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Post by riconijhof on Apr 7, 2016 13:40:26 GMT
My 998 auto drops out of gear with a loud squeek when standing at the traffic lights for longer than 5 seconds. To get going again I need to rev it up and then it catches gear with another squeek. Rest of the box performs normally. Oil levels are perfect and using fresh mineral 20W50. Are there any known causes for this?
I suspect an oil pressure issue but want to rule out any other possibilities. The block oil pressure when hot is about 22lbft at idle and goes up to 50 in revs, this is a bit low but should still be fine for lots of miles (no oil burning). The gearbox oil pressure (measured from the oil filter housing plug) is also about 25% too low in all conditions. I wonder if the gearbox oil feed comes after the engine crank feed or directly from the oil pump? Is there a known fault point or accessable valve that can be modified to raise the gearbox pressure?
Thank you all, I tried searching the forum but nothing similar came up.
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Post by 69hcode on Apr 8, 2016 1:23:53 GMT
Switch to 10w40. I had the same problem running 20w50 on my 81. Mine shifts great now. Only problem is it takes a little while to go into gear sometimes. Always stays in gear once in now.
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Post by wimfournier on Apr 8, 2016 8:58:37 GMT
You must be aware of the fact that there are disc clutches and brakes inside the box, emerged in oil. Each at their turn have to catch each other. With oil pressure the plates and brakes are applied. That means, the oil has to be pressed away between the mating surfaces. Because your oil pressure is low and you use a thicker oil, you have problems.
So use 10W40 or better perhaps motrcycle oil that is meant for cycles with wet clutches. You can read all about that here on this forum.
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Post by riconijhof on Apr 8, 2016 10:21:23 GMT
The funny thing is, I bought it from the previous owner who had filled it with mineral 10W30. Problems seemed way worse with the thin oil in (dropping out of gear as well as rough shifting up and down) plus the thin oil makes my crank pressure dangerously low. So I think the only solution is getting the pressure up somehow. The only way is having the crank reground? Are the Auto oil pumps vulnerable?
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Post by limby2000 on Apr 8, 2016 15:40:30 GMT
Hi, what year, mileage is your engine. The auto oil pump is pretty much indestructible, but can like any car with poor maintenance wear beyond working tolerances. You can boost the engine working oil pressure by fitting a stronger spring to the bypass valve (on front on engine), but I don't know if this increase the working pressure in the gearbox. My guess is you have tired/worn (o) ring,s inside the box leaking pressure internally. 10w40 is pretty much accepted to be the correct oil for all auto,s. Keeps us updated on this issue. Terry.
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Post by jockduck on Apr 8, 2016 23:54:42 GMT
Hi, does the same thing happen if you sit at idle with 2 selected in manual, if so its a forward clutch problem, low pressure, worn plates, leaking oil feeds. If the problem goes away then its probably a 1st gear spraq clutch issue.
Jock
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Post by mra-minis on Apr 10, 2016 21:23:20 GMT
I can be contacted on martin@kmprecisionengineering.com
When you say "dropping out of gear" did you mean it some how goes to neutral ? or that it freewheels until you rev it up again ?
If the latter then you have a low pressure issue, ie low pressure at the servo, piston seals but just as easily it could be all of the above mentioned issues and it could also be a faulty valve block, a lot of faults I see are caused by oil, but invariably the faults show themselves once it is past it's best before date so a full rebuild is often the best option, fingers crossed that you have caught it in time.
Whilst changing the oil you may have "cleared" some debris, changing to 10/40 or preferably MA2 motorcycle oil (MA2 not MA or MA1) and it may clear the fault, the pumps on auto's are a completely different beast to the manual pumps that are made of chocolate... the auto pump rarely causes fault or fail, however I have dozens of the things if anyone wants one :-) also your engine oil pressure is not really linked to the automatic oil pressure as you have 2 PRV's one in the transmission and one on the engine.
It can also be a one way valve sticking on the convertor letting oil out and back in to the box, also one more thing, I hear this a lot so I have to ask, how did you check the oil level ?
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