Overdrive Stops Working After Oil Change

[DLJ]

I recently drained and refilled the gearbox in my BT7, including the overdrive. Oil was pretty dirty, and since the car is a recent purchase, I'm thinking it might never have been changed. I put in Amsoil GL4 75W80 gearbox oil, supposedly close to SAE 30 engine oil in terms of viscosity and recommended (I thought). My OD worked perfectly prior to changing the oil, now it doesn't work. Relay and solenoid work, but not the OD. Looking for suggestions on what might be the problem.

 

[dcarlg]

Disclaimer, I'm a learn as I go. With the help of the smarter guys here I'm becoming more hands on. More seasoned guys please jump.

1st I'd check the pin hole in the operating valve to see if it's plugged. Wouldn't that be fantastic if that was the root of the problem.
2nd I'd continue to flush the system until no debris shows up and the oil is clear and clean. (Even if it doesn't fix the problem, what's the down side to having debris free clean fluid.)

Food for thought. I believe the 3 types of oil we use are 20w-50 motor oil (which is a detergent), 30w non detergent and Redline MT?
I used 30w over and over for the flush because I thought it was the correct oil per recommendation of Healey Surgeons web site and phone call to Bruce. From their website:
Fill the transmission with 30 weight NON DETERGENT oil. If this isn’t available at your local auto parts store, machine shops will carry it. Or we can supply it. Change oil after an initial test drive and has gotten good and hot.. It will need 3.75 quarts for sideshift and 2.75 quarts for centershift

BCS has an orange Austin-Healey Tech Talk Technical Article Book (I use all the time and recommend) that states on page 23, 20w-50w is satisfactory or to be correct, 30w non-detergent. (photo attached of that from the book). HOWEVER, I believe David Nock of BCS now recommends Redline.

My point for your situation is flushing the system with 20w-50 seems logical because of the detergent. Healey's have been using it for a very long time with no issues.

I also wonder if you can remove the plug at the base of the pump and by turning the driveshaft, see if the plunger moves.
Sorry, no. You'll see the bottom of the oil pump body (moss 97)

Do you think it is very likely that the pump or the ball valve just 'went bad' all of a sudden?
Seasoned guys, please field this one.

Does the cam follower and return spring come out through the bottom with the pump?
Cam follower aka oil pump cam (moss 92) is slid on the main shaft, and held in place when the the OD and Transmission are pressed together.
Return spring (moss 96) is part of the oil pump plunger and will come out with the unit from the bottom of the OD.

I'm worried it won't and then I'll have to take the OD apart.
If it come so that, feel free to PM me. I've had the tranny/od out many times and there are some some things that make it easier once you know how. You don't need to take the OD apart, just remove it from the transmission. Removing the adaptor plate (moss 11) from the transmission is the best easiest way. Then you'll be able to see if there is any damage to the pump or cam and confirm pump moves. Putting OD back on, well it's heavy and you need the mainshaft spline to line up with the OD spline. Then use the string procedure to keep the oil pump plunger roller down so the mainshaft will not contact it allowing the shaft to enter the OD.

Hopefully flushing the fluid will dislodge any debris, gunk or stuck parts.
You may look into the accumulator housing assembly.

Best of luck.

Double check the oil level?

 

[DLJ]

Double check the oil level?

Yes, I've thought about oil level a few times. It's full on the stick, and according to the workshop manual, it should take 3.6L with overdrive. That's very close to what's in there, thought I even considered overfilling it because it just seems strange to me that I'm getting no oil at the operating valve at all.

 

[AUSMHLY]

Underfilled and overfilled will cause problems.

 

[DLJ]

Good to know about overfilling. I have a question about the pump plunger for anyone who has had the pump apart. Someone mentioned that the plunger might be backward, which I don't think is possible since its been working fine up to the oil change, but it does bring up a question in my mind. Is the plunger keyed so that the cam follower stays in the proper orientation relative to the cam, or does it simply 'find' the proper rolling orientation?

 

[roscoe]

If you OD was working before you changed the oil your pump plunger is not 180 degrees off. The plunger is not keyed but the fork that holds the roller cam follower is assymetrical and cannot rotate without its being removed.

 

[DLJ]

Thanks for the insight about the plunger and follower. Not sure what I will do next but I think the pump must be stuck in the down position and either needs to be freed or maybe I should just drive it more and see what happens.

 

[Bob_Spidell]

Here's a WAG: Manual gearboxes can be run on ATF; in fact, I think some gearboxes call for it. I don't know if ATF has any detergent properties--probably not--but its chemical composition is different than motor oil (I think it's actually vegetable oil). Maybe fill the gearbox with it, drive it around for a while and see what happens? Or, you can try hydraulic fluid, available at places like Napa (I go though a lot with my (leaky) tractors). You could also fill the box with mineral spirits, but don't drive anywhere with it, just run it at idle for a few minutes and drain.

It may take a teardown, but I wouldn't go through that without trying all alternatives.