop Area Engine Shop MY6 (89mm) Transmission rebuild

Doug 'desertdog' set me on the right track by recommending a GM shop manual. I found a unit repair manual on ebay for 81 light trucks, and it's all there. Also found a rebuild kit from Denver with same part number as another ebay website selling it for twice as much.

Now to my first challenge: when removing the main shaft, the forwardmost sychronizer assembly (3/OD) became separated before I read the statement that these are a 'selected assembly' and are to be kept together in their original positions. I was able to keep the springs and keys(struts) in their original positions, and the clutch gear sleeve has a paint mark, but there is no evidence of a paint mark on any other piece. By my examination of the components, I can't see how the position of the clutch sleeve in relation to its clutch gear makes any difference, but obviously I am missing something critical. Thanks in advance to anyone who can set me straight.

Russell, Some synchro assemblies had a mark on the clutch gear hub AND on the sleeve. These were to be put in alignment. This was determined at the factory to give the smoothest & least sliding spline resistance under load when the two pieces were indexed in that position. I would probably try them by hand in all the spline positions & if some seemed a looser fit, I'd use that position. More likely, they'll seem all about the same, so just pick a spot & go with it.
Did you get new brass blocker rings? I like to have a new one just to compare the others with. Any doubt, I'd replace them. These are pretty heavy 1st & 2nd gears & put a pretty good load on them. My driving style is to double-clutch on a 1st or 2nd gear downshift.
Hopefully your mainshaft nose is in good shape. I've got a pic of a bad one in my album below.
Hope this helps - Doug

Doug--thanks for the reply. The rebuild kit came with 4 identical new brass stop rings. I studied them carefully before determining they were identical. They fit perfectly and are the same as the old ones EXCEPT they have 3 pairs of slots cut into the inner surface, each pair midway between the raised bosses on the outside of the ring. I presume these are designed to fit a different version of the trans, but their presence will not affect mine. Sound correct?? I am glad to report that the nose of my mainshaft looks like it just came from the factory. Your nose looks like it sat at the bottom of a lake for 10 years.

As I disassemble and examine this trans, I wonder if it has been rebuilt before. Several of the gears show scratches and tiny nicks, but the roller bearings appear new, and there is no wear on the shafts. When I separated the mainshaft from the drive gear there was a single roller bearing inside the drive gear, but none missing from the cluster of 16 rollers which the support the mainshaft nose. The reverse idler gear has nicks in every cog indicating a cover bolt that was about 0.0030" too long. Finally, the gaskets appear to be in too good a condition to be 30 years old. PS, the big bearing on the drive gear shows no sign of wear--very tight and smooth.

Russell, sounds like you got a really good trans. I really can't recall how the blocker rings are configured but I have replaced some & should have a couple laying around somewhere here.
I think the mainshaft nose pitting & related bearing wear is usually from mis-alignment. I never used to check it but after changing motors & using a proven bellhousing & trans combo & having grinding occur when shifting into reverse I now do. I found the back of my 292" block to be off-square from the crank centerline & the dowels to be off too. Wore out the crank pilot bushing real quick too. Fortunately that was with a 4-sp. Saginaw so the parts weren't too expensive. I have since seen that on some MY6 gear sets in core transmissions.
Can you post a link to where you got your parts?
Nice truck you've built. The 3.36 axle should be about right for this trans. I run a 3.08 on the sea level flatland here.- Doug