Currently stopped at the West Gardiner plaza on the Maine turnpike and need assistance.
Transmission seems to be hunting, particularly on hills, mostly when gear selection is D/6. Not as much in D/5. Notice speedometer is a little "jerky" as well.
Fluid is fully warmed up and keypad shows level OK.
No codes on the Allison transmission keypad. No obvious codes on VMSpc history. No warning lights on dash. All parameters seem to be OK.
Calling James T. now but if anyone has an ideas. Thinking of looking for the output speed sensor as others have had that problem, but don't know what it looks like.
Try this info on trouble shooting
http://www.rvtechlibrary.com/transmissions/3000_4000_operators.pdf (http://www.rvtechlibrary.com/transmissions/3000_4000_operators.pdf)
I wish I could help. I can only suggest the computer is getting that same jerky speed reading you see, so is confused as to road speed and gear selection. Possibly whatever speed transducer Allison uses is having issues, or a bad connection.
Thanks Dave - Steve's now checked all the connections on the transmission itself. None were loose but he did clean and CorrosionX each one and make sure it was properly reseated.
He's also checked the Allison ECM connections and all seemed to be tight.
Nothing looks loose or chewed on the engine.
We're about 45 minutes from the Allison shop in Portland and it's on our way to our next campground in Vermont. We're going to head towards them and see how it goes.
At this point would zero in on the speed sensor on tail shaft, mag p/u, maybe loose or dirty with a chip on the magnet fluttering. Have seen that lil bummer.
K.
No repeat of issues since connections were cleaned/cx'd. Thanks for that doc Dave. We are continuing to the campground and keeping our eye on things.
Great news Michelle! Hope that did the trick.
Richard B
Another thing you might want to check, is do you have a brake dragging? Or if you have a braking system on the toad, is that ok?
Ben Harris
1999 U320 40'
Started back up
Please keep us updated on the final diagnosis. This will be another good piece of information to add to our individual troubleshooting guides.
If you can determine that it isn't the speed sensor here is some more things to look at.
Have Steve check the wires to the engine position sensor (cam sensor) It has 4 wires they are actually 2 pair. One set for the main sensor and one set for the backup. If the main fails it will go to the backup. If it is swapping back & forth it will cause a surge but it will be noticeable in all gears. If it completely quits it will leave you stranded as the ECM don't know when to fire the injectors. Pull the loom back & see if the wires are oil soaked and mush.
Have you checked to see if the throttle position sensor hasn't vibrated the screws loose. It could cause same problem but would most likely be noticed in all gears.
Pamela & Mike
My road speed sensor was bad and it threw the check engine light. It will eventually derate the engine too.
I have seen this when the cruise control is on going up hills and speeds and RPMs are right about where you might expect a downshift. It does then up then down. I just shut off the CC on hilly roads.
Hope it is n easy fix.
Roger
You may have solved the problem with the cleaning & CorrosionX. How long were you set at the campground before this problem surfaced?
The issue is definitely intermittent, and with there being no codes showing on the keypad, the Allison shop in NH felt it is most likely electrical and unique to FT. They didn't want to touch it. We are continuing to the campground and will check the wiring as suggested by Pamela and Mike. Will also check with Allison shop closer to campground tomorrow.
One thing I noticed this second episode was a brief series of tapping sounds with decreasing amplitude just before the downshift or torque converter dropping out of lockup from the general area of below our shower base. That's driver side rear wheel area.
Oh, and it's also thrown an abs light on the dash both times.
(Sorry for any typos, I'm posting from my phone)
Michelle,
With this new info, slide under and see if you have lost one of your caliper slide pins. Not likely but possible. While under there check U joints & driveshaft slip joint for excess wear. A U joint going bad could shake the rear axle housing enough to set off an ABS alarm also.
P & M
Definitely check everything in that general area under the coach. It could be one of any number of things, and the transmission issue could be only a symptom. Intermittent issues are always so much fun to diagnose!
No kidding ;)
After the second "act up" and stopping in Concord, NH at the Allison shop, no unusual hunting the rest of the drive into central Vermont, although the ABS light is still on (we'll pull its code tomorrow). We are safe at the campground and will start looking at everything tomorrow.
It and you and Steve need a glass or two of vino and all will look much better!
Keep us posted!
Output speed sensor externals are fairly greasy/oily, especially compared to other sensors. Steve had cleaned it yesterday and again today but we are thinking of going ahead and replacing that sensor.
P&M - where would these sensors be? Steve's ID'd the output speed, input/engine speed, what he believes is the retarder temperature, and turbine speed on the Allison, we don't know where the engine position sensor and throttle position sensor are.
All slide pins are present, nice and shiny with their helper springs attached. U-joints, etc., all seem fine.
ABS code was 3rd axle left, no response/signal and 3rd axle left, low current. Steve's inspected and cleaned the driver tag ABS sensor, it also was somewhat oily.
Hey - just found this on the forum. Our ABS light didn't flutter, but wondering if it is the case than a wheel speed sensor could cause torque converter issue
Torque converter locking up and then unlocking at highway speeds. (http://www.foreforums.com/index.php?topic=13997.0)
Thoughts?
That is a good find and possibly the problem. Another great advantage of the forum. If you can determine it is a bad wheel sensor they are relative cheep not even 1/10 of a coach buck.
Pamela & Mike
Michelle, that sounds like you're on to something! I love this forum! :dance: :dance: :dance:
Michelle,
The throttle sensor is easy to find & get to it. It is on the bottom of your throttle pedal and is held on with a couple of screws. If you lift the throttle petal and look on the right hand side you should see the 2 little screws.
The engine position sensor is located behind your air conditioner compressor & in front of your air compressor. Yes it is hid in a little hole. If you look down through the A/C compressor belt you can see the wire loom. The sensor is screwed it the block actually pointed toward the rear of the coach.
We were told by Cummins that the first generation of wire insulation that they used was sensitive to oil & would deteriorate over time the new ones have a different insulation to cure the problem.
Here is the best pic. I could get. The first is of the plug looking through the belts. The second is the sensor & plug.
Pamela & Mike
Thanks - checked and good.
Great - thank you!
Michelle, No idea how the interconnect between the ABS & the Allison, but it makes perfect sense why the hunting/searching due to the lock/unlock of torque converter as described.
Would guess FOT & James T would be on my list.
Might be a fuse to pull to eliminate it temporary.
I am lost beyond that.
Good luck
Problems like this often won't throw a code, because the system is operating as it is designed for a given set of input variables. I'm not sure if all the module communication on your coach is via CAN bus or if it is like mine with mostly discreet inputs. If the latter, you can probably find the communication between the ABS module and the Allison computer and disconnect it and see if the problem goes away. On my diagram, there is a communication between ABS and ATAC computer--most likely to disable the retarder (just a hunch).
A torque converter lock-up clutch kicking in and out will feel like a gear change/hunt.
Received the ABS sensor test procedure from James T. today (attached below).
Thanks to Barry B. we have the tag sensor P/N and have ordered one from FindItParts (it's cheap enough at $47 and this particular sensor has acted up in the past, although not the same extreme symptoms).
We'll know in about 2 weeks if our efforts have solved the problem as that's when we leave this campground. I'll report back, and in the meantime thank everyone for their ideas, photos, and support.
Reporting after 2 drive days, roughly 8 hours total. No "hunting" since replacing the tag ABS sensor, the transmission output speed sensor, checking and cleaning/securing all other obvious connections and suggestions from Pamela and Mike.
A couple of times over a fairly "assertive" expansion joint or pavement void we did have the torque converter drop out of lock-up, but only when on cruise control in 6th/OD. It didn't happen when speed limits kept us in 5th and it was only 2 or 3 times yesterday and once today. Of course now we're hyper-sensitive to shift/tc behavior so this may be perfectly normal.
How about some photos of replacing ABS sensor. I have a bad one that needs replacing so was wondering how hard it might be.
Jim
Jim, if it's the tag it is pretty easy. I'll scan the instructions and post them soon.
If it's the drive axle, according to James Triana the coach has to go into a shop (I suspect you have to remove wheels).
I didn't ask about the steer axle since the VMSpc code said "3rd axle left", meaning driver tag. We bought the part at the local Freightliner shop, $43.xx. Meritor R955335 is the part for a 2003, per one of Barry B's posts (and what we bought).