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John McCormack

Overdrive electrics

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Mt restoration TR2 overdrive dropped out yesterday while driving on a freeway. The solenoid wasn't working.

Now electrics are my very weak skill set.

I tested the dashboard switch and the cutout switch on the gearbox and they appear to be working.  Operating the dash switch and the cut out (by moving the car into 4th and out) you can hear the relay operating which it wouldn't if the switches were inoperative. I removed the dash switch and tested it with the multimeter and it appeared OK.

Under the car the wiring at the gearbox was tight.

With no obvious faults I took the tunnel off.

The solenoid wiring, where it goes into the solenoid was frayed and wasn't in good condition. The solenoid I thought was pretty new but when I looked at it closely it is likely it is the original 1954 one.

When I hot wired the solenoid it it did work, once, later attempts it didn't work.  After a bit of fiddling the solenoid did work each time I hot wired it. However, if I held on the hot wiring the wires got very hot so I disconnected. The solenoid will be replaced but I'm not sure that is the full problem.

When I measure the voltage at the solenoid, cut out switch or dashboard switch I get about 5 volts.

The system goes through a relay.

I expected I would see 12 volts at the solenoid. I can't see why I am only getting about 5 volts.

????????

 

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Like you John  look forward to reading about how to test these things.......i'm not good with electricery!

I have my original..failed solenoid or so I thought. After sitting in a draw for 9 years when i put a battery across it it works? However is that a proper test?

Iain

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I know IanC did an article on this and it may we’ll be in the Technicalities cd

Something about 10 amps to pull in then 1 amp to hold.

No doubt he will be along in a while.

Peter W

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Thanks Peter...I seem to remember something along those lines...must find the Technicalities CD!:D

Iain

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Peter you are quite correct and  no we don't need the CD (which i have put somewhere very safe:lol: so safe i have no idea where it is!)....its all there in the Members section of the Website.

Page D-49  Gearbox and Overdrive 

 

Iain

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The A type OD solenoid has two coils - one a high current winding which does the initial pull-in and a second low current winding which holds it in once operated. There is a switch inside the solenoid which should break the connection to the high current winding when the armature has moved. 

If the wires were getting hot with your jury-rigged connection, it's probable the solenoid is faulty and the switch is not operating so that the high current flows all the time. If that happens in use the solenoid will burn out and may take the wiring with it.. 

I can't really comment on your odd voltage reading without knowing what meter you are using and how you had it connected, but it could be that the relay contacts are only making a poor connection and if you had the duff solenoid in circuit it could be pulling the high current so causing a voltage drop. 

Edited by RobH

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Hi Rob any chance you could describe how to connect a meter to test the two coils? 

Electricalknumpty

Iain

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This shows you how:

 

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All fixed. The solenoid holding coil wasn't working and the pull in coil was staying on. When we tested it on the bench we didn't have it on long enough to reveal the problem. It packed up after about 10 minutes on the freeway in od.

I replaced the solenoid, I wanted to avoid taking the tunnel out again having just had the new carpet installed.

I subsequently found the fuse the auto electrician had installed was blown. I didn't do the od wiring so had to trace it all and write it down to figure out what was wrong. The fuse wasn't in an obvious place.

In parallel my headlights stopped working. Again I had to trace it all and start a process to find the fault. It turned out to be the switch. I had a spare, that didn't work properly and I was just about to order a new one when I found another spare, this one the original from the car. It works perfectly.

The car is back together, the carpet returned to its place ok, and everything is working.

Happy days. Three working TRs!

                                             

                                                           

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Hi John,

Not to go through this all again but a fuse will not help you as the damage is done before the fuse blows unless a very low rated one and then again I don't that works either.

The issue is as always moisture which causes the internal switch pin to stick meaning exactly what you found that the pull in coil is live and stays live causing the fuse to burn out. The repro ones have a nasty plasticy cover which allows water to run don and into the upper part of the solenoid this eventually causing the pin to stick. I got about a year and a half out of a new one and so am now on my third, You need to really coat the piston in grease and seal the cable entry so that moisture can not enter. It would pay to split the gearbox cover in to two parts as the works cars had and this allows only the rear cover to be removed to gain access to the overdrive solenoid. f you do not pay attention to this you can bet that you wiil have to sort in the near future if unlucky.

Rod

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Here is the works car solution for inspection/ adjustment and replacing the solenoid. The 2/3 did not split the cover.

.post-7533-0-36573400-1523345219_thumb.jpg

post-7533-0-79982600-1523345723_thumb.jpg

post-7533-0-31906700-1523345289_thumb.jpg

very simple mods. The cover on the solenoid side is held in place by two drugs fasteners and is a piece of shaped aluminium.

on the hand brake side two addition holes are cut to allow access to the actuating lever and valve. Two extra rubber bungs seal the holes.

Iain

 

Edited by iain

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