M46 first and second gear slip - bad overdrive?

Okay so tonight I put the front end up on stands and crawled under. Bone dry under there [pats self on back]. I took the clutch fork boot off and had a look inside the bellhousing, again no evidence of anything weird, no moisture, nothing splattered on the bellhousing, no evidence of any residues etc.

I checked the transmission fluid level and added maybe 200ml to raise it up to the fill port. Bear in mind the fill port is at the front of the transmission, and the car was slanted back quite a bit, so I think the level was probably fine.

Then I took it out for a drive to try and better characterise the issue. With everything cold, I was actually able to pull quite hard in second, although I could still get it to let go in first. But as it warmed up the slipping got worse. So I suppose that doesn't really tell me much, as the transmission and clutch would both heat up with use, but a data point is a data point.

No burnt clutch or oil smells ?

Oh yeah I forgot to mention, I did stick my head under the car after and have a sniff but nothing out of the ordinary.

jamesinc

Oh yeah I forgot to mention, I did stick my head under the car after and have a sniff but nothing out of the ordinary.

If the clutch were slipping I think you'd definitely smell it...so it all seems to be pointing to the overdrive. I have a disassembled overdrive unit - let me know if you want me to check the condition of any of the parts that you may need. I can't recall what condition the friction surfaces were in.

It sounds like overdrive clutch to me as well. You don't have a spare for an under car change I take it.

I encountered a similar issue with a m41 a few years back. Same overdrive unit. It appeared to have had a heavier gear or engine oil in it. People used to say this was correct for M40. Perhaps your box has had incorrect oil? If it is getting better as you describe, perhaps more driving to allow your fluid to penetrate and wash the friction surfaces? It may continue to improve. Some ATF (that I assume you are using) is high detergent and will wash out the residue over a few weeks.

Out of interest, what fluid are you using? There was a special Volvo fluid, and I know that most people use a version of ATF here. I use a Penrite product for the overdrive application because of its better wear resistance. Gear change is a little slower for the first five minutes, but overall much nicer after the oil warms, compared to ATF. I'm particularly interested in the greater wear protection as parts get harder to find.

1971_144GL

https://penriteoil.com.au/products/gear-box-oil-40

FWIW I believe the M46 calls for ATF type F.

Yes they do, and it is probably what most people should use.

For me because I'm willing to put up with the oil warm up period I use other oil. Apparently customers weren't, according to an old dealer service guy I used to know in Canberra, and volvo use an ATF type oil for "get in and drive application". It makes sense given the overdrive internals.

However on the big6 Healey, Triumph and other machines with not dissimilar mechanical and somewhat truck like gearbox's and the exact same overdrive unit they use a more conventional oil with better performance for the gearbox side of the equation (bronze parts, tapered roller bearings, needle bearings. I've taken this avenue as I don't usually take an old car to the shops for five minutes.

Interestingly IPD make reference to the use of engine oil in the M46: https://www.ipdusa.com/Articles/597/M46-M47-Transmission-Oil The thing with engine oil, especially modern oil, is they are short lived and have additive packs with chemistry for mopping up combustion produced. I was looking for something with the additive designed for wear/lubrication under tougher conditions (like a good drive on a bendy Tasmanian road). ATF is a bit water like when it heats up for my liking, given the very conventional nature of the gears inside the box.

Supposedly this is the oil Volvo used to recommend prior to the change to ATF, much more of a conventional gearbox oil. I think the change occurred around 1984?

So back to the original problem, a good few drives with the ATF to see what happens, then fresh ATF (if its a second hand box, good to do anyway) might fix the problem? Another oil down the track might be another option to look into? I know I have had both slipping and non-slipping outcomes depending on the choice of oil.

This assumes its not clutch related, or the gears are not slipping out at the selector momentarily under load, a bit like the earlier box's when the brass surface becomes a little worn.

I use Castrol Transmax Type F mineral ATF.

I do have another overdrive...both my cars have an overdrive.

I've had two offers to borrow a known-good unit, one in Dubbo, the other in Canberra, I am tempted to drive to Canberra on the weekend and get that one as I could pop in on my best friend while I'm there. Plus it would mean I would have a working overdrive for the Oz Volvo Birthday Cruise. If I don't, I'll take the yellow carb turbo 244 but it uh significantly increases my fuel expenditure haha.

Volvo has always recommended Type F ATF for the J-type OD. The specs state anything up to around SAE-30 and nothing thicker. You can get away with an old style engine oil too.

Roinik

Volvo has always recommended Type F ATF for the J-type OD. The specs state anything up to around SAE-30 and nothing thicker. You can get away with an old style engine oil too.

For some reason I thought the M41 in the 1800ES called for SAE30 engine oil, not ATF Type F, but I'd have to check my owner's handbook.

carnut222

https://ozvolvo.org/discussion/comment/219323#Comment_219323

For some reason I thought the M41 in the 1800ES called for SAE30 engine oil, not ATF Type F, but I'd have to check my owner's handbook.

Just checked my 73 144's owners handbook - it recommends SAE 30 or multigrade SAE 20 W-40 engine oil for the M41. 73s had a J-type.

The 93 940's owners handbook recommends 'Volvo synthetic transmission oil' or ATF type G for M46 and M47.

M46s of that vintage got type J, type J/P or type P overdrives, depending on market and engine.

It says on top of the gearbox to use ATF, which is ironic as the top of the gearbox is the one thing you can't see when it's under the car ?

jamesinc

It says on top of the gearbox to use ATF, which is ironic as the top of the gearbox is the one thing you can't see when it's under the car ?

Volvo gearboxes don't leak, so no need to worry, right?

I tested reverse and got the same slip and vibration as in first, which I think means the unidirectional clutch is the issue.

I invested in the tool that CVI sells for removing the valve body retainers, and under the main filter there is much glitter (first photo). So it seems like we definitely will find some carnage.

However, I must keep you waiting! I'll hopefully have more time tomorrow night to continue.