PacBrake Question

[NIsaacs]

OK, and what do you think tells the torque converter when to lock, and unlock?

My question was for this: "I couldn't imagine a non-integrated brake on anything"... ...



Nick

 

[ScottLewis]

OK, WITH ALL THIS CRAP I'LL STEP IN. I replaced my dealer installed Jake on my '06 at about 70K miles when the vacuum pump failed. I CAN attest with personal experience that the PAC performs almost identically to the Jake. The only detectable difference I can see is that the Pac holds to a couple of MPH slower before disengaging. It also seems a bit louder. That's all. All the great features of engaging, downshifting and re-engaging, etc. still work fine.

The end, period.

 

[AEdelheit]

Careful there, you just went way out on a limb with no practical experience about what you are talking about.



You had a JACOBS brake, the OP has a PacBrake. Take a look at Pacs install documentation and it is clear it is NOT fully integrated into the ECU. That means no throttle blip, no unlock, no downshift automatically. All it seems to do is control TC lockup.



In that case, the mechanic is a whole lot closer to correct than you think. Comparing an integrated EB to a non-integrated EB is a bad idea, they work differently.



I would NOT put an EB on a stock unit without modding the trans, period. The only exception is the Jacobs due to its integration. If it can't control downshifting and TV pressure, its gonna be a problem.



I would check with Pac and see just how tight it is before assuming the mechanic is wrong.

You seem to know alot about these trucks, Just to make it clear Im not arguing with anyone or saying either is right/wrong. So educate me a little if you will, I installed a PRXB on my 06 but it was a G56, from what I can tell the ECM sends a signal to the exhaust brake to turn on while it controls the transmission perimeters, so why does it matter what brand the exhaust brake is if it just turns on when instructed by the ECM?? I cant how it would know or care what brand it was, they perform the same function just depends if its with air or vacuum operated but the ECM shouldnt care.

 

[HBarlow]

I will try to explain it, I had one in my 2005 for 95,000 miles, and I installed it. It has the exhaust brake, YES, but it also has a little box, that is designed for specific applications, it is in other words a computer, it tells the trans what to do, so install the wrong unit, and yes the trans is toast in short order, this is not a 6 speed, it's a 48re that requires some thinking help.

So what?

You're talking about an '05. It did not have the integration of engine, transmission, and exhaust brake.

The '06 and '07 incorporated the results of several years of extensive testing and when released, were capable and fully compatible with an exhaust brake. The Jacobs Exhaust Brake was offered as a factory option on '06 and '07s.

 

[HBarlow]

OK, WITH ALL THIS CRAP I'LL STEP IN. I replaced my dealer installed Jake on my '06 at about 70K miles when the vacuum pump failed. I CAN attest with personal experience that the PAC performs almost identically to the Jake. The only detectable difference I can see is that the Pac holds to a couple of MPH slower before disengaging. It also seems a bit louder. That's all. All the great features of engaging, downshifting and re-engaging, etc. still work fine.
The end, period.

Thanks for the proof.

Unfortunately your hands on experience will not be sufficient to convince some.

 

[AH64ID]

Why not? All three of my trucks are just on/off, with a secondary switch on the throttle. Course they are all old and all standard transmissions



Nick

:-laf Yeah not much you can do there. But on the newer truck the ECM is the way to control it. It's great to be able to be in cruise control and have the EB armed.

The Jacobs Exhaust Brake was offered as a factory option on '06 and '07s.

I believe it was a dealer installed option, not factory installed.

 

[cerberusiam]

I installed a PRXB on my 06 but it was a G56, from what I can tell the ECM sends a signal to the exhaust brake to turn on while it controls the transmission perimeters, so why does it matter what brand the exhaust brake is if it just turns on when instructed by the ECM??

All the EB's essentially work the same way, they track APPS signal to when it goes to 0 volts. A relay is powered to stop EB operation and when APPS hits 0 the relay closes activating the brake. Whether you do it with an external controller or the internal circuit matters not one bit. They big question is how the EB is actually wired and can it take advantage of this system. From all accounts it implements the same way so that question is moot.



However, if the installer does not know this and wires in a seperate controller the results may not be the same.



From the Jacobs install information, it taps 2 pins on the ECM B connector Both look to be part of the APPS and CC control circuits. This is the SAME for 2003-2007 per their instructions. There is absolutely no information stating there is a special circuit, or controls, or programs to implement this with an auto transmission on any year. I will know more when I get mone installed and wired. If I don't like how it works then BD makes a controller that will solve the problem.



The transmission control circuits show no sign of being aware there is an EB there or not. The original problem that caused Dodge to disallow the EB on autos, mind you they had been installing them for years until this point, was the control of the specific transmission circuits on deceleration.



It didn't down shift and hold the pressures correctly on the TC and TV circuits so slippage was possible. This has been an issue since the lockup TC was offered. The problem was fixed YEARS ago with controllers that did what Dodge finally got around to offering as a standard feature.



As I said before, EB on a stock auto transmission is a crap shoot, blessed by Chrysler or not. I would not do it without transmission enhancements. There still exists the very real possibility the trans will fail due to the EB and crappy implementation of transmission algorithms.

 

[ScottLewis]

I guess Harvey's right, you won't be convinced. But hows this: when decelerating with the exhaust brake, either Jacobs or Pac, at about 40 MPH the brake momentarily disengages, it downshifts and the brake re-engages. That certainly seems to be fairly full integration of the PCM's brake and transmission controls. There is NO controller other than the factory ECM/PCM. While the Pac instructions showed how to tap into the ECM, I just used the wiring already installed for the Jacobs.

 

[AH64ID]

Depending on tire size the ECM shouldn't command a downshift out of 2nd until 30 mph (4. 10) or 32 (3. 73). There is also the note "The exhaust brake and transmission are not designed to offer significant retarding in 1st gear. "

 

[cerberusiam]

I guess Harvey's right, you won't be convinced.

Seriously??? You guys really gotta get a handle on the double standards here. You rather insult somebody than offer ANYTHING but a opinion. Next thing you will be trying to sell me one of those bridges. :-laf



Thanks for the operational impressions, maybe you can shed some light on these questions: Why is the wiring the same for 2003 thru 2006, auto or manual? Why does the FSM specifically NOT address the engine brake as a seperate subsystem? Even the PTO pin out is called out and labeled yet nothing about engine brake operation?



Then there is:

when decelerating with the exhaust brake, either Jacobs or Pac, at about 40 MPH the brake momentarily disengages, it downshifts and the brake re-engages.

How do you KNOW the brake disengages? You do realize that the process of dropping OD results in a momentary free wheel condition and engine load goes to zero, right? What you feel and what is actually going on can be totally opposite.



I don't know that the ECU does or doesn't contain a whole sub-system around EB control. I do KNOW the FSM does not detail it, the Jacobs install does not MENTION it, and the install is EXACTLY the same for 2003-2006 auto or manual with slight differences in the relay. B connector pin outs are the same. Knowing that, does that suggest anything?



Maybe the elephant fart test is the final detemrination. AH64ID should be able to confirm that.

 

[AH64ID]

The Jake is supposed to disengage for down shifting on an auto, which is a difference in auto vs manual as with a manual it's always on when the speed >~3-5 mph and the throttle is zero.



There are 2 wires connected on the ECM. One is for the switch telling the ECM you want to "arm" the EB, the other is the output from the ECM to the EB relay when it's safe to turn the EB on. On a manual it just takes wheel speed (assuming coolant is >180°) and zero throttle, on an auto. . who knows.



The most important thing is that on an auto, especially a stock one, you let the ECM have 100% control over the EB or bad things can happen. The delay isn't built in for the trans, as manuals have it too, it's there to save the turbo (it's a lot of force to go from 20 psi of boost to 50 psi of back pressure and no flow, and that is not uncommon in the PNW). The fact that aftermarket controllers advertise quicker engagement has always made me laugh. . it's there for a specific reason!



Elephant farts... hmm, if they are worse than my farts I am NOT, repeat NOT, running that test...

 

[AClayton]

I would like to add something here... Cerberusiam stated that a modded transmission is needed and/or preferred and I agree with that. Not because I have a vast knowledge of transmission circuitry and TC lock-up strategies or whatever, but because I have driven my truck with the EB both ways. I'm not saying that a driver can't put a 100k or more miles on a stock transmission with the EB, but what I will say is that it is much more confidence inspiring knowing your transmission can accept an EB without failure. If you're coming down a hill with your EB engaged and your transmission wants to downshift, it will kill the EB, un-lock the TC and then downshift and THEN operate the EB again. I've done no specific tests prove anything but my seat-of-the pants impression is that it takes a few extra feet to do the same work that a modded transmission could do because you don't need as much lock-up control to 'save' an unmodded 48 or 47RE from eventually failing.

The only other thing I would like to add is that if a truck owner is to consider an EB then he should have the mechanical background and knowledge to be able to use it properly and without damaging his truck. A modded transmission can withstand any abuse the EB can dish out without all that electronic crap and that, to me, makes it worthwhile to upgrade.

Not for everyone but I drive my truck similarly to driving a manual transmission. I use my only electronic box in the truck that controls my TC lock-up. I have it set for 20mph. Meaning, I can utilize my EB all the way down to 20mph by manually shifting my 47RE. In between shifts, I goose the throttle a bit to ease the transition between the two gears and keep slowing down with my EB fully engaged. Sounds complicated but you do it enough and it becomes second nature. It is no different than what manual transmission drivers have done for yrs!

 

[HBarlow]

The OP's question and the early discussion was limited to the '06 and '07 Rams which were set up and capable of providing long service with an exhaust brake.

Cerberusiam steered the thread off into a lot of unrelated details to try to cover the fact that he was wrong and blowing smoke when he started.

 

[NIsaacs]

The delay isn't built in for the trans, as manuals have it too, it's there to save the turbo (it's a lot of force to go from 20 psi of boost to 50 psi of back pressure and no flow, and that is not uncommon in the PNW). The fact that aftermarket controllers advertise quicker engagement has always made me laugh. . it's there for a specific reason!







Huh? I am lost on this one. When, how or why would you be under boost conditions and activate the brake?



I know I tell my boys, my truck has so much power I need to use the exhaust brake up hill... . but I am only joking



Nick

 

[AH64ID]

Huh? I am lost on this one. When, how or why would you be under boost conditions and activate the brake?



I know I tell my boys, my truck has so much power I need to use the exhaust brake up hill... . but I am only joking



Nick

It's the time it take for the turbo to slow down from the rpms required to make 20-30 psi going up a grade. Not that you would be boosting and braking at the same time.



You want the turbo to slow down before you stop up the flow and slam it to a stop, or stall condition.



There are plenty of hill around here where it only takes a few seconds to go from 70% throttle to EB.

 

[LWalsh]

Well, I'm glad to report that after about 2200 miles with the PRXB "on" most of the time, it performs exactly as advertized... Just like Harvey said it would.
About a 1/4 of the miles were with my 4000 lb Lance camper sitting in the bed, and the rest were with one trailer or another averaging about 4500 lbs GVR. The exhaust brake is a blessing and works GREAT!!
The acid test was coming out of NC on I-26 into East Tennessee. Previously had to manually down shift the transmission and tap the brake often to stay @ 50 mph. This trip, I never had to touch the brake pedal and the truck stayed within 3 mph of the cruise control setting of 50... and that was with a 19 ft trailer in tow with 2000+ lbs of steel siding strapped on it.

Thanks again, Harvey and all.

Larry

 

[HBarlow]

Well, I'm glad to report that after about 2200 miles with the PRXB "on" most of the time, it performs exactly as advertized... Just like Harvey said it would.
About a 1/4 of the miles were with my 4000 lb Lance camper sitting in the bed, and the rest were with one trailer or another averaging about 4500 lbs GVR. The exhaust brake is a blessing and works GREAT!!
The acid test was coming out of NC on I-26 into East Tennessee. Previously had to manually down shift the transmission and tap the brake often to stay @ 50 mph. This trip, I never had to touch the brake pedal and the truck stayed within 3 mph of the cruise control setting of 50... and that was with a 19 ft trailer in tow with 2000+ lbs of steel siding strapped on it.

Thanks again, Harvey and all.

Larry

Thanks for the report, Larry. I'm glad you are satisfied with your PXRB. It will greatly extend your brake pad life while giving you and your passengers an improved sense of control and comfort on steep downhill grades with your trailer in-tow.

If you ever need to descend a very slow speed switchback grade it is possible to lock the torque convertor in second also. I'm trying to remember the procedure from memory - I think if you downshift into second gear while accelerating moderately with the load you'll feel the transmission torque convertor lock in second then, if you back off the throttle pedal and activate the exhaust brake, it should hold second all the way down the mountain as long as you keep road speed about 20 mph.