I have a problem. My RPM's are real high. I don't remember what they use to be (haven't driven that much since I bought it 4 years ago) but I'm sure they weren't this high. 65mph is 2800 Rpms, that’s over the rated engine specs.

I made sure my Allison 4 Speed is shifting into 4th. Below is what I feel during shifting.

1st to second, rpms drop o shift. 2nd to 3rd, RPMs drop on shift about 200 or 300 then drop more after a couple of seconds (must be torque converter locking?) then from 3rd to 4th the RPMs drop but I don’t get the 2nd drop in RPMs like I do in 3rd.

I'm not sure if the tranny is acting right?

I didn’t drive for a couple of years. I am almost positive that I use to downshift to get up to speed on a few small hills by my house, now I don't have to downshift. That makes me think the tranny has an issue. At first I thought it was the Tach showing high rpms but now I think it’s the tranny that is causing the high rpms?

Another guy with my Engine and tranny cruises at 1900 rpms @ 60 MPH. We both have same rear end as well.

Now I have 2 places that diesel is leaking on the Intake side (around injector), I'm thinking it's because the engine is screaming to go 60-65mph?

I've noticed on the Barth forum that more of the Barth Motorhomes have the same drive train as I do. I only found 1 guy with a Safari that has the same 8.3 & MT643.

Any ideas or help would be appreciated.
Thanks, AL

Does your Allison have an Extarder tranny switch on the dash? Is it in the "on" position? If so, turn it off. Have you mounted lower profile tires?
Don

Hi Don, I don't have the Extarder Switch. I have a Pac Brake that isn't connected to my Allison.

Fluid looks and smells good, it's about 3 years old but only 1000 miles on it. No leaks.

Tires are 9R22.5

I'm not sure what else besides the tranny that would make the RPMs run so high. I'm sure it want that high when I was driving it a couple of years ago. The engine would have probably blown up by now.

quote:

I have a Pac Brake that isn't connected to my Allison.

1st: 1900 RPM at 60mph sounds right to me. Now: It isn't the transmission. At what RPM do the 2nd, 3rd, and 4th shifts occur - above 1800? Perhaps the PacBrake is closing off the exhaust under acceleration (instead of deceleration, as designed) and the engine is responding to your pressure on the footfeed as it tries to force the exhaust out the pipe as you try to increase road speed??
nb: This is a suggestion, not a knowledgeable statement.

I would suspect the torque converter isn't locking up; possibly one of the tranny sclutches is slipping. What is the tranny temp?

Here are the RPMs is shifting at:

0-12ish MPH 2500ish RPM 1st Gear
12-20ish MPH 2300ish RPM @12mph it shifts to 2nd gear
20-25ish MPH 2300ish RPM @20mph it shifts to 3rd gear
25-35ish MPH 2500ish RPM @35mph it shifts to 4th gear

Roughly this is about the RPMs its shifting.

I can see the RPMs drop twice in 3rd gear, I guess thats the converter lock, but its not happening in 4th.

are all the RPMs too high? Its pushing the MAX on the engine according to specs for the 6CTA8.3

Gunner:
I not only turned off the pac Brake, I also pulled the Air line to make sure it wasn't closing.

Even the low RPMs seem high, I'm not sure?
All shifting is happening well above 1800.

Thanks.

How sure are you that the PacBrake isn't frozen in the almost shut position? Does it move freely over its entire range if you attempt to move it by hand (in place of the air solenoid)?

Mike

Are you sure your tac is correct? Also if you state you rear end ratio I can tell you what you speed vs rpm should be.

The Pac Brake is working good.

With someones suggestion I checked the RPMs with a handheld digital Tach with the peddle to the floor (governed rpms). My dash tach matched the laser tach at 1200 & 1500 rpms. But when I had the peddle pressed to the floor the dash tach is at 3000 rpms and the laser tach is at 2550. So apparently the dash tach is wrong at higher rpms.

I've got a couple of diesel leaks that could be causing me to lose some power and causing the kickdown to be in the wrong place, causing higher rpms. Below are a couple of PICS of leaks. I would like to repair myself if possible. Do the leaks look like they can be repaired in my driveway and not a shop?

Have you tried tightening the injector lines yet? If they don't seal, replacing the lines is a pretty easy job to do - just make sure you reinstall the hold down isolator braces.

Bill, I did turn the 19mm nut just a little bit. I was afraid of stripping it. It's still leaking (maybe not as much).

If there is nothing else that can leak near the top nut of the injector then its probably just the injector line as you say.

Do they sell the injector line and I'm guessing I tell them I need the high pressure line for injector #4?

Also, do you think the leak on the high pressure line at the pump is the same issue as the injector leak? It is only leaking at the top near the nut as you can see in the bottom picture I posted?

Thanks, AL

Chances are good then that there is a hairline crack in the flanged area of the line - replace it.

Here is a little tutorial I did on engine identification for a 5.9L - the same thing applies to the 8.3L too.

ESN or Engine Serial Number. <> CPL or Critical Parts List

You should sign up to the online account that I have posted at that link.

It's the Red and Silver Tag in this image of an 8.3l

BILL NY...I signed up for site. The old owners wrote the ESN in the manual! Sure made it easy.

I found the high pressure fuel line I need.

Does it make sense for me to replace the fuel line first. If the injector still has a leak then order an injector?

Also, where is the best place to buy the fuel line, aftermarket houses make the fuel line?

Thanks, for the link, great info!

AL

You stated that the fuel leaked less when you tightened it up - so a new line should fix the problem.

My guess is there's a hairline crack in the flange of the injector line - nothing is probably wrong with the injector.

Get the line from Cummins and make sure you use the isolators - vibration plays hell on these lines.