Allison Transmission Questions

Allison Transmission Questions

Hi there Ken Powell,
Yes it should be done by authorized Allison mechanic because the whole valve body module needs removal to replace the temp sensor or repair the wiring that may have rubbed thru the insulation.
If it were as simple as not warmed up, there would be a flash of OL70 on your display. I hope you still have warranty. This takes approx 4-5 hours to do but the parts are not that bad. If I can help any more, please call me at 360 887-7556 my direct line at Pacific Detroint Diesel Allison. Thanks and have a great day! :)
Allison Transmission Questions

Hi allisonman,
My hat is off to you for being an Allison man. Before I retired I was a Cat man. In my career I did one Allison out of a 50 Terex rock truck. When I got it torn down I couldn't believe all those pieces would go back into that case.
Anyway, I have been reading your posts and it sort of looks like the average life expectancy of a MD-3060 is 150,000 miles. Is that right? My motorhome has 140,000 so that makes me a little nervous. What is the predominant failure? Is there usually a warning so a guy can limp home or is he dead in the water 500 miles from Nowhere?
My rig has developed the same problem that several of the folks on here have that is harsh downshifts. It makes no difference what mode it is in. I installed the exhaust brake myself about 9 years ago and the guy at Pacific in Anchorage told me not to have the Ecu programed for downshift pre-select. He told me to try it as I might like it and I did. I just use the toggle switch to control it because the throttle micro switch never worked right in real cold tempatures as the throttle cable is 40 feet long and runs outside. I have always been happy turning on the switch when I needed it and not having a pre-selected gear worked fine too.
It always had a little harshness downsifting from 5th to 4th and it seems like I remember in my rapidly diminishing memory that there was a service bullitan years ago on this. I did my usual nothing about it as it wasnt to bad but now it is. It also bangs into gear on an upshift if I turn off the exhaust brake and let it roll down a hill with just a tad bit of throttle
I am through Portland twice a year as I am an Alaska snowbird.My motorhome is a 1993. Do you have rebuilds available?
Allison Transmission Questions

Allisonman, I did the diagnostic check and what I get is: D then 1 followed by a 2 and 1 followed by a 1 and 2. wassat mean? thanks
Allison Transmission Questions

Thanks AllisonMan--you da man!

My service manual says 25k or 50k for xmsn service depending on short or long schedule. No where did it mention or did I receive from Chevy a 5k initial service interval. I am getting ready for intial service at 25k.
1)Do I have a potential problem?
2)Is this worth pursuing with GM? (lack of notification etc?)
3)Do I need to remove/clean the screen in the pan or is the spin on filter good enough?
4)Where is the fill point for this trny in this application?
5)Can a firmware flash be undone (return to orig flash)

Thanks for the answers all.

Allison Transmission Questions

Hi there rbraught,
I am also the AllisonMan you asked this question on adifferent post. Man this keeps me busy but I really enjoy it.With the code 21 12, your throttle position sensor is either disconnected or the linkage is worn out. Sometimes the cotter pin just comes out. Check to see if the cable is just sitting next to your throttle cable.The good Ol' Boys from Pacific can help you but I bet it is just disconnected or the pin it goes over is worn out. You probably have a "service light on your tower too.
That transmission you tore down is the easy model, now with electronics, valve bodies, computers you almost have to be rocket scientist to keep up with all the models and updates. I appreciate your comments. I also went into a little more detail on my other post so check that one also.
Being a 93, there Allison will not take the core (too many updates but we can rebuild yours on a time and materials basis unless the solenoids are the very first vintage then we'll talk LOL)but don't worry, 150,000 is great but I have seen even garbage trucks with the same transmission go 250,000.The TPS linkage is installed by the OEM and I see this problem all the time so I believe yours will shift fine after repairs.
You must really be enjoying some wonderful trips. Please stop by on your way past and take me with you! LOL
Thank you and have a great day. Pacific DDA 360 887-7400 Ridgefield, WA
Allison Transmission Questions

Hey there wingnut,
Yes you should have done a service initially at 5k but the dealer don't tell you does he? Look in the Allison booklet they gave you or the owners manual. No problem, if asked just always say "yes I serviced it myself at 5k" so act as if this is the second service. We never require proof so I don't see a problem.
Yes remove the pan but the filter is ok as it is. It only gets replaced at overhaul. You can use the same gasket over since it is metal over rubber and torque the bolts to 20 ft lbs.
Then change the external filter, add oil (3 1/2 gallons) and flush if possible by removing the cooler return line marked on case with arrow pointing towards trans (special tool needed)and have someone start while hose is pointed to bucket. You will see when the oil comes out clean then remove about 1-2 qts more. The oil really pumps out of this trans fast. Your transmission oil dipstick-filltube is on passenger side by the firewall,
Nothing can be done with the software programing on a GMC or Chev pickup truck. There is only one calibration unfortunatly. I wish GMC would come up with one that would work with bigger tires but as of now, if you put bigger tires on, it voids warranty and possible failure of transmission.
Thanks for the question and have a great day! :)
Allison Transmission Questions

Hi wingnut,
No problem with warranty and GMC, just tell them you did change it at 5000.You do need to drop the pan and remove the oil, no need to do anything to the filter. Re-install pan with original gasket (re-usable) and torque to 20 ft lbs. Change the external filter and make sure the magnet gets taken off old filter and put on new one.Add oil and flush cooler if possible by removing cooler return and putting in a bucket, then flush until clean oil comes out of hose.You trans dipstick-filltube is on passenger side by the firewall way in back.Sorry you cannot change a thing with the TCM calibration it voids all GMC warranty, Sorry I was not too detailed but my computer is actin up. If you have any more questions, please post and I hope this thing works LOL. Thanks and have a great day! :)
Allison Transmission Questions

Hey Allisonman ,Thank you for replying to my post.
Unfortunatly, The problem isn't in the throttle position cable. I checked it and the pin ,all ok. On mine, if the cotter pin falls out or the linkage pin wears plumb out and breaks, there is a spring (must be in the tranny ) that holds it in the idle position. This happened to me once about halfway through Yukon Territory on one of my many trips north. The transmission would not upshift and I was gleefully looking forward to the next thousand miles or so in first gear. Must have been a subliminal message from God or maybe George Burns that made me push the mode button. It shifted great even without the cable then.
Any other thoughts about the 21 and 12 codes I get.
Really appreciate your help.


New Member
Allison Transmission Questions

I'm a do it myself kind of guy, and a Yankee. Can't I do these changes myself, both the trany and the engine oil? It seems to me that all I need is the correct filters and oil and I'm done and saving money. Looking back, the last owner (97Monaco Winsor) paid $733.00 for changing the oils. Seems high to me. :bleh:
Allison Transmission Questions

Hello rbraught,
the TPS is spring loaded but if you remove the cotter pin and it doesn't spring back something is wrong with the tps. It should spring back about 1/2" when you remove the pin.The only other thing would be someone moved the bracket that holds the cable and moved it too far forward, this will give code 21 12 and even tho you can move the bracket, you need to have someone with the software re-calibrate the tps.
The reason it shifted great with the mode button on is because that lowers the shift point to like you were at 80% throttle, not the 100% that a failed tps will give for a signal. Is it disconnected? There is a connector that plugs into the tps but I bet the adjustment is off or tps is no good.
If you talk toGod or George Burns again, could you ask him for a new Dodge Viper for me? Thanks for the question and I hope this resolves your problem. Have a great day! :)
Allison Transmission Questions

Hi Bob W,
WOW he got taken. We just came out with specials for Transynde synthetic for a lil over $400 and our complete engine service and 34 point chassis inspection is only $195. I guess with tax we are close but he must have put in synthetic. Is there a tag on your dipstick? If so no need to change transmission just have an oil sample done every 2 years until sample comes back bad and tell you to change. For this price it had to be synthetic and most of that cost is the oil. In bulk it cost 40 a gallon and thats why so high.The cost of a Dexron service is half the price.
As far as the engine goes, yes you can probably do that yourself too but careful if you lose the prime in the engine.
Im sure if you are mechanically inclined so if you are sure, go for it (you can always call me with questions but all of the transmission instructions are in the filter package if you have a world transmission)
Thank you Bob and have a great day! :)


New Member
Allison Transmission Questions

:bleh: You said " As far as the engine goes, yes you can probably do the oil change yourself, but careful if you lose the prime in the engine." Just what does that mean? I've never heard of that before. And if I do loose the prime, then what?
Allison Transmission Questions

Mr. AllisonMan, two months ago I purchased a Chevrolet 2500HD with the Duramax and Allison Transmission. Within the past three weeks I have noticed an intermittent problem. The truck sits for about 10 to 11 hours during the day. Within one second after starting the engine I hear a dull thump and the truck moves like someone has hit you from the rear. The first time I actually looked to see if someone had hit me. This has happened three time. It is like a valve is stuck and when it releases, the fluid is immediately pumped through the system and you have movement. Over the July 4th weekend, the truck did not move for three days. On the fourth morning I started the vehicle to go to work. I placed the transmission in reverse and with my foot off the brake, it did not move for a few seconds, then slowly it started to back up. This time it acted like all the fluid was in the pan, and it had to pump it through the system before I could move. When the truck had less than 1000 miles on it I remember the solid feel as it locked up when selecting reverse or drive. I now have 2000 miles on the truck and it acts as if it eases into gear. After you get moving everything appears fine. I checked the fluid level and it is within limits. The local dealer said they have no idea as to the problem and there are no service bulletins concerning my situation. Can you help? Thank you in advance for any assistance in this matter.
Allison Transmission Questions

Hi BobW,
Didn't mean to scare you LOL. I meant the fuel filters. If you change them, make sure you fill with fuel before install. If you get air into the system you "lose prime". Just make sure when you fire up your engine after installing new fuel filters, that you keep the rpms up for about 20 seconds, this should allow fuel to fill up air pockets and run smoothly. This is why I change fuel or oil filters one at a time because you have to make sure your fuel system is back in order before you rev the engine at startup. Thanks and have a great day! :)
Allison Transmission Questions

Hey Mr. Allison man - Just the guy I needed to check with...
We are considering the purchase of a '94 Damon 29.5' Challenger MH with 190Cummins / Allison 4 spd, 63k miles. GVW 16,000; Front GAWR 6,000, Rear GAWR 10,000; Spartan chassis.

1st Question: The previous owner had an exhaust brake installed. Further research has led me to believe that an exhaust brake will not work with the Allison 4 spd. Despite 2 medical degrees, I am not educated enough about transmissions et al to explain the exact details why, etc. I don't understand why anyone would install something that didn't work (?) - but know that you will be "the man" who can 'splain it to me. I do believe that I understand how the exhaust brake should work on the engine, just not how the transmission is involved.

2nd Question:
The previous owner (same gentleman) replaced the rear end with a Dana 331. Supposedly, this ratio provides a slight bump in gas mileage as well as speed. Comments? I also assume that the change in rear ratio would alter the coach's ability to pull a small car (specifically 2,600lbs). We would like to occasionally pull our Toyota. Seems to me that the change would decrease payload capability, but I would prefer a professional opinion.

3rd Question: I have also been warned to "steer clear" of any product with the 4 speed transmission; seems that the engine can be altered to increase hp beyond the abilities of the transmission, and that the transmission is 'a great limitation.' These comments, however, are usually made by people who wish to drive 70mph while towing a full size SUV, it seems to me. We usually drive significantly slower.

All of the above are requested to aid in our decision making; the price is attractive, but I don't want to end up with something that I can't get rid of/nobody wants after a few years. Normal depreciation is enough!

Many thanks for any assist that you may be able to offer.

John Scarbrough
Allison Transmission Questions

Hello Armstrong,
Hmmmm this is a tuff one. Has anyone looked to see if your linkage is in adjustment or even connected? This is a problem that definatly needs attention before someone gets hurt. What state do you live in and I will try to find the nearest, best location for you to take your truck to? Most GMC dealers do not know enough about the Allison and unfortunatly they are the ones that have to do warranty work until warranty runs out, but there are heavy GMC truck dealers and they are most familiar with the Allison. Thanks and have a great day! :)
Allison Transmission Questions

Hello tursiopsfl,
(1) first off I believe you may have an AT545 or a MT643. You can look at the tag on the right side of the transmission and it will tell you the model number. An AT545 does not have a lockup torque converter meaning your transmission is hydralic controled not manual locked to the engine, thus, no holdback. You can use an exhaust brake in a MT643 because there is "converter lock-up" once you reach 3rd gear. An exhaust brake holds you back with exhaust backpressure in the engine and if that is hydralic, no holdback.
(2) Boy you sure should be able to get some road speed with that but I agree, take off should be tough. I do not understand why people do that because the vehicle is engineered engine-trans-diff to all match up. All I can say is that if your take off is ok, you might be lucky but I would definatly install a temp gauge and watch it especially if it is an AT545. I am sure you must have felt safe when you test drove this and yes you should get great mileage.
(3) 4 speed Allisons a great but where we get a bad rap is when people alter their original engineered coach and modify with either more engine hsp or like in your case, the differential gearing. If you have a local Allison distibutor I would call them and ask if they would test drive it before you bought it and either give a thumbs up or down. If you do not know of a local distributor, write me back and I will find one if you leave your location. I can't speak for any other distributor but I would test drive for free and check it out.
These were all great questions and I admire you for asking them before you bought this vehicle. I usually see the customer after the purchase when they aren't in such a good mood because something broke. I hope everything goes well and you can get on the road with your new RV purchase. Thanks and have a great day! :)
Allison Transmission Questions

Mr. AllisonMan:
I haven't been anywhere because the dealer stated they were not aware of a service bulletin and didn't have a clue. Reference the linkage, would this cause and intermittent problem? I drove approximately 400 miles over the weekend and everything worked great. As long as you keep moving, there is no problem. You requested my location, it is Jackson, TN. We have the following dealers in town: Freightliner, Kenworth, Mack and International. The yellow page listing for International advertises service for Allison. I read your response to JimT back in April concerning loss of pump prime where you referenced an Allison Service Letter SIL 29-1k2k-02 concerning a lube regulator spring and a new converter relief valve spring. As you think on the matter, is it possible for me to check anything or remove and replace anything exterior to the transmission?
Thank you for your willingness to help!
Allison Transmission Questions

Hi Armstrong,
Yes I would definatly look into that SIL. I will look for the nearest good dealer or distributer in your area tomorrow since I have that at work. Check tomorrow or Thursday. Thanks and have a great day! :)