727 w/manual VB issues

Hello all,

I apologize for my first post being a plea for assistance. I have done thorough searching and am struggling to understand the issue my transmission has.

Situation:
The transmission was removed from a car set up by PO for drag racing. The trans had a manual valvebody of unknown origin.
The transmission initially displayed a severe shift flare when conducting the 2-3 shift. And the 1-2 was not as firm as I felt it should be, even with 4500 stall converter.
I decided to take a gamble that the issue was with the valve body as it appeared to me a modified stock unit.
I then ordered a cheetah Xtreme action manual valve body, with band apply (17875XA).
There was a note included that specified that the rear servo MUST use the factory spring.
Being unsure of the spring utilized in this transmission I gambled and went for a drive.
After 2 miles of around the block testing the trans temp was climbing fast and began to show symptoms.
The transmission then began to produce forward motion in all gears including neutral with reverse not functioning.
Frustrated, I parked it back in the shop and let it cool down.
Today I tried it dead cold just to see if it would act the same.
Today it went in to reverse and neutral perfectly but would not produce adequate forward motion in any of the drive gears, 1-2-3. With enough RPM it would move slightly forward, enough to pull back in to space.
I pulled the pan again expecting to find a pile of friction material.
Pan was clean and fluid only contained diluted particulate most likely from the residual previous fluid.
Basically I am trying to figure out how changing to a new VB could have possibly caused this?
I am not sure what to check next, I have Cope Racing's number practically dialed but would really hate it if it was a simple fix...

Thank you in advance to anyone with an idea, major bummer at the shop today.

-Andrew R

Welcome to the board Andrew.

You have a classic case of a failed rear clutch; not uncommon when installing a performance VB, the high line pressure overpowers the clutch piston return spring and allows the clutch piston to pop out of its bore. The trans has to come out.

The lazy shifts with the previous VB indicate that the trans was probably short-lived anyhow.

Thanks for the quick reply John. I did some searching focused on your response and it sounds exactly like what happened.

Now I just need to make sure it doesn't happen again...

Andrew welcome aboard & no apologies needed cuz that is what we are here for, is to solve mechanical issues/maintain Mopar superiority!

The factory experienced enough of these failures that they revised the rear clutch with a heavier return spring and some matching components. It would be wise to upgrade these parts at overhaul when using a manual VB.