How hard is it really to rebuilt a 928 transmission?

The parts, as long as the gears are in good shape, don't look that pricey.

Anybody done it in thier garage?

I'm about a 6 on the Mechanical Ability scale of 1-10 if:

1 is the woman that puts coolant in the cap marked "washer fluid" and
10 is... uh.... John Lingenfelter (now dead) of Corvette Fame.

 

I'd say it's about a 7.

Seriously, it's not too hard, but FWIU:
1. You need a good press (most people don't have one)
2. There's some tedious shimming and tolerence measuring that goes faster if you have more experience,
but mostly,
3. It takes a fairly experienced eye to be able to tell by sight which gearsets/dog teeth/syncros should be swapped out and which are fine.

If you're going to replace everything then 3 is not an issue, but you'll probably spend more than you would on a rebuild.

All that said, I'm thinking about trying to do the box on my '82 project shark myself. I know it needs new syncros so I'll probably just do them and hope everything else is OK. If not, all I'm out is the PITA of my own labor.

 

P.S. I assume you're talking about a manual box. Auto boxes require some expensive specialized tools to fix and are just about impossible for the home mechanic.

 

Hey Sub, you sound experienced with 928 S4 transmissions. Someone was telling me a while back that if you remove the torque convertor on the auto transmission and flip it face down, all the components (gears, synchros, rings, etc.) will just fall out of it as if there is nothing but the torque converter holding it in. Is this true? if so, that's creepy

 

I had my local 928 mechanic, who was really good, rebuild the transmission twice, before he took it to a Benz dealership to have it rebuilt. So I would say that if someone who works with 928s all the time, can not rebuild it properly, even the second time around, it's not an easy job...

After the Mercedes tech did it, it worked perfectly...

 

Figure it takes about two days labor to rebuild a box. But the older gear boxes need far more than "just syncros" ! When you hear the crunching grinding which everyone calls "worn syncros" that is the gears engaging teeth sliders making the noise NOT the syncros. The question becomes how badly damaged are those parts and will new syncros be enough ? Building gear boxes is much like selling insurance ...nearly anyone can do it ! But how much learning and experience does it take to do it well ! So the process is pretty simple I have seen Mark here blow apart a box in maybe 30 minutes to retrieve a good gear set but he was never planned to put it back together ! Brendan come to Sharktoberfest and you can look at boxes of gear sets , ring and pinons etc.

 

Great Comments Guys, thanks.

Sub - its a 78 5speed. Probably has over 100k miles. 2 and 3rd were notchy, at 175hp. Fluid was old, and Clutch was not properly adjusted.

Car will go back together with the proper clutch adjustment, new fluid, and about 400rwhp.

 

FWIW: My mechanic has rebuilt 4 that I know of in the past few years. He even built a custom 87 box with the final drive out of an early one. This was many years ago when the GT boxes were only a few years old and a lot harder to find than they are now. When I mentioned doing the synchros on my trans, he said its one of the harder things to do on a 928.
He has an 88 trans all apart on his bench right now. I'd rather do an engine rebuild after seeing all the parts laid out.

 

I'm hearing you Jim. There wasn't so much any serious grinding as there was some "nicking" if you know what I am describing.
I'll be at fest.
I've seen them apart on a table quite a bit in different states of disassembly.

Right now I'm tempted, but I have to assemble an entire car now, so I am holding back a bit here.

It's always "I've come this far"...

 

Yes Hacker, it looks quite complex.

 

I'd say its my last 928 frontier.

 

i've done this on an 84 and am doing it again. first time my 1st gear synchro and bands/blocks were toast, this time, i'm not sure what the problem is, it's locked in 2nd for some reason, i haven't dropped it quite yet. i think if the tranny is currrently together and the shims/tolerances are already measured, it's not that bad. you don't need any of the special tools listed in the manual, but i'm sure they make it easier. to change the synchros other than the 5th gear synchro, you need a 2 ton press to get the gears off. i didn't do that part myself as i didn't have the press, so i paid a local tranny guy to do it. it's not all that difficult, just take your time and note how parts go together.

 

If Erkka doesn't see this and reply on his own, you might want to send him a PM.

 

2 ton press huh? Like at harbor freight?

 

i was strongly consider purchasing a manual press from rural king for this job. i think the price was around $200. only problem was i didn't have space in the garage to put it. if you have the press and the manuals i don't see there being any issues. just have a large clean table to lay the parts down in some logical order so you put everything exactly back in order. i had a post on my tranny removal, but i don't know how to link it.