Another transbrake thread, & tires

[Michael Pliska]

I would be curious to know which brake is the fastest, and how much RT you picked up with it. I'm running a TCI brake from the mid-1980's, so I imagine there is some room for improvement.

As far as tires, IIRC when I swapped from 25" front tires to 23" (which actually measured around 22.6"), I gained between 0.015 and 0.020 in RT. I've got the 25's back on the car right now for no-electronics bracket racing, but will probably switch back if I can't redlight with them when I run S/G in a few weeks.

Regards,

[63corvette]

JJ, you want to stay away from the aluminum valve bodies in my opinion.
I build race transmissions and that has been my experience.
Ten or fifteen years ago I worked with B&M on their development on their alum. valve body for a powerglide.
Those just did not work out very well at that time. My personal feeling is that the pistons and valve parts are steel and with the body being alum the growth rates being different the clearances changed as the transmission heated up. That in turn affected the consistantcies and another problem was if the pump pressure ever fell below 150 to 170 at idle when you applied the brake the car would back up a short distance. That issue was a major one as you stage the car. I first thought it was a clearance issue with the band for first gear or the reverse pack but found it was with the body.
Just my opinion is that you stay away from the alum bodies.
Most of the GM bodies that have been converted to a brake are all done the same.
The major difference on all the manufacturers is whether they use a spring on the reverse apply piston in the body.
Most all the major manufacturers will work the same if the brake solenoid is shimmed.
The torque converter also has an affect on how fast the car leaves and if it matches the cam torque band.
JJ, with a Davis car you should be able to go red anywhere. I can with mine which is an 07 model.
Good Luck at the races.
My 2 Cents
Rick

[S/G 386N]

Thanks for the responses. I think the problem I'm having is we changed the suspension so I can bracket race the car and run it flat out. Moved the instant center quite a bit forward, and can actually pull a 1.15 60', launching at 3400 rpms, riding the bar the whole time. Have had the car down to 7.99 flat out, which I'm told is not possible in a Davis car. Any higher launch RPM, and it just rides the bar forever. Thinking about taking the suspension back to the way it was, and just bracket race on the throttle stop and see what happens, but would like to explore other options first.

[Rick Blake]

Have the same problem off the stop....wants to go on the bumper and carries the hoops clear through the 60', best to date was at Immokalee: 1.13 60' & 5.13 @ 136mph in 95* very high humidity and 3500+ air. I don't bracket race much, mainly Quick 32 stuff and just use the stop, don't want to touch my .90 setup, works too good.

I'm using a "BTE" Pro Brake and it's quick, just my .02

[Keith 944]

my question, how to shim the solenoid, between the trans case and solenoid or the plunger itself ? and how much shim? use washers, or is there a shim for this purpose?

[Bryan Gillespie]

mine had 2 shims (washers), but brake wouldn't hold @ high rpm, unscrew solenoid and place shim or shims and screw back in.

[63corvette]

Keith, you shim between the solenoid and the case with a washer or washers.
You need to have the pan off and it is much easier to do with the trans on the work bench. Back out the solenoid to see when the reverse piston is engaged into the valve body .010 to .020 with the solenoid in the activated position. Then measure the distance between the case and the base of the solenoid and find a washer that is that distance thick or just a few thousands less and install that washer.
I have found transmissions that needed as much as .150 and some that needed nothing with the average being around .090.
I would guess and that is only a guess that if you needed a shim of .090 you should pick up about .020 of reaction time or maybe just a little more. There are lots of variables on this but it will help the reaction time for sure.
If you shim it out to far the trans brake will not hold or it will shudder the whole car and not hold so be careful if you are not sure what you are doing.
Just My 2 Cents

[ray sowers]

Originally Posted by 63corvette

JJ, you want to stay away from the aluminum valve bodies in my opinion.
I build race transmissions and that has been my experience.
Ten or fifteen years ago I worked with B&M on their development on their alum. valve body for a powerglide.
Those just did not work out very well at that time. My personal feeling is that the pistons and valve parts are steel and with the body being alum the growth rates being different the clearances changed as the transmission heated up. That in turn affected the consistantcies and another problem was if the pump pressure ever fell below 150 to 170 at idle when you applied the brake the car would back up a short distance. That issue was a major one as you stage the car. I first thought it was a clearance issue with the band for first gear or the reverse pack but found it was with the body.
Just my opinion is that you stay away from the alum bodies.
Most of the GM bodies that have been converted to a brake are all done the same.
The major difference on all the manufacturers is whether they use a spring on the reverse apply piston in the body.
Most all the major manufacturers will work the same if the brake solenoid is shimmed.
The torque converter also has an affect on how fast the car leaves and if it matches the cam torque band.
JJ, with a Davis car you should be able to go red anywhere. I can with mine which is an 07 model.
Good Luck at the races.
My 2 Cents
Rick

Rick, I also build/repair Powerglides for our car and friends that are having lots of problems.
We have ran Hipster modified stock pro valve bodys and their Aluminum Pro ones for some years and on the aluminium ones they have a totally seperate steel screw in pressure control that also has an adjustment for setting the line pressure as you wish, Ray.

[63corvette]

Ray, the B&M had the same pressure adjustment you describe. The issue was with the pressure falling off (just a short blip) as you apply the brake. That was a pump pressure/volume issue with the passage size. To make the brake react quickly the volume is reduced in the passages to dump quickly for quick reaction but you have the same issue on the apply side. Applying takes longer that dumping with the port size. You could remedy that issue by going to an after market pump with the larger gear set or using a stock pump/gear set and setting the engine rpm no lower than 1200 to 1400 in low gear as you stage the car. It was just an issue that could bite you at the wrong time as you go rounds and I decided not to build those problems into a transmission I was using or selling a customer.
I build them and I race them so I don't want any possible issue I can get away from. I also do not want a customer with any of those issues either.
Everyone has his or her own way to do things and their opinions but for me I stay away from the aluminum bodies from all the manufacturers if at all possible. All the major transmission people still have the cast body model and that is what I always use. Some of the people I build for want a specific brand of brake. I believe most are all about equal so I give the customer the choice of what they want.
My 2 Cents

[Floyd Staggs]

Another question, Guys.
What size wire and where do you pull the power from. A buddy said he increased the power to his brake and quickened it up. Mine is coing from the fuse block under the dash with what looks to be about 14-16 guage wire. That's what my trans guy put in.
Thanks