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MG MGB Technical - OD failing after renewing o-rings

Instead of asking at the end of a very long thread I'm starting a new one. Love to figure this out. Really bummed.

Went for a long run flipping the OD on/off at proper speeds. Went in and out like butter.

Then.

It engaged a little slowly. No problem disengaging. Then more and more slowly until it would engage partially then jump out of OD.

Suddenly flipping the stalk did nothing. Occasionally it would come on but jump out.

When I got it home I hoped maybe there wasn't enough oil getting back there. To my surprise when I pulled the side bolt oil came rushing out with the tranny being overfilled. Odd since it did it slowly until it started to drip and let it for a while before I put the plug back.

So what does this sound like to all of you? Too much oil? Solenoid not functioning right? One of the other ones I rebuilt ie pump or low pressure?

I don't understand why it worked perfectly then stopped. Sucks. I was very proud of the job.

Aside from the leak it worked fine (although not as smooth) previously.
Max71

Max, I'm no expert on LH Overdrives, but have been doing a bit of reading from Paul Hunts website. On the LH Diagnostics section, have you fully checked the solenoid electrics? The last couple of paragraphs seem to describe your symptoms

"even though OD may work when cold, there may be insufficient current flowing when things get warmer for the solenoid to do its job. However in this case I'd expect OD to go from being engaged, to drifting in and out of engagement, before it disengages altogether."

http://www.mgb-stuff.org.uk/gearstext.htm#


"The first test with a non-functioning OD should be to insert an ammeter in circuit, and check the current. With the ignition on and manual switches on and the gearbox in an overdrive gear you should see about 800 milliamps, equating to a solenoid resistance of about 15 ohms. If you have the manual switch on the dash insert the ammeter here. If you have the column switch then find the bullet connector where the yellow in the main harness joins the yellow/red in the gearbox harness at the back of the right-hand inner wing and insert the ammeter here. For a car with the manual switch on the gear lever look for where the white/brown from the gearbox harness joins the two from the main harness (shown as white in this image) in the same position, pull out the wire from the gearbox harness and insert the ammeter.

Note that if the current is significantly less than 800mA, then even though OD may work when cold, there may be insufficient current flowing when things get warmer for the solenoid to do its job. However in this case I'd expect OD to go from being engaged, to drifting in and out of engagement, before it disengages altogether."

I'm not sure about the gush of oil you had. Are you sure you have not over filled the gearbox? 6 Imperial pints or 7 US pints

Andy
Andy Robinson

Thanks Andy. Believe me I'm going over everything in my mind especially because it worked before I 'fixed' it.

I must have over filled it which when I pulled that filler plug I would say 1/5th of a quart came out. I left it for several hours under the dripping stopped. 30wt non-detergent, Valvoline - which was always used.

Zero problem on disengage. Just engage.

These are the things I did:

Regarding the solenoid which I wondered about - the line to the bullet connector seemed fine with a slight break in the shielding but no fraying or broken wire. I cleaned the bullet connector and pulled the wire off the junction - cleaned the push on connector and tab. Put it back on verifying its on properly.

On the unit itself I slightly bent the copper disk tabs a little more as per an issue described here on the board where paulh4 found that was the issue with his old one. I also carefully cleaned it until it was bright and shiny again (no pressure applied - I used a solution I use on electronics with a Q-tip.

I then did a continuity check to be sure there was a solid connection. The break in the casing was checked by having continuity and moving this break in many directions to assure it was just cosmetic and not a sign of malfunction.

I'll do that electrical test. Odd since it worked flawless before.

The low pressure valve: Cleaned it well and per the Twist video I polished the bits that mated. Found they were tight and did not slide in and out freely. Kept all bits together on a clean rag and assembled in the same order with all the shims.

Pump. Filthy and black. The worst of the assembles as far as that goes. This was also the worst in terms of the pump plunger and the body. It would go in 3/4 of the way then meet stiff resistance. The bottom 'ring' of the plunger showed pitting like it was attempting to go in and out and that harmed the metal. Carefully with minimum polishing as possible until it smoothly went in and out.

Again, I'll check as per Paul Hunt. My DMM has complete range of settings.

Again, thanks!
Max71

Just got back from a run and same results. In the meantime, I spoke with John Twist.

He's thinking it's the oil pump in the OD. He also suggested the electrical test which I will do now.

I really don't think it's the switch either on the trans nor the stalk. In classic trouble-shooting, retrace from the last changes.

Since I did all 3 assemblies that's hard to pinpoint and a shame I have to drain out all the brand new oil. It would be nice if I could get the back up high enough to force the oil well into the trans and only lose a small amount in the OD while working on it.

Since it worked prior to this I'm thinking the most work I did was the pump assembly. I did a lot of polishing to get it to bottom out going into its housing. Even at the top it was rough although that was minor polishing. I did do a considerable amount on the plunger and its housing to get it to mate all the way.

Don't know if this has anything connected. I have a meter on the voltage to see what the alternator/battery is doing. Without lights on it's 13.9VDC. With lights its 13.2VDC. Lights have a new Moss relay system.

Anyway, if any of this turns on a light for a member I greatly appreciate it. As stated, electrical test is next.
Max71

I doubt it is electrical.

That pump can easily go in cock-eyed and if there is ANY dirt in there it WILL jam up - the cause of the marks you found.

Drop it out and check it again for sticking.

Did you use any auto trans fluid in there to clean things up in the gearbox & OD?
Chris at Octarine Services

Chris - as usual, I believe you're correct.

I've taken a lot of reading static and while running and while they do not have the numbers in Paul Hunt's article when compared to new coils a friend at Moss pulled and tested for resistance it's very close. None, btw, were 15 Ohms. One new one was 13.6 and the other 14.2 right off the shelf.

On a run the mA dropped only .3 when the OD stopped working.

Again, static numbers at the solenoid.

13.4 +/- .3 Ohms resistance
11.7 VDC

Battery with key on measures 12.2VDC

Paul has been kind enough to correspond and I spoke with John Twist again today. He's coming out this way and I'm hoping to get this sorted so I can drive up to see him.

After listening to the new readings he feels its the pump. He said it's very unusual I had to do so much polishing. Which I did as described above. At this point, John thought I should replace the pump assembly. Since all the polishing did was probably create wear I'm shy to just remove and replace the same assembly. One thing I did not do was set the ball that sits on the spring inside the screw cap. John didn't think it should matter but suggested I do that in the future.

Do you have a proper way of inserting the oil pump assembly?

I didn't run auto trans fluid but maybe I should. The oil came out clean although the pump was filthy as mentioned. If I stick a finger in the drain to get inside the trans it returns with grime.

Should I still do this now? Since the new oil is coming right out? If so should this be done prior to working on the OD?

If the answer is yes, then the method? Fill up and drive until warm then drain?

Thanks for the educated help. Its greatly appreciated.
Max71

Chris - I re-read your suggestion from the other thread

"Once you get it out then use clean kerosine / paraffin and a soft paintbrush to clean everything.

I use a wash pot on a high pressure air line to blast out all the dirt from the oil galleries and wash out the bearings / valves etc."

I do not have air and the brush could only be used in the exposed part of the OD. Any alternatives for a garage mechanic?
Max71

I took a final run measuring from the Y/YR junction (FWIW its the same as measuring from the stalk)

Cold/working: 191 +/-2 Cold steady 189 mA
Resistance: ~5 Ohm
13.1 VDC

Stops working: 186mA
Resistance: 12 Ohms
13.1 VDC

I'm not sure where Paul Hunt got 800mA. I don't get close. Unless I'm on the ragged edge dropping 3mA shouldn't have such a drastic effect.

Very curious what others OD runs at resistance and mA
Max71

Problem solved. If requested I can create a new thread to help future DIY'r people from falling into the same trap.

In the end, it wasn't the coil as predicted by Chris. It was the oil pump and the fact I did not orient it correctly. I never saw mention of orientation until I read my Bentley. Much too late.

When I removed the pump assembly I tried to drop it straight out. It was off - if it did not rotate it was offset 45 degrees.

I corrected it and put a new assembly in that I had ordered. Took a run and it ran fine and well past the marker where it normally failed.



Max71

Just to clarify the electrical situation, Max did in the end see 800mA.

But I'd love to know what keeps the oil pump in the correct orientation with the cam. I'd imagined that it was the flat on one side of the pump plunger meaning that it could not be fully inserted any other way, or twist in use, but apparently not. Even if that were the case, if it did try to twist then it would be rubbing on the casting, which doesn't sound like a Good Thing.
paulh4

I recently pulled my oil pump and learned a new installation trick that might help. If you look closely into the OD casing you can see the pump cam. You can then turn the propshaft (assuming you raised the car off the rear wheels) so that the low point of the pump cam is facing downward. That makes putting the pump back in a lot easier as the pump spring will not be depressed. Do not forget that the flat side of the pump plunger faces to the rear. Also, after you install the pump, you can turn the propshaft to verify that the pump plunger is moving correctly and not binding. The John Twist video gave me the "courage" to open up my OD unit, but he glossed over some of the procedural details.
R LEARY

This thread was discussed between 24/08/2017 and 30/09/2017

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