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Overdrive not engaging when engine warm

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BN6_2197

BN6_2197

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My overdrive does not engage when the engine is warm, i.e. about 30 to 40 minutes after driving. Before that is works reliable. Any idea what the reason could be?
 
If operation is completely normal when cold my guess is that you have marginal oil pump pressure and when the oil thins a bit it drops below what you need to stay engaged. If it isn't that I suppose it is possible to be on the feather edge of proper adjustment of the operating valve and when everything expands and heats up it goes out of adjustment a hair more and de-activates. I you have a shop manual there is a pretty good description of how it all works. It ain't rocket surgery but it takes a little study to do the cerebral troubleshooting. The most useful tool is a pressure gage to actually see what your oil pressure while running is. Once you know that you can make intelligent decisions without doing so much guessing.
 
Hey BN6 2197,
Don't know if this could be it but when your oil heats up it thins down in viscosity - one reason hot oil pressure runs lower. If your oil level for the O/D is just at the minimum for it to work and gets hot with running,maybe the lower visocosity is not allowing enough pressure in the O/D system and it will not work. This may be completely off but all I know is when the oil level in my BN6 O/D fell just under where it should be and stupid here did not think to check I ended up running every other check known to man before I realized the oil level was down and when added oil, O/D has worked perfectly !
Good luck,
Mike
 
I concur, my OD went erratic for a while, finally proved to be slightly low oil level. Since top up, 20/50 engine oil, it's been fine.

Ian
 
Guys, I checked the oil. It is filled up just a little bit (2-3 Millimeters) below the max mark. Does it make sense to add more until the max mark is finally reached? Volker
 
Sounds like you have enough oil in the transmission. Check that the OD relay is operating correctly. Turn ignition on but don't start, move the shift lever L and R you should hear a metallic 'click'.
 
Before you go too far, check the switch - there are some faulty ones around - I had the same symptoms, faulty after 30 minutes or so - swapped with the panel light switch and the problem went away.
 
KCC, what do you mean by "swapped with the panel light switch"? Did you replace the OD switch with another one? Could you please clarify your suggestion. Thanks in advance.
 
Yes, just tried another switch - in my case I used the panel light switch as I knew it worked, but the wiper switch or a new switch will do.
 
I have the very same symptoms. BJ8. Recently replaced switch with a brand new one...but still having the same issues.

Hoping it's not something more serious and will revisit the workshop manual to see if it's an easy fix.
 
BN6_2197 said:
My overdrive does not engage when the engine is warm, i.e. about 30 to 40 minutes after driving. Before that is works reliable. Any idea what the reason could be?
Click to expand...

It could be caused by internal leaks / low pressure in the o/drive.
You can try a thicker viscosity motor oil than you are using now in the gear box/ overdrive to see if that helps.

Ed
 
I have experienced a similar problem but the OD was clicking in and out and that was due to a worn contact switch that connects with the anti reverse plate adjacent to the gear lever.

Bob
 
#749217 - 03/06/11 08:26 PM Overdrive
Check out this thread.
 
I changed the OD switch today as suggested by KCC. Unfortunately this did not solve my problem. I also checked the solenoid when the OD did not engage. It worked as expected. Any idea what I could try next?
 
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