My amazon estate O/D clutch is slipping after a 2 hr run. When the unit is left for 30 mins or so it works fine again.

I have checked the oil level which if fine and am using 20/50 as per the manual.

As it works when not too hot assume the plates aren't worn.


I believe you may be able to adjust the oil pressure/operating valve? Any tip, hints welcome!!

Slippage in OD when hot but not when cold can be caused by:

Worn actuating piston seals. They seal well when the fluid is cold and thick but not so well as the hot thin fluid blows past..

Just plain low fluid. Gets picked up and sticks to stuff so not enough to get pumped.

Old fluid with worn out additives. Particularily the additive that minimizes foaming. Whip the fluid into a foam and air just does not compress like fluid.

OD/Tranny fluid debate. OD's on M41 or earlier tranny's use gear oil. M46 tranny/OD use Type F ATF. M46 trannies, staright 30 wt if temp never below 20 degrees F.

Oil additives. Not recommended in the OD added trannys. IF the additive is supposed to "cling" better or make things more slippery, you may have trouble not with the tranny but the OD. The OD has two systems that when at operating parameters, there is NO fluid between the mating parts. Any fluid or additive that interferes with this NO fluid parameter is worse when cold. Slippage during the wrong time can destroy the OD internally, or just hurt performance and fuel milage before wearing out the OD prematurly.

Duane

Just out of curiosity... wehre in the manual does it say to use 20/50 oil? I used that in my last gearbox and wasted a bearing... not sure if the oil caused it or not though.

But keeping in mind that multiweight oil is that way to act like thinner oil (20wt) when cold, and act more like 50wt when the engine is warmed up. A transmission never gets that hot, so that oil is acting like the 20wt in there all the time... and if you check again, you'll probably find that VOlvo recommended straight 30wt engine oil. I personally think thats a bit thin too, so I always go with straight 40wt non-detergent as a compromise, and I've never had a problem with it....and never never never add any sort of slippery additives.

Although...maybe someone else can help with this one:

I posted a month or two about the slipping automatic on my Cadillac, and folks thoughs on additives. General consensus was that it was time for a rebuild. Of course, the additives are cheaper than a new trannie, so I gave it a try... "transEx" to be specific... the kind in the steel can engineered to stop slippage. It worked a LOT better than I expected... THe car now drives almost normally.

I wonder if anyone has thoughts about using that product or something similar in a overdrive Volvo box...? I sure wouldn't try it without some good advice from someone more knowledgeable than myself.

Admittedly though, it sounds like you have other problems, but were I you, I'd change out the fluid first and see if it helps.

-Matt
--
-Matt '70 145s, '65 1800s, '66 122s wagon, others inc. '53 XK120 FHC

A common mis-conception with "multi-weight" oil is that they act like 20W cold and 50W when hot. Not exactly. Their cold-flow properties are like 20w and their ability to support loads in shear when heated are like 50w... saying the same thing a different way: 50W that flows like 20W.

The tranny-fix stuff should ought to work so long as it is compatable with the seals, syncro cones and bushes in the manual part of the tranny, after all these are hybrids, basically a 4-speed with an "automatic" 2-speed coupled to it.

Hypoid 80 wt?!?!?! wow. I know gear oil is rated differently but that seems pretty thick. I was thinking of using a Redline synthetic racing gearbox oil (90 wt... acts like 30 wt engine oil) that did not have the friction modifiers. This supposedly makes a limited slip (clutch type) "lock-up" better and harder and is compatible with GL 5 specs (OK for all syncros and bushes). Has anyone tried such an item???

Heavy oil is not always better as it has trouble (especially single-grade) actually getting into and through some of the spaces it is supposed to flow into to form it's "dynamic" wedge on which the rotating part rides. On the other hand too light an oil will "flush-out" too easy.

Oil is always a certain way to get people riled on any board!

Mike!

Yeah, we have this discussion periodically. Irv Gordon uses gear oil in his, as do Art Banks and assorted other high-milers. I've gotten some other people to try it and there's been no downside at all.

My understanding is that the only reason Volvo specified motor oil for trannies 30-40 years ago is that the gear oil of the day was corrosive to the gear bushings. No such problems with modern gear oil.

I'm using 80/90 hypoid gear oil without any problems. Stays in a lot better too.

Sounds like worn piston O-rings in OD. Most common problem with OD units.

Paul

BTW- Is it a D-type OD??

Read the excellent article at http//www.buckeyetriumphs.org/technical/JOD/
It describes lots of ways to trouble shoot and check up on your overdrive. Most likely is a loss of hydraulic pressure from low oil, clogged filter(s) or worn mechanism. If the oil is OK then the most likely source of trouble is the filters (screen and fine particle filter). Also, dying solenoid can cause partial engagement of the hydraulic system leading to erratic performance. I'd start by draining the OD unit (shares oil with gearbox) and check the screen (magnet in sump) and pull the plug that allows access to the filter (consult manual). If all OK there then perhaps new oil will fix er up.

Mike!