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MGB OD question - need to warm up?

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drooartz

drooartz

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I've noticed a behavior with the overdrive on my MGB and I'm not sure if it's normal. This is a 1970 MGB with a black label overdrive. During the recent rebuild the transmission was swapped with one I had from a known good parts car (my car was already an OD car, the shop just wound up using my spare).

What I've noticed is that if I use the OD in the first couple miles of a drive from cold it will click in okay -- maybe a little slowly -- but won't click back out again. After 2-3 miles it will function normally without issue. The shop originally used a heavier oil then I liked, so I did drain and refill the transmission and now it has 30w non-detergent in it.

Is this normal behavior? It's been 9 years since I drove this car regularly, and at my old house I wouldn't have used the OD for a few miles anyways. Want to make sure I don't need to go deeper into things if this is normal stuff.
 
Drew, I had a similar situation on the 72 and the cure was cleaning the solenoid that activates the unit. Mine was a little gummy, just enough to cause it to initially stick. Dropped the piston out cleaned it and the problem went away. (y)
 
On the subject of overdrives - is there any reliable way to see if one works while the transmission is still sitting on the workbench? I replaced O rings and cleaned out passages/screens on mine (the actual soleniod was very stuck as well) since the trans is conveniently sitting on a table, but I either don't have any kind of rotary tool that can spin the trans fast enough to build adequate pressures to activate the mechanism, or the thing still doesn't work. I hooked up a speedo to the trans and I can get it to spin almost 20mph with a heavy duty 1/2 inch drill, but either thats not enough or its still not working. I've never owned an OD trans before, and never seen this one run in an actual car (its a black tag 1970 MGB unit). I'd rather not put the whole engine/trans combo into the car and then find out something is wrong if there is a way to check it (and I don't have the materials/resources to build a full run stand).
 
Drew -

I've had two MGBs with OD (one is the current Victor TF with B running gear). The '73 MGB acted a bit like yours, but I never really investigated it. The transmission had sat a while and all I did was drain it, flush it with fresh 20W50, then refilled and drove it until passing it on.

The Victor's transmission was an unknown, so I sent it to John Esposito at Quantum Mech. for a complete refresh. Shifts are quick and smooth, again with 20W50.

If it were mine, I'd drive it until it displays some troubling issues.
 
Thanks all for the thoughts. when I get a minute I'll put the car in the lift and take a look at the solenoid. For now I'll just drive it.

Mickey, you mention flushing the trans. I did a drain and refill, but nothing else. Other steps I should consider?
 
Flush was probably a poor choice of wording; not sure how one would do that. Draining, refilling and driving a bit; then draining and refilling is what I did.
 
You shouldn't have any issue of you use 30 wt oil. I use 50 wt in the race car and it exhibits exactly what you describe - until warm (c. 1 lap) it wouldn't engage OD. No reason to use that heavy an oil on the street (in racing conditions the trans oil well over 220+ F. and runs like water).
 
Thanks. I'm thinking another drain and fill, along with cleaning the solenoid, should get me back to normal. That should get enough of the old, too-heavy oil out.
 
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