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86 EH Auto Delayed Shifting

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Rangi246
Posts: 5
Joined: Sun Mar 26, 2017 9:03 pm
Location: Christchurch

86 EH Auto Delayed Shifting

Post by Rangi246 » Sun Jul 15, 2018 1:24 am

Hi everyone

Took the car for a nice long drive this weekend, approx 1,000 km's all up. Car went like a dream apart from one issue that I've noticed.

Its an 86 Euro 635csi with the EH Auto. What happens is i'll accelerate up to 100km/hr and the transmission will work perfectly. Smoothly shifts up through all the gears and into 4th OD at 100km/hr. It shifts smoothly down when decelerating too.

Now, if I approach a hill in 4th OD and I mash the gas, it kicks down to 3rd and takes off. Great :D

This is where the problem arises. When i've buttoned off the gas and am cruising down the other side, it sits in 3rd and refuses to change into a higher gear for about 5 WHOLE minutes. The effect is that i'm heading along the road at 100km/hr at roughly 3,000 rpm.

When its doing this I've tried manually selecting the gears and it doesn't seem to help either. If I put it in second, then third and finally "D", it changes down to 2nd and then shifts to 3rd and holds it again. Changing the switch to "S" mode and back to "E" does nothing either, likewise with "123" and back to "E".

After about 5 minutes it DOES change into 4th and then OD but in the meantime the only way to solve it earlier is to slow down to about 50km/hr where the car drops down the gears itself. When I start accelerating again, it all works nice and smoothly shifting all the way through to 4th OD. The transmission has already had a new filter and fluid change and I remember it had this problem beforehand too.

Does this sound like a TPS problem? Or is it likely to be something in the box itself?

Any help with this would be much appreciated.

Cheers
Mark

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Brucey
6 Series Guru
Posts: 9796
Joined: Fri Apr 09, 2004 7:17 am
Location: Cambridge, UK

Re: 86 EH Auto Delayed Shifting

Post by Brucey » Sun Jul 15, 2018 10:29 pm

a few times my car has done the something similar. No problems with my TPS; if fact I found I could regularly provoke this behaviour on one particular hill but only when the engine was not fully warmed up (five miles only driven). I think that the problem is at least in part to do with

a) the hill
b) the acceleration
c) the oil level

I think what happens is that oil surges to the back of the gearbox and then the oil that is sucked up into the pump is mixed with air and gets very frothy. Any shifts then carried out are done with pressurised (but frothy) oil in all the shift servos. I think that this can send the gearbox a bit doolally for a while afterwards, but I'm not sure how exactly. I think that when the gearbox oil is still cold, it takes longer to run back into the sump and this causes the effective oil level to be lower until the engine is warmed up.

Anyway the pattern of driving at lower speeds on level roads, with the box making shifts seems to sort it out after a while; maybe it clears the servos of frothy oil?

Be sure to check the oil level in the gearbox as per the book; i.e. on the level with the engine running, and fairly well warmed up.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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