So, I'm putting the M41 back together,

(no, never found the needle bearings- they can be had from Sweden, but I found a good used set)

and I'm wondering- is synthetic gear/motor oil (specifically Redline) compatible with the overdrive?

I could see problems with the friction surfaces not getting sufficient grip.

Also, ALL of the M40's and 41's I opened had gear oil, not motor oil. The official spec was 30 wt for the OD units, no? What do you- all run?

Thanks!
Toby

I put an M41 w/ Dtype into my 444 back in '76(?). Ran it for 20 years with Castrol 20/50, including two cross country trips. Only problem, was that it leasked a little from a broken off stud. I'd know I was low when, going down the road at 75, it'd drop back into 4th. Pull over, undo the shifter and and add 1/2 a quart.
5 years ago, I got a 122 and rebuilt an M41 with J type and have been running it with 20/50. No problems yet. I live in the northeast where it gets colder, and wonder if climate should be any kind of determining factor in this discussion. Would there be a reason not to use a multigrade, if you were going the enine oil route as opposed to 90 weight or ATF?

Well,
I was thinking more in terms of the M41 than the OD-
the pressures on the bearings and gears in it are pretty high, while the OD is relatively understeressed. THere's someone out there selling J (or P?) thypes as overdrives for big pickups!
Actually, I was thinking maybe 60wt straight synthetic (racing oil) might be an entertaining compromise!
But I got the transmission closed back up today- now on to more entertaining (?) things like plumbing the oil and water to the turbo....

Toby

I put mobil 1 15-50 in my M400. I drove it around for
a couple months, and the shifting problems I had with it
didn't get better. I pulled out the oil and put in some
mobil 1 gear oil. The 15-50 motor oil had lots of brass
in it and there was also some metal on the drain plug
magnet. I didn't flush out the transmission prior to
putting in the new oil, but I recon that lots of that brass
and those filings were new and caused by the 15-50.

Weirdly, my M400 is dead silent on the road, it is just
a bit stiff going into first sometimes (this mostly went
away by overfilling the transmission with the gear oil).
chris

Yea...If I didn't have overdrive (or an overdrive that didn't work), I'd use gear oil all the time...but the overdrives don't take kindly to it it seems.

-Matt

Strangely the J type was used on the Ford Transit van, and Ford recommended gear oil for that setup.

From experience I'd say the overdrives aren't that bothered what they've got in, but they do insist there's enough of it. Personally I use engine oil since that was what Volvo recommended.

Regards


Pete

OK, but what grade are you using? 30wt or multigrade?

Err, truth be told, whatever happens to be sitting around. I normally simply can't be arsed to go look for single weight oil. Normally I'd use a 10w40, or a 20W50. I honestly reckon this overdrive oil malarkey is a blind alley. they're simpy not fussy about their oil, but like lots of it. Invarably when they die someone has run it out of oil, not put the wrong stuff in. And I've had lots of them apart over the years. Never wrecked one twice.

Regards


Pete

I've seen many overdrives gummed up by gear oil....usually the Jiffy Lube type folks that don't know what needs to be in there. Sometimes draining them and replacing with thinner oil gets 'em going, sometimes it doesn't. Admittedly, many manufactures have used the Laylock overdrives, but that is not to say that they all use the same fluid. Manufacturer recommendation....

As for multigrades...keep in mind that a 10w40 is designed to act like 10 weight in the cold, and 40 weight when warm. Warm being like a warm engine where the oil can be upwards of 250-300 degrees F. A transmission under normal operating conditons would never get that hot, thus, the multi-grade 10w40 would be somewhat more like running 10-20 weight all the time. Not a good idea in my opinion...

-Matt

When I get an M410 for my 164, I'll probably use
some kind of synthetic gear oil in it. I noticed
that the mobil 1 stuff was pretty runny, a tiny
bit thicker than 20-50. It certainly isn't as
heavy as some of the other gear oils that I've seen.
I think the original question was about synthetic
motor oil (which I tried once for a while in my
M400 and which produced quite a lot of brass in
the oil when I drained it) while I'd say that
a good synthetic gear oil is probably not a bad
way to go for these, so long as it is the lighter
version not a heaver differential oil.
chris

Thanks, all, for your advice

Ok, I'm gonna do it- after 500 miles with motor oil (a good way to let new parts wear in quickly!) I'll try the Redline Trans fluid, and let you know what happens! The car won't be on the road 'til spring, but I'll report back once I do the fluid change!


Toby

Good luck...

I've said it before, and I'll say it again... If ever there was a place to stick with the manufacturer recommondation, overdrive transmissions are it. You wouldn't stick transmission fluid in a motor that calls for engine oil...I don't see why you'd stick transmission fluid in a transmission that calls for engine oil.

If you put in transmission oil and the overdrive quits working, I would wager to guess that the overdrive will never work again until you rebuild it.

You may well be fine though...but I wouldn't risk it were I you.

Cheers,
Matt

Just my $.02...

I have NEVER, and been told many times to NEVER run gear oil in the OD units. I would also tend to stay away from synthetics or slippery additives. A friend of mine once put the tranny equivlant of slick50 in his overdrive gearbox...and the OD never worked again. My experience has been to stick with dinosaurs.

My choice...I run straight, non-detergent 40wt engine oil. A little thicker than the recommended 30wt, but seems to work fine. Admittedly, my OD on my M41 in my 1800 quit working recently, but the whole unit was found in the trunk of a parts car, and its condition and mileage were and are still unknown. I expect it wasn't very good when I started though, as the sincros were bad when I installed it. The overdrive still worked for more than 150K, and the tranny itself is still quiet.

Like others, I've not had too many problems with excessive gearbox wear on the M40 or M41... They seem to hold up longer than the M400 and M410, so I wouldn't worry too much about running the lighter oil. I expect that the tranny will still outlast the overdrive. When the overdrive does finally quit working for good, then go with gear oil until you do a rebuild.

-Matt
65 1800s
71 145s
72 164e

Interesting debate especially as I am preparing to install M41 of unknown origin, one experience I can relate is a friend put an oil additive ( proma )in a M46 and the overdrive was stuffed, no amount of flushing/cleaning would fix it and it had to be completely rebuilt with lots of new parts, shows the additive worked I suppose.......
Hans

All M41 needs the gear lube or equivalent in synthetic. The 30 wt oil is for the newer M46's that need Type F ATF in cold weather or the 30 wt if temp always above 10 dgrees Celcius.

The OD can use either. The lube specification is for the gear wear and lubricatio issues.

Duane

Hi Toby,
I run gear oil on the advice of our local Swedish Mechanic (yes, he's from Sweden). He says the mild Pacific Northwest weather doesn't call for anything thinner. I would choose oil weight based on your local average weather.
85/90 for 4+ yrs. and counting. Problems? Zero.

I run 30 wt. It has been doing fine since I put the tranny in in
about 1986. I've changed it once. Tranny has never missed a lick.
(Can't say that about the M410!)
--
George Downs Bartlesville, Oklahoma

I might have missed this thread..but what were the issues w/ your M410?


back to the subject: In my particular M41 (it's..ahem..pretty crusty)...I had a LOT of internal slippage (dropping out of od) with 80/90...but less slippage with 30wt. Still some..but not as much.

..but I've got a "better" M410 on the way..

Per

The issue is with the tranny. In my experience the bearings give out
at about 100,000 miles or less. That is one of the reasons why I got the
M410 - I had new bearings put in the original M400 in Panama in about 1973 or
1974 and by 1981, when I was back in Panama again, it got noisy again.
I found an M410 in Pennsylvania, shipped to me in parts, about 1988 or
so and put it in and it is noisy now. I have another M410 that I will put
in when either the noise bothers me too much or there is some other problem.
(They seem to work OK in spite of the noise, which I think comes from the
layshaft bearings, since it is worst in 2nd and 3rd.) I have not had that
problem with M40 or M41 trannies. Someone told me once that the layshaft
bearings in the M400/410 don't get lubed as well as they should.
--
George Downs Bartlesville, Oklahoma

If you read the sides of the Redline gear oil, and there are several types, plain gear oil and manual transmission oil, and at least one other, there's a bit of explaination/reassurance about that friction issue, though more for syncros.
On the other hand, with worn sycros it makes shifting a little "riskier", about the same as fresh gear oil of teh regular type