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Re: testing an overdrive

To: "James Harwood" <>, <>
Subject: Re: testing an overdrive
From: "William Mills" <>
Date: Fri, 20 Feb 2004 21:07:12 -0500
I have heard of bench testing with a variable speed drill coupled to the
input shaft but I cannot remember the details.  I did save this post from  a
few years ago by Don Walton on checking out an O/D tranny before it goes in
the car.

Bill Mills
'74 BGT with O/D

here is what Don wrote:
Hi Larry, I just went through this for my 77 and I also helped a friend add
an OD to his 74,  One question is did you know the condition of the tranny
before you bought it?  I have had success with the two of them I have bought
but I knew who I was getting them from.  I think as a rule MG transmissions
are pretty stout so odds are the mechanicals should work OK for you. I did
see one once which had various parts fall out of the filter housing when the
cover was removed, so you never can tell.
I would change the filter and gasket and the gasket and grommet on the
solonoid.  Chances are that the solonoid wire is going to be brittle so be
careful with that, the wire on my 77 tranny broke off but I just removed
enough of the solonoid coil wire to solder a new piece on and it worked
fine.  If you remove the solonoid make sure you have a manual so you can see
exactly how the thing goes back together.
It is also a very good time to change the oil seals both front and rear,
Remember to get all gaskets needed for the job.  One thing I forgot to do is
to check that the speedo drive is good, I found out mine wasn't after the
fact.  I have a new pinon but I havn't put it in yet but with my luck the
drive gear will be stripped.....
Check and replace as needed the backup and OD isolation switches, also make
sure that the shifter is actuating the switches, you may have to play around
with the fiber washers to get them right.  This is not a big deal with the
BU switch but with the OD switch it is do it now or it becomes a big PITA
later because unless you have alien-like 15 inch fingers, you can't get to
it once the engine/tranny is installed  .  Just mount the shifter and use an
ohm meter to check the action of the switches.
In short, check everything that you can't get to when the engine/tranny are
in the car, also look closely at the motor/tranny mounts, my transmission
mounts had just about turned to chewing gum.  I also used a lister tip on
drilling holes in the crossmember to aid in re-assembly.  EXCELLENT IDEA!
                Good Luck and enjoy the overdrive!

                        Don Walton in NC  73 74 77 B's

 01:37 PM 02/16/2000 -0500, you wrote:
>Hey Listers, need more OD advice (and I suspect some others might too)--
>Finally got an overdrive for my '72 B, now I'd like to know what checks and
>preventive or restorative maintenance can be done with the thing out of the
>car, before the big swap exercise.  Tips on checking the solenoid,
>gaskets/seals, checking innards, etc., will be greatly appreciated.  Gotta
>get rolling on this (plus engine freshening) so's I can make the big June
>Cleveland show.  Cheers!
>Larry Ruggiero
>Warner Robins GA
>'72 MGB
>'65 Midget
----- Original Message ----- 
From: "James Harwood" <>
To: <>
Sent: Friday, February 20, 2004 8:05 PM
Subject: testing an overdrive

> Having aquired a supposedly rebuilt overdrive
> transmission, I thought it would be a good idea to
> test it before installing in the car. Turning the
> input shaft by hand, all for forward gears and reverse
> seem to be working as expected. An electrical test of
> the two switches revealed that the o/d isolator is not
> closing.
> My question: is is possible to bench-test the
> operation of the overdrive? Does the box have to be
> turning at some sort of speed before it will operate?
> Thanks in advance,
>   James
> 74 MGB

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