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Laycock lh overdrive

Posted by bardan 
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bardan Avatar
dan risz
Cave creek, Arizona, USA   usa
I need some tech advice on this. I put a 4 sync lh O.D. in my MG. It shifts fine but the OD doesn't work. It has new 30 wt oil filled according to the dipstick. Screen is cleaned. 12v is getting to the soleniod wire. Did the OHM test at the relay under the dash and got 17OHM. I got under the car and applied 12v directly to the solenoid wire and didn't hear any clicking normally associated with solenoid movement. I pulled the complete solenoid assembly out and applied 12v to the wire and got no movement. The little ball at the top of the assembly seems to be free and clean.
Question; am I testing this correctly? Is the solenoid bad? Any Ideas on this would be appreciated!

Thanks guys

bernard lanigan
montgomery al, USA   usa
1976 MG MGB "The B"
Check solenoid with ohm meter (dont know what resistance should be)for continuity.
Weather too crappy to ck on mine

bardan Avatar
dan risz
Cave creek, Arizona, USA   usa
Resistance from the wire to the solenoid body varies from 13 to 3.5. It varies more as the wire is moved around.

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GeeMoo Avatar
Greg M
North of the City, Ontario, Canada   can
1970 MG MGB
1972 MG MGB GT
Sounds like a bad wire somewhere in the solenoid's lead or windings.
When I applied 12v to mine in the basement, it threw the rod across the bench.

1970 MGB Black Label OD, APT VP12, Fidanza Flywheel, Flowspeed Head, Hilton AUD405 HS4 SU's, Schlemmerized Distributor, Pertronix Ignition, Saturn Alternator, 15" Dayton Wire Wheels, Falken ZE 912's, Falcon Big Bore
1972 MGB GT Blue Label OD, APT VP14, Fidanza Flywheel, Flowspeed Head, HIF SU's, Schlemmerized Distributor, Points Ignition, Saturn Alternator, 15" GC360 Wheels, Falken ZE-950s, Peco Exhaust, Frontline Costello front valance

applebj8 Avatar
Jon Appleby
Lake Wylie, SC, USA   usa
1971 MG MGB
Sounds like your relay is okay if it's sending 12V down to the solenoid.

First thought is either something's binding the solenoid & preventing it from activating, or wire on the solenoid or solenoid itself has failed.

Solenoid has failed if 12V applied directly to it will not cause it to fire. It is thirty+ years old after all.

Moss part #466-375

Good luck...

Blake Sonnier Avatar
lake charles, Louisiana, USA   usa
1956 MG MGA "Maggie"
1963 MG MGB
1972 MG MGB "Sweet Thing"
1974 MG MGB GT "None Yet"
You will only hear the solenoid click once with the car stationary...
Sounds like you may have a bad wire on the solenoid.. check it where it attaches to the windings.. I had luck soldering one one time.... I seem to remember 17ohms for the windings on the solenoid but I could be wrong...


bardan Avatar
dan risz
Cave creek, Arizona, USA   usa
I may have found the issue. The little disc with the ground wire was partially separated. The solenoid works. Now I need to put it back and see if the whole thing works.
Thanks for the info!

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JohnMacks Avatar
John McAneney
Upstate NY, USA   usa
1976 MG MGB
I am in the process of trying to make sure the OD I have on my bench is working before I replace the working non OD transmission I have in my '76B, you stated you tested your solenoid, how did you do it? Did you just put 12volts to the wire from the solenoid? do you have to ground the housing? I too want to try and ensure the OD unit is good before hand. Thanks for any help you may have for me.

bardan Avatar
dan risz
Cave creek, Arizona, USA   usa
Put an OHM meter on the wire to the solenoid and ground it to the trans case. you should get somewhere around 17 OHMS. (plus of minus a few). If you apply 12v to the wire you should get a click out of it but you will only get that click once because the soleioid closes the valve and there is no spring to open the valve. The valve opens with hydraulic pressure that you don't have because the transmission isn't turning. If you pull the solenoid out you can bench test it and see how it works. Not too hard to get out with the traans on a bench.
I saw a website for that he uses an electric motor to turn the input shaft to build enough pressure to test the OD on a bench (I wish I'd done that). Once it is in the car it's a real chore to work on this stuff. A local MG mechanic told me to just "throw it in and see if it works". That was easy for him to say.

JohnMacks Avatar
John McAneney
Upstate NY, USA   usa
1976 MG MGB
Hey Dan,
Thanks for the info, I have to ask a couple of stupid questions, my mechanical skills are OK, my electrical skills not so good, so here goes, I took the solenoid out of the OD unit and placed it on my bench, I turned my meter to DC and set it to the ohm setting(thats the horseshoe looking symbol right?) at 200, next I placed the red lead to the wire off of the solenoid and the black lead to the steel sleave that the solenoid sets in, I got a reading of 13.6 or so? Did I do this correctly? is that reading adequate? When you stop laughing and get a sec maybe you can let me know, Thanks John

bardan Avatar
dan risz
Cave creek, Arizona, USA   usa
Trust me on this , I'm NOT laughing. Your reading is OK. If you place it with the valve end up so the little post in the center falls down (1/8 inch maybe) then apply 12v to the wire and ground the case. The post should then jump up and close the valve. The valve is a tiny little ball in the end (hard to see that it is a ball). Since there is a bunch of oil in the valve and around the post it will stay up. Tap it on the work bench and the little post will drop again. If you are easily entertained like I am, just repeat the experiment about 10 times.

JohnMacks Avatar
John McAneney
Upstate NY, USA   usa
1976 MG MGB
Hey Dan, Thanks for the help, I did as you said and when I touched the lead from the selonoid to 12volts the plunger jumped, sounds like my sonlenoid is ok, one more item to check off the list before the install, thanks again, John

Dereck C
San Antonio, USA   usa
I am doing a bench test. Applying 12v to lead wire and grounding the case of the solenoid. I don't get any movement. Did an ohm test and get 14.5. So everything is connected inside, I gather. I need a new solenoid, right? Can I just purchase the Coil Assembly moss 466-380?

This overdrive was working fine and was cruising at 65mph when it downshifted without my involvement. Never could get it to engage since. No noises when it stopped working.

scottydawg Avatar
Scott B
MTP, SC, USA   usa
1973 MG MGB
Might be a pump problem or a bypass valve stuck open

"Since the creation of the Internet, the Earth's rotation has been fueled, primarily, by the collective spinning of English teachers in their graves."

"Keep in mind that free advice can frequently be worth less than you pay for it."

bardan Avatar
dan risz
Cave creek, Arizona, USA   usa
If you have the solenoid out of the trans on the bench, to test it you need to open the valve manually. The best way to do this is to tap it on the bench till the center post drops. Caution; don't let it come totally out of the solenoid unit or you will lose the ball valve inside. When you apply 12v, the center post should go up to close the valve, but when you remove electric power oil will keep it closed. When it's installed in the trans the oil pressure opens the valve when you turn the switch off. Scotty may be correct. If the valve tests good, you have another issue

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