TH200R4

[Gilles]

Hi everybody,

TH200R4 transmission, intalled in a 1935 Ford sedan owned by a friend. I rebuilt it for him a few years ago and he added a transgo kit. It worked nice for around  15000 miles.

In a hot summer day (around 105°fahrenheit) while on a motorway the transmission quitte working. No drive in all shifter position, a "clonk" in reverse and that's all! And reverse acting like in park. The fluid was leaking by the small event tube on top.  I think it was boiling.  He waited a moment, controlled the fluid level, it was ok. Even after letting cool down, no way, it did not work.  He went home on a tow truck.

I dismantled the transmission again, found nothing broken or wrong except the discs brown a little. The fluid was clear and no debris in the oil pan. I controlled every thing, all pistons in valve body, all seals. And rebuilt it again with hi-perf discs, new bushings, gaskets, seals. My friend installed it in the car with a brand new torque convertor, just to be sure.

It did not work and acted exactly the same as before. 

I dismantled it again entirely. Found that the little cup seal under the valve body was not hammered enough.  Though I found the mystake. Reassembled it again.

Did not work.

Took pressures measurements with a pressure gauge in each shifter position, all are correct according the  ATSG book.

This is a big mistery!  I don't know if there are transmission expert here, but I act like a bottle in a sea!

Gilles

[Crosley.In.AZ]

Simple answer is : you are not finding or  fixing the problem. Seems pressures are good from your testing. That indicates a large internal leak and / or a cross leak.

Since the trans worked for quite a while , I would not think the internal shift linkage is a problem.

The 200-4r steel drums can develop cracks .  Are you pressure checking the assemblies on the bench before you install them into the case?

DO you have a method to resurface the pump halves? Lots of cross leaks can develop in the pump from age , heat and pressure

[Gilles]

I air checked the pistons  clutchs, that's all. Did not see any cracks on the drum, but not entirely sure. The pump halves not flat after been too hot is not a thing I thought about. Maybe the answer.

Thanks for the replie. It seems that I will put it in pieces again!

[Crosley.In.AZ]

You can do some air checks on the bench with the trans assembled, v-body Not installed.  Couple of the ports for air check are 1/2 inch or so into the case.. You can use a small piece of rubber hose on the air gun to reach the holes to apply air to listen for large leaks.

Check areas where the sealing rings ride. Sometimes deep grooves are worn in from the PTFE material sealing rings are made of

[Gilles]

I think that maybe, it was a very small warpage on the pump halves, but very, very slight.  I  surfaced the two halves on a marble, with 600 sandpaper and petrol.

Tony, you say steel drum can have cracks, is this the one where the band apply?  I will have a look at it.

[Crosley.In.AZ]

I think that maybe, it was a very small warpage on the pump halves, but very, very slight.  I  surfaced the two halves on a marble, with 600 sandpaper and petrol.

Tony, you say steel drum can have cracks, is this the one where the band apply?  I will have a look at it.

Cracks at welds on the drums can develop , not a real common item in the 200-4r trans.  If you air check the  drum clutch packs on the bench , it will be obvious if there is a large air leak..