Supplemental Brakes

Topic: Supplemental Brakes (Read 1200 times) previous topic - next topic

Supplemental Brakes

August 16, 2018, 01:40:03 pm

My wife and I recently purchased a 93 GV U280 and are about to be full-timing it. We are wanting to head towards the mountains but I realized (a little late) that our coach does not have any type of supplemental braking system. After doing some research we found that a PRXB exhaust brake was probably our best and only option. However we discovered, after calling Cummins, Freightliner, MOT, and several RV and fleet shops that an aftermarket brake system is not something they will install due to liability issues. I am new to driving one of these rigs and do not want to put my family at risk, the thought of brake failure coming down a mountain is concerning. Are these rigs designed to be driven in the mountains without a supplemental braking system or should we avoid any steep grades?

Thank you

Re: Supplemental Brakes

Reply #1 – August 16, 2018, 01:54:06 pm

Welcome to the ForeForum.

I would contact PacBrake-- they should have a list of shops in your area who are authorized to install their exhaust brake.

Let us know where you are and someone may have a recommendation.

Re: Supplemental Brakes

Reply #2 – August 16, 2018, 02:04:57 pm

Thanks for the quick reply, we will contact them for sure. We are in the Tulsa area.

Re: Supplemental Brakes

Reply #3 – August 16, 2018, 03:21:53 pm

Your coach has a 647 Alison trans. The torque converter locks up in the upper third gear and in fourth gear.

In the lower gears the engine and trans slip versus each other.

So a pac brake would be less effective and might cause trans heating in the non lockup ranges.

Always wondered if an Allison shop could change the torque converter lockup safely on your trans.

Good luck with your adventure

Re: Supplemental Brakes

Reply #4 – August 16, 2018, 04:08:05 pm

Soft,

We had one on our '92 and it worked fine when we were in the mountains.

If you are a tinkering king of person it isn't that hard to make this a DIY. The hardest thing about it is you need to research as to what PRXB is properly set up for your engine. The wire run from back to front is already in the wire loom. You should even have a blank switch hole in the console for the switch. You will have to modify the exhaust pipe which will require a weld (or it did on our coach) If you can't do this one thing any muffler shop will be able to fix you up.

Mike

Re: Supplemental Brakes

Reply #5 – August 16, 2018, 04:58:03 pm

Thanks for the replies everyone. Ours has the 4spd and the 8.3 cummins. I've read that the exhaust valve springs would need to be upgraded if we did a pac brake. Has anyone else heard this? We're fairly handy with certain things but I'm not sure we could do this considering the risk involved.

Re: Supplemental Brakes

Reply #6 – August 16, 2018, 05:22:01 pm

We drove a 35 foot GM 4107 ex-Greyhound bus conversion for years all through the mountains in the west without any additional braking system. We even had a VW Rabbit as a toad. You do have to pay attention but Greyhound probably put a million miles on our bus without crashing it.

Our 1993 U300 does have a Jake brake and I love it but would not have any problem driving without it. I do check air pressure at the top of steep grades and keep it in a gear that keeps the RPM high so the Jake is effective.

Fitting an exhaust brake would probably be the most cost effective solution. A Jake could be fitted but would require more $$.

Pierce

Re: Supplemental Brakes

Reply #7 – August 16, 2018, 07:41:48 pm

Quote from: The Soft Boulders – August 16, 2018, 04:58:03 pm

I've read that the exhaust valve springs would need to be upgraded if we did a pac brake. Has anyone else heard this?

A quick call to Cummins with your engine serial number will tell you the max permissible back pressure.

Suspect PacBrake has the same information.

Let us know the answer-- if too low, not worth the $$.

And, no a Cummins 8.3 (C engine) can not be equipped with an engine compression brake. So an exhaust brake is the only choice.

Re: Supplemental Brakes

Reply #8 – August 17, 2018, 01:11:01 pm

The gentleman at Pac Brake told us that the MT647 does not have lock-up and that an exhaust brake wouldn't do us any good. And that he did not want to sell us something that wasn't going to work. We didn't want to persist until we get some more info. Some of the Allison paperwork that we have say it has 3rd and 4th gear lock-up but I may be misreading it.

Re: Supplemental Brakes

Reply #9 – August 17, 2018, 02:01:10 pm

Please confirm exhaust brake functionality with your transmission with Allison: Allison help line 800 252 5283

Have not worked on that transmission, but it is my understanding as well that it has a torque converter lock up in 3rd and 4th gear.

Re: Supplemental Brakes

Reply #10 – August 17, 2018, 02:02:49 pm

You are correct. Mid third and all fourth is lockup.

Feels like it shifts four times. Third "feel" is the trans lockup.

Third lockup always may be an Allison option. The trans maybe adjustable.

You would have to know where the trans is in the lockup setup.

No indicators from Foretravel on gears.

Re: Supplemental Brakes

Reply #11 – August 17, 2018, 03:20:58 pm

Just got off the phone with Allison and they said that our transmission, based on the serial number, was a lock-up type and that we can have the TCM re-calibrated to lock up in as low as 2nd gear. Awaiting a call back from the local shop that Allison recommended to have that done. Also found out from Cummins that our installed valve springs were pt# 5292625 but they were unable to tell me if they were the heavier-duty one or what the maximum back pressure was. I will call Pac Brake again once I get conformation on the TCM calibration.

Re: Supplemental Brakes

Reply #12 – August 17, 2018, 03:30:12 pm

It's easy to tell if you have lockup in 3rd and 4th. Like Bob says, it seems to shift 4 times and feels like you have 5 speeds.

Ours has lockup in 2nd, 3rd and 4th. It shifts from first to second and then makes another pretty firm shift into second lockup, then to third and fourth so it feels exactly like a 5 speed. You can't miss the third to third lockup on your coach. Ours really flies once into lockup. It's just a matter of programming to make it lock up in second gear. A good deal and will make the coach faster.

The exhaust brake should work fine on your transmission. It will be just a little less effective in the non lockup gears.

Pierce

Re: Supplemental Brakes

Reply #13 – August 17, 2018, 03:45:50 pm

Quote from: The Soft Boulders – August 16, 2018, 01:40:03 pm

My wife and I recently purchased a 93 GV U280 and are about to be full-timing it. We are wanting to head towards the mountains but I realized (a little late) that our coach does not have any type of supplemental braking system. After doing some research we found that a PRXB exhaust brake was probably our best and only option. However we discovered, after calling Cummins, Freightliner, MOT, and several RV and fleet shops that an aftermarket brake system is not something they will install due to liability issues. I am new to driving one of these rigs and do not want to put my family at risk, the thought of brake failure coming down a mountain is concerning. Are these rigs designed to be driven in the mountains without a supplemental braking system or should we avoid any steep grades?

Although I have never driven your model of coach, I think the answer to your last question is yes about driving in mountains and most roads are usable by big trucks. Just select a lower gear that will keep you from having to ride the brakes, and don't worry about any traffic backing up behind you. Pull over when possible to let traffic pass. Supplemental brakes help you descend a bit faster than without. Topic seems to have gone off track with a lot of technical talk.

Re: Supplemental Brakes

Reply #14 – August 19, 2018, 10:16:57 am

We also have a 1993 U280 and have driven it through the mountains (Canadian Rockies, coast to prairies) several times (without and with a functional PacBrake) The first two times was without the Pacbrake and I did downshifting in manual mode wherever I needed it. I was also very anxious about using the brakes since I had been told by the mechanic who worked on our unit for the previous owner that the cost of redoing the brakes was significantly expensive (multiple thousands of dollars)!
The second trip through with a functional ( I had to redo some of the wiring connections and reconnect the switch) PacBrake was much more relaxing. Downshifting was assisted with the PacBrake exhaust brake and I only had to use the brakes three times coming down from one of the four mountain ranges in the Rockies.
I believe that having the exhaust brake has provided not only peace of mind but added untold life to our brakes.

Re: Supplemental Brakes

Reply #15 – August 19, 2018, 11:17:05 am

My mountain tamer exhaust brake (no longer in business as the owner passed) uses a guillotine exhaust valve and a 1" pipe external bypass is effective as how far you can close the valve is controlled by a lever next to the shift lever and has an exhaust manifold pressure gauge to help prevent you from floating the exhaust valves and possibly destroying the engine. It's all automatic and idiot proof if you don't move the lever past the max position, but additional exhaust braking can be used by careful modulation of the lever and vigilant monitoring of the exhaust manifold pressure, but in reality who has time for that during a grade decent. Could be used in an emergency. In the idiot proof position with the 10.6 liter cat service brakes are normally not engaged until about 30 mph. Still working but have no idea how complex or what controller it uses. Engages automatically when you lift off of the throttle, if switched on. Rolling hills you can switch it off and let your speed drift some.

Re: Supplemental Brakes

Reply #16 – August 29, 2018, 07:31:46 am

I called the place that Allison recommended and was assured that the MT647 does not have a TCM to recalibrate but that the lock-up could be adjusted by changing out some springs somewhere in the transmission. He said however that there was no way to know exactly how it would change without driving it after doing so and that the process would need to be repeated until we got the desired results. Unfortunately it would be 3 hours labor each time the springs were adjusted. He also said that, to his knowledge, it could not be set up to lock in 2nd gear. I don't know who is correct or who isn't and I apologize for perpetuating any misinformation.

Re: Supplemental Brakes

Reply #17 – August 29, 2018, 08:23:59 am

Quote from: The Soft Boulders – August 29, 2018, 07:31:46 am

I called the place that Allison recommended...

It sounds to me like that shop doesn't want to mess with your coach, for whatever reason, and are making excuses. Are there any other Allison shops within reasonable driving range of your location? I think a second (qualified) opinion would be in order, before you give up on this idea.

Re: Supplemental Brakes

Reply #18 – August 29, 2018, 08:55:49 am

You may also check around and see if there are any diesel performance shops around, they may be able to help you. Some of there guys know their stuff. Like Chuck said sounds like someone doesn't want to work on your coach.

Re: Supplemental Brakes

Reply #19 – August 29, 2018, 09:42:15 am

Quote from: The Soft Boulders – August 17, 2018, 03:20:58 pm

Also found out from Cummins that our installed valve springs were pt# 5292625 but they were unable to tell me if they were the heavier-duty one or what the maximum back pressure was.

Regarding your valve springs...

There is a fairly simple way to determine the rating of your valve springs. You can register your engine at Cummins QuickServe Online. It is a free, no charge service provided by Cummins...all you need is your engine serial number. This is found on a data plate affixed to the cover on the front of the engine. Standing at the back of your coach, facing the engine, look right below the A/C compressor mounting bracket - should see a black metal plate stuck to the sheet metal cover.

Once registered at QuickServe, you can pull up a wealth of info on your specific engine. This info was generated at the time your engine was manufactured, and stored for posterity in the Cummins database. It is a very interesting site - well worth a visit from all Cummins engine owners.

One of the pages listed under "PARTS" will show a line diagram of your cylinder head and all the components, including the valve springs. It will give the part number, which should match what you got from Cummins (5292625). There is a "Remarks" section on each parts diagram page, and this is where you can really find some good info.

For instance, the valve springs in my particular engine are listed as part number 3906412. In the remarks, it says these are "Standard" and also says "Exhaust Valve(PSI): 30". So my valves came from the factory with the standard 30# springs. Of course, it is always possible that the springs were replaced by a prior owner, but my coach records do not mention that fact, so I assume that I've got the standard springs.

You should find similar info for your engine - all you have to do is sign up!

Cummins QuickServe Online

Re: Supplemental Brakes

Reply #20 – August 29, 2018, 12:38:58 pm

I will do some more checking around to see if anyone else is able or willing to work on it and will also sign up on the Cummins registry. Thanks again to everyone for all of the help!

Re: Supplemental Brakes

Reply #21 – August 29, 2018, 04:37:40 pm

No need to pull the head if you have to replace the springs. Bring piston close to TDC with both valves closed. Have a injector replacement air chuck fitting installed so you can pressurize the cylinder and then use a ebay $10-$15 tool to remove spring, retainer, keepers. With piston close to TDC and valves closed, if you make a mistake, the valve won't drop to the bottom of the cylinder. Replace valve seals at the same time. Don't use a socket with a hammer as that scars the valve stem and will shorten valve seal life.

Pierce

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