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Vintage M41 fluid questions

AndrewNance

AndrewNance

Amateur hour!
Joined
Oct 24, 2011
Location
Winston-Salem, NC
Is there a fluid better suited for that particular box?
Is there a need to fill the OD separately from the gearbox (I'm not sure I saw a fill for it)?

I'm thinking just some Redline MTL unless there's something I can get better results from. I've heard of using BG SynchroShift II as well but I don't know where I can get it locally.
 
In my years of driving M41's, I used 10W40 motor oil in them, same as I put in the engine.

You fill the gearbox, and oil runs over into the OD. Because the passage joining them is not at the bottom, it may not fill up the OD the first time. Give it a little time, then fill again, and repeat until it stops going down.
 
I always use Delo. Isn't it supposed to still have zinc in it? If not, I know Rotella does. As for gear oil, I think I'm just going with 80W90 gear oil as recommended by Phil Singher.
 
You can get Lucas 'Motor Break In' oil additive at parts stores - it is mostly ZDDP.

You really don't want anything super slippery - there's a clutch in the OD that needs to grab.

Opinions vary on it, straight 30W motor oil, variable viscosity oil, ATF.

In general, it really doesn't seem to care *that much*. As long as it's full of something (so the OD doesn't run dry and kick off).
 
Probably want to avoid the 80w90 in there as that box was never designed to run gear oil due to the OD unit. SAE30 was factory spec on those, where the M46 ran Type F.

Personally, I'm a fan of the MTL route. I've run it in M46's over the years, ran it in the M40 and M41 back in the pre-W50 days of my car, never had an issue with it, shifted nice (well, as nice as those boxes would shift), OD was very happy with it.
 
AndrewNance said:
I always use Delo. Isn't it supposed to still have zinc in it? If not, I know Rotella does. As for gear oil, I think I'm just going with 80W90 gear oil as recommended by Phil Singher.
Click to expand...

Isn't the M41 a M40 with overdrive? If so,........................

Volvo recommends SAE 85W90 *transmission oil* If overdrive is installed, an engine oil with a viscosity of SAE 30 or multigrade oil with a viscosity of 20x/40 should be used. Do not use hypoid oil in the transmission
Click to expand...

THat is qouted from page 111 of the the 1976 Volvo Car Handbook, for the 1976 240s & 260s. I would think the M41 OD is no different from the 46 OD in oil app?
 
smokeyfan1000 said:
Isn't the M41 a M40 with overdrive? If so,........................



THat is qouted from page 111 of the the 1976 Volvo Car Handbook, for the 1976 240s & 260s. I would think the M41 OD is no different from the 46 OD in oil app?
Click to expand...

:nod:

You don't want to use gorilla snot.

Straight 30# will get worn out OD O rings down the road a bit longer, but after that you should address the OD itself.
 
The M41 in the PV leaks, but only on long road trips. I can drive it around town for years and not need to add oil, drive it in OD for 3 or 4 hours at a time and it leaks a quart of oil out.

*sigh*

Must be a high pressure leak somewhere that only leaks when the OD is engaged?
 
Okay.

Well next up is this. I got this driveshaft with my M41 and both were supposed to have been pulled from a 122. Notice the center support bearing isn't where it needs to be. Can that be moved forward or do I have the wrong driveshaft?

2RbJtEV.jpg


It seems a little short but I haven't fitted the transmission yet.

H9AulKo.jpg
 
Redwood Chair said:
No idea but a quart is most of what's in it. :omg:
Click to expand...

Yeah, on road trips I'll go until the OD won't engage, then I unscrew the shifter, pour a quart in, replace the shifter, and continue.

I'd probably figure it out and fix it if I took it on more long road trips.
 
I think I'm catching on to RWC's drift.

There are two M40 lengths - a short tailhousing, and a long tailhousing?

This certainly doesn't look like it's appropriate for an M41, though. Too long. I really don't think it came off an M41 equipped 122.

I had the driveshaft shortened on the PV, it needed to be about 11 1/2" (as best as I can recall, +/- 1/4" or so) shorter to account for the difference between my M40 and the M41.
 
It's starting to make sense now. I compared it to my old M40 shaft and it looks like if I use the long rear section from my old shaft combined with the front section of my new shaft that everything will line up right.

I think I'll get the transmission in the car first just to make sure.
 
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