Gearbox flaring on 107 380sl

[Isdyldan]

Hi - Having just solved one problem (thanks Myros) I now have another! My auto box is flaring on the upshift when the engine is cold. Once the temperature us up after a mile or so it is fine. I have topped up the fluid when hot (took 2.5 litres), and the fluid is clean and looks in good condition. Could this be some sort of vacuum problem please, or am I looking at a big bill!
Many thanks, Dylan

 

[Isdyldan]

Ok, I've found gearbox oil dripping - seems to be coming from lots of places so will have to investigate. Seems odd that the revving between changes only occurs when cold. I'm thinking are that the leak is from an area which causes the flaring and takes a while to fill up again once the car gets running.

 

[Wellington]

If the oil level is low the pump will pick up air instead of fluid and the flare will occur, when the oil warms up and expands to a higher level the fluid will be picked up all the time.

 

[Isdyldan]

Thanks - that makes sense, but didn't think that much fluid had leaked out - it takes a pint between low & full on the dipstick. I'm looking for leaks anyway, and the Haynes manual I have covers 350 & 450SL & gives a list of possible leak places for the W3A 040 gearbox - my 380SL has a W4A 040 gearbox - does anyone know if these are similar or if there are any particular areas most likely to spring a leak please?

 

[Wellington]

When I was repairing automatic transmissions leaks were always a nightmare,
Try the simple things first like a rubber pan gasket which could have become hard and incompressable, do not overfill because the fluid will whip up into a froth and come out of the breather and cover everywhere, a leak in one particular area will be spread all over the place by slipstream whilst you are travelling, oil loss can also be via the vacuum modulator but that oil would be burnt in the engine and not decorating the outside of the transmission.
There are O rings on the servo covers but unless they have been disturbed do not cause much concern, unless again they have become hardened by age.
See if the interior of the bell housing is dry or wet, an external leak is not going to wet inside there but a leaking pump seal or pump O ring will

 

[Isdyldan]

Thanks - I'm not sure it is leaking now, and what came out must have been due to me over filling it. It's still doing the revving between changes, just not all the time - maybe every other time I set off from a junction etc. I think I'll do a gearbox oil & filter change - maybe the filter is blocked & restricting the oil flow.

 

[Myros]

Dylan

I've only done 15,000 in ours, and had the filter and oil done when I got it. Then, about 2 years later, the sump warped and dropped all the fluid in the garage between one drive and the next. I thought it was just the seal, so i put a new seal in , and a load of fresh fluid, and it did it again. So i got the message and put a new sump on, and a new seal , and a new filter, and another load of fresh fluid.
None of that has cured the little drip I get all the time, which amounts to about 100ml a year (I know, I catch it in a drip pan). That drip seems to come from the torque converter, as the rest of the sump etc is dry after I assemble it, but I can see the leak in the garage after re-assembly jobs.
There is a school of thought, which i do subscribe to, is that a few small leaks you know about on an older car aren't really a problem.
Your problem might be something to do with the seals. these trannies do need a refurb every 75-100k, and if yours hasn't had one, it may be due. Go for the sensible, low-cost option of filter and fluid ( and new seal) first though.

 

[Isdyldan]

I spoke to an experienced mechanic about this problem a few weeks back, and he said it it most likely to be sticking valves/pistons which lock the rings in the gearbox. He said to drive it more and thrash it about a bit to free them off. I have done this, and have noticed an improvement. It is still 'flaring' occasionally but not nearly as often. I have also heard that flaring can be caused by a badly adjusted kick-down linkage, but I haven't investigated this further. I also may change the oil & filter since I have already bought them, but when I went under the car to start the job a while back it looked a whole load of hassle - lots of shields & covers to remove.

 

[wireman]

The covers are easy to remove and relace.

Do take care not to over tighten the box sump bolts when you change your filter, the pan can distort and you will have an oil leak.

 

[SilverSaloon]

The covers are easy to remove and relace.

Do take care not to over tighten the box sump bolts when you change your filter, the pan can distort and you will have an oil leak.

yeah i tightened mine finger tight and then nipped up a very very slight bit..... after i warped the pan the 1st time!

i think the proper torque value is very very low, but i didnt have torque wrench at that point

 

[Isdyldan]

Thanks for all the advise so far. I have not actually done anything so far - regular driving seems to keep the flaring at bay, and when hot it is a rare occurrence. I am investigating the theory that adjusting the oil pressure (?) will cure this problem as this has been suggested by a local expert. It seems to make sense as it happens only at low revs - booting it away from stationary will not produce a 'flare'. If anyone is interested still, I'll post what I find as it may help someone else with similar symptoms.