Community Forums

deanrd · 03-18-2023, 03:00 PM

I'm not sure what to expect from the exhaust brake. I also have a 2018 F350 6.7L diesel and using the exhaust brake with my 5th wheel is very noticeable, but using the exhaust brake on my MH isn't. What should I expect from it? Max speed to use, proper gear, max rpm? The previous owner told me not to let engine rev over 2k using exh brake or it caused it to dump antifreeze (maybe from engine overheating) Every time I've tried it, it just keeps speeding up until rpms get too high. Just not sure what to expect. It was one of the reasons I wanted a diesel and I don't seem to get benefit.

Thanx - Dean

96 Wideglide · 03-18-2023, 03:21 PM

The previous owner didn't know what he was talking about!

VGT exhaust brake is barely doing anything below 2000rpm.

Transmission will upshift at about 2650rpm. I'm usually briefly using my service brakes at 2500, to drop 500rpm.

Quick68 · 03-18-2023, 10:45 PM

96 Wideglide hit it right on the money. Nothing else to add.
But if you are having overheating issues, that's something to address.

Chef Guy · 03-19-2023, 08:29 AM

Dean,

Upgrade to the PRXB. You will notice a significant improvement, especially in the lower RPMs when the OEM '06 exhaust brake was installed. I never did like nor feel that the OEM exhaust brake did that much either.

Whenever I engage my PRXB on the freeway going 100 Kph (60 mph) it immediately drops the speed, increasing the RPMs and then at approx. 45 mph reduces it significantly again, then again at around 30 mph.

You will notice on the PRXB better response at lower RPMs than the regular exhaust brake. I rarely use my service brakes during stopping, except for the last 50 feet or so. My coach will slow down and almost come to a stop on level ground upon application from 50 mph within 1/4 - 1/2 mile.

Make sure to occasionally lube the suggested lubrication points annually with a high temp silicon based lubricant. PRXB sells one.

I believe one of our members, Nodine, did one of his usual fact based and research based papers on this upgraded exhaust brake. Mine has been bullet proof since I upgraded it years ago. On the original one I had from the factory, I was always sweating bullets coming down long mountain passes.

....former Charter Bus Driver and retired Chef

wolfe10 · 03-19-2023, 08:35 AM

Different comments here based on exactly what kind of auxiliary brake members have on their Cummins B engine:

VGT

Separate exhaust brake

But in any case, 96 Wideglide's advice is absolutely correct.

96 Wideglide · 03-19-2023, 10:18 AM

Quote:

Originally Posted by Chef Guy

Dean,

Upgrade to the PRXB. You will notice a significant improvement, especially in the lower RPMs when the OEM '06 exhaust brake was installed. I never did like nor feel that the OEM exhaust brake did that much either.

Unless his '08 model came with a leftover pre- DPF engines, he got the VGT exhaust brake.
You cant install any kind of flapper valve exhaust brake behind the VGT!

deanrd · 03-21-2023, 12:40 PM

Quote:

Originally Posted by 96 Wideglide

Unless his '08 model came with a leftover pre- DPF engines, he got the VGT exhaust brake.
You cant install any kind of flapper valve exhaust brake behind the VGT!

I don't have to use DEF fluid but I do have some kind of exhaust heater that cycles occasionally depending on driving cycles.

My manual and research says that I'm governed at 2200rpm. Does that mean I can't accelerate past that, but it can still exceed using exh brk?
I obviously need to try a different approach. Maybe I was going to fast at 45mph and expecting to hold that going downhill?

Thanx Dean

wolfe10 · 03-21-2023, 12:52 PM

Quote:

Originally Posted by deanrd

My manual and research says that I'm governed at 2200rpm. Does that mean I can't accelerate past that, but it can still exceed using exh brk?

Thanx Dean

Yes, diesel engines have two "how high is safe" limits:

Governed RPM-- how fast can the engine go under load.

No load RPM-- when not working most engines allow for a higher RPM.

Call Cummins with your engine serial number and ask for BOTH numbers.

BTW, your Allison transmission should be programed from the factory to not allow the engine RPM to exceed these specs.

Cummins 800-286-6467

96 Wideglide · 03-21-2023, 07:05 PM

Yeah, you have either a '07 or early '08 built ISL with a diesel particulate filter (DPF).

Like Brett says, the 2200rpm limit is only while your on the throttle!

Going downhill, off the throttle, with or without your exh brake on, your rpm limit is 2650.

As long as your not already in 6th gear (God help you

), your transmission will automatically upshift to the next gear at that RPM, to protect the engine.

Happycarz · 03-21-2023, 08:16 PM

What color is your engine?

Cummins engines were black until January 1, 2007 when EPA 2007 became effective. With EPA 2007 the Diesel Particulate Filter, DPF, was introduced .

Also, when cummins started producing EPA 2007 engines, they painted them red.

I ordered my 2008 Camelot in April 2007. Monaco had three black Cummins engines left in stock and they gave me the choice of either engine. I took the proven black engine, sans DPF. Hence, I have a 2008 coach with a 2006 engine.

Also, my coach came with a Cummins/Jacobs exhaust brake, not to be confused with the Jacobs engine brake, soon to be changed to a PacBrake.

The red engines, EPA 2007, used the variable geometry turbo, VGT, as the exhaust brake.

So, what color is your engine. Then we will know what kind of exhaust braking you have and answer your questions better.

jarwiebe · 03-21-2023, 09:09 PM

Quote:

Originally Posted by 96 Wideglide

Unless his '08 model came with a leftover pre- DPF engines, he got the VGT exhaust brake.
You cant install any kind of flapper valve exhaust brake behind the VGT!

Not to derail this thread, but curious about your statement about not adding a flapper valve EB behind a VGT. Does this pertain to the Monaco's only?

My Dutch Star on a Spartan chassis (MMGT/Cummins ISL370) came with a Holset VGT part# 3598154 with a Jacobs EB part #3969392 and no EGR valve as seen the the picture.

96 Wideglide · 03-21-2023, 09:18 PM

They don't have your Holset VGT programed to be used as an exhaust brake.
When you turn on the exhaust brake switch, the Jacobs closes, but the vanes in your VGT remain open.

Sinyyl · 03-21-2023, 09:24 PM

I too upgraded PRXB last year. My previous setup has air leak on the actuator, it was not doing much at all. The PRXB on the other hand is much noticeable. It significantly reduced the use of service brakes. However, the braking power is still rather limited. To me, it feels like lightly press the service brake. Because I leave plenty space in front, and usually I drive pretty slow, this level of braking power is enough for me.

One more thing, my exhaust brake do not engage if speed < 20 mph (won't have too much braking power under this speed anyways). Probably, has something to do with transmission and/or engine software.

Happycarz · 03-22-2023, 11:19 PM

If you ever encounter a STEEP decline where you are using 1st gear, select 1st gear on your transmission keypad and the exhaust brake will activate.

Normally it kicks out when slowing down and the transmission drops out of 2nd gear into first.

Before the bridge was built across the Colorado river, you would have to drop down a steep incline, drive across the Hoover Dam and back up the steep other side.

I would to go to Las Vegas twice a year across the top of the dam, and used 1st gear, with the PacBrake, descending either way.