Trans brake question

[S/G 386N]

The car = '06 Don Davis Corvette roadster.

The Transmission = ATI

I have heard ATI makes a pretty slow transbrake. After talking ato ATI, I have the fastest one they make in the car. Reaction times still aren't where they should be, especially with a car that is designed to race super gas. I should be going red with the delay I have. At Gainesville, .020 delay, reaction times were in the teens most of the weekend. At Indy, had to drop my delay to .000, and still couldn't get any faster than the teens.

I know pro brakes are faster than a regular trans brakes, but what makes them different? I have swapped trans brakes out of an old transmission I had in my old Camaro. Going to see if that helps any.

Any other suggestions?

[63corvette]

I also race a C-5 and it is all in the suspension, converter and launch RPM with my car.
Hughes converter with 6400 stall.
Last year I had to carry .040 to .060 to keep from going red. I ran as high as .090 at one race.
I was using 5400 to 5600 in the low chip depending on adjusted altitude and bringing the stop on at .007.
Rear shocks rebound in the middle and 2 clicks off of full soft on the compression side.
Front shocks in the middle on adjustments.
4 link holes set as Davis set them.
I did have to adjust the right rear preload to get it to go straight on launch from where Davis set it up.
Every car is different as I have friends who use totally different setups.
If someone else does your transmissions and it is a Dedenbear case have you checked the release adjustment on the rear of the case?
Hope maybe some of this helps.
Good Luck with the issue.

[Ron Finney]

The difference is in the release, typically the regular brake uses a spring behind the valve for the release. The pro tree brake uses a fluid release. It also requires a second hole be drilled into the case, so once you go pro brake you can't go back. Pro tree brake requires pushing button to get reverse also.

Ron
33 S/C

[ray sowers]

Originally Posted by S/G 386N

The car = '06 Don Davis Corvette roadster.

The Transmission = ATI

I have heard ATI makes a pretty slow transbrake. After talking ato ATI, I have the fastest one they make in the car. Reaction times still aren't where they should be, especially with a car that is designed to race super gas. I should be going red with the delay I have. At Gainesville, .020 delay, reaction times were in the teens most of the weekend. At Indy, had to drop my delay to .000, and still couldn't get any faster than the teens.

I know pro brakes are faster than a regular trans brakes, but what makes them different? I have swapped trans brakes out of an old transmission I had in my old Camaro. Going to see if that helps any.

Any other suggestions?

Make sure the stock Powerglide case reverse fluid passage from the valve body to the reverse piston is 3/8" Dia. all the way.and clear of obstructions, Ray

[S/G 386N]

Maybe I need to be more clear. This is an ATI transmission with an ATI case with their transbrake, which has the reverse lockout. I have swapped valve bodies and probrake from a stock case Coan transmission I had in my old Camaro into the ATI transmission. Have not swapped the whole transmission. Hoping this will help.

63corvette - What size tires do you run up front? I have 24" on it now. Wondering if I go down to a 23", how much that will help. I have a Hughes converter, 5800 stall. I used this same converter in my dragster back in '07, with similar motor. Wondering if it might be a little too loose for this car. I launch on the chip at 5600. When I got the car, the suspension was all out of whack. I'm not sure if the previous owner did something to it or not, but it did not launch straight, pulled the the left, steering wheel off center. So we started from scratch. Have the 4 link bars adjusted to bring the instant center more forward on the car. Bracket raced it last year, running flat out. Got it down to a 7.99, launching at 3800rpm. So I guess it's kinda setup for bracket to help keep the front wheels down. Going to have to go back to bracket racing on the throttle stop though. New motor making more power and riding the wheelie bar too long and unloading the rear tires more than I'd like.

[63corvette]

JJ, I run a set of 24" on the front. As I mentioned in the previous post every car is a little different even though they all come from the same jig. I have friends with the same car and we all use a little different setup. It also depends on the engine HP you run and the rear gear. I run a 4.30 rear gear.
I bought mine new from Davis and went through a long visit with Don on how and why the car works as it does. Don builds the car to be consistent on launch by planting the rear tires and pulling the front tires out of the beams and not driving them out. I have found mine likes to move up and out not just up. Last year I struggled with the tree and like I mentioned in the previous post ran far to much delay at times. The car was jerking the front end out of the lights instead of a controlled up and out. The launch would change with the density altitude and thus the more delay in the box with a low adjusted altitude. Over the winter I thought long and hard on how to tame the car down and make it consistent. I ended up lowering the launch chip and carrying the car out farther before bringing the stop on. That has worked well for me and has made the car more consistent on the launch. At my 3rd race of the year (Las Vegas Nats) my worst light was .028 and a best of .000 in 3 time trials and 4 rounds of racing. That was with .020 to .033 in the delay box. I always add time to the delay for eliminations as the starting line is usually better especially at the National Events. I have been very pleased with the way my car is working this year and we have been going rounds.
Don Davis also recommends you lube the 4 link hiem joints before every race weekend to allow the suspension to work as well as possible.
I use a B&M trans brake but all the pro tree brakes are about the same. I build race transmissions so I do have some experience there. If you have a pro tree brake and the clutch clearances are correct you should be able to go red easily with the Davis car.
I hope this helps and wish you the best of luck with the car.
S/G 5887

[S/G 386N]

Thank's 63. I also run a 4.30 gear. Engine dynoed at 934hp. Going to see what happens this weekend. Have a bracket race, but am going to run it on the stop and see what happens. Here is a video from Gainesville this year if you want to see how it launches. I go on the stop at .100.

http://www.agbulletracing.com/Videos...%20run%201.mpg

[63corvette]

JJ, it looks like it is launching pretty good to me. From the video it looks like it moves up and out like mine. What kind of rear tire pressure do you use? If you can get a good video of the tire sometime make sure it is not wading it up to much on the launch. If it is wading the tire to much that can also slow reaction times down (As Per Don Davis). I run my Hoosiers at 6# cold and that seems to work for me.
Good Luck this weekend and let me know how it goes.
Rick

[S/G 386N]

I run the the rear tires at 8psi, fronts at 40.

[S/G 386N]

Think we fixed a majority of the problem. Swapped in a Coan transbrake and valve body. Kept the same delay as I did last bracket race, and reaction times were .030-.040 quicker. Even pulled off a .001 in round 3, and a .002 in round 5. Track was going away at this time, and couldn't run the #.