# 2007 2500hd tranny problems



## dlcs (Sep 2, 2004)

My truck has the new 6 speed hydromatic. lately it seems toi be shifting quicker than normal when you take off, almost like the shift points are messed up. Sometimes when you come to a stop it feels kinda like its in tow haul, like its downshifting to help with braking? Tranny was rebuilt at aprox. 45k last year, mechanic thought it was a defect from the factory, said it was nothing that I could have done. My question is does the computer tell these transmissions when to shift, could it be something programable? I rememberthe mechanic that rebuilt it last year said there is two programs for the tow haul feature. I'm taking it in tomorrow morning and see if the tranny mechanic can drive it and have a looksee, hope it something simple but I'm worried its not. I love this truck, its got 56k on it but is like new still.


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## chitown sparky (Sep 24, 2009)

I have an 07 also and I noticed it I have not the trans flushed yet from the winter but then again I really don't drive it that often when I do drive it I feel the same thing please let me know what they tell you and when I get the trans flushed I will let you know if it fixes mine thanks Ron


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## dlcs (Sep 2, 2004)

I took it in on friday and the mechanic who rebuilt it last year drove it. He didn't think it was shifting hard and couldn't feel anythign wrong while driving it. He hooked it to the computer to check for codes,nothing on the transmission. But it did have a code saying the brake switch wasn't releasing. He said this would cause the transmission to act up while decelerating, cause the transmission would think I was braking. This also explains why when I pull a trailer (which I do 5 days a week), the trailer brakes are not in sync and would stay on after I release the brake pedal. I have the built in brake controler. This brake switch will also effect the tow haul mode because the transmission breaking uses this break switch on the brake pedal to know when to start downshifting the transmission. Since when you hit the brake pedal the trnasmission will start down shifting to slow you down. Also, he said after i unhook my trailer at the end of the day and drive home. My truck will act a little differently cause it has to learn that the trailer is no longer being pulled. He said the truck computer will compensate for the extra weight being pulled and will adjust the shift points "somewhat". So all in all he thinks some of what I was feelign is normal and the new brake switch helped everything else. Actually the truck rides much better, especially in tow haul.


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## dlcs (Sep 2, 2004)

Ok, well today I notice the saem thing as last week. Truck acts like its 30 below outside and the transmission isn't warmed up yet. When you come to a stop, you can feel it downshift, similiar in how it does in tow haul but not as extreme. I could never feel the truck down shift before unless I was in tow haul. I don't know but this truck has been driving me nuts lately. Mechanic said last Friday that it was fine and he couldn't pull ay codes from it, except for the brake switch problem. Anyone else have this problem with their 6 speed hydromatic? Up until tonight I thought maybe I was imagining things but my 5 year old asked me whats wrong with the truck as he could feel it too. LOL


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## RedArrow (Sep 10, 2010)

I can't add alot to your sittuation or help much other than to say that yes, the computer does control the shift points. I know this because I had the BlackBear tune and he changes the shift points to your liking with that tune. I know that doesn't solve your problem, but maybe it takes some of the fog away.


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## BDEMOTT (Oct 10, 2005)

i have the same truck. when i first got it last year at20k miles i was freaking out as to how funny it shifts. I asked my mechanic who has an 08 and he told me its the nature of that tranny. First gear is so low that it shifts out quick and hard, to keep it moving. And yes even out of tow haul it will downshift to an extent. Do you tow alot with the truck? Everytime i pull a good size trailer it rides and shifts like a caddy. The only conclusion i can make is that they plan for heavy loads and trailers and in tern causes it to be finiky when its unloaded


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## dlcs (Sep 2, 2004)

*Update*

Well on Sunday, I took the truck over to my uncle's house and let him drive it, to see what he thinks. He used to be a mechanic. He could tell right away that the truck was hesistating going into 3rd gear. Well we got to talking and I told him the only thing that i have done lately is change the air filter but that was 4 weeks ago or more. Well for grins and giggles we pulled the air fliter out and drove it around the block. The truck shifted flawlessly. Well, when I bought an new air fliter I got a Fram extra guard( only Fram air fliter available for the HD). This filter is obviously too restrictive for this truck. I went to the Chevy dealer first thing Monday and bought a oem filter, truck runs fine. When I first changed the filter it was still colder but when the temps warmed up is when the truck was starved for air. Makes sense to me cause the truck ran worse as it got warmer outside. Oem filters only for this truck! I never thought the air filter would affect the transmission. problem solved.


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