The all-new Front Page News Feed is now live   Read the announcement
MGExp

MGB & GT Forum

Overdrive cover bulging!!

Moss Motors
AutoShrine Sponsor
AutoShrine Sponsor
AutoShrine Sponsor
AutoShrine Sponsor

dickmoritz Avatar
dickmoritz Platinum Member Dick Moritz
Philly 'burbs, PA, USA   USA
Both the upper plate, into which the plunger and check ball fit, as well as the solenoid, are barely visible in his second photo down...

Dick



In reply to # 3905746 by Richard-Kloss Just a thought here, in looking at your dismantle it appears that there might be part of the solenoid housing missing. I do not see "both" of the metal end pieces that are in my solenoid housing. You do not picture the solenoid either. The new replacement one from Moss does not look like the original. First photo original second replacement.



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

. Hide this ad & support a small business by becoming a Gold Supporting Member
Was this post helpful or interesting?
Yes No Thank
dickmoritz Avatar
dickmoritz Platinum Member Dick Moritz
Philly 'burbs, PA, USA   USA
Mike, I've never seen an LH overdrive pressure valve that required five shims to achieve proper operating pressure, which is 400-420 psi. And each shim increases the operating pressure by a lot, despite their very thin construction. Further, that appears to be a replacement pressure valve assembly. An original black label overdrive would have a perforated tube around the pressure spring, and the non-perforated tube you show is typical of the replacements. Further, the components of your pressure valve appear unusually clean and shiny, again suggesting that it is a replacement.

I have had trouble with the replacement pressure valves, including over-pressurization. One problem has been that the funnel-shaped low pressure bleed at the top of the spring does not fit freely down into the tube. This can bind the spring, causing over-pressurization. The first such new valve assembly that I installed, right out of the box, pegged my pressure gauge at 600 psi, so this may very well be where your over-pressurization originates.

If at all possible, I would encourage you to affix a pressure gauge in place of the hex plug on the bottom of the pressure valve so you can monitor the actual operating pressures. Then I would "massage" the upper part of the tube to assure that the low pressure bleed moves freely within it. This is quite tricky, because you cannot increase the O.D. of the tube very much or it will not fit all the way into the bore in the overdrive main housing. It took me quite a bit of fiddling to achieve both clearances.

You might also consider assembling the pressure valve without the tube for diagnostic purposes.

Next I would re-assemble the pressure valve with none of the shims installed and run a bench test so you know exactly what your pressures are.

If you don't have access to a proper pressure gauge, here's a link to a very nice and affordable task-specific gauge. For your LH overdrive the gauge is just fifty bucks: http://www.geocities.ws/jholekamp/

Please do keep me and all of us apprised of your progress.

Also, please check for a friendly Private Message...

Dick




In reply to # 3905760 by mgann Yes, I do not picture the steel housing as it is still in the gearbox. It is being difficult to remove. I think the over-pressure expanded it a bit.
I have removed the control valve and attached the assembled and expanded view in the pictures. There are five (5) shims in the assembly at the bottom of the spring. It all seems to be ok. Not sure what else to do. Reassemble and test?



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

Was this post helpful or interesting?
Yes No Thank
mgann Mike Gann
West Point, UT, USA   USA
I have ordered the LH Oil Pressure gauge to do some testing. I will start with no shim washers and go from there.
Just a question. I know I put the gauge in place of the 3/4 inch plug, but do I have to have the gearbox in at least 3rd gear with the OD engaged to read the pressure correctly? When are the hydraulics pressurized I guess is my question.
From the picture of the flattened cover you can see that it was stretched a bit when it was deformed. I am hoping that it will still fit.
Thanks for all your help.

. Hide this ad & support a small business by becoming a Gold Supporting Member

Attachments:
IMG_6038.JPG    43.6 KB
IMG_6038.JPG

Was this post helpful or interesting?
Yes No Thank
dickmoritz Avatar
dickmoritz Platinum Member Dick Moritz
Philly 'burbs, PA, USA   USA
Mike, if you're concerned about the flatness of your black label plate you can simply make a replacement out of aluminum as OE, or steel. There's nothing special about it.

As for overdrive engagement pressure, two criteria must be met in order for the overdrive to engage.

First, do note that the overdrive pump is always pumping oil. When overdrive is not selected, the oil from the pump is directed directly back into the overdrive sump and recycled. When the solenoid is energized, it pushes the plunger up against the check ball, which in turn blocks off the return passage to the sump, such that the oil pressure is instead directed to the passages that lead to the operating pistons and, ultimately, overdrive engagement.

So whenever B+ is applied to the solenoid, the overdrive should engage. However with the gearstick in neutral this engagement may not be apparent, and the "clicking" so often referred to at the solenoid is rarely audible. So, since you have the gearbox in the car, I suggest that you support the back of the car safely under the rear axle housing, such that the axle is in its normal "loaded" position and the driveshaft angle is as it would be if the car were on the highway.
Then you can run the engine, with the gearstick in third or fourth gear, and apply power to the solenoid.

If you like, for diagnostic purposes you can use a jumper wire and apply B+ directly to the solenoid, bypassing both the on/off switch and also the 3/4 switch. The solenoid in an LH overdrive draws less than one amp, only about 800 milliamps, so you can use pretty much any gauge wire for diagnostic purposes.

If overdrive engages as it should, then you'll note either an increase in the speedometer reading or a decrease in engine speed as noted on the tachometer. The difference will also be audible.

Note that, in normal operation, two criteria must be met in order for the overdrive to engage. The overdrive must be on (with ignition key on...), and the gearstick must be in third or fourth gear. Under these conditions power will flow from B+, through the on/off switch, through the 3/4 switch and on to the solenoid. Whenever either of these criteria are not met, the overdrive will be disengaged. That's why you don't have overdrive in first or second gear (or reverse...).

Once you have your pressure gauge attached, it is normal, once the solenoid is energized, for pressure to build to about 75 psi, pause, and then move on up to operating pressure. This typically takes about two seconds all told, at which point your gauge should show operating pressure. The reason for the delay is that, each time the overdrive is engaged, it takes just a second or two to re-fill the various oil passages throughout the overdrive unit...

Dick




In reply to # 3906276 by mgann I have ordered the LH Oil Pressure gauge to do some testing. I will start with no shim washers and go from there.
Just a question. I know I put the gauge in place of the 3/4 inch plug, but do I have to have the gearbox in at least 3rd gear with the OD engaged to read the pressure correctly? When are the hydraulics pressurized I guess is my question.
From the picture of the flattened cover you can see that it was stretched a bit when it was deformed. I am hoping that it will still fit.
Thanks for all your help.



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

Was this post helpful or interesting?
Yes No Thank
mgann Mike Gann
West Point, UT, USA   USA
As soon as the gauge is delivered I will begin testing. I will probably start out with no shims and see where I am as a baseline. Thanks again for all your help.

Was this post helpful or interesting?
Yes No Thank
Donthuis Avatar
Donthuis Don van Riet
Rijswijk, ZH, Netherlands   NLD
5 seems a very high value, most OD's come with none or one (Imyself had only one), lower numbers with 2-3. Never heard of another person finding 5. eye popping smiley
Of course if the shims are all extremely thin one never knows. Still this case almost asks for a oil pressure check with the special tool fitted to the OD in place of the bottom cover of the valve. eye rolling smiley

I include once more my picture of all the parts -coil itself excluded- lying on my bench before remounting. The pressure gauge was mentioned on MGE, but I lost the ref....

PS For the valve cover I had two types of sealing ring: the original copper and a fiber one, of which I only used the new fiber one after all

In reply to # 3905760 by mgann Yes, I do not picture the steel housing as it is still in the gearbox. It is being difficult to remove. I think the over-pressure expanded it a bit.
I have removed the control valve and attached the assembled and expanded view in the pictures. There are five (5) shims in the assembly at the bottom of the spring. It all seems to be ok. Not sure what else to do. Reassemble and test?



Edited 1 time(s). Last edit at 2019-03-11 11:27 AM by Donthuis.


Attachments:
2017-10-08 15.51.25.jpg    59.2 KB
2017-10-08 15.51.25.jpg

Was this post helpful or interesting?
Yes No Thank
mgann Mike Gann
West Point, UT, USA   USA
I finally got the solenoid cover and top cap out today. The picture is what I found. I think the o-ring failed during the over pressure event. I tried to see if all the pieces were there.
Valve and solenoid are all back in the gearbox. Valve with no shims.
Awaiting my pressure gauge. Thanks all.


Attachments:
A11FEAFA-FECE-428F-AEF3-F08F3963D7C8.jpeg    43.9 KB
A11FEAFA-FECE-428F-AEF3-F08F3963D7C8.jpeg

Was this post helpful or interesting?
Yes No Thank
Donthuis Avatar
Donthuis Don van Riet
Rijswijk, ZH, Netherlands   NLD
Well done. If the small ball is not lost you've now got everything that is needed; BTW the smallest O ring on the plunger can give a rather tight fit, slightly hindering the plunger movement....
In my case this large O ring on top had flattened and hardened, so the coil was no longer pressed downwards enough to assure a dependable mass contact via the solenoid cover & OD housing

I'm curious on which number of shims you finally end up with to reach the usual oil pressure range. One member of our Dutch MG Car Club once calculated the springs inside the OD mechanism equate to about 270psi pressure on the large pistons pressing against them. Well below the usual pressure valve adjustment range around 400psi (380 min - 420 max)

Recognising this 270psi value IMO 380psi should already do the trick in a dependable way, but on MGE lots of members advocate raising the pressure by another 10% to 420psi instead
BTW the later issues of the factory manual specify 400-420 psi as well eye rolling smiley

In reply to # 3907159 by mgann I finally got the solenoid cover and top cap out today. The picture is what I found. I think the o-ring failed during the over pressure event. I tried to see if all the pieces were there.
Valve and solenoid are all back in the gearbox. Valve with no shims.
Awaiting my pressure gauge. Thanks all.



Edited 1 time(s). Last edit at 2019-03-16 05:25 AM by Donthuis.

Was this post helpful or interesting?
Yes No Thank
mgann Mike Gann
West Point, UT, USA   USA
I am continuing this on another topic. I couldnt find this one until now. Thanks all.

Was this post helpful or interesting?
Yes No Thank
. Hide this ad & support a small business by becoming a Gold Supporting Member

To add your reply, or post your own questions




Registration is FREE and takes less than a minute!


Having trouble posting or changing forum settings?
Read the Forum Help (FAQ) or contact the webmaster