Correct way to service 2024 l8t allison trans?

Chuck FB · March 19, 2025

2 hours ago, No F-bdy Bs said:

I've considered doing that. Definitely not a bad idea, especially if your roads see salt. 30min and some anti-sieze could save a lot of grief in the future.

I made a note of doing that myself just now on my growing list of items to do or check over on my truck ... the list is getting longer all the time. Unfortunately I have to contend with both salt and calcium chloride, substances that make for repeat customers to the new section of a vehicle dealership.

Chuck FB · June 10, 2025

Lately I had dropped in at a locally owned transmission shop to see what if any thoughts they had on the 10L1000 issues and he said as of yet they haven't had a truck come there for a transmission issue because the theme has been the GM dealers around here anyway are getting the problem trucks because the valve bodies are hard to get even for the dealer and a lot of the trucks would still have warranty ... yet that is. However he has had some customers bring their trucks to have the fluid changed and has changed the fluid on the gas version and has dropped the exhaust to get at the pan. They were not flushing the trans because of concern of breaking up some buildup pushing some crap into it so just changing the fluid in the pan and a new filter. He said labour makes the job expensive as the total bill he has been charging is 900.00. This is in Canada and labour rates are stupid high and I had not asked if he changes the pan gasket but I found out the dealer list price is 139.00 on the gasket ( they might be able to be reused if not damaged ) and the filter kit is 115.00 and the oil would be 153.00 for 10 quarts of oil. So a maximum of over 400.00 in parts going by that but the GM dealer will knock some off the prices if the truck was purchased there and by buying the oil by the 12 quart case they drop the price quite a bit so my price at the dealer for the parts was around 300.00 . I never did ask at the dealer what they charge for the same service and the dealer did not have a pan gasket in stock which makes me wonder if the dealer is re using the gasket, they had the filter and oil in stock.

The owner of the trans shop recommended ideally doing a pan drop every 25000 miles if towing and from what trucks he has changed the oil on he figured it seems to be around the 9.5 quarts required but like he said its important to go through all the bs of warming it up to the temp specs to check the level because he found that oil seems to expand a lot and of course as its hotter it drains back to the pan faster anyway.

EXSlider400 · June 15, 2025

This may seem crazy, but has anyone rerouted the exhaust crossover away from the pan? I was thinking about doing this on 2025 2500. I did the exhaust disconnect on a 2019 6.2 with 10-speed with over 100k miles and it was a pain and assume the 2500 will be very similar.

64BAwagon · June 15, 2025

I paid around $5 qt for the GM ULV fluid from Rockauto. I got the filter for less than $35 (obviously US$)

as far as the pan gasket its reusable and should be good for several pan drops. I have all the stuff for my 2024 gasser but I sold it with less than 12,000 miles so I never had to do it. It does however look like the trans crossover bolts could be backed out and the trans jacked up enough to clear the exhaust. My plan was to install a drain plug or buy a Dorman pan with the plug in it (about $150 on Rockauto)

As far as refilling I bought a m18 nipple that screws into the fill plug on the side of the case. It would allow me to run a hose to the normal dipstick area and fill the trans that way. If you use a clean pan you can measure the amount of fluid that drains out and replace that amount.

Chuck FB · June 15, 2025

19 minutes ago, 64BAwagon said:

I paid around $5 qt for the GM ULV fluid from Rockauto. I got the filter for less than $35 (obviously US$)

as far as the pan gasket its reusable and should be good for several pan drops. I have all the stuff for my 2024 gasser but I sold it with less than 12,000 miles so I never had to do it. It does however look like the trans crossover bolts could be backed out and the trans jacked up enough to clear the exhaust. My plan was to install a drain plug or buy a Dorman pan with the plug in it (about $150 on Rockauto)

As far as refilling I bought a m18 nipple that screws into the fill plug on the side of the case. It would allow me to run a hose to the normal dipstick area and fill the trans that way. If you use a clean pan you can measure the amount of fluid that drains out and replace that amount.

I've talked to friends that have ordered items from Rock Auto that live here in Alberta but the reason they bought the parts through the states was that it was for vintage vehicles that they couldn't source the parts through a Canadian supplier that had could get them or had such an outrageous price. For the fun of it some time back I did a pretend order through Rock Auto to see what it claimed the price would be and by the time the exchange was done and the huge issue being the shipping, it made no sense at all to order from them unfortunately, also I was not entirely sure they would even ship oil or certain items like that up here because of it being a hazard product. So locally I had priced out the Delco ULV oil as one automotive supplier I am aware of even handles it and their price was just as high as the full list price at the dealership, the trans filter was about the same as what my so called "good" price was at the dealership. Basically the theme is we get bent over the counter and pounded hard with no offering of dielectric silicone lube to lessen the pain !. They know that ULV is in demand as they also sell the Delco Vi and its a fair bit cheaper then at the dealer.

I had seen a video a guy did not that long ago where he undid an exhaust bracket hanger that I think bolts to the trans, then pulled out one of the rubber hangers back near the pipe joint. He did not loosen off any exhaust nuts though, on the manifolds or at that connector joint which I believe put way too much stress on the piping joints as he use a ratchet strap to literally suck down the exhaust pipe until it contacted the frame cross member at the back of the trans. By doing that he was able to just get the pan out but it was so tight that even the thickness of the gasket would not fit in that gap as he went to fit the pan back up ( he chose to use a new gasket ) and the pan with the gasket laying on it would not fit as an assembly so had to refit the gasket after the edge of the pan passed by the tightest area. The reason he did not undo the exhaust nuts was because of the risk of twisting off studs and basically a whole experiment to see if it could be done that way. As to the rear of the trans being lifted, I wonder if that would be more than the exhaust to engine manifold joints would like. That same bracket on the trans would have to be undone as otherwise the trans would be lifting the exhaust up, I haven't looked closely at that assembly myself. But in that video it was quite evident that without doing anything there was no way his pan was going to be able to be pulled out of there, all GM had to do was design the piping a bit differently and would make life easier but they probably really didn't care as vehicles these days don't seem to be made with working on them easily, instead make it complicated so the dealership gets the work. That's the bonus of the diesel version of this trans, you will be able to drop the pan without all this hassle.

Speaking of the Dorman pan, the aftermarket parts supplier locally has Dorman P/N 265-587 listed for this truck and the price here is 552.00 in Canadian funds of course.

64BAwagon · June 15, 2025

Oh man, you guys are getting hosed on prices. Thats sad

Chuck FB · June 15, 2025

Its typically tended to be that theme over the years to an extent but I would say its gotten a fair bit worse with things in general these last years and part of it is our scum bag government with outside the country ties that's destroying our country from within and our dollar with it. There is no good reason for us to be in the situation we are and yet ... here we are.

Chuck FB · June 25, 2025

On 6/15/2025 at 12:05 PM, 64BAwagon said:

I paid around $5 qt for the GM ULV fluid from Rockauto. I got the filter for less than $35 (obviously US$)

as far as the pan gasket its reusable and should be good for several pan drops. I have all the stuff for my 2024 gasser but I sold it with less than 12,000 miles so I never had to do it. It does however look like the trans crossover bolts could be backed out and the trans jacked up enough to clear the exhaust. My plan was to install a drain plug or buy a Dorman pan with the plug in it (about $150 on Rockauto)

As far as refilling I bought a m18 nipple that screws into the fill plug on the side of the case. It would allow me to run a hose to the normal dipstick area and fill the trans that way. If you use a clean pan you can measure the amount of fluid that drains out and replace that amount.

I was thinking about the M18 nipple you bought, was that a straight nipple with a barbed end ( and not a 90 degree fitting ) and do you know what hose size your fitting was made for as the larger a barb size one could get assuming it would work in that confined space, the faster the flow into the trans and easier on the upper/engine end to adapt a funnel to pour the oil into the hose.

On the left side of the case there is supposed to be a filler plug that faces up and is higher up on the case as the drawing shows, I haven't looked much to find that one and probably need a mirror to locate it and the challenge there would be to clean the area up good before removing that M18 plug if used but the hose would not have to have a sharp bend, that could be the possible issue with the right side plug that is on the side of the case. Wouldn't really know until a fitting and hose was set up on the right side to see how it worked out.

Yes I could buy a fancy air pressured unit that I could see the volume of oil going in or instead buy a dedicated five gallon pail pump and dump in quarts into the pail and pump it in by hand, have pumped quite a lot of gear oil out of five gallon pails over the years and certainly that would do the trick too. Of course this is all nit picking stuff relative to that exhaust to pan clearance issue which turns a bit of a job into something many times more complicated for no good purpose.

Edited June 25, 2025 by Chuck FB

Chuck FB · 2026-07-16T21:33:22Z

I decided to give it a shot and see what sort of a gong show it would be to a pan drop themed oil change on my 2025 gas truck with the 10 speed. All indications I had seen so far was that there was no way that pan was coming out of there due to the cross over exhaust pipe not allowing enough clearance for the back end of the pan to duck out from under the valve body since it hangs lower than the pan to trans mount flange and certainly the filter does. I never touched any of the exhaust mount hardware at all, be that the engine manifolds to Y pipe, the bracket on the side of the transmission, or the two bolt flange further back behind the trans/transfer case. I put the truck up on four jack stands as there was no way I was going to struggle with that lack of clearance under the truck. The truck was cold as it had sat over night so all the trans fluid had drained to the pan, so I drained the bit of oil that would come out of the level check plug at the bottom near the front of the pan and put the plug back in to reduce the ensuing mess after that. Then took out all but one bolt front and rear and then pushed up on the pan and took out the remaining two bolts and then let the front of the pan tilt and spill out most of its contents into a drain pan. I then popped the pan gasket off its two locating nubs and kicked it a bit to the left side so it was no longer on the flange of the pan to get all the clearance I could and managed to get the pan slipped out of there by swinging the front of the pan to the right but keeping the rear part of the pan inline if not slightly to the left of its mounting flange area and lifting the front of the pan enough to keep the rear part of the pan low enough that allowed the pan to "JUST" slip out without forcing anything. I installed a new trans filter and seal and as per GM instructions on this site I torqued the two bolts to that 44 inch pound goal ( they take an 8 mm socket ) In reversing the pan procedure after I had cleaned up the pan both inside and out completely ( touching the outside of a dirty pan and dealing with installing a gasket at the same time would be a disaster ). First I slipped the pan into place and yes it took me a while as it won't go unless its slid in just at the right angles, then once the back of the pan was into the area of the flange mount, I went and got the gasket and then threaded that through the front of the pan and feeding it under the filter etc and finally working it onto the flange of the pan and lining up the two locating nubs to drop into the pan. Then lifted the pan up into place and get a couple of bolts started and check and make sure the gasket is where its supposed to be as the bolts were being put in. I never used any power tools as I don't have any of the whimsy little drive guns, I use what looks like a small screw driver handle with shank that has a 1/4 drive on the end of it and added an extension and those bolts use a 10 mm socket as some times power tools can bite a person if used on delicate parts ( torqued to 80 inch pounds ). Also should note as per rules around pulling the add plug out first, yes I cracked that loose with a 8 mm Allen bit socket on a 3/8 slim head ratchet as there isn't a lot of room to work with there either due to the exhaust on the right side of the trans.

I already had delco ULV oil on hand and of course the quart bottle pump wasn't made for those small cap threads so I had to use some other containers that the pump would fit and keep transferring oil over into them so a wasted exercise there but indeed the small pump did work just fine as ULV oil is thin and easy to pump in summer time weather. I put in 9.5 quarts as per prior minimum recommendation and yes that cut it pretty close as once I had the truck ( off the jack stands so its level ) and the trans oil up to 167f , about 6 ounces came out but a level kit or what have you could throw it off just enough that it wouldn't be enough oil so probably that 10 quarts is a good amount to put in so one doesn't have to add more oil as when its hot I sure wouldn't want to be adding oil so would have to let the exhaust cool. All I do for warming up the transmission is sit there with it in park and rev it to about 2500 rpm and it takes close to 20 minutes to get it up to that lower limit of 167f, weird how it will warm up more doing that then by driving it, I am not real keen on power braking the truck to get the temp up there and don't seem to have to either. By the way I only have 9000 miles on the truck so probably not a very good payback on doing it that soon and the magnets had such a minor thin layer of fines on them so that was good to see and the color of the oil was a darker red then new oil but still looked very good as it should and I've not done any towing with it so its been living a pretty easy life so far. The filter is made in such a way that its next to impossible to pull out the filter media but there certainly was some fines showing up there which makes sense give the trans having to break in.

I hadn't really planned on explaining this much of what I had done since there are various instruction videos kicking around or I think so, as the gist of my message as that by fluke or what have you, for some reason my truck has just enough clearance to slip the pan out from the trans. Of course there is no guarantee that other trucks like this in general will also allow the pan to be taken out without messing with the exhaust as I expect its probably a crap shoot if it will or won't, I was just happy to find out that mine would work and avoid all the other struggling and possibly damaging things in the process,

carkhz316 · 2026-07-17T11:05:36Z

On 3/16/2025 at 1:07 PM, Chuck FB said:

I was wondering if you were referring to your 2021 model with the 6 speed or the original posters 2024 model with the 10 speed as I am only guessing there is going to be difference in the relationship of the exhaust and clearance to slip the trans pan out.

Sorry I didn't see this until now, but it works on both the 6 speed and 10 speeds, as well as all the half tons too.