Sbc powered dragster with power glide. Stage,set the brake,wait for tree,and when you deck it the car will move forward about 2-3". No line lock. It is not rolling as have tried keeping foot on the brake but the trans is moving the car forward. It doesn't do it every time,just most of the time. Transmission temp doesn't seem to effect when it will do it. Transmission is apart and "everything"looks good. Clearances on reverse clutches are a fudge on the tight side. Band,pump look like new. Only thing I wonder about is when it was new from a big name racing trans company the trans brake did not work. The solenoid engaged but nothing happened so I replaced solenoid with a spare I had and it worked. Depth???? What to check??

So you got a PG from a big name company, the TB didn't work, so you tried a different solenoid and it worked? It just rolls forward now on TB, not all the time but most?

What's the reverse clearance?

Pro brake?

Can you post pics of the two solenoids?

.075

Have been running this combination 5 years with no problems.

Side note: this is my wife's car and sometimes it is hard to get good Intel on what's going on. Erratic lights got me on the starting line watching.

A stock pump may do it..
An aftermarket pump won't...

I had one trans that did it and installed a Dedenbaer pump and it never moved again
Dragster, stock case, shorty std brake....

In door cars we tied the line lock to t-brake so it would not move when setting the brake...had a toggle switch or could use a diode to prevent t-brake apply doing a burnout...

The new solenoid has the brake valve depth wrong when you deck it on the brake. Put it back together and put a guage on the reverse tap. Report back with pressure in reverse and on transbrake.

I'll tell ya what you can do from there. You might even be able to use the solenoid you have in it now.

it sounds like the solenoid is not pushing the valve quiet far enough

Thanks, will check things out with solenoid depth.

First thing you need to do is get a pressure reading at both the servo cover and the port for the reverse piston. Remember the trans is already in low when you push the button and reverse is applied. If you have low pressure then there will be a delay in filling the cavity behind the reverse piston which will cause the car to rock forward. Also if the pressure is low then the clutches will slip
Personally I like to see my reverse pack clearance .050-.060 but that just me, .075 should be fine if you have enough pressure.
You should be looking for around 230-250 PSI line pressure. The pressure at the servo port will drop then jump right back up when you push the button, that is the reverse piston cavity filling and is normal. If the reverse pressure is lower that the servo pressure in reverse or with the trans brake applied you either have a leak or an issue with the solenoid length and the apply valve. I had an issue once with the solenoid throw being too long and reverse was always slightly applied and had to shim it back, if it is too short it will have the opposite effect and not fully or slowly apply reverse
Hope this helps

This message has been edited. Last edited by: Big Steve,