Update: I got the solonoid lever adjusted to give me about .040" lift of the operating valve using the solonoid. I made a fitting that duplicated the plug above the operating valve and allows a pressure gage to be installed. Took the car for a drive and after engaging the OD I got no pressure and needless to say the OD did not work. What is my next step to get pressure? Thanks again and have a good day!

John

Well sound like you may need a new pump!! But check the one way return valve it may be cluttered up with dirt.???--Keoke

Keoke,
I read that this could be the problem. Do you know if this can be done with the tranny in the car. It looks awful tight to get the housing with the solonoid off the tranny. Thanks and have a good day!

John

If memory serves me correctly, the pump can be accessed from the bottom, beneath (or above) the big brass plug.

The later model (>68) MGB overdrives were so much trouble to mate to the back of the trans without jamming up the cam/plunger, that I made up a tool so I could install the pump after the overdrive was attached.

Point is, I'm sure it can be removed, but I don't know if it will be easy. I have an ovd unit on the bench, so I'll make it a point to take a look for you.

The pump can be removed if you don't mind being on the floor with the car on ramps or jack stands. Before you do anything else you should probably make sure the pressure relief valve is not stuck open. As long as you are to the point where you know you need to drain the oil, go ahead and do so. Then remove the side cover from the overdrive (being careful to release the accumulator spring by leaving the rear bolts a little behind the others as you go around). When you get the cover off and look in to where the pump sits you will see the relief valve. It is the same sized cap as on the operating valve. Take it out and see if there is debris or a stuck ball/broken spring etc. You may be able to restore pressure by cleaning this out and putting a new ball bearing in (I got a lifetime supply at Orchard Supply Hardware). If this all looks good you may have a pump problem. With mirrors and flashlights you should be able to see the pump piston go up and down if you turn the transmission mainshaft (which would be a trick from under the car). If the pump piston goes up and down and follows the cam lobe, and the relief valve is good you could still have an accumulator problem. If the pump is not operating normally and you need to pull it out, it is just above the oil screen when you take out the big plug on the bottom. It is withdrawn with a puller that threads into the bottom of the pump. I've got one, but it is possible to make one from a section of pipe a bolt with the proper thread and a little welding. The thing to remember if you do this is that the pump roller attached to the piston can be spun 180 degrees when the pump is removed. If it goes back in like this it can bend the piston rod and you will then have a real problem. The pump can be tapped back into place, but extreme caution is needed to ensure the roller is properly on the cam as you do this (and the relief valve must not be installed before the pump goes back in). You will see that where the roller is pinned is not quite symmetrical. The chances are that if there is a pump problem it pretty much has to be that either the roller is broken and thus not following the cam on the mainshaft, or the piston is bound in the pump body. Obviously if this happens the cam will shove it down and the spring will not have enough expansion force to put the piston roller firmly on the cam. If you need to remove the accumulator it is another post for that. Also not terribly hard to do, but do not remove the piston from the accumulator body unless you know the piston is frozen in place (which would not allow the OD to work, but you could still have pressure (I think). My guess, bad press. relief valve or bad pump. Relief valve easier than pump. Check it first. Laycock-de Normanville...where is Normanville anyway and just who was Laycock?

I had similar problems (loss of pressure). I took off the accumulator cover and removed the accumulator springs and cleaned out the sludge. I also messed around with the ball bearing (that is pushed up by the operating lever/solenoid), put everything back together and it worked fine.

OK that will be my next step. I have spent so many hours under this car in the last 27 months a few more is not going to be a problem! I will have the wife turn the wheels while I watch the pump. When I rebuilt the unit I did replace the accumulator housing but the piston looked fine so I reused it. Might have been a mistake. So from what I understand I should be able to do all this with the tranny in the car, yes? Again thanks for the help and encouragement and have a good day! And by the way I think I mispoke about the OD not disengaging. I think it disengaged ok just not when I flipped the dash switch. The gear selector switch has always worked without a problem.

John

At the risk of my sounding stupid, I must ask if it disengages when you accelerate after turning off (normal) the switch? This is how it is suppose to work.

WHAT!! You telling me: If you turn the OD dash switch off then depress the accelerator pedal and it disengages you are good to go-OK. If OD is engaged only turning OD dash switch off will not cause it to disengage--Keoke--

Naa you be OK!! TH

I did everything with the trans in the car.

To repeat clearly what everyone else is also saying:

The OD will only disengage when you depress the accelerator down somewhat AFTER turning off the OD switch. Turning off the switch will not disengage the OD until you depress the accelerator sufficiently to move the OD throttle switch. The designers only wanted disengagement when under acceleration, not deceleration.

Okay, my overdrive is about half disected, here: http://www.rfdm.com/gallery/album144

Nothing says it better than photos, Randy.

Well I checked the pump and it was moving fine. The non-return valve looked dirty and the ball looked suspecious so I replaced it. I packed the pump with grease and reassembled and adjusted everything and went for a test run. OD would not engage! Went home an put my pressure gage on and no pressure. Drove around a little and noticed that the pressure came up to 225 lb, promising at least. After a little longer low and behold the pressure was up to about 475 lb and the OD seemed to work fine. I am going for a test run this morning and hopefully it will be OK. Thanks and have a good day!

John

Behold, the pump. More pictures at: http://www.rfdm.com/gallery/album144?page=9

Randy,
The seat for the ball bearing in the check valve on your pump looks good in the photo. As I mentioned in pervious posts (other threads) when I pulled mine the seat was badly pitted and I ended up lapping it with a ball bearing glued to a drill mandrel. That fixed one of my problems. Hey, if you could just roll that piston with the roller so that you can show that the two ears of the fork that hold the roller are not of equal thickness, that would point out why you have to pay attention to how it is oriented when you re-install the pump. The main problem I had was that fork was cracked, slightly bending the piston assembly; I think from the po installing the pump 180 degrees out, and it caused the pump piston to jam in the cylinder and not go up and down.

DOH! I just looked at your other photos and you've already got a great shot of the ears.

Just for future reference if needed, how do you orient the "ears" of the pump (what is the reference point) to make sure it is in correctly?

John, I'm glad it seems to be working now. You have shown a lot of perserverence. I also recall that after working on my OD that it took a while for the pressure to return after taking things apart. It may have something to do with getting the pump primed, but I had a similar loss of pressure, then it returned after running for awhile with the top plug off. When oil starting bubbling up, I reinstalled the ball, spring, and plug and its been working perfectly ever since.

I'm not entirely sure of what you're asking...

John was saying you had to orient the pump correctly. I was asking how you know it is oriented correctly. Looking at your new pictures, it appears the thinner ear is under the brass thing. Is that the key? Does the cam go in the brass hole? I suppose it would be obvious if I took it apart, but John said his was in wrong to begin with, so I wondered how you'd know if were right or wrong.

No, right in front if it:



Cruise through this album, and it will probably answer a bunch of your questions. http://www.rfdm.com/gallery/album144