• Hey Guest!
    British Car Forum has been supporting enthusiasts for over 25 years by providing a great place to share our love for British cars. You can support our efforts by upgrading your membership for less than the dues of most car clubs. There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Upgraded members don't see this banner, nor will you see the Google ads that appear on the site.)
Tips
Tips

MGB OD question - need to warm up?

Share this page

drooartz

drooartz

Moderator
Staff member
Gold
Country flag
Offline
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.
 
Back
Top