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MG MGB Technical - mgb overdrive solenoid its oily

Trying to get a 1977 mgb back on the road which has stood for 3/4 years - however the overdrive is working in all gears - ( overdrive enagages - disengages as it should) the interlock switch appears to work ( ie ive removed it and its makes a complete circuit when I press the actuater in) ive just removed the solenoid from the o/d and ITS COVERED IN OIL) should it be like these or have the "o" rings failed ??

I think the interlock switch could be at fault because testing the circuit with the interlock swith screwed in at verying degrees i get a reading on my meter and the swith almost feels like its got a "2 stage" engagment on it

BUT THIS IS THE PART I'M MORE WORRIED ABOUT - !



and something else a bit more worried about !! - having removed the interlock switch and added an additional washer I took the car for a test drive to see if the od would only work in 4th gear like it should do - however the od appeared not to work in any gear - but after a returning back after about 2 miles there appeared to bb what felt like "drag" when driving forward - on jacking the back of the car up and with the car in neutral the rear wheels felt as they were locked or very stiff - I left the car at this point and this morning the wheels were moving freely - good news i thought - but with the car in any gear, the rear wheels spin freely but do not turn e prop shaft - also it now will not start !! I think the starter motor is failed because its just clicking - the battery is fully charged and I have a spare - I have had the ignition on while testing the OD wiring, so have I burnt something out ?

so 3 questions should the solenoid be covered in oil, have I damaged the starting circuit and have wrecked my OD ?

best regards

Matt
M Benoy

some progress -

the car wasnt starting because I'd dropped the cross member at the back of the gearbox to gain access to the inhibitor switch so the car now starts and has drive in all gears - no experience with overdrive so freewheeling rear wheels with the engine switched off and the gear in gear is normal ?

still keen to know if the solenoid should be sitting in oil ?

Matt
M Benoy

The solenoid is designed to be immersed in oil. When you say that the rear wheels are "freewheeling" with the transmission in gear, do you mean that you can turn one wheel forward while the other wheel turns in the opposite direction? If so, this is normal and indicates that the deferential gears, inside the rear axle, are working correctly. As for the starter, make sure that all of your connections are clean and that the ground strap is connected from the crossmember to the transmission. RAY
rjm RAY

many thanks Ray - the solenoid appears to be working having put it back in the OD unit - I was expecting the rear wheels when off the ground to "drive" the the prop and gearbox and engine (with the engine switched off) when you try to spin the rear wheels (i'd expect the rear wheels to "un turnable by hand when the cars in gear) does that make sense ? the rear wheels do turn in opposite directions when in these conditions.

will try an new interlock/ inhibitor switch and before driving the car use atest meter to make sure that od onlt engages in 4th gear.

very worried about wrecking the od by using od on 1st and 2nd and reverse.
M Benoy

I've been running without an OD isolator switch for over 20 years, with no ill effects on the OD unit. I use OD in second quite a bit, but not while under full power. I even occasionally use it in first gear. I fitted a cutout relay, in the reverse light circuit, to kill the power to the OD solenoid, in case I forget to turn off the OD switch. This prevents the OD from engaging in reverse, which is the kiss of death for the OD's one way clutch. RAY
rjm RAY

many thanks Jim -
the new isolator switch from Moss has turned up and Im trying to fit the right number of washers so that it only works in 4th.so far i can only get it to to either work in all gears or not at all ! would be very interested in the cutout relay details - i.e if its possible to get one in the uk I'm suitable encouraged to know how tough the OD unit is - will keep experimenting the the isolator switch but do like the idea of the cutout relay

many thanks

Matt
M Benoy

Matt, the overdrive should work in 3rd and 4th!
The switch detects the position of the gear change linkage being in the 3rd/4th plane if you get my meaning. You won't be able to adjust it to only come on in 4th. I think overdrive on 4th was only for the V8 (too much torque otherwise) and for late American MGBs (to meet emissions regulations).

As RAY said, you won't wreck the overdrive by driving the car in first or second with the overdrive on, as long as you don't welly it. Reversing in overdrive is the kiss of death.
Mike

I used an $8 relay, wired into the reverse light circuit, to cut power to the OD solenoid when the shift lever was placed in reverse. It makes an audible click, indicating that the OD circuit has been broken. I wrote an article, for the AMGBA, in '93, detailing what is required to do the conversion. It should be in their archives. RAY
rjm RAY

Thanks again Ray - have looked at the AMGBA but can't find the article - i cannot adjust the the inhibitor switch - it either works on all gears or not at all no matter what position its screwed in. the relay needs to open the circuit on the od solenoid when the circuit is closed on the reverse light switch like you mention - question is what type of relay do I need ? any ideas ?
M Benoy

Hi, Matt,

the usual type of relay for cars is one which switches the switch on when current flows through the relay coil. This relay has four connections. There is another type which has five connections, the extra contact is on all the time, UNLESS current is flowing through the relay coil. I think this is the type RAY is talking about.

There is a Bosch version (Bosch 0 332 204 150) and these will probably have contacts 87 and 87a marked on the bottom (as well as 30, 85 and 86). 87a is the contact which is normally connected to supply 30, unless current is flowing through the coil from 85 to 86.

Good luck!
Mike

You shouldn't need a relay, the inhibitor switch has worked perfectly well on hundreds of thousands of cars for dozens of years. Not allowing it to operate in 1st and 2nd is a deliberate policy to prevent excessive stress on the unit, the same as restricting it to 4th only on V8s. There is also more likelyhood of a relay and its wiring failing than the original inhibitor. If the original and a replacement inhibitor switch both exhibit the same symptoms, i.e. it operates and releases as it screws in and out, but in no position does the gear lever cause it to operate and release as it is moved back and fore across the gate i.e. between the 1/2 plane and the 3/4 plane, then there is a fault in the gearbox tower levers.
PaulH Solihull

Mike and PaulH - many thanks - PaulH both the old and new inhibitor switch act the same - ive tried screwing them in and out and then testing with a meter - and as mentioned they both either allow the solenoid to operate in all gears or not at all ie when screwed in it will allow the solenoid to operate, screw it out, and the solenoid will nor operate. all the wiring is good and the od switch on top of the gear leaver works as it should.(I put a dab of white paint on the back of the inhibitor switch so I could gauge how much i was scrwing it in and out) The gearbox feels fine - indeed excellent when driving - therefore as i don't wish to remove the engine and gearbox and think I would like to protect the od unit from damage in reverse gear by fitting a "cutout" controlled by the reversing light circuit.

mike - a "5 blade change over" relay seems to fit the description of the bosch relay you mention - worth testing one once if confirmed how to wire it in to the o/d solenoid and reverse light circuits

many thanks

matt



M Benoy

Are you sure your screwing the switch in the right hole? The OD goes on the left and the reverse light switch on the right. Make sure your reverse light circuit works properly! And remember that if anything should fail in the green circuit feeding that switch the relay won't inhibit the OD, which works off the white circuit. In your position I'd be powering the OD from that green connection to reduce (but not eliminate) the chances of damaging the OD.
PaulH Solihull

I used a relay available from NAPA, which is a automotive chain store in the U.S. It operates as described above and its application is for an AC system. Paul, when I shift into reverse, the relay makes a very loud "click", indicating that it has cut power to the OD solenoid's circuit. I've had this system in place for well over 20 years and have suffered no ill effects. These Black label OD units are quite strong and as long as you don't abuse the OD, in the lower gears, it doesn't pose a problem to the longevity of the parts inside. At least this has been my experience. I would never had written the original article, describing how to install this bypass system, if I hadn't tried it out on my own car with success. RAY
rjm RAY

paulh believe me the inhibitor is in the left hand of the gearbox ! Ive spent nearly 4 hours with 2 inhibitor switches and a meter ! I really cannot get the inhibitor switch positioned so that it only allows the OD to operate in 4th gear only (which the 1977 onwards MGB should do NOT 3rd and 4th) its seems to operate on all gears if screwed in or not at all if screwed out- the wiring is good condition and ive pulled all the bullet connectors apart cleaned them checked all side of the circuit - think I'll try a 5 blades change over relay and see how i get on.
many thanks to all for your input and thoughts

cheers


Matt
M Benoy

"OD to operate in 4th gear only (which the 1977 onwards MGB should do NOT 3rd and 4th)"

Not correct, only North American spec cars limited OD to 4th at around that time, as it used the same switch that limited vacuum advance system to 4th gear only. The vacuum advance limitation was to counteract surging which was a side-effect of all the emissions reduction kit, which the UK never had. For a short period North American cars had a third switch - a micro-switch that operated in the 2/4 plane as well as the original OD switch in the 3/4 plane, and by wiring the two switches in series vacuum advance could be limited to 4th only while OD still operated in 3rd and 4th, and this is what the schematics show. However after a few months the micro-switch was dropped and the OD switch operation changed to 4th gear only, possibly because of problems with the micro-switch.

UK 4-cylinder cars had OD on 3rd and 4th right through - Clausager page 85, and the Parts Catalogue lists different selector levers for North American and UK cars.
PaulH Solihull

yes pauH - you are indeed correct - anway ive found a bosch 5 pin change over relay in the garage so will fit iit an see how things go

cheers

Matt
M Benoy

This thread was discussed between 22/05/2011 and 30/05/2011

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