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Transmission/ OD psychosis

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BoneIdle

BoneIdle

Jedi Trainee
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I figured I'd throw this out to the collective wisdom here:

Model:1974 GT with OD

The problem first occurred after driving 1300 miles from Tampa to Cedar Rapids. By that, I mean that I had no problems driving the 1300 miles, but after about 3 weeks here, it began to show up.

Here's what happens:

I can drive the 25 miles or so from Mechanicsville to Cedar Rapids at an average speed of 65 MPH. Typically the OD is engaged for most of the trip.

When I exit the freeway, I disengage the OD. 4th gear is fine as is the downshift to 3rd, but downshifting to 2nd is essentially te same as putting the transmission in neutral; in fact it feels as if I have shifted into neutral.

The same applies to 1st, but if I shift back into 3rd ( from 1st or 2nd ), I can tell that I'm in gear again.

Now, if I shift back into 2nd or 1st at this point, everything is working again.

Sometimes the same thing will occur on the way home, but since the last 7 or 8 miles are pretty much "non-OD" miles, more often than not, everything will be normal.

What I've done so far is to drain the transmission and OD, remove and clean the sump cover/filter for the OD and clean the OD relief valve. Of course, I refilled the transmission and OD with clean oil afterwards.

I suspect the transmission hadn't been drained in decades.

Has anyone encountered this sort of behavior before?
 
Years ago I had a similar problem, including no enging braking in "overrun".

When I started out cold everything would be fine in all gears. After I ran for awhile with the OD engaged I would have massive slipping in all gears (including reverse) with the OD off. In other words, when everything was slipping (sometimes as bad as if it were in neutral) it would be fine with the OD engaged (in 3rd or 4th gears only on mine).

The only clues I could find from books and the net was the same as that thread first mentioned, a worn or glazed cone clutch. Since it was a fairly new transmission I didn't think that was it - but the slipping made me think the OD clutch wasn't moving all the way, or the oil wasn't right (maybe they filled it with slick-50 or something equally silly).

Anyway, I drained the transmission, replaced the gaskets/screens, and replaced the o-rings in the valve assembly, topped it off with Castrol 20w50 and haven't had the problem since (that was 5 years ago).
 
Interesting input, everyone!

The odd thing about this is that it doesn't happen consistently. It does happen every time I drive down I-380, though /ubbthreads/images/graemlins/devilgrin.gif

I've driven almost the same distance with a brief stop ( < 5 minutes ) and then driven back the same distance ( 2 times in < 3 hours ) and nothing's happened.

I think I'll take another look at the o rings on the relief valve when I drain the oil again .
 
Sounds to me like the dirt/debris gremlins have invaded and the outer clutch surface (sliding member)is not being held tightly against its steel friction surface (brake ring). Before you go taking too much apart you might want to clean up things that you can easily get to.

Pull the solenoid out and clean it. Don't lose the check ball when you pull the plunger out of the center of it though. You might also want to replace the little rubber or ring on the end of the slug. Moss has them and they are cheap but they are a common size (tiny) and might be available from a local parts house. Also, pull the pump assembly and clean the "filter" gauze that is about midway up the length of the bits. It looks like a little round screen. Don't lose the check ball form it either.

The next step would be a full tear down to get ALL of the goo/debris out of everything. Not a particularly difficult task but not something that will happen, start to finish, in a few hours either.

Jack
 
The most common cause of freewheel effect on over-run with the Laycock is a faulty sprag clutch. But having said that, the thing that is puzzling my 3 brain cells, is why on second gear downshift. Sprag would do that on 3rd downshift, out of o/d. I could be wrong and probably am, but it does sound as though something is moving inside the gearbox..mainshaft gears.(circlip).. or a broken thrust-washer in the o/d.
Best of luck
Cheers Ric
 
IMHO...

The sliding member has two friction surfaces to it. One for the engagement of the OD function and the other for the re-engagement of the "normal" drive. If for some reason either surface doesn't get a good bite the freewheeling will result. My suggestion for cleaning of the system was the thought that too much trash could have accumulated in the hydraulic passages to allow either full engagement of the OD or full pressure lose when electrically disengaged and thus full engagement of either sliding member surface. In either case the result could be that stuttering effect as the friction material skitters against the brake ring or the annulus cone.

Jack
 
I'm gonna jack it up this weekend, drain it, and pull the relief valve, the solenoid and the non-return valve. I'll clean all that up and then refill. It's got to be sludge. This thing's too intermittent to be mechanical, I think.

...just watch. It'll probably turn out to be mechanical /ubbthreads/images/graemlins/devilgrin.gif
 
If you have the patience I would suggest several drain and refills, perhaps three, and at least one of them in the early going should be fifty percent ATF and fifty percent K1 kerosene. Drive the car for about ten miles NOT under excessive load with that mixture in it and drain it hot. Go in and out of OD SEVERAL times as you drive. You can reuse the filter screen every time except the last time if you take it over to the vat and clean it well. It would also be a good idea to drop the pump assembly each time and clean that screen too. Time consuming I know but it is the best way to insure that you are getting all the grunt out. Jack
 
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