When I put the Jake brake on driving on normal streets the Jake slows the unit down when I take my foot off the peddle. When I am going down a steep hill at say 40mph and do the same, the jake downshifts into 2nd gear and the unit drops into 3rd gear but the RPM is nearly 3000, 2800+ or so.

I talked to Service at Cummins South and they did not know how high the rpm should climb, suggested that was high and I should bring it in for a check up.

I suspect I have a 8.3 electronic cummins which could be electronically governed at 3000 rpm but that high of an rpm worries me, I just shut the Jake off and have not used it. I am headed into the rocky mts and would like to use it if necessary.

Tom

"When I am going down a steep hill at say 40mph and do the same, the jake downshifts into 2nd gear and the unit drops into 3rd gear but the RPM is nearly 3000, 2800+ or so."
Your Cummins was available with a transmission retarder as an (expensive) option. This sounds like a retarder instead of a "Jake" or PacBrake. Look at your engine and see if it has a large cylinder mounted on the side of the transmission (driverside); if so, you have a retarder...AAAND if so you MUST change your 6-gallons of transmission fluid YEARLY.
In '96 -and perhaps earlier- the Spartan MountainMaster chassis/w/Cummins that Barth had in inventory came from Cummins with the Pacbrake device mounted on the exhaust manifold, ready for the actuator to be added. If you have a "Jake Brake" it is probably a PacBrake, which is an exhaust brake. (Raise the bed and look at the top of the engine: on top, centerline, is the exhaust manifold; if it has a Pacbrake it will be on top of the exhaust, centered - "Pacbrake" is embossed on the brake valve, staring up at you.) If you have the PacBrake valve on the manifold it doesn't mean it is being used; if it is hooked up the valve arm will have been moving, and it will be obvious. It doesn't seem logical for an exhaust brake to downshift??? I urge you to have it checked. Rocky Mountain Cummins did work for me some years back and I was content with them.
"I am headed into the rocky mts and would like to use it if necessary."
2800-3000 rpm seems high; I would have it checked. ($100 per hour - one hour for a diagnosis- reasonable)

Gunner
Could you explain how the Jacob's extarder works? We have one (I think!) on ours with an MT643 4 speed Allison. I don't have the big Cummins book here, it is in the Barth, but from memory I remember reading about it's purpose but don't know if it actually works. I had the switch in the on position last year on the trip to Arizona but did not notice much of an affect on the down grades. Maybe it needs to be re-programmed? Never had any problems slowing or stopping either so maybe it is just more subtle than I imagined it would be.
Of course, I thought it was an engine brake back then and was expecting more noise from it anyway. I didn't even know there was such a thing as a transmission brake when we first got the Barth!
I would really appreciate all the info on this you could provide.

Tom
Did you use Rocky Mountain Cummins Service in Phoenix? If so, how did you like them? I had a full service done at Massey's last year and I thought they were ok. This year I was going to take the Barth in to Rocky Mountain Phoenix for its service, just to compare. It will be around $450-$500 but for that you should geteverything checked and all new fluids. The report from Massey was very detailed. They even called to report a bent front leveler and said it would be an extra half hour charge to r&r and fix it.
I like that kind of thing. I hate it when you come back to pick up the vehicle and they tell you about a minor problem they could have jumped on, but instead suggest you bring it back a week from Tuesday instead of just getting at it while it's there!
Don

"Could you explain how the Jacob's extarder works? We have one (I think!) on ours with an MT643 4 speed Allison. I don't have the big Cummins book here, it is in the Barth, but from memory I remember reading about it's purpose but don't know if it actually works. I had the switch in the on position last year on the trip to Arizona but did not notice much of an affect on the down grades. Maybe it needs to be re-programmed? Never had any problems slowing or stopping either so maybe it is just more subtle than I imagined it would be."

I know NOTHING about Jacobs; I thought (perhaps erroneously) a "Jake Brake" was an exhaust brake: a restriction, usually a butterfly valve, in the exhaust pipe which lowered the engine rpm which in turn slowed the coach. My "knowledge" dates from 1996 when I ordered my coach and discussed the engine/transmission with the factory; I understood the "retarder" option was Allison (MD3060 6-speed with the retarder is MD3060-R) but it may have been a Jacobs-brand factory accessory.
If you never had any problems slowing or stopping it was working!

I just needed to look at the switch, it says Pacbrake and not Jake brake. I don't know why the tranny would down shift when I turn that on, it should just retard the exhaust. My cruse KC2500 does not work, but I did not check out the box yet to see why.

Need to get that checked out.

Tom

The traditional jake brake is an engine brake. At the top of the compression stroke the exhaust valves are opened releasing the compressed gas and making the engine into an air compressor. These are the noisy ones but very effective.

The small Cummins (B & C) engines have no provision for an engine brake, so the advent of the exhaust brake. This plugged up the exhaust pipe. They are programmed to downshift the transmission when activated as higher engine rpms means much better braking. 3000 rpms sounds a little high, but keep in mind you are dropping two gears. You must have a stone-bennet air shifter that is electricly controlled. You could simpy remove the wire from the exhaust brake to the stone-bennet and down shift it your self or you could probably change it to drop to 3rd.

I would be very surprised if you have a retarder in a rear engine setup as they add length to the transmission and there is litte extra room available

Gary, thanks for that info. I am not sure which engine I have but according to Cummins a 8.3 electronic is governed at 3200, my tack only goes to 3000. Another engine was maxed at 2800 rpm which is about where I let my engine to up to before I shut the switch off. How do I find out which engine I have? It is an 1998 8.3 325hp and in 97 Cummins started the electronic engine.

How do I manually down shit the tranny? I only have three buttons, D, N, R?

Another question? The Cummins guys told me I have a broken bolt on the exhaust manifold, would using the Pacbrake accelerate the need for repair. They told me to wait until it was leaking as it could be easy or difficult to fix, depending on how the broken bolt comes out. If they could not get it out it would require a new head and turbo for several grand. Or it could be easy if the bolt came out. The said it could be ok for years or break next week, no way of knowing for sure.

Tom

Can't comment on the broken bolt, but if it were me I would try and remove the exhast manifold. Would try and replace the bolt before getting a cracked manifold.

My stone bennet only has a toggle switch. When in drive I can pulled back one click and it will drop down one gear. Now this applies to the 600 and 700 series. The 6 speed should have a similar method. The 2000 series I put in the barth uses the 542 cable shifter, but drive is both 4th and 5th gear, so I have an overdrive switch on the dash.

The electronic controlled engine was the 4 valve per cylinder and was known as the ISC for the 8.3 and ISB for the 5.9 liter.

I found the serial number on the work order from Cummins South. I logged into the cummins site with the serial number and this is the info it gave me:

Engine Dataplate
BASE ENGINE INFORMATION
Upfit Original
Engine Serial Number 45151329
Shop Order # SO84419
Plant CNS - CONSOLIDATED DIESEL CO.
Build Date 06 Mar 1995
Warranty Start Date
Customer Number 75147
Customer Name
ECM Code Not Available For This Engine
Fuel Pump Part # 3922425
Fuel Pump Calibr.
Film Card Z
Engine Config # D413024BU01
CPL # CPL2102
Model Name C8.3-BUS(300)

So it seems the engine was built in 1996 and is listed as 300hp. I could not get any operating specs off the web site, such as rpm, temp, oil pressure. They don't seem to offer operating info other than general stuff like don't run it too fast. I also don't know what CPL number is or Config number, anyone know?

They also state there is a wait to start light for cold weather and that the engine is equipped with a Flame starter. I don't have a wait to start light on my dash, is it burn't out? Does any one else have a wait to start light?

Tom

"They also state there is a wait to start light for cold weather and that the engine is equipped with a Flame starter. I don't have a wait to start light on my dash, is it burn't out? Does any one else have a wait to start light?"

The "wait to start" light is for engines equipped with a "glowplug". Yours literally has a "flame start" which injects a mist of fuel into the intake and lights it off - a great, very effective diesel starting technique. DO NOT EVER USE ETHER (or equivalent) AS A STARTING AID!! Since you don't have a glowplug Barth had no need to install a "wait to start" light on the dash.
Also: The "300" refers to an engine family (there is also a "400" which may be 350hp or 400hp); yours may be 325hp and be called a "300"; the actual engine label will signify hp. Cummins shipped two books with each engine; one is "service" and the other is detailed instructions for repair. Perhaps these are available to purchase from Cummins??

Engine Config # D413024BU01 is the bill of materials listing. It defines which injectors, turbo, etc. that makes up you engine.

300 is probably the rated HP. As there is no EMC (engine control module) available you have a 12 valve mechanical engine. You can hot rod this engine to well over 400 HP using Cummins parts. The problem with doing so is the transmission will probably complain if you go over 350.

How do I manually down shit the tranny? I only have three buttons, D, N, R?

Your phrasing is perhaps a Freudian slip related to your 3000 rpm downshifts. Anyhow:
You have a flat panel; on the left are touch pads labeled D-N-R (top to bottom) with a display above "D". When you start the engine "N" appears in the display; when you touch "D" the xmission shifts into 1 and the numeral 1 appears; you are now in "Automatic". On the right side, at the same time, the numeral 6 appears in the other display which is above "up" arrow and "down" arrow touch pads. The 6 will remain as long as you are in "automatic shifting" mode, as it is the highest gear available. As you drive, the transmission will shift and as it does the leftside display will show 2,3,4,5,and 6 corresponding to the gear; as the gears change so the numerals -up and down.
One downshifts by pushing the down arrow, which determines the highest gear available - as one pushes the arrow, the "6" on the right will drop one gear for each arrow push. Meanwhile, the numeral on the left continues to show the actual gear being used. Upshifts are accomplished by pushing the "up" arrow. The arrows select which gear is to be used - a "manual" shift device- e.g. the down arrow is pushed twice to select 4 when going down a steep grade. Remember to use the "up" arrow to select 6 and go back into "automatic". If one wants to remain in first gear, push the down arrow until "1" appears.
Familiarize yourself by cruising in 6th at about 1700 rpm and push the down pad - it will downshift to 5th and the tach will go up; slow down to about 1600-1700 rpm and touch the down arrow again, and it will downshift to 4th. Touch "up", and it will upshift back to 5th.
Separately: Pushing the "up" and "down" pads simultaneously presents a diagnostic code in the display, e.g. "low transmission fluid".

I don't know if I am losing my mental abilities or not. Some of my questions have been down right dumb. I have looked at the transmission shift pad for over 2 months now and HAVE NOT seen the two arrows for up and down on the pad. They are right there in plain sight. I also had the question on the jake or pac brake and right on the switch was written pacbrake.

I hope you guys bear with me, I may I recover soon.

Tom

Too much Thai food. Or maybe TFETL. That was the acronym for Too Far East Too Long we used 60 years ago when people were "going Asiatic." Then again, when I do stupid things, I just refer to it as "a case of advancing maturity."

"I would be very surprised if you have a retarder in a rear engine setup as they add length to the transmission and there is litte extra room available..."

The Allison book says specifically the Retarder does not add length to the MD3060 transmision - it is all internal.
Also: Maximum RPM is 2800. Also: Minimum engine oil pressure under load is 30psi. (I know; this is waaaayy removed from the majority of Barthboys, but it is part of the family.)