Pacbrake PRXB w/ Allison MT643

Topic: Pacbrake PRXB w/ Allison MT643 (Read 1291 times) previous topic - next topic

Pacbrake PRXB w/ Allison MT643

October 13, 2011, 07:27:55 pm

Has anyone used the PRXB with a Allison MT 643 and Cummins 5.9? How well did it work?

Re: Pacbrake PRXB w/ Allison MT643

Reply #1 – October 13, 2011, 07:39:34 pm

Jeff and I both had the Pac Brakes on our 93, U225's. Mine worked pretty well but Jeff's worked better. He had the Allison Transmission lockup (it was $800 additional installed) in addition to the Pac Brake so his transmission kept the rpm's up as it down shifted all the way to idle. I also had to replace the exhaust manifold gasket and have several places in the pipe welded multiple times on the pressure side of the brake. The last time I went to a real welder and not Cummins. He welded it right, I hope.

I was able to go down Palo Dura Canyon's 12% grade with the Pac Brake without any problems. I don't think I would have tried it without the Pac Brake. I hope this helps. I would have it put on again if I had the choice but I would also get the Transmission Lockup.

Re: Pacbrake PRXB w/ Allison MT643

Reply #2 – October 13, 2011, 09:37:07 pm

I think the 643 was like the 647 in my 93, lockup is only in 3rd and 4th... Like Kent said, there is a service bulletin to modify the valve body (new control plate and some other things) to allow lockup in all gears. I documented the TSB number in a post a long time back.

Re: Pacbrake PRXB w/ Allison MT643

Reply #3 – October 13, 2011, 11:18:45 pm

Yep, it only locks up in 3rd & 4th. Having it installed, and the guy is top notch.

Found a new mechanic who really knows his way around the diesels and building up pulling trucks. I talked to him the other day and he knows stuff that had my old mechanic talking in circles about and spewing out nonsense.

Re: Pacbrake PRXB w/ Allison MT643

Reply #4 – October 14, 2011, 12:01:12 am

Pat,
I installed the PRXB in my coach with the MT-647, which as Dave said, only locks up in 3rd and 4th. However, it worked especially well going down grades in the Rockies, the Cascades, and the Coastal Range, keeping the speed in the 50's with the transmission in 3rd. It remained effective down to about 1200 rpm's.
It's possible that the compression in the 8.3 Cummins might produce more braking than the 5.9, but then again the weight of the U-225 is proportionally less, so it might work out about the same.

Re: Pacbrake PRXB w/ Allison MT643

Reply #5 – October 14, 2011, 12:43:46 am

Quote from: Don Hay – October 14, 2011, 12:01:12 am

Pat,
I installed the PRXB in my coach with the MT-647, which as Dave said, only locks up in 3rd and 4th. However, it worked especially well going down grades in the Rockies, the Cascades, and the Coastal Range, keeping the speed in the 50's with the transmission in 3rd. It remained effective down to about 1200 rpm's.
It's possible that the compression in the 8.3 Cummins might produce more braking than the 5.9, but then again the weight of the U-225 is proportionally less, so it might work out about the same.

That is what I was hoping to hear. I already know it will not be like the 3 stage Jake that I am use to. Now if I could find a accelerator pedal switch for it. One where the pedal when released would turn it on. Someone out there much make such a animal.

Re: Pacbrake PRXB w/ Allison MT643

Reply #6 – October 14, 2011, 07:12:27 am

There are plenty of foot pedal controllers out there avail with both NC and NO contacts.

Re: Pacbrake PRXB w/ Allison MT643

Reply #7 – October 14, 2011, 09:47:56 am

Pat, both Jeff and I had a toggle switch on the dash to activate the system and a switch on the engine that was mechanically activated to turn the Pac Brake off at idle and on when you pushed the accelerator. I though it came with the Pac Brake but maybe not.

I was told that the newer Pac Brakes were more effective than the older ones like mine.

Re: Pacbrake PRXB w/ Allison MT643

Reply #8 – October 14, 2011, 10:54:43 am

Pat C. said: "Now if I could find a accelerator pedal switch for it."

Pat,
The instructions for the PRXB recommend that it be turned on (via the toggle switch) when the engine is started and left on for the duration of travels that day. The reason is that the mechanism is basically self-lubricating as long as it is on. Only if left for periods of inactivity will it need external lubrication. Therefore, I just turn it on in the morning and leave it on. As soon as I let up on the accelerator or hit the brakes (only if on cruise control) the exhaust brake is working.

Re: Pacbrake PRXB w/ Allison MT643

Reply #9 – October 14, 2011, 12:19:03 pm

Don,

While it is true that it is best to exercise any exhaust brake to keep it from seizing up, there is no reason to sacrifice MPG to do it. Said another way, I would never eliminate my favorite gear-- COASTING! Use it, yes. Use it every time you take your foot off the throttle, no.

Also, be aware that PacBrake sells a special high-temp lube. One bottle will last the life of the coach/brake. If lubed, the chance of seizing up is materially reduced.

Brett

Re: Pacbrake PRXB w/ Allison MT643

Reply #10 – October 14, 2011, 02:07:27 pm

Brett, it was my understanding and experience that the PacBrake would not engage when coasting if the cruise control was on. I used my cruise control all of the time unless in heavy traffic.

Re: Pacbrake PRXB w/ Allison MT643

Reply #11 – October 14, 2011, 02:26:13 pm

Brett Wolfe said: "Said another way, I would never eliminate my favorite gear-- COASTING!"
Brett,
That's a very good point and when I am in town driving I will keep the exhaust brake off. However, when I am on the road, I use the cruise control at least 90% of the time and only take it off when I need to slow down. That is when the PRXB helps, reducing my need for using the air brakes as much. For this last trip of 6,300 miles through the Rockies and Cascade range my mileage in the mountains for two tankfuls was 7.75 mpg. On the flat lands, 9.6 to 10.1 mpg. Rarely have I had much better than this before the PRXB was installed.

Re: Pacbrake PRXB w/ Allison MT643

Reply #12 – October 14, 2011, 03:06:14 pm

Kent,

With the variation in engines, years and cruise controls used, not sure there is a "standard" way these are set up. Indeed, the way you describe yours is different than the way mine works. No right or wrong ways-- just determine how it works and works best for you.

Don,

What I did is build from walnut to match the interior an extension of the vertical panel on which the electronic shift pad is mounted (with MD3060 transmission shift pad-- the manual shifter may be in the same location to the left of the driver). I canted it at about 30 degrees in both vertical and horizontal planes so that both the shift pad AND exhaust brake switch fall readily to hand next to the wheel. So it is easy to turn on/off the exhaust brake and/or up/down arrow without having to take your eyes off the road or left hand very far from the wheel. Then I leave the exhaust brake switch off except when needed or in real tight stop and go traffic where I leave my foot very lightly on the throttle to achieve coast.

A lot of this is personal preference-- trading ease of driving with performance and/or economy. No right or wrong answers. Me, I consider every extra gallon of fuel pumped to be dollars thrown away forever, so MPG is king for me. But, the extra work (mechanical setup as well as maintenance) and driving style have returned a coach life MPG of 11.3 MPG (and yes, the speedometer is calibrated and every gallon of diesel recorded).

Re: Pacbrake PRXB w/ Allison MT643

Reply #13 – October 14, 2011, 05:35:50 pm

In other words, I don't use it like a 3 stage Jake which had clutch, brake and accelerator controled switches.n These all prevented the jake from stalling out the engine.

Going to be doing some learning here. And did not know about it working with cruise control. Am updating that too! So I am going to be behind the learning curve for a while. But I want to make sure I have it hooked up right. The way I understand it, the only choice I have is "manual" because of the Allison MT 643.

Both the PRXB and Cruise King Cruise Control are in route. Best part of it is the guy who is doing the installation is knowledgeable with both systems.

Re: Pacbrake PRXB w/ Allison MT643

Reply #14 – October 14, 2011, 06:00:56 pm

Somebody might check the books, on Cummins C series using the exhaust brake, the valve springs need to changed to a stiffer spring. I NO NOT know about the 5.9 B series, but I would expect the same issue as the C engine. Surely some one knows about this valve spring issue ?
FWIW

Re: Pacbrake PRXB w/ Allison MT643

Reply #15 – October 14, 2011, 06:12:54 pm

Dave, you are correct that the valve springs need upgraded even on a 5.9. The cost of the PacBrake in 1998 was $2100 without the addition of the transmission upgrade. The valve spring upgrade was about $1200 according to the old receipts as I recall.

Re: Pacbrake PRXB w/ Allison MT643

Reply #16 – October 14, 2011, 08:02:12 pm

94 up C8.3 had upgraded springs. 93 down check your engine number with Cummins. My 93 neededthem.

Re: Pacbrake PRXB w/ Allison MT643

Reply #17 – October 14, 2011, 10:28:06 pm

Prior to having the PRXB installed this past June, I bought a set of heavy-duty valve springs (they are actually 2 springs, one inside the other) to install in the C8.3 for $160. Labor was quoted at $600, but when they took the valve cover off, there was already a perfectly good set in there. Turns out that a previous owner had them put in but didn't document it. So, I've got a new setof valve springs for a C8.3. if anyone wants to buy them.

So, to answer Dave M's question, yes, if an exhaust brake is to be installed in an early '90's C8.3 Cummins, heavy-duty valve springs should be installed.

Re: Pacbrake PRXB w/ Allison MT643

Reply #18 – October 15, 2011, 11:42:22 am

My 5.9 got the 60 pound springs when the original owner had a Jacobs Extarder exhaust brake installed back in 1996. Installation was at Cummins in Nashville, Tn. Have documentation for that. The coach was extremely well documentated for upgrades and repairs by the first owner, Jack Thomas.

In my research, I found that Cummins is now calling for 65 lb springs as a upgrade to the 60 lb ones. But I have not talked to anyone at Cummins about this and am not going to bother with it. They went from stock 30 lb springs to 60 lb springs for the original exhaust brake, and I can't see the expense for another 5 lbs.

Oh, the operation options are different between the Allison MD3060 and the Allison MT643. The MD3060 allows for the brake to be operated in a automatic mode and interfaces with the transmission, while the MT643 allows for manual operation only and does not interface with the transmission. It is switched on and off by the operator. At least that is what I think I understand.

Re: Pacbrake PRXB w/ Allison MT643

Reply #19 – October 15, 2011, 12:12:10 pm

PatC, As a retired professional truck driver, I would guess you have much experience with the Jake Brake system, My question is concerning the effectiveness of the Exhaust type brake compared with the Jake brake setup.
For me, the DDC engines with the Jake Brake are not real effective unless you are up against the governor in RPM, Have no experience with the Cummins or Cats with the Jake Brake. SO just wonder what your thoughts are along this line.
Thanks.

Re: Pacbrake PRXB w/ Allison MT643

Reply #20 – October 15, 2011, 01:40:24 pm

Quote from: PatC – October 15, 2011, 11:42:22 am

Oh, the operation options are different between the Allison MD3060 and the Allison MT643. The MD3060 allows for the brake to be operated in a automatic mode and interfaces with the transmission, while the MT643 allows for manual operation only and does not interface with the transmission. It is switched on and off by the operator. At least that is what I think I understand.

Pat, I am pretty sure Jeff Savournin's 93, U225, now jor's, had a connection between the PacBrake and the transmission. It had the manual 643 as I recall. Somehow when the PacBrake was powered by the toggle, the transmission lockup was also activated. The on/off activation of the brake flapper was mechanically triggered by the throttle position with a simple on/off electric switch.

Maybe Jeff or Jon will shed more light on the issue.

Re: Pacbrake PRXB w/ Allison MT643

Reply #21 – October 15, 2011, 02:25:00 pm

I had some photos of the whole setup but I lost them with a bunch of others in a recent tech meltdown. Anyhow, the 93 5.9 had a microswitch that was activated when the throttle was in idle position (with the panel rocker switch in the on position). The 643 had been modified so the trans would lock up below 4th gear. In my experience with it, the PAC was ineffective in 4th gear at speed (50 to 55) but very effective in 3rd and 2nd at lower speed and higher revs. On a six or seven percent grade, I would start down at about 45 in 3rd gear, let it build to 50 or so and stab the brake back down to 45. All in all, very little service brake usage. I would say the PAC did an excellent job.
jor

Re: Pacbrake PRXB w/ Allison MT643

Reply #22 – October 15, 2011, 02:27:18 pm

Thanks Jor,

Believe you posted pictures here on Foreforums, but can't locate

Re: Pacbrake PRXB w/ Allison MT643

Reply #23 – October 15, 2011, 06:36:59 pm

Quote from: Jeff Savournin – October 15, 2011, 02:27:18 pm

Thanks Jor,

Believe you posted pictures here on Foreforums, but can't locate

this thread: exhaust brake problem. But they don't come up under his photos.

Re: Pacbrake PRXB w/ Allison MT643

Reply #24 – October 15, 2011, 06:41:07 pm

Am playing to put a switch in the engine compartment to make it easier to lubricated it.

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