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All you need to know about the M90

  • Thread starter Thread starter frpe82
  • Start date Start date
As I said in earlier posts, I have a 1992 240 with a B230fk tuned to around 200Hp with a M90 and dogdish flywheel and diesel clutch. The noise on overrun when the gearbox is warm is driving me crazy, sounds like a bag of nails. I tried every oil, helps a bit, but not enough. I use the car as a daily driver. I want power, but it has to be smooth and silent, like a 940 is supposed to be.

4 months ago I pulled the plug and bought 2 used, supposed to be good dual mass flywheels and a new clutch. I paid 50 euro for the DMFs and 240 euro for the new clutch and relaease bearing. A local mechanic had and old manual on how to diagnose used DMFs. Both were in spec as to axial and torsional play. So I fitted the one with the least surface wear. I cleaned and scuffed the surface with scotchbrite. I used the new SKF release bearing with plastic housing . So no grease at all! When I installed the B230FK a few years ago, I put clutch grease on the release bearing shaft. But the pedal became very sticky after a while because the grease atracks the friction matiral from the cluch. I put everything back together and went for a testdrive.

WOW! This is how Volvo designed it! No more noise on overrun. I can pull up much lower in gear without vibrations. And overal much less small noises and vibrations. Slow driving in heavy trafic is also much more pleasant and smoother. I have driven the car for 4 months now and everything still works fine. We will have to see how the DMF holds up to the 200hp (or the torque, but I don't know how much that is) I don't do dragraces or hard pulls from standstill, so I think it will be fine.

Sidenotes:
  • I weighted the dogdish and DMF and the difference is not enough to notice.
  • The clutch pedal is still buttery smooth without grease on the plastic parts.
  • The clutch never slips with the used DMF, but mine was in nice condition.
  • Don't forget to remove the spacers from the clutch fork balljoint, as you are going back from the dogdish to the original Volvo setup.
  • I also removed the M90 input shaft support bearing and fitted the original Volvo bearing in the crankshaft.
  • This way I ruled out bad bearings in the M90.

I still can't explain why some people don't have noise with with the dogdish setup. I guess it's also personal how you experience noise and vibrations. But for me the used DMF is the solution! I think there are many good DMFs hanging around in scrapped volvo 940s. I will try to find the DMF diagnosing manual and post it here.
 
My 240 with a b5234t and M90H is pretty bad too. Mostly between idle and 1800 rpm. Single mass flywheel, stock 850 glt clutch. It is especially bad when towing a trailer. Mine is quiet on decel though.

Funny thing, my old (high mileage) 940 with a M90L2 and dogdish/ diesel clutch setup is quiet. Can't hear a thing in the cabin. Night and day difference when driving back to back.

So maybe it is more a 240 thing? A 940, this one being a 1997 is has much more sound deadening compared to a 240.
 
Question for the group, I have a 94 940 with a B230FT that was retrofitted with an M90 before I got it. Took out the engine for a rebuild and there was no bearing on the input shaft. Didn't think much of it, reassembled it all and it runs great, but it's clutch time. So when I tear it apart again should there be a bearing in the crankshaft for the input shaft??? If so, how do I find the part number?
 
Question for the group, I have a 94 940 with a B230FT that was retrofitted with an M90 before I got it. Took out the engine for a rebuild and there was no bearing on the input shaft. Didn't think much of it, reassembled it all and it runs great, but it's clutch time. So when I tear it apart again should there be a bearing in the crankshaft for the input shaft??? If so, how do I find the part number?

This is what AI comes up with:

The M90 gearbox in Volvo 700 and 900 series vehicles does not require a traditional pilot bearing. Instead, it uses a metal or plastic ring (also referred to as a “steel bushing” or “retainer”) to support the mainshaft.

Key Points:​

  • The M90 gearbox design eliminates the need for a pilot bearing, as the mainshaft is supported at both ends: at the front of the transmission and at the back, where it meets the flywheel.
  • Without a pilot bearing, the mainshaft does not wobble when the clutch is disengaged.
  • Some users have reported using a retro-fitted pilot bearing, but it’s not a necessary component for proper transmission function.
  • The Volvo 9er Series with M90 Gearbox uses a retainer (part number 1018634) to fixate the steel bushing (part number 1015633) instead of a traditional pilot bearing.
 
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