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Transbrake thoughts?

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WesternRed View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote WesternRed Quote  Post ReplyReply Direct Link To This Post Topic: Transbrake thoughts?
    Posted: Mar/16/2023 at 5:03pm
Contemplating future upgrades for the Gremlin and thinking a transbrake might help me out a bit.

Currently foot braking and finding that 2000-2500 is about the limit for holding it on the line and getting off the line relatively consistently. Any more and it really loads the suspension up, leaf springs and slapper bars, which tends to result in wheel spin. The convertor will hold maybe 3500 stall on the brake and flashes to around 4400 when launching.

I'm a bit of an online calculator fan and based on my latest run at 119.3 mph, I should be able to pick up a couple of tenths in the 1/4 mile if I can knock a tenth off my 60' time, which is currently around 1.65, Wallace is giving me me an ideal 60' of 1.54.

Also looking at doing a bit more bracket racing next season, so I'll need to be a lot sharper on reaction times. I'm slowly getting a little better at this, but the guys I'll be racing against are pretty sharp and it would be nice to be able to go a few rounds since we run knockout eliminations.

I gather a transbrake will help with both of these ambitions, however I know it will potentially put a lot more stress on the driveline. Realistically, what needs to be done to the 727 transmission to make it live with a transbrake and what about the rest of the driveline? 

 


Edited by WesternRed - Mar/16/2023 at 5:07pm
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Post Options Post Options   Thanks (1) Thanks(1)   Quote PROSTOCKTOM Quote  Post ReplyReply Direct Link To This Post Posted: Mar/16/2023 at 8:48pm
I am not sure you're going to gain the ET you think you will from running a transbrake, but you will gain consistency for sure if leaving off a box.

A 727 rebuild with good clutches is all I feel you'll need at your power level.

What will you need? Having blown out a driveshaft at 120 mph I tend to lean on the bullet proofing concept anymore.

I run 1350 U-joints, a billet transmission yoke, and a billet rearend yoke.

Also if you don't already have it stepping up to a 20,000 pound rated transmission cooler is a must.

Once you put it on the brake the transmission temperature starts soaring quickly and can get 300 degrees in no time if you don't have a proper cooler.

Tom
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Post Options Post Options   Thanks (0) Thanks(0)   Quote WesternRed Quote  Post ReplyReply Direct Link To This Post Posted: Mar/16/2023 at 11:00pm
I did find a Motortrend article where they installed a transbrake and actually lost ET. 

I’m thinking I would be able to launch at a little higher RPM and maybe pick up a little in the 60’, maybe a couple of tenths over the 1/4 mile, not expecting to pick up half a second or anything crazy like that. 

Consistency and better reaction time would certainly help with bracket racing. At the moment I mostly run off street meets which are essentially test and tune, you are mostly racing heads up with the car in the other lane but not matched up into any sort of competitive format, so you might be up against a 16 second car or a 9 second car. They do run a best package competition for a bit of extra interest, person with the best combination of reaction time and closest to dial in wins a free ticket for next week.

At the moment it costs me $70 to enter and I might get 8 to 12 runs in a night, if I step up to the main events it’s $195, you get 3 qualifying runs and then it’s knock out eliminations, so might only get 4 runs if you get knocked out in the first run. Eliminations are seeded too, so if you are a bit ordinary, you will get matched up with the better qualifiers.

So anyway, my 727 as it stands is pretty standard other than some performance frictions, a bolt in sprag, reverse pattern manual valve body and billet servo piston that was recommended with the valve body.

I could build a new transmission if I need to run things like a steel drum (sounds like that might be a good idea) or other aftermarket hard parts, would be replacing the valve body anyway. Might be a good time to look at a more serious race converter as well, since that would likely help too, can get something that is setup for the transbrake.

Probably wouldn’t hurt to put some new uni joints in. Does anybody make a billet yolk for the AMC20, assuming the AMC20 is up to it with a tru trac centre and Moser axles.

I did upgrade the transmission cooler recently, but might need to revisit that by the sounds of it.




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Post Options Post Options   Thanks (0) Thanks(0)   Quote PROSTOCKTOM Quote  Post ReplyReply Direct Link To This Post Posted: Mar/16/2023 at 11:38pm
You won't need a billet drum for the power output you have, but I would ditch the Truetrac and put a spool in it. If you break anything in that differential you be headed to the wall or the other car. 

I've seen it happen many time with non spooled cars.

I would think that with all the Jeep crowd there has to be a good yoke available. 

Depending on how hard you can leave the AMC20 might be a weak link. They don't have the most robust ring gear.

Should be fun to see what you come up with.

Tom


Edited by PROSTOCKTOM - Mar/16/2023 at 11:40pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote WesternRed Quote  Post ReplyReply Direct Link To This Post Posted: Mar/16/2023 at 11:46pm
That will be just what I need, more money into a new rear end, which would raise a whole heap of other things to think about. That said, I am probably starting to push the limits of RPM across the line with the current setup running 4.10 gears and a 27” tire. Maybe I can get a 28” tire in there, which might help a bit.

PS: my CSR transmission shield is still sitting on the shelf, might be a good idea to install that if I don’t get a steel drum.


Edited by WesternRed - Mar/16/2023 at 11:51pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hurst390 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/18/2023 at 8:24am
You will need to plug the vent in the pump and install a vent in the extension housing.
You already have the billet servo that is required. I run an early 5/16 rod rear servo.
I also run a billet aluminum drum. A billet front drum is highly suggested as well as a shield!
A low band apply brake v.b. like an A+A is also suggested.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote WesternRed Quote  Post ReplyReply Direct Link To This Post Posted: Mar/18/2023 at 6:57pm
Seems like a billet drum would be good insurance. Probably a good idea to work with one of the suppliers and buy a rebuild kit with all of the necessary parts to support the tranbrake.

This seems like a reasonable sort of list from the Moparts forum:

Quote   - A good valve body (with a brake if applicable)
  - Check everything for wear (pump rotors, drums, ring rubbing surfaces, etc.)
  - Relocate the vent with a brake (plug the front vent)
  - All new bushings (just do it now, any refresh maybe not)
  - All new thrust washers (cheap insurance)
  - Set clutch pack clearances for the application
      ex/ 0.015" per front disc (0.075" for 5 discs)
      ex/ 0.025"-0.035" rear with 4 discs
   - Check sprag for wear, at a minimum new rollers and springs
  - The best improvement would be with a 16 roller sprag like the A&A Ultimate or Coan Super Sprag
  - 3.8 or 4.2 front band servo lever (see valve body instructions)
  - Rigid/solid front band (IMO releases better than flex band)
  - Reinforced front band strut (servo to band)
  - Babbit converter bushing in the trans pump housing
  - Pre-'71 "solid" front servo with 2 springs, or shim the newer oil cushioned servo so it is solid
  - Shim the rear servo so the cushion spring is almost solid
  - A billet rear servo with a stronger retainer and stiffer spring is good with low band apply valve bodies.

I like the oil passage enlargement mods (ported reaction shaft support between the rings, clutch retainer holes 5/32", 1/16" oil hole to the sprag).

-And an aluminum or aftermarket steel front drum is a safety consideration.

Probably just do the 16 roller bolt in sprag and be done with it.

That should be pretty bulletproof at my power level and support any future power upgrades that I am likely to make.
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