Looking for some input on my issue before I pull the trans. Jakes Stage 3 4l80E with 4K+ miles. When hot (140*+) no reverse or trans brake, works fine when cold. I pulled the reverse servo and discovered that the pin was short, added length to the pin to .070" clearance. Everything else appeared fine. Reassembled still had same issue. Fluid level is good per Jakes instructions. Also per Jakes, added a .070" washer to the pump PR valve with no change. All fwd gears hold fine at 900+ HP. Engine braking is present in 1st. When RPM is increased PSI will jump to ~180 PSI till tires spin. Reverse line PSI is dropping when hot. Video of the following results:


Thanks for any assistance!

 

D1 or D3
Active EPC or no?

 

Transbrake is activating. You don't have enough line pressure to activate the brake. What is mainline pressure at 1500+ rpm?

 

D3, yes active EPC. Using HP turners I was able to adjust PSI thru the vehicle controls. At 0Ma PSI will jump to 180 PSI then progressively drop when Ma are raised.

 

Program it for max pressure at all times.

 

Went for some more testing. This time with trans hot, Force Motor Current manually controlled thru HP tuners, "On" 0 Ma saw no rise in line PSI at Idle. When RPMs are increased (1500+) line PSI will climb to 300+ PSI. 500Ma PSI will climb to 210 PSI. Idle line PSI seems unaffected by commanding FMC to 0 Ma in any gear. This seems different than when I tried it earlier today.

Should line PSI change at idle with FMC set to 0 MA?

 

Video of line PSI at 1500+ RPM in reverse

 

Idle pressure is dependent on the volume of oil that can be generated by the pump at idle speed.
That's why it is important to check at 1500+ rpm, when the pump is making sufficient volume for normal operating conditions.
I thought jakes D3 had you grind away the center land on the EPC to cause max line? for exactly the reason of this post...Am I remembering a different Valve Body?

 

I cant say for sure on the EPC, Jakes built it not me. They would have to chime in on that. I tried to max the line PSI, but not effect at idle, but max PSI is higher with RPM. Trying to stage the truck without being able to activate the brake at idle is going to be a huge pain.

 

It's pretty typical to use the footbrake, bring up the engine rpm a little, then set the transbrake and let off the footbrake.
More than just because of the trans pressure...but also because it pre-loads the whole drivetrain from converter to tire. Helps reduce some of the shock to the driveshaft/rear end/axles when you release the brake.

COAN, BTE, etc I've read in different versions of their transbrake instructions to do the same. Footbrake, then set transbrake.

 

When built at the shop we aim for 100 psi minimal at idle. What is "warm or hot" temp?
What type of fluid?

The D3 needs 100 psi to activate. They usually will at 90 ish but its borderline.

There should be NO issue getting 100 psi at idle. Unless the fluid is super thin or the pump is damaged.

Add a qt and see what it does.

 

Trans has worked great for last 4K miles, no issues activating brake/reverse at idle. Fluid is fresh dexron VI. Reverse PSI progressively drops more with heat compared to the rest of the gears. I'll add a quart and see if there is any change

Trans PSI COLD 75-140*
P: IDLE: 85PSI,
N: IDLE: 85PSI
R: IDLE: 130PSI(95 brake engaged)
D: IDLE: 80PSI
3: IDLE: 80PSI
2: IDLE: 80PSI
1: IDLE: 80PSI

Trans PSI HOT 150-190*
P: IDLE: 75PSI
N: IDLE: 75PSI
R: IDLE: 85PSI (65 brake engaged)
D: IDLE: 70PSI
3: IDLE: 70PSI
2: IDLE: 70PSI
1: IDLE: 70PSI

 

What torque-converter are you using with this... Brand, diameter, stall speed, STR???

 

Also, did you get the clearance on the low-reverse band figured out???
This clearance is very important with the Trans-Brake.

 

Torque converter is Circle D triple disk 3200. Clearance on the band is set to .070" now. My issue is low line pressure at idle in reverse. When hot the idle psi is 65 with trans brake activated in reverse, not enough to activate the brake. When I command the EPC to 0Ma in HP tuners, PSI does not rise at idle. When its cold in reverse PSI will rise to 180PSI when commanded to 0Ma. Im guessing I have a bad EPC or PSI is bleeding off some where when its hot.