Transmission gurus, please comment, Wear on bearing retainer plate Options

[MrKona]

I'm nearing the final stages of a "partial" transmission rebuild. To make a long story short. I started off with my original and a donor tranny. Turns out the donor had a broken shift fork, but no other problems that I can see, all synchros and gears look alright, case bearing races fine. No reason to take the shafts apart, so I'm reinstalling the drive and pinion shafts into a freshly cleaned case with all new gaskets and seals, and a brand new pinion shaft intermediate plate bearing (The old one fell apart in my hand, sound familiar?). I'll use the shift fork from the original transmission.

My concern is wear that I spotted on the bearing retainer plate that mounts on the intermediate plate. First gear had worn a groove in the plate, just less than a mm at its deepest. There was no more metal-on-metal contact, as first gear appears to have completed it's job of clearing away metal. I couldn't see any wear on first gear, tells you how tough these gears are. (As I can tell from the blue goo gasket sealer, this transmission looks to have been part at least once before).

Anyone have any ideas what could have caused this... where the tolerances could be off? It's going to nag at me as I'm putting this thing back together. Thanks.

By the way, I had the outer case plastic bead blasted and it looks absolutely beautiful. When it's done, I've got to post some before and after pics. I can't believe the difference!

[bondo]

Yikes, not sure what would cause that.

As for mixing and matching parts... the pinion and ring are a matched set and must stay together. If you transfer them to another case or intermediate plate, you will have to re-set the pinion and ring geometry (requires special tools).

In other words, if you want to go easy on yourself: use the ring, pinion, case and intermediate plate from the same transmission, and use the same gaskets between the intermediate plate (they're color coded for thickness). That way you don't have to mess with pinion geometry at all.

[MrKona]

Thanks for the reply.

Oh yah, I'm using the case, and intermediate plate that came with the shafts. I got that same great guidance on the 914club when I first started this project. The only part I used from the original transmission was the rear cover, as one of the transmission mount "ears" was cracked on the donor.

When I took the donor apart, the only gasket between the case and intermediate plate was the factory paper. I was planning on replacing it with a new paper gasket.

[MrKona]

One more question.... what do you mean by "ring"?

Ya know, I'm afraid that whoever rebuilt this transmission last messed up some tolerance... and now I'm screwed!

[bondo]

QUOTE (MrKona @ Nov 5 2005, 10:53 AM)

When I took the donor apart, the only gasket between the case and intermediate plate was the factory paper. I was planning on replacing it with a new paper gasket.

There are different thicknesses of paper gasket, color coded. There can be up to 3 in there to make up the rerquired gap. Measure it if you can't tell what color it is. If you don't have it anymore, umm... guess? (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif)

[MrKona]

That old paper gasket is long gone... All I can say is that it was the same tan color as the replacement gaskets I got from pelican. I see what you're talking about with the different thickness gaskets. I just took a closer look at the replacement gaskets and I can see that there are three of them, in at least two different thicknesses - thin and thinner.

(IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

[brp914]

what can happen is, the 19mm stretch bolt on the pinion shaft decides to back off, allowing 1st driven gear its independence (with disastrous consequences). as this develops, play increases. the mainshaft drives the pinion shaft which turns the ring, but the ring finds it not easy lugging around 2200+ lbs, so the ring shoves the pinion shaft into the intermediate pinion bearing, hammering it to bits. and thanks to the added play, it gets a running start, so to speak.

note the previous post about color coded thickness for the case/int. plate gasket. it sets r&p backlash.

btw, the following doesn't relate to anything, but it sure is funny
(IMG:http://www.914world.com/bbs2/html/emoticons/dead horse.gif)

[MrKona]

Interesting... it took me awhile to digest that. I guess the takeaway is to tighten the stretch bold to the right torque. I guess it's time for Saturday morning transmission class...

Two questions:

1. What part are you referring to as the "ring".

2. What is "r&p backlash".

Thanks in advance.

- Bryan

[bondo]

QUOTE (MrKona @ Nov 5 2005, 11:54 AM)

Interesting... it took me awhile to digest that. I guess the takeaway is to tighten the stretch bold to the right torque. I guess it's time for Saturday morning transmission class... Two questions: 1. What part are you referring to as the "ring". 2. What is "r&p backlash". Thanks in advance. - Bryan

Ring = the big gear around the differential that the pinion gear meshes with.

R&P = ring gear and pinion gear (matched set)

backlash = how much you can turn one gear without turning the other.. a measyre of "slop". In an ideal world you would have zero, but things expand when they get hot, and machining tolerances aren't perfect, so you need some backlash to keep the gears from eating each other.

BTW, backlash isn't the only thing that's critical when adjusting the R&P. The ring gear can move side to side (based on shims under the differential bearings) and the pinion can move forward and back (based on shims on the pinion shaft, fine tuned by paper gaskets under the intermediate plate). All this adjustment allows the force of the engine to be transmitted to the middle of the teeth of the gears, instead of closer to any edge. Get it wrong and it can be loud, wear funny, or both.

Things are further complicated because the total of shims on both sides of the differential also sets the differential bearing preload.

[davep]

I think your only option at this point is to take the tranny to a recognized shop to set the R&P. The thickness of the paper gaskets you threw away are absolutely critical to a good rebuild. There is a procedure to be followed in measuring/calculating that thickness. Done wrong and the tranny will be trash.

[MrKona]

Thanks guys for your input. It's amazing how much information you can get so quickly on this board.

[McMark]

Great thread! (IMG:http://www.914world.com/bbs2/html/emoticons/smilie_pokal.gif) Yay, 914Club!

[Bleyseng]

Last set of gaskets I got were all tan too, so I had to measure the old ones and the new ones to figure out what to install. What happened to the color coding?

[MrKona]

I'm glad you said that. I wasn't sure what everyone was talking about with color coding...