tranny brake ....need help

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68gts340

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ok this is not a mopar, but my neighbors kids car .the kids only 18 and i have been trying o help him out.. tonight we ran the car, its a monte carlo w/ a sb 406, chevy,,, 4000 converter. msd w/ 2 step... here is the problem.. upon lauch using the t-brake the car jumps nicely. but falls and breaks up. off the foot brake tonight the car ran a new best of 11.29 @117.... 1.59 60ft.... the best 60 ft we got off the t-brake was 1.74....it almost seemed like the two step was comming on late,,any one ever had this problem before ? I did pull the battery out of my ram pickup and put it in the chevy about half way threw the night. his battery did have a bad cell, so voltage was down to a little over 10.5 ...the car did seem to run better then ,but it was into eliminations and we decided to foot brake for the rest of the night ,,,the carb is a 3310 holley w/ vac secondarys.. would a double pumper help or make that bog worse....it got late and we didnt have time to run the trans brake with a fresh battery , so is it possible that it was a low voltage problem?? any help please... i am new to this electronic stuff and am a little lost..

2 nd question ....how do you guys launch with a trans brake... up tight on the converter or set the two step lower and let it flash some? .. gas pedal to the floor when staging ,or just enough to bring to revs up against the converter ? ( at launch rpm ) thanks for the help .....trying to get the kid into the 10s ....
 
I dont have mouch experience in brake cars..Only one that I've helped wrench on. But, in terms of electrical, you NEED 12 volts present all the time. That's with the fuel pump, fan(s), waterpump, lights, ignition, and race electronics on and drawing amperage. For some timers, this is very critical, same with some ignition boxes. Also, wire size and routing can make a probelm. So, a low cell may have caused the bog from weak spark, and not using the trans solenoid and footbraking helped. Or the carb could be partially openning on the two step, making the engine bog when the brake lets off, and the engine goes lean for a sec. A double pumper is probably the better choice for a carb on that setup. The owner of this car goes full throttle on the 2 step and his two step is chipped 700rpm below flash stall. So the driveline has a little momentum to get it moving. (351Cleveland/ C4....) I think it may take some experimentation to determine exactly what the combo likes, once the electrical system is up to snuff.
 
Thanks moper, I have checked everything i could think of , the voltage is the only thing i found that may be the cause. next week I will try to make it to the track with him and try it again, mean while he has a 850 dp , I think I ll set it up and take it along next trip to the strip. it sucks not being able to drive it on the street, makes tuning a race day event.plus the kid is excited and wants to change every thing at once.....damm I miss being 18............
 
I only miss the stamina during...ah..forget it.. ;). The rushing into things I dont miss at all...lol
 
well we now have a new battery , and i ran a #4 welding cable for the charging wire, the car never ran so good,..... 14.2 volts every where....but the same thing happened again last night... this time I drove the car... Launch control set at 4200 I left on the second yellow, car jumps like it serious ... but about five feet out it breaks up sounds just like i hit the rev limiter ... but tack was just about 5000. about three dits ( dit dit dit ) and the motor is back on and pulls like a freight train....terrible short time.... 60 ft was 4.60 .. the tires unloaded when the motor faultered and when power came back on the tires went to smoke, i had to back pedal before i lost it...... off the foot brake it did a 1.55 on the next pass....run strong all the way........looks like it is time to call msd... the only thing i have not tried is connecting the carb vents with a vented hose ,,, thats the last option I know of ,,,,possible that fuel is spilling out the vents? well so i was told anyways..........one other option came to mind ...i think i am going to unhook the two step all together , and try a launch off the t brake with the throttle right up against the converter.. that shoud tell me if its fuel or msd box thats bad.............should be a fun ride ....
 
well we now have a new battery , and i ran a #4 welding cable for the charging wire, the car never ran so good,..... 14.2 volts every where....but the same thing happened again last night... this time I drove the car... Launch control set at 4200 I left on the second yellow, car jumps like it serious ... but about five feet out it breaks up sounds just like i hit the rev limiter ... but tack was just about 5000. about three dits ( dit dit dit ) and the motor is back on and pulls like a freight train....terrible short time.... 60 ft was 4.60 .. the tires unloaded when the motor faultered and when power came back on the tires went to smoke, i had to back pedal before i lost it...... off the foot brake it did a 1.55 60 ft on the next pass....run strong all the way........looks like it is time to call msd... the only thing i have not tried is connecting the carb vents with a vented hose ,,, thats the last option I know of ,,,,possible that fuel is spilling out the vents? well so i was told anyways..........one other option came to mind ...i think i am going to unhook the two step all together , and try a launch off the t brake with the throttle right up against the converter.. that shoud tell me if its fuel or msd box thats bad.............should be a fun ride ....
 
New guy here,Glad to be here!
I would keep working with the carb.You might need jet extensions in the rear to pick up the fuel when it hits the back of the bowel.Remember when you footbrake, your getting that nice fat pump shot.If you use T/brake and/or delay box your decking it before you leave the line and your pump shot is gone.It might just be not getting fuel.
 
When you are foot breaking the car you have vaccum so the secondarys open imedeately upon flooring the car.
If you want to use the trans break get a double pumper.
Light the first bulb,Clear the engine out,put it into 2nd run the rpms up to 1500 roll into the 2nd light,don't deep stage.Pust the trns break button,let the foot break loose.When the lights start to come down floor the throttle let it hit the rev limiter,release the trans button and have fun.

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you can run a vacuum holley on a trans brake...I did it for several years..

are you sure it is the two step...you might need to put a piece of rubber hose from the front carb vent to the rear carb vent...with a cut in the hose at the top..carb could be slogging gas out of vent into main body at the hit of the brake....
 
Are you sure the switch isnt trying to set again, thru vibrations or launch G's, sounds far fetched but I have seen it happen before.
 
I'm sure you've already done this, but have you
checked the grounding straps on everything?
Shifter included.
 
Don't know what I was thinking.You Need to roll into the lights in 1st at 1500 rpm'sGet a adjustable button so you can adjust your launch.
 
I do believe that Parrothead is on the right track. Sounds like on the transbrake launch (which is violent) the sudden movement momentarily uncovers the jets which is instant bog. Try jet extensions first.
 
I'm not an expert by any means, I've been in the family drag car a few times tho. when we launch that on the T brake we just hold the button and floor it, it hits the bars right away and stays there for 20-25ft or so, I don't know much abput the electrical side of things with that tho, kind of a WTF area. Just a thought, What size fuel line are you running and are you sure that your fuel line is free of any kinks or clogs that would prevent the flow? Maybe your fuel pump is going bad? Maybe it needs a Mopar power plant :lol: hehe. Good luck with it, hope you get it sorted out
 
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