Bus for the Mountains: 35' RE Cummins 5.9 w Allison MT643

[Mgnmpi]

Greetings Fellow Travelers...

We are bus shopping for a full-time rig that will do well in the mountains. My lady has a remote job that requires she live in Colorado. We are currently looking at a 1997 35' Rear Engine Bluebird with a Cumming 5.9 and an Allison MT643 and 190k. I don't know what the rear end ratio is. While I would prefer a Cummins 8.3 with at least one overdrive and an exhaust brake, this bus is gutted and already has the roof lifted 20". My questions are:

How well will this 5.9 and 643 do in the mountains?

Once fully loaded will the 5.9 be big enough?

It does not currently have a Jake Brake - will this configuration allow one to be installed, or will downshifting be enough to handle descending a miles long 6%+ grade without it?

Is 190k just too many miles for this combo already?

I would love to hear from some folks who have a RE 5.9 and 643 with experience in the big bad rocky hills.

Thank you kindly!

 

[Iceni John]

The Cummins 8.3 / C-series cannot accept a Jake brake. You could use a Williams exhaust brake with it, or a Telma (or similar) electromagnetic retarder on the driveshaft. Only when you get to the big-block 14-liter Cummins such as the 855 can you have a Jake brake, and for that you'd need a Crown or Gillig...

 

[Drew Bru]

If you're still shopping, then look in Colorado or other Rocky Mountains states. I believe CO buses are spec'd for mountain driving and all have secondary braking systems (ours has a Klam retarder). It'd probably be cheaper to buy one so equipped than adding something later on.

 

[Booyah45828]

5.9 in 97 would be 6bt. No issues with that, except for a few odd ones here and there(KDP, etc). With the inline pump, you can bump the power up to something unusable/unreliable, so I wouldn't worry about that.

Make sure it actually has a 643 and not the 545, as in crawl underneath and verify. Don't take a sellers word for it. They made buses with a 545 10 to 1 then with a 643. And sellers will often list things incorrectly and claim ignorance as to the reason why, while you're stuck with a less desirable bus because of it, or at the very least, a headache in return/refund process.

Telma retarder is the way to go, or change to a mtB643 and gain a brake there. No need for jakes on a small displacement engine, they just make noise, and then wouldn't work at all if the converter isn't locked. Same deal with an exhaust brake. Telma unit has no such issue, neither does the allison retarder.

You'll have a hard time finding a bus that doesn't have 100k+ miles on it. And if it is less, be wary, as there is likely a reason why(lemon).

 

[Mgnmpi]

The Cummins 8.3 / C-series cannot accept a Jake brake. You could use a Williams exhaust brake with it, or a Telma (or similar) electromagnetic retarder on the driveshaft. Only when you get to the big-block 14-liter Cummins such as the 855 can you have a Jake brake, and for that you'd need a Crown or Gillig...

Thank you for this. I love rabbit holes and just went down a deep one re Jake vs Exhaust vs Retarder. Knowledge is king.

 

[Mgnmpi]

If you're still shopping, then look in Colorado or other Rocky Mountains states. I believe CO buses are spec'd for mountain driving and all have secondary braking systems (ours has a Klam retarder). It'd probably be cheaper to buy one so equipped than adding something later on.

We are indeed shopping in Colorado, but turns out this bus is from western Washington state... therefor no mountains. Gonna seek out a bus prebuilt for the big hills. Thank you!

 

[Mgnmpi]

5.9 in 97 would be 6bt. No issues with that, except for a few odd ones here and there(KDP, etc). With the inline pump, you can bump the power up to something unusable/unreliable, so I wouldn't worry about that.

Make sure it actually has a 643 and not the 545, as in crawl underneath and verify. Don't take a sellers word for it. They made buses with a 545 10 to 1 then with a 643. And sellers will often list things incorrectly and claim ignorance as to the reason why, while you're stuck with a less desirable bus because of it, or at the very least, a headache in return/refund process.

Telma retarder is the way to go, or change to a mtB643 and gain a brake there. No need for jakes on a small displacement engine, they just make noise, and then wouldn't work at all if the converter isn't locked. Same deal with an exhaust brake. Telma unit has no such issue, neither does the allison retarder.

You'll have a hard time finding a bus that doesn't have 100k+ miles on it. And if it is less, be wary, as there is likely a reason why(lemon).

What do you mean by "6bt"?

I will certainly crawl under the bus to double check everything listed. That is a great idea. Thank you!

Seems like an electromagnetic retarder is the way to go, with an Allison transmission retarder being second, and exhaust being 3rd.

 

[Booyah45828]

6bt is the engine model.

The "5.9 cummins" came in a handful of different iterations over the years. 6bt is the iteration of the 5.9 that that bus likely has, and would be referenced when searching for more info if you needed it.

No retarder is cheap, but they're invaluable when in a situation that they're needed. A lot of your buses used in the mountains can have them already installed by the district. Might save you some coin if you locate one of those vs buying a new/used retarder and having it installed.

 

[Mgnmpi]

6bt is the engine model.

The "5.9 cummins" came in a handful of different iterations over the years. 6bt is the iteration of the 5.9 that that bus likely has, and would be referenced when searching for more info if you needed it.

No retarder is cheap, but they're invaluable when in a situation that they're needed. A lot of your buses used in the mountains can have them already installed by the district. Might save you some coin if you locate one of those vs buying a new/used retarder and having it installed.

Gotcha. Thank you kindly, B.

What are your thoughts on the 5.9 in the mountains?

And in regards to the mtB643, I am assuming that uses some sort of fluid redirect to slow the transmission (?)... besides heat buildup and more regular fluid changes, what are other the downsides / upsides compared to an electromagnetic retarder?

 

[sportyrick]

I didn't go with the 6BT because it's only 359 cubic inches and with my bus weighing in at 26,000# I did't think it would have the ass to haul that much weight up a mountain, I installed a DT 466 and am loving it.

 

[Elliot Naess]

https://www.skoolie.net/forums/f33/how-to-tell-at545-from-mt643-w-pix-and-specs-1641.html


Identifies 545 versus 643.

 

[Booyah45828]

Gotcha. Thank you kindly, B.

What are your thoughts on the 5.9 in the mountains?

And in regards to the mtB643, I am assuming that uses some sort of fluid redirect to slow the transmission (?)... besides heat buildup and more regular fluid changes, what are other the downsides / upsides compared to an electromagnetic retarder?

Preference would be something with larger displacement/more hp. But if you found a bus that you love, and it has an mt643, and it's a good deal, then I wouldn't pass it up.

Some of your smaller engines will get you by, simply because they can be modded to make more power then they originally had. The 6bt is one of those I feel can.

Yes, fluid flows into the retarder housing and is then pumped/sheared to absorb energy. The energy turns into heat within the fluid, so additional transmission coolers are needed. There is a slight delay between activation and engagement with hydraulic retarders, whereas electronic units are instant. A benefit though, is that hydraulic retarders are mounted on the transmission, and require no modifications to the driveline to install. The MT643 and MTB643 are the same length. Whereas an electric unit will require different driveshafts.

 

[s2mikon]

I have the MTB643 and I can tell you that it works real good in the mountains, but there is a small learning curve as in all machinery. I installed over sized coolers for the retarder and the main transmission and that gives you longer uses at a time. You still have to use proper down hill driving skills though. Heavy vehicles on mountain grades and driving HUA is a good way to earn a dirt nap. If you go up the hill in second you come down in second. The larger the displacement of the engine the better it is cumming down.

 

[Mgnmpi]

I have the MTB643 and I can tell you that it works real good in the mountains, but there is a small learning curve as in all machinery. I installed over sized coolers for the retarder and the main transmission and that gives you longer uses at a time. You still have to use proper down hill driving skills though. Heavy vehicles on mountain grades and driving HUA is a good way to earn a dirt nap. If you go up the hill in second you come down in second. The larger the displacement of the engine the better it is cumming down.

This is good to know. Thank you for you input. What engine do you run in your rig and how do you find it handles going up the slopes?

 

[ism minerals]

Just to give you an example. I have a 3126 with 210 hp /605 ftlbs of toque.

5.39 rear ratio and 11r22.5 tire. It does 25-35mph uphill on 7-8% grades pedal is to the floor. So it slow going up hill and down hill is always fun without exhaust or retarder brakes . I take it easy, but would love to be able to do 40-45 mph uphill on some of those grades as i know it will be some time before going back down. Maybe time to upgrade the cat to a higher Hp/Tq configuration. if looking at a cat 3126, make sure it is at least 250HP, as they are easily rerate to 300hp motors, although cooling might be an issue.

 

[kulbuskid]

Ha

Most all D.O.T laws came into effect 1989 and 1990 due largely to the 5.9 Cummins diesels that were being produced in 1988,89,90.
People were running down the road back in those days with 36 and 40,000 lbs on flatbed and were circumventing the weigh stations.

All of the 5.9 Cummins engine will do whatever you want as long as you keep an eye on the egt's.

You can load a 5.9 down with as much as you can put behind it and it will go up all grades, again as long as you keep an eye on the egt's.

The parts for the 5.9's are night and day difference from the 8.3.

AutoZone, oriely auto, advance auto and NAPA will all have your filters, and parts for the 5.9 motors.
Parts for the 8.3 motors is a whole other ball game and you are in a whole different price range as well.

8.3 parts are gonna be at your local semi truck repair shop and are going to cost a whole lot more.


The brakes on a TC2000 have beast of a brake system. Massive drums with nice half moon shoes.

Same exact style as firetrucks, trash trucks and semis..

In appearance the brakes are perfectly capable of keeping control and any amount of grade.

Just takes a good conscientious driver to keep in mind proper braking.
This style of braking is taught in CDL school which is basically what these vehicles are.

 

[shorthair-SKO]

With the 6bt Cummins for which mods are easy and pretty darn reliable, most exhaust brakes ( shutter style ) require 60lb exhaust springs to prevent damage. The P7100 pump will tolerate lots of tweeks though at some point in your quest for more power you will need to replace the head bolts with studs and a performance head gasket.
I know several of these 6bt's with 500,000 miles and still going strong.

 

[Mgnmpi]

With the 6bt Cummins for which mods are easy and pretty darn reliable, most exhaust brakes ( shutter style ) require 60lb exhaust springs to prevent damage. The P7100 pump will tolerate lots of tweeks though at some point in your quest for more power you will need to replace the head bolts with studs and a performance head gasket.
I know several of these 6bt's with 500,000 miles and still going strong.

Do you know how I can determine what sized exhaust springs are in this 5.9 cummins? I assume they are still stock. At this point my primary goal will be going slow down the mountain, not up it, though an eventual upgrade in power would be nice.

 

[Golden_Otto_Bus]

So I live in Golden Colorado and drive a 30' 2003 Bluebird TC2000 with a 5.9L cummins 24 valve diesel, I believe it has an Allison AT-545 transmission. My weight is currently running around 18k lbs. What I have seen with my rig over the mountain passes is that I can usually stay ahead of the semi's out there. I can pass them if I have the passing lane (interstates). So basically I am not the slowest rig on the highways. Even towing my jeep wrangler I can still stay ahead of the semi's.
I of course downshift going down the passes and try to keep it slow and use brakes sparingly. The worst I have experienced is I-70 through the Colorado mountain passes - worst roads I have ever seen - huge ruts, lack of painted lines, ahhhhhhh. But just keep it slow, down shift, etc. Jakes brakes would be awesome if possible though.
Good luck.

 

[Booyah45828]

Again.

A retarder, whether electric or hydraulic, is much better suited for grade descent on a bus.

If your trans doesn't have a lockup clutch, the braking effort the engine applies is very little due to the unlocked torque converter. I wouldn't even bother with an exhaust brake or compression brake.

With a lockup clutch, it's much better. But the problem with those is that most mechanical allisons will only apply the lockup clutch in 3rd or 4th. So if you're downshifting into 1st or 2nd on a grade, the lockup won't be engaged and braking effort will be similar to an at545. An exhaust brake is better then nothing, but not even close to the effect that an electric or hydraulic retarder will have.