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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?
 
herbiedriver said:
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?
Click to expand...

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.
 
RolinOldies said:
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.
Click to expand...

About the retainer and sleeve, does those parts are applicable to diesel crankshaft and diesel gearbox?

If I refer to the part number I can find, there is a sleeve (part number 9186601) for 2.5 tdi with M56 (which is the same platform as M90 but transversal). Anyway this one I can't find anywhere...

But for a 1996 940 which have an M90 bolted on, I find a pilot bearing (3507628)

I'm asking because looking for what I need to install on my combo D5252T/M90

For what I understood, sleeve is not really needed, but then why their was one strait from the factory?


And I have an other question :

Diesel M90 existed in only two version M90H and M90L2
Does anyone know in what car specifically I can find M90L2? Diesel M90 are pretty rare but I was able to find 2 of those M90H, but I'm interested in a M90L2 for strength and longer ratio.

Thanks
 
This is still a confusing topic to many people. Bushing at the end of the redblock crankshaft with the M90 was put there only to guide the clutch disc centering tool during assembly. Nothing else! It is simple steel.
Diesel M90 also do not need a pilot bearing.

Personally I usually do not use any tool during clutch disc centering, but rather trust my eyes. Surely it is a bit longer process to gently pry the disc to the correct location, but i like challenges. It works every time, with pilot bearing designs too.

If the input shaft of the gearbox needs support, then it would be a needle roller or deep groove ball bearing. If plain bushing is used, it would be at least some kind of bronze or use a plain bearing sleeve. But in cars, as the rpm differences are quite high at times, it would not be long lasting in such open environments, without oil circulating near.

Sadly I do not know where to find the longer ratio M90 boxes. I also found that my diesel box does not have the longest fifth...
 
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Thanks for the answer!
I didn't had the complete explanation yet, it makes sense.

I also checked today, the M47 main shaft is longer than the M90 shaft. The 47 main shaft protrudes more than 1cm from the gearbox housing, whereas the M90 shaft is recessed by more than 1 cm. So the end of the M90 shaft couldn't even reach the end of the crankshaft and the sleeve is their is one.

Would be interesting though if someone could say more about the M90L and L2 application.

Edit : I did some research and I don't even know if the L2 version was produced for diesel models. I can't remember where I got this, but they are a lot of false information on internet (for example, the wikipedia article says "The differences are the bell housing bolt pattern and the output shaft flange with a 3-bolt flange for the redblock/diesel engines and a 4 bolt flange for whiteblock engines", but in reality, diesels have a 4 bolt flange).

Also, for what I found, H2 and L2 version's production started in 1997, and for what I know, they were no FWD diesels produced after 1996.

I don't know if someone has some real documentation about this?
 
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I wish there was a new set of gears available for 5th in an M90. I have an L2 box but would like to raise it a touch for cruising at 70mph
 
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