Dedenbear Case

[Squirrell]

Hi Guys, can anyone tell me if you need to make the holes any larger in a Dedenbear case for the transbrake to dump the fluid ?. Box is fitted with a TCI Probrake. The guy I bought the car from has drilled a hole near the standard 3/8" hole and modified the valve body to allow fluid to come out the new hole as well. I forgot to take photos when I had it apart. he then had a problem with the car creeping so he plugged the hole. My question is do you need to put any extra holes in to make the transmission dump faster ?. Has anyone had any problems with a TCI Probrake ?. Car is still a little slow leaving on a .400 Pro tree.
Thanks for your help, Patrick.

[Squirrell]

Hi Guys, I forgot to mention, the reverse piston had two small holes drilled in it. One straight through and one in from the side. I belive this is to let the air out. Is this normal or has some made this modification for a reason ?.
Thanks again Patrick.

[Roberts Motorsports]

The reverse passageway in the Dedenbear case is big enough as is. Of course you want to make sure that the adjuster is set so that it is not obstructing the passageway. The adjuster is the way that you can adjust the "hit" of the T-brake releasing. I've experimented with extra holes in the past and never found any benefit.
Of course, you want a quality trans-brake. TCI's T-Brake is not what I consider one of the better ones. I'm partial to the Transmission Specialties T-Brake
The small holes that you have in the reverse piston are air bleed holes. Allows any air in the reverse cavity out so it fills more efficiently on T-Brake apply.
The Dedenbear case has an air bleed hole in the case, so the ones in the piston are not needed. You can seal them with epoxy. Remember, once the air has bled out of reverse cavity, the holes become a very small fluid leak. Normally one .032" to .050" hole is sufficient

[Squirrell]

Thank you for your reply. We found the bleed hole in the case and have replaced the piston with one with out holes in it. The adjuster is all the way out so is not in the way. I will have a look at the Transbrake, but also have a new one in the cupboard as a spare. Thanks again Patrick.

[Roberts Motorsports]

Your Welcome.
I should also mention that your reverse clutch pack clearance can affect your R.T. The general "rule of thumb" is .010" clearance per friction plate. So if you have 5 frictions you'd be looking for .050" total clearance, 6 frictions = .060" etc.
You often have to machine the reverse piston in a lathe and / or add an extra steel to get it where you want it.
The available heavier reverse release springs can help R.T.'s too.

[Squirrell]

Thanks, I will check with the trans builder to find out about the reverse pack setup. Can you tell me if I wire the transbrake direct to the button not through the delay box will be faster or the same ?.
Thanks again Patrick.

[Roberts Motorsports]

With the good quality delay boxes of today like Dedenbear, K&R, Biondo, if the box is at 000, the trans-brake should release exactly the same as if you had it wired direct.
The older delay boxes of 20-25 years ago used to have about a .005 to .01 difference, but that is very old technology and I would hope that all of those have gone to the scrap pile long ago.

[Squirrell]

Hi Guys, I have had a chance to catch up with the transmission builder, and the reverse pack had 5 clutches , he took one out because he likes low gear to be better than reverse. If something starts to slip , the car will go forward and not backwards. He replaced the clutch disc with an extra steel disc and we have a total of .055" clearance. Is this were we should be ?. Thanks Patrick.

[Roberts Motorsports]

Your clutch pack clearance at .055" is fine. I disagree with going from a 5 friction pack to a 4 friction pack however. If you are making less than 600 HP the 4 friction pack will probably be OK, BUT if you are making more than that you are asking for trouble. Your reverse pack longevity will suffer and you open up the possibility of creeping when you go to W.O.T. on the trans-brake. The thinking of making low stronger than reverse is flawed. The object of a trans-brake is to HOLD the car stationary and not move. To do that, both low & reverse must be able to hold equal amounts of torque and not slip.

[ray sowers]

[QUOTE=Roberts Motorsports;424171]The reverse passageway in the Dedenbear case is big enough as is. Of course you want to make sure that the adjuster is set so that it is not obstructing the passageway. The adjuster is the way that you can adjust the "hit" of the T-brake releasing. I've experimented with extra holes in the past and never found any benefit.
Of course, you want a quality trans-brake. TCI's T-Brake is not what I consider one of the better ones. I'm partial to the Transmission Specialties T-Brake
The small holes that you have in the reverse piston are air bleed holes. Allows any air in the reverse cavity out so it fills more efficiently on T-Brake apply.
The Dedenbear case has an air bleed hole in the case, so the ones in the piston are not needed. You can seal them with epoxy. Remember, once the air has bled out of reverse cavity, the holes become a very small fluid leak. Normally one .032" to .050" hole is sufficient[/QUOTE

I drill a .032 Dia. hole in the reverse piston just under the piston seal and the Dedenbear case air bleed hole is way too low that still leaves some air in it.
I am not in the commercial transmision business and have been helping people with
Powerglides built by other people since 1985 including ones we race in our car.