What is a trans-brake, how does it work, vs line-lock?

Discussion in 'Technical' started by scooper77515, Jun 12, 2005.

  1. mavman

    mavman Member

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    Not all of us have $600+ for a transbrake for a C4.

    Yeah it is. C4s usually don't last near as long when using a 'brake. Neither do Powerglides. Puts a TREMENDOUS strain on the shafts and clutches. Remember the torque converter's torque multiplication? Well...at a 2:1 TM, that means if your engine makes 300 lb-ft torque at converter stall speed, the trans is seeing 600 at the input shaft. Then consider that a C4's low gear is 2.48, you're putting 1488 lb-ft of torque against the high clutch when the brake is applied, also the same torque goes to the gearsets. It ain't gonna last forever like that. Not to mention the extreme heat built up inside.

    With the footbrake held, the suspension is loaded...and the car reacts quicker. I proved this to myself a long time ago....by watching a vid of my car launching. That's how I actually can scrub off a slight amount of ET if I know I dialed too tight...a little less RPM at the launch and bumping in a bit further.

    Yes, the transbrake releases reverse gear, and shocks the drivetrain. It also tends to be a little rough on driveshafts, gears, third members, chassis, and everything else driveline-related. If you have a car that traction is marginal, it won't pick up that much, if any. I know that on my car the transbrake doesn't pick up ET at all...MAYBE .01 on a good day/night, but that is negligable considering the shock that the drivetrain takes. And yes, the Transbrake valvebody is easy to install.....actually, it just bolts in. Putting the solenoid on and running wiring is a challenge sometimes, and modifying the case (if needed) can be a bear if you don't know what you're doing (like backyard guys like me!). Also, a GOOD wiring job has to be done for it to work right....skimp on the wiring and the solenoid won't hold, and a red light is almost a guarantee. Keeping the internals of the transmission in tip-top shape is paramount. Any slippage in the high clutch (C4) or low band (also C4) will cause the car to roll when the 'brake is engaged and worse...if that multiplied torque makes it's way back to the one-way, it can explode....ever seen a sprag let go? It ain't pretty. TF727's are notorious for that, and they were exactly the reason that trans shields were mandated! They literally rip a gaping hole in the floor and fill the interior of the car with hot trans fluid, parts, springs, rollers, sometimes the shaft will bend and continue to swing around inside the car at thousands of RPM.

    Transbrakes are great, but you had better be ready to take on some expenses. I would suspect that a 'brake C4 could easily set a man back $2000 all said and done (with converter)...where we've been running stockers for years, pulled from scrap metal recyclers and rebuilt with a good manual valvebody...total investment under $100 minus converter. Bottom line is that if you want to race, they're fine....but they don't always pick up that magical full second of ET that you're sometimes lead to believe! Like I mentioned before, they're great for cars that need to leave quickly (.400 pro tree racing) and fine for bracket racing....on a heavier car that needs the 2.46 low gear (or 2.48...whatever it is, cant' remember) to get it moving. The primary purpose in brackets is to just keep the launches consistent from round to round...NOT to improve ET. In fact, most times it doesn't improve ET. On a heavy car with a too-tight converter, yes, it may pick up a little. Not always though. I didn't want to start a pissing match here, but I feel that all the information that one can gather (especially real world information...like what we've done over the years) can be very beneficial. After all, what good is knowledge if you don't share it (or if it gets exagerated a little)?
     
    Last edited: Jun 15, 2005
  2. 74merc

    74merc computer nerd

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    Educate me a bit here. I never understood the torque converter to multiply torque x2. How is this? I understand essentially as the converter slips you get more rpm crammed into the input vs output, so a little torque is gained.

    As I've always figured it, torque gains by the converter are limited, torque multiplication comes in gear, 300lbs torque x 2.43 (I *think* its 2.43, 1.46, 1) so 729lbs of torque to the rear of the tranny, or front of the gear set when under transbrake... gotta learn more about trannies.

    Bottom line, 300lbs torque with a C4 and 3:1 gears puts 2187lbs of torque to the rear wheels, not accounting for 20% drivetrain loss. If the converter multiplied torque x2, you'd be putting over 4000lbs of torque to the ground with a warm 302, which should be more than enough for a good wheelstand with traction, and most people can't do that.
     
  3. Andysutt

    Andysutt '72 Comet GT

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    Not arguing over anything here, as I don't know much about transbrakes.
    But i do know they just help you leave earlier if you know how to use them right.
    ANyways, reason I posted was the ratios are 2.46, 1.46 and 1:1
     
  4. 74merc

    74merc computer nerd

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    I have no experience with transbrakes, so I don't have a comment on them. Holding the foot brake to stall has always made launches slower for just about every car I've worked on and played in.
     
  5. CometGT1974

    CometGT1974 Gearhead

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    Man, I can't believe I missed this thread.....

    Listen to Mavman, transbrakes are definitely hard on stuff and they create a tremendous amount of heat in the tranny. Any reputable builder will tell you that if you plan on transbraking it a moderate amount, it will need to come apart once a year (usually at the end of the race season) and need to be looked at and possibly freshened up. Of course, that all depends on how many passes you make in a season and if you do any street driving.

    I've transbraked my C4 probably 50 times this year with plenty of street driving and there are no signs of any problems from the trans but it will be coming apart soon to be inspected and checked for wear.
     
  6. scooper77515

    scooper77515 No current projects.

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    glad you finally got in on this thread :Welcome:

    Sounds like I am not "hardcore" enough for a T-Brake. I will stick with the "one foot on the brake, and one on the gas" method, and maybe go line-loc later.

    I currently have a leak in two places on my trans, and just refill it once every few months, and cannot find the time to actually fix the leaks. Does it count that I have already purchased the seals, just need to get under there and replace them. I HATE working upside down... :mad:
     
  7. okibono

    okibono Member

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    yeah, what CometGT and Mavman said...
     
  8. Phyphor1

    Phyphor1 Member

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    Torque multiplacation is caused by the Stator inside the TC. This can cause up to 200% torque multiplication to be applied to the input shaft, from a dead stop. Once the vehicle is actually moving, the stator isn't as effecient.
     
  9. mavman

    mavman Member

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