Thursday, April 24, 2008

Allison Transmission Problems-Hard Shifting

Allison Transmission Problems vary and one typical complaint is hard shifting. I recently looked at a 1999 Thomas Saf-t-liner [pusher] with an Allison MD 3000 series transmission. It had a hard shift into 2nd gear and a hard downshift as well. No codes came up so it was time to check the mechanical side and do a clutch pressure test. The test has to be turned on "enable clutch test" with the "ProLink" so each shifting range can be turned on with the unit running in the shop.
The pressures are compared to main convertor pressure and sits around 270 psi on this test. The individual clutch pressures must be within 5 psi. If there is a big difference that tells us the clutch itself is worn or there is a hydraulic problem. This test revealed no problem in this area and one conclusion could be a clutch that has to be physically inspected for imperfections. There is always 2 clutches applied to get a forward gear in this case it's C1 and C4 for 2nd gear.
The next step is a big one, whether to disassemble the trans and inspect for problems or live with the hard shift. I tried to "fast adapt" the shift parameters with the "ProLink" which did not change anything. This is one of the allison transmission problems you might encounter, if we get into this project any deeper I'll keep you posted.



22 comments:

Anonymous said...

Hi John, My name is Chris. I have a Blue Bird bus, International 3800. It has a 6 cylinder, 360 cu. in. 170hp diesel engine. I don't know what the transmission is. My problem is that the transmission will slip out of gear constantly. If i turn the engine off and start again it will go. I got it home this way but would like to know if you know what the problem might be?

Thanks'
Chris

Anonymous said...

Hey John Whelan,

I noticed you "fast adapted" the shifts but it does not say anymore. I recommend re-setting to unadapted shifts first and then running fast adapt, generally you will see much better results especially for harsh shift concerns. Just a thought, good luck!

Mike

John Whelan said...

The fast adapt was to focus on that particular range but it did not work. Resetting unadapted shifts works as well [takes awhile to get it all done]but I haven't been 100% percent successful with that mode either. In this case we're thinking it's mechanical. Next step might be removing trans. for repair.
Thanks Mike for your input, your always welcome to comment...

Rob said...

One suggestion is to document your pressures with the unit cold, warm it up, and compare the numbers again.
The thinned oil will show a differential pressure drop that will help zero in on a problem.
You are looking for a major drop(75-100+) in psi to find the faulty clutch leak.
Anytime you see more than 100 rpm difference between input rpm and turbine speed rpm, C3 or C4 clutch are dragging(physically damaged)ie burnt and cupped. This causes the C1,C2 rotatig clutch to slow giving the rpm seperation. It can't be fixed from the outside. This is done in neutral position at idle, warm oil
Chris You must find out what model you are dealing with before anyone can help zoom in on a problem. There are a few different models used in that app.
I hope I'm not stepping on anyones toes.
There is a more accurate way to nail down clutch seal on the Allisons.

Rob said...
This comment has been removed by the author.
John Whelan said...

Thanks for your input Rob,it's related to the post and good info.

We finally got the hard shift out by "resetting unadapted shifts" it took a couple of hours of running around but finally cured the problem.

Gary said...

Thanks for your info John. Will a possible electrical issue show in the code check or will further diagnosis be needed to track it down?

Thanks....I don't believe this is in the same area as my original post..still learning to navigate around

John Whelan said...

Gary,
All you will get is a 4 digit code. Send it to me and I can tell you what is is.

It could be a bad sensor sending the wrong info to the ECU as I mentioned before.

Do a "search" in the top left field of this blog homepage for "allison transmission" and you will get all my posts on this subject.

If there are no codes then you might be facing a mechanical issue.

jewhelan@telus.net

Gary said...

John

I ran the check for codes using the shift pad and there were no codes. Sounds like it is a mechanical issue. It looks like a trip to an allison shop. Are there any specifics checks I should ask for? Also, other than it is annoying, do you think there would be any harm to the transmission in not fixing the problem?

Thanks

Gary

John Whelan said...

The check you need is a clutch pressure test. This will tell you if you have wear in your clutch packs.
An intermittent problem isn't something you have to get on top of right away. It depends on how hard the rough shift is and how long you are intending on keeping your vehicle.
We had a bus that had a hard shift into 2nd (intermittent) and let it go until it went to auction.
If you take it to Allison get the condition analyzed and find out cost of repair. Then you can make a decision on which route to take.

Gary said...

Thanks John. Looks like a trip to the shop. I was hoping it was the easy fix.

Is it possible to simply not use first or lock it out? I know in the newer Sportchassis RV haulers, they have somehow locked out or disabled first.

Thanks

John Whelan said...

Hi Gary,

There's no way to disable a range in these transmissions. It's possible to add a gear through the dealer (reprogramming) but that's about it.

Good luck.

Sydeny said...

i have a 1999 gmc with a 3126 cat and 3rd and 4th gear sounds like the clutches are coming together to enguage next gear and they have no fiber between them this noise just started a couple days ago?? Im not sure I changed the filter and fluid and cut the filter open and saw nothing

John said...

If there is no wear material in the oil or filter I would check the codes on the trans. shift pad.
Push both arrows together with the key on for the 4 digit code. let me know if any what the code is and I can let you know what it is.

Sydeny said...

I am not sure how to pull the codes but I am very familiar with pulling codes and engine diagnostics but on cars and trucks , medium duty is all new except changing parts. is there an obd2 connector or a connector on the trans thanks for any help you have to offer
Dan

John said...

You need a Pro Link to plug into the data link connector but if there is an active code from the shift pad you will be given a 4 digit number like 24-11 0r 35-00 etc.
There may be a signal problem in the wiring to a shift solenoid for example. We've had several wiring issues with these transmissions.
It's worth a check to eliminate that possibility...

jordy said...

hi my name is jordy. i need to know what an sid 51 code is? im a school bus mech in la ronge sask.we have 10 77 pass thomas buses 2000 5.9 24 valve cummins. 545 allison trany. thanks.

jordy said...

hi there . my name is jordy im a school bus mechanic in la ronge sask we have 10 77 pass thomas buses year 2000 i keep getting a sid 51 code what is this ?

Anonymous said...

I have a 2008 Itasica rv with the Allison 3000 transmission. I have a humming sound in 6th gear at 55-58 MPH, sounds like a prop out of sync. The sound goes away when I down shift to fifth gear. Need help

John Whelan said...

That's hard to distinguish but I would drain the oil and check the filters for contamination. It's a big job to start removing the modules. If there isn't anything obvious you'll have to let it develop.

Peter said...

I have a 1993 holiday ranmbler diesel pusher with a allison 3000 series tranny last winter I had the heat on all winter and the only problem i had was when i went to put it into drive or reverse I had to push the button so hard it almost didnt shift.this year it is not heated and in the cold when i turn the ingnition on i have ne lights on the shifter and the engine will not crank over. turned on the furnace warmed it up everything works. Lights on shifer and engine starts. Could it be ecm or shifter ??? I checked all conections.

Tony Stephens said...

I work for a large school distict. I have ran into a similar issue before. It turned out to be the tone ring on the output shaft. it is the ring that the output shaft sensor gets its signal from. its a easy to check also just pull the sensor out and see if the ring rocks back and forth on the shaft. The pin that holds the tone ring in place is harder than the metal the ring is made out of and it wears a small grove into the ring letting it rock back and fourth. It causes havok with the computer causing very hard shifts. Replacing the ring requires pulling the driveline and back section of the trans be sure to install the updated output yoke bolt kit. And to perform fast adapt when finished..........hope this helps good luck