TH700 no upshift.

[Gilles]

Hello,

I have a problem with a 1992 TH700R4 transmission. :x  This transmission installed in a 34 Ford coupe of a friend of mine started recently to slip a lot. I rebuilt the transmission for him using a transtar rebuilt kit and transgo correction kit. It's the fifth Th700 I rebuild,  including the one I have in my roadster. The forward discs were totally burnt and the piston cracked, I replaced it, and all the discs, the band and gaskets availlable in the kit, like I always do.

Now the mysterious problem : The transmission works in reverse, works in first gear but there is no upshift watever the shift lever is, second, drive or overdrive. We tested with different TV cable adjustment. No success. I read carrefully the ATSG technical book. For no upshift they say it can be : the governor,  pin band not correctly installed, #322 piston in the valve body sticking, 2/4servo band damaged, separator plate or gaskets damaged. I spent 5 hours last night crawling under the car  carefully checking all these things. Nothing wrong as I can see. Except maybe some minor marks on the separator plate where the check-balls hits. After all of this another test drive : no success same problem.
According to the book in first gear there are 3 clutch engaged, in second gear the only difference is the band holding too. So it seems there is is something wrong somewhere in the 2/4 band pressure circuit.  As my friend lives 100 km from my home we removed the transmission from the car, and I bring it to home, arriving at 1 am. Ouch!  I have really to find what's wrong. It's the car show season, we already- him but me also- canceled a big one this week-end. Grrrr!!! :cry:  :cry:
Any suggestions?

Gilles

[Crosley.In.AZ]

Gilles;

check the governor for movement of the inner valve.  Must be loose - easy to move.  Plastiic gear must be good , not loose.

Check shift valves in the valve body.  Must be clean , move freely each way.

Check TV inner valve in the v-body. Must be free , move easily.

You may be having a "false fail safe" mode IF you installed the 5/16" diameter check ball near the TV valve assembly in the trans case.  This check ball is  LARGER than the 1/4" check balls.

The TV bore can wear and allow fluid to bypass more.. with 5/16" check ball in place it may have a "false fail safe" and transmission will shift late - high RPM of engine.

Did you remove - replace the thimble screen filter in the governor passage of the trans case?

[Gilles]

check the governor for movement of the inner valve. Must be loose - easy to move. Plastiic gear must be good , not loose.

The governor is OK and inner piston is free.

Check shift valves in the valve body. Must be clean , move freely each way.

Apparently everything OK.

Check TV inner valve in the v-body. Must be free , move easily.

OK too

You may be having a "false fail safe" mode IF you installed the 5/16" diameter check ball near the TV valve assembly in the trans case. This check ball is LARGER than the 1/4" check balls.

There are 4 check-ball in the trans case all the same size.

The TV bore can wear and allow fluid to bypass more.. with 5/16" check ball in place it may have a "false fail safe" and transmission will shift late - high RPM of engine.

The transmission does not shift watever the engine RPm!

Did you remove - replace the thimble screen filter in the governor passage of the trans case?

Yes I replaced this filter.

I will have a look this week-end and remove another time the valve-body, for wich I don't have another pair of gaskets!

Gilles

[Gilles]

One fact that's maybe important  : I did a mistake assembling the TV piston, the pin wasn't in the good location. The result was the TV cable travel too short because the piston hiting the pin. I fixed this problem before the first start of the engine but I had to remove the valve-body. As I don't have spare gaskets I reused them, unable to know if I was doing a big mistake or not.  I wonder if it can cause a leak and explain the problem?

Gilles

[El Jefe]

One fact that's maybe important  : I did a mistake assembling the TV piston, the pin wasn't in the good location. The result was the TV cable travel too short because the piston hiting the pin. I fixed this problem before the first start of the engine but I had to remove the valve-body. As I don't have spare gaskets I reused them, unable to know if I was doing a big mistake or not.  I wonder if it can cause a leak and explain the problem?

Gilles

bttt

[El Jefe]

One fact that's maybe important  : I did a mistake assembling the TV piston, the pin wasn't in the good location. The result was the TV cable travel too short because the piston hiting the pin. I fixed this problem before the first start of the engine but I had to remove the valve-body. As I don't have spare gaskets I reused them, unable to know if I was doing a big mistake or not.  I wonder if it can cause a leak and explain the problem?

Gilles

bttt

[Crosley.In.AZ]

couple of other thoughts are:

mis-matched gaskets. Wrong gasket in place?

reuse of the gaskets should not be a concern since they were very new.

Any threaded holes in the v-body not plugged with a switch or plug?


in photos posted:

i have seen some DIY folks rotate the valve sleeve and place the retaining roll pin in the wrong slot. this will usually block off passages in the v-body

[Gilles]

Thanks for the reply.

Last WE I dismantled entirely the valve body, cleaned and verified everything. Also for the pump. The only not in perfect condition part is the separator plate, bent where the 1/2 accumulator spring applies.  Watching carrefully it seems that at the accumulator housing place the gasket is not regularly dwarfed (because of the warped separator plate), maybe causing a leak in the second gear circuit.
We ordered a new separator plate and gaskets, we are crossing our fingers right now that it will work! :?

Gilles

[Gilles]

Some news :  Put a new separator plate and gaskets.

There is only first and third gear, no second and no fourth.  Now I absolutly don't know what to look for. for. :cry:  :cry:  :cry:  :cry:  :cry:  :cry:


Gilles

[Crosley.In.AZ]

No 2 or 4th gears is a servo problem .  servo for the 2 - 4 band.

[Gilles]

No 2 or 4th gears is a servo problem . servo for the 2 - 4 band.

Thanks for the advice.  last night I get a servo from a transmission I have for spares, cleaned the parts and put new rings on.  My friend had to cut a hole in the floor to be able to remove the 2/4servo without to remove the transmission from the car!  I cross my fingers!

Gilles

[Gilles]

Some news.
Found a broken ring in the 2/4 servo. :x Was too much in a hurry last time I worked on it. Replaced it.
Result : 1/2 shift ok, 2/3 shift with a "false neutral". In facts it shifts in third with light throttle but at loud  throttle it acts like in neutral. No fourth gear :x  :x  :x  :x
Replaced the entire 2/4 servo by another. Exactly same sympthom. So I hope the servo is not at fault  :cry:
I feel very sad. This week-end there is the French street-rod Nat's and my friend is not able to go with his 34 coupe because of my fault! Certainly the last time I rebuild a transmission for someone. It's my fifth TH700 and the 4 previous works! Really don't know what to do now, except to take it apart for the third time and carefully inspect each component?  

:cry:  :cry:  :cry: Gilles :cry:  :cry: :cry:

[enjenjo]

Sometimes that happens. I have done them as many as 4 times to get them right. that's why I will only do my own.

[Gilles]

Hello everybody,

Finally after a few months I decided to take apart again this transmission (fortunately the owner is on another project and not in a hurry).
I found mud in the pan and 3/4 clutch discs fried :x . Probably something wrong on the servo or valve body or 3/4 piston, I didn't tried yet.
I will  order another rebuild kit.
But what about the torque converter?  :?: It is new and used only for a few kilometers during the drive tests. But as there is mud in the pan there is mud in the torque converter too.
Is there a way to clean it inside? Drill and tap a small hole and put a drain plug?
Thanks in advance for the answers.

Gilles