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M90 3rd gear synchro welding photos??

Well you've seen the Whiteblock M90 thread in the FS section, and I'm sure you realize that those boxes are rare as hen's teeth in North America. However if you can source one (as Homer did) the rest of the bits appear to be pretty straight forward. The M90's (as far as I know) are all configured for the external hydraulic slave, and they are reputed to work well. I think for your application the question is, will you plan to bang shift the hell out of it (get the T5 and easy replacement/rebuild), or if you intend to drive it "sensibly" then the M90 might be for you. Gearing for a Whiteblock should have that 3.50 first, and a couple choices for 5th OD. From a true performance standpoint, I doubt you can do better than the T5 2.9 first gear, 0.79 5th to match your 3.91 final or even a 4.10 final. Build yourself an Excel spreadsheet, or just use the online calculators to find your RPM drop between gears. I'd opine that a complete M90 kit will be a simpler solution, but the T5 more of an optimum solution......just my $0.02.
 
DET17 said:
I'd opine that a complete M90 kit will be a simpler solution, but the T5 more of an optimum solution......just my $0.02.
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Agreed.
The big attraction (in the UK at least) is that the M90 is cheap, strong and easy to fit.
Not all of that may apply to you.
If you have to import one, it's not so cheap.
If you have to convert to hydraulic clutch actuation, not so easy.

Remember that the whiteblock and redblock M90s are different and not interchangeable due to the integral bellhousing.

The downside of the M90 is the first and second gear ratios, which are, odd. They're both very low, I assume for pulling caravans.

The M90 is rumoured to have the same internals as the M56 850 gearbox, so there may be some scope for spare parts to be acquired that way.

This is why the 850 clutch is suitable, it has the correct number of splines to fit the M90.

DET17: eabras' photo shows the typical failure mode. Teeth breaking off the non-gear.
 
Cromlech said:
I just wish I could swap the ratios between first (3.91:1) and reverse (3.00:1) on my M90 saloon. :-(
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Ratios, as you know, from the WIKI summary:

The M90 gearbox is available with different gear ratios
G M90H1 M90H2 M90L1 M90L2
1 3.54:1 3.54:1 3.91:1 3.91:1
2 2.05:1 2.05:1 2.20:1 2.20:1
3 1.38:1 1.38:1 1.38:1 1.38:1
4 1.00:1 1.00:1 1.00:1 1.00:1
5 0.81:1 0.70:1 0.81:1 0.70:1
R 3.00:1 3.00:1 3.00:1 3.00:1

That 1-2 transition doesn't really lend itself to performance, does it? :wtf:
 
Guy I got my m90 from told me they are the same as M56 transmissions and you could put the gears from the m56's in the m90's if you want. Not sure on that but if so then parts like syncros and bearings should be same then right?
 
Most of the internals are the same, i used a syncro from an m56 when I broke the m90 third gear syncro. Just be sure to get the right type, m90's first came with single syncros and later three piece syncros.

3delt.jpg


1del.jpg

sprekk.jpg
 
m90turdgear1.jpg


m90turdgear2.jpg


I figured why not have a pro welder weld it. Pics maybe video probabbsly showing how to take it apart coming or is it put it back together. Basically if you want to take it all the way out you gotta take out all the bolts out from the front of it, then there is a snap ring you gotta take out, then all the guts will fall out if you turn it upside down. Sort of how I did it.. That is the input shaft Eric is holding there in the pic above. Also the turd gear stop ring weld shaft. Same thing. Don't forget to take that bolt goes into shift rod in trans and drop out ball bearing first...

Fortified one M90L1 with 38k to take the forthcoming abuse.
 
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Anyone has any info about setting up coutershaft axial clearances in these boxes? Just by curiosity...
 
Thanks to all the fine folks that posted here. You are a big help to me on my 740 Turbo cheapo endurance racing car, the Happy Moose Racing sedan. I have an M90 in it, sourced from a friend in UK, but I did not do the weld upgrade...yet. Seems a big job, but smart to protect my rare bird tranny. Even got lucky on the ratios, it is the closer ones, whew. No, we didn't know beforehand, he just had one and sent it, boom.
 
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