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Old 08-18-2010, 08:49 PM   #1
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Question Trans-brake pressure relief orfice ?????

My car is a 3300lb 1972 Nova on a 275/60/15 drag radial tire. The trans I have is a PG with a 1.80 low gear set, pro brake valve body, and lots of other good parts.
The trans came out of a top sportsman car and the trans-brake pressure relief hole has been drilled out to a 3/8 size hole. How will this affect how it work for my car or does it matter?
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Old 08-18-2010, 11:12 PM   #2
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Default Re: Trans-brake pressure relief orfice ?????

bump i'd like to hear about this myself any imput on this hutch
thanks
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Old 08-19-2010, 01:38 AM   #3
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Default Re: Trans-brake pressure relief orfice ?????

Thats just the size of the exhaust hole for the transbrake.I personally feel that you can't make a transbrake release too fast. That should work great.


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Old 08-19-2010, 09:10 AM   #4
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Default Re: Trans-brake pressure relief orfice ?????

that is a little excessive, but like hutch said, too fast is not an issue. Frankly in most transmissions the bottleneck is the drum apply hole or stator supports, ect, any hole larger than those downstream are really a waste. Like clutch apply, it doesn't matter how big the valve body supply hole is, when the casting it weaves through is smaller.
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Old 08-19-2010, 02:08 PM   #5
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Default Re: Trans-brake pressure relief orfice ?????

There are many that are much bigger than 3/8". Not that bigger is better and for the most part it is not as there is more to it than just that.


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Old 08-19-2010, 10:14 PM   #6
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Default Re: Trans-brake pressure relief orfice ?????

If I launch it on the brake with the 2 step rpm over 3000 it will smack the tires so hard the car doesn't even move and nothing but tire spin.

I also have a set of 4.30 gear in the rearend and a 1.80 low gear in the trans. I'm wondering if it is just too much gear for the tire and the launch has too much leverage on the tire.

I want to put a 3.70 in the rear and see what it does...
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Old 08-20-2010, 01:48 AM   #7
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Default Re: Trans-brake pressure relief orfice ?????

Its not the 3/8" hole doing it. Fix the car don't try to take away ratio.


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Old 08-20-2010, 02:34 PM   #8
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Default Re: Trans-brake pressure relief orfice ?????

Quote:
Originally Posted by Hutch View Post
Its not the 3/8" hole doing it. Fix the car don't try to take away ratio.


Hutch
I had some of the best DR tire guy's in the area look at it and say change the gear.....

So what else is to fix? If there is nothing wrong with the trans.

Last edited by $upernova; 08-20-2010 at 02:37 PM.
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Old 08-20-2010, 08:20 PM   #9
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Default Re: Trans-brake pressure relief orfice ?????

Understand with a transbrake, you don't want a soft release because that could wear out the reverse clutch. If your spinning the slicks, you'll need to launch at a lower rpm or maybe work on some right axle preload. Do you know if you have a single or double dump valve body and case drilling. A double dump normally releases quicker than a single however both are going to have a good hard shock to the driveline. I'm not too sure changing rear gears will really fix a traction concern.
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Old 08-20-2010, 08:32 PM   #10
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Default Re: Trans-brake pressure relief orfice ?????

I have no idea on the double dump thing. I'm not running a slick, it's a drag radial.... 275/60/15 Micky Thompson. And yes I do think a gear change will help......
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Old 08-21-2010, 12:04 AM   #11
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Default Re: Trans-brake pressure relief orfice ?????

Then put a gear in it if eveyone thinks thats the fix. I told you what I think but you make the final decison. I predict no change but you let me know how you make out. Looking forward to your reply.


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Old 08-21-2010, 04:37 AM   #12
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Default Re: Trans-brake pressure relief orfice ?????

its a nitrous car correct ? the 3.70 will help but you may neet to work on the car still. If you make the car work the taller gear will let you get after it sooner. Are you pulling timing with the 7531, or using your controller ?
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Old 08-21-2010, 04:41 AM   #13
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Default Re: Trans-brake pressure relief orfice ?????

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Originally Posted by $upernova View Post
If I launch it on the brake with the 2 step rpm over 3000 it will smack the tires so hard the car doesn't even move and nothing but tire spin...
Ive sold fast releasing valvebodys to guys who installed them and went totally backwards, and others who worked with their chassis until it would literally "hook up at the car wash". Here are things you need to work with;

center of gravity, along with...
weight percentage (front to rear and diagonal or preload)
instant center
spring rates
shock rates (up and down)
suspension travel
tire pressures

I am not a chassis guy, but here are some of the thing I have picked up on;

the faster the trans brake releases, the harder it smacks, or "hits" the tires, to the point of cupping the tire. To cure this, take the "hit" out by moving the instant center towards the front of the car, along with more air in the tires, and the best shocks money can buy. Soften the shock on the separation so it wont hinder the footprint, and stiffer on compression to keep the weight of the car on the tires as weight transfers.

You have a chassis problem, not a transmission problem, ask around on the chassis forum, or better yet, lay out a game plan at a test and tune session.
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Old 08-21-2010, 07:41 AM   #14
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Default Re: Trans-brake pressure relief orfice ?????

Quote:
Originally Posted by ERV JR View Post
its a nitrous car correct ? the 3.70 will help but you may neet to work on the car still. If you make the car work the taller gear will let you get after it sooner. Are you pulling timing with the 7531, or using your controller ?
Hey John,

I've had 25* out for up to .5 in the 7531 box. I've had the progressive starting as low as 20% and dual ramped it in at a 1.25 seconds. Very soft tune up stuff. I can launch on the brake at 2500 rpm's wih these setting and that's about it any higher on the rpm and it just slaps the tires.
I looked at all the data and found that no matter if it's on or off nitrous, it will only handle a mid 1.4 60'. Try to tune it up and spin the tires
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Old 08-21-2010, 07:48 AM   #15
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Default Re: Trans-brake pressure relief orfice ?????

It's a leaf spring car.
I think that too fast of a brake at a high rpm causes higher fluid pressure and will hit so hard that it will slap the tires into a hard spin.
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