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Old 09-15-2020, 12:57 PM   #1
J518
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Default Transbrake or Electrical issue?

Hey Guys looking for some guidance here...
The issue I am having is my transbrake will not hold when I bring the rpms up to the two step. Not all the time but of course the last two divisionals in second round it decides not to. I run super street with a powerglide and sbc setup. When I stage the car I set the transbrake and let my foot off the actual brakes, car holds fine then, when I mash the gas its like I never had the transbrake on. It has tried to engage before about 3ft out and sent me into the steering wheel before I was able to release the button.
I had the same issue at the end of last year when running at Great Bend so over the winter I put a total different transmission in. Happen at topeka this year so I thought my steering wheel button was the issue, on my third button this year with same result. I've checked every wire connection I could think of. Also another side note is I run top and bottom bulb races in between divisionals with no issues. Put 24 passes on at Onawa two weeks ago without an issue. Last week at Earlville, 2 out of 4 passes it happened. I put a camera inside the car to make sure I wasn't flinching of some sort and its clear I am not.

Leads me to think of 3 scenarios:
1. My delay box has an issue(Elite 500) when I only run around .030 of delay in it but I would think it wouldn't hold the car in the first place then??
2. Voltage issue -The only difference in the car from when I run top/mod vs SST is the added electric throttle stop. I run a 40 amp alternator but is the added load of the throttle stop putting me where there is not enough juice to hold the transbrake but if it holds at idle shouldn't it hold at higher rpms? or is fluid pressure higher and overcoming it.
3.Grounding issues- This wouldn't explain why it only happens in SST form but the car is Chrom Moly, is there a rule of thumb when grounding to chrom moly chassis?
Sorry for the long post but pulling my hair out on this one...
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Old 09-15-2020, 11:24 PM   #2
voltdr
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Default Re: Transbrake or Electrical issue?

Not sure of a lot of details about your car. Motor plate? Is it powder coated? Do you run a separate ground wire from the battery to the engine block? Do you just ground the battery to the frame? Do you ground the TB to the transmission?

Good rules to follow when wiring a race car.

1. Chrome moly does not make a good ground.
2. NEVER ground the TB to the transmission.
3. There is a lot of vibration on wire connections in a race car.
4. Use “star” type lock washers on all ground connections.
5. Poor grounding connections are the most common and the most difficult problem to diagnose.
Dan
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Old 09-16-2020, 06:55 AM   #3
J518
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Default Re: Transbrake or Electrical issue?

Quote:
Originally Posted by voltdr View Post
Not sure of a lot of details about your car. Motor plate? Is it powder coated? Do you run a separate ground wire from the battery to the engine block? Do you just ground the battery to the frame? Do you ground the TB to the transmission?

Good rules to follow when wiring a race car.

1. Chrome moly does not make a good ground.
2. NEVER ground the TB to the transmission.
3. There is a lot of vibration on wire connections in a race car.
4. Use “star” type lock washers on all ground connections.
5. Poor grounding connections are the most common and the most difficult problem to diagnose.
Dan
Dan,
We run a front and mid plate. The batteries are grounded to the main 2x3 frame rails which now that I think of it are actually mild steel and all round tubing are chromoly. At the mid-plate which is also mounted to the main rails I run an 8 Guage ground wire to a distribution block inside the car. From there I run indivisual grounds to the transbrake and tb button. Delay box is npn, if you are wondering about the ground to the tb button.

Is my theory of not enough voltage for the transbrake and that when I apply gas the higher fluid pressures over come the transbrake out of the question? Not much of a transmission guy....
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Old 09-16-2020, 11:24 AM   #4
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Default Re: Transbrake or Electrical issue?

I had a friend with a very similar issue years ago, and it was the transbrake ground having intermittent contact when the car started shaking on the chip.
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Old 09-16-2020, 12:11 PM   #5
James Sessoms
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Default Re: Transbrake or Electrical issue?

I had a similar problem with a mega 450. The problem was the driver in the delay box. I called and talked to Digital Delay. When I described the problem they said to send it to them. The driver was fixed at no charge and sent back to me.
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Old 09-16-2020, 07:47 PM   #6
sgasman
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Default Re: Transbrake or Electrical issue?

Do you switch from Full tree to Pro tree?
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Old 09-17-2020, 06:48 AM   #7
J518
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Default Re: Transbrake or Electrical issue?

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Do you switch from Full tree to Pro tree?
I do not. I figured this was just to change the layout?
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Old 09-21-2020, 01:05 PM   #8
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Default Re: Transbrake or Electrical issue?

I would bypass around the delay box and any other electronic devices you have between the button and the solenoid and test that to see if it works properly with the electronics out of the system. If it still does the same thing then it can only be the button, solenoid, voltage or ground.
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Old 09-21-2020, 01:18 PM   #9
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Default Re: Transbrake or Electrical issue?

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Originally Posted by Mike Pearson View Post
I would bypass around the delay box and any other electronic devices you have between the button and the solenoid and test that to see if it works properly with the electronics out of the system. If it still does the same thing then it can only be the button, solenoid, voltage or ground.
Good suggestions however, that is not the only thing left.
If it has an aluminum valve body that is one more thing to check.
I have had somewhat the same thing happen on a customers aluminum valve body when it goes from cold to hot and the pump pressure is also low.
If it is a old GM stock pump that would be my first thing to change to an aftermarket pump. The aftermarket pumps with the bigger gear set puts out more volume and pressure that the valve body regulates.
I am just not a fan of the aluminum valve bodies.
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Last edited by 63corvette; 09-21-2020 at 01:20 PM.
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