TH400 No forward gears after rebuild??

nhill_05 · Oct 12, 2015

I recently did my first transmission build on a TH400. The transmission did not have any hard part failures. The clutches were smoked and the torque converter was damaged. I replaced the torque converter before reinstalling the trans.

As far as the rebuild I did the dual feed modification as well as installing the transgo shift kit. I got rid of the wave plates in both the direct and forward drums. I omitted the 2-3 accumulator spring and plugged the 3rd accumulator feed. I also omitted one check ball per the transgo instructions. I've air checked both the sub assemblies and they seem to be working fine. I installed the transmission and filled it with fluid. Now it only has reverse. The tires will spin forward slowly in neutral, first, second and third. It seems like the forward clutches are not applying for some reason.

Is it possible that i installed a valve in the VB incorrectly that could be causing this??

Any help is greatly appreciated!

nhill_05 · Oct 13, 2015

I also installed the 4l80e direct drum with the 34 element sprague. I'm not sure that makes a difference but it's worth mentioning.

stuarta · Oct 13, 2015

Not knowing what you did or how it was done it is impossible to give you any answers.

The forward clutch is not applying.

Tear it apart and start again.

nhill_05 · Oct 13, 2015

Thanks! I already tore it apart once and air-checked the pistons in the sub assemblies. Both are working fine so I pulled the clutches and steels out to check them. It seems like the innermost steel in the direct drum was catching the inside lip of the drum. I started with a thicker steel this time and it seems to be fine. I took the forward drum apart next and it seemed perfect. There are no marks on the steels to show it was applied. Everything else appeared to be correct.

Any other thoughts before I tear it down again?

Hutch · Oct 14, 2015

It appears as though you may have the drum terminology mixed up. You said it had reverse so that tells me the direct drum was working yet you say that steel was under that ledge. I have to assume the steel was under the ledge of the forward drum hence "no forward".

Hutch

nhill_05 · Oct 14, 2015

Hutch,
Unfortunately not... It looked like it bent a couple of the tangs on the steel and pressed into a cone shape. Once enough pressure was on it it applied the direct drum.

As far as the forward clutch pack there were no witness marks showing it had spun. I used all new kolene steels. I pulled the trans back out and plan on tearing it down tomorrow.

Is there anything in the valve body, i.e. valves installed incorrectly or in the wrong order, that could cause this?

Thanks again for the help. I'll be sure to post what I find. Rookie mistake of some sort I'm sure.

transbuilder83 · Oct 14, 2015

look at the fwd clutch hub in the drum see if the teeth are stripped rare but can happen before u pull it put a line psi gauge on it see if u have a psi drop when u go to drive also double check u dont have a check ball in the wrong place blocking a fluid passage

TH400 No forward gears after rebuild??

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