Transmission experts please advise on tow/haul mode.

[Chris B.]

My 2003 1500 Silverado 5.3 with the 4l60e seems to shift harder then it should when I use the tow/haul mode. It shifts fine when it is in normal mode. It is supposed to shift harder in tow/haul mode to help tow but when it shifts from 1st to 2nd sometimes it really slams into gear and the whole truck shakes.
Now I had it at the dealer and their transmission expert who has 28 years working on GM transmission went for a ride with me said it was building to much pressure and shifting to high an RPM. He said some little pressure or regular valve is at fault(I forgot what he called it). He also said that that is not really bad thing and would make the transmission last longer getting nice solid shifts in there. I asked him if I should leave it like that and he said if it was his truck he would leave it like that. He said it was kind of like adding a shift kit and getting nice solid shifts and not slipping and was eaiser on the clutches.

Is this guy blowing smoke up my butt to get rid of me? He seemed very nice and knowlgble and took quiet a bit of time to explaine how this worked so I feel he was honest with me. What do you think? Does he sound like he knows what he is talking about?

 

[MolaKule]

It sounds as if he is talking about a valve body spacer plate to retime the valving, such as to shorten the time of the transition from one gear to another:

http://theoildrop.server101.com/ubb/ultimatebb.php?ubb=get_topic;f=16;t=000713#000003

Do some "Googling" for the keywords mentioned in the above link.

How does the tranny shift when there is no load?

Also investigate whether or not there is a code upgrade for the computer.

 

[JohnnyO]

What he's saying could be true but....
When a normal automatic shifts gears, for a few fractions of a second it runs in both gears at once so as to shift smoother. Now, if you put in a shift kit, it reduces or eliminates this because #1, it reduces heat buildup, #2, acceleration is better, and #3, for a racer comfort is not a factor. My somewhat educated guess is that the Tow/Haul mode does this too, again mostly to reduce heat.

 

[JTK]

Chris, I wouldn't worry about it unless it bangs through the gears (in tow/haul mode) while towing/hauling a heavy load. I had a 1998 K1500 4.3L with a 4L60E that shifted hard from day one. I dropped the pan at 30K & 60K mi for regular tranny service & the ATF always looked new- never had any problems with it. Shifting was always smooth as silk with weight in the back.

G/luck
Joel

 

[Chris B.]

I don't think I'm going to worry. The tech showed me a tranny he was in the process of fixing and showed me the exact part that causes this. He took quiet a bit of time which impressed me as dealers usually try to get you out of their hair fast. He really tried to assure me it was fine so I hope he knows his stuff. I have a 100,000 mile warranty anyway.

 

[Weatherlite]

To get that smooth feeling when shifting there is always a compromise. On a tranny it's the clutches. They are slipped to provide smoothness which wears them out more. A hard shift is good. Less wear, less heat, better mileage in the long run.

However, like said before, if it's banging through the gears HARD then it may not be good. I drove a truck with the same tranny and it had shifts so hard that it sounded and felt like someone was pounding the floorboard with a sledgehammer. That was bad. Tranny was definitely messed up. If yours is that way then get a second opinion.

Otherwise, enjoy the firmer shifts and the benefits that go with em!

Mikie

 

[Chris B.]

When it is not in tow/haul mode it shifts smooth and on bangs in tow/haul durring the 1st shift from a stop the rest of the gears are firm but not quiet as hard. I showed this the the tech and he still was not worried about it.

 

[47HO]

If its only doing it in tow mode I wouldn't worry about it. As has been said, that's a good thing for towing.

 

[Chris B.]

And it only does it on the 1st to 2nd shift the others are more of a smoother clunk. The tech said each gear has it's own pressure valve(or something like that) and the one for the 1st to 2nd gear was building more pressure then the others.

 

[Bob Woods]

I have a 2002 GMC Sierra and it doesn't shift harder in tow mode, it just shifts at higher rpm's and speeds. Hard shifts on these transmissions lead to bigger problems. If you don't get it fixed make sure you have it documented so when it fails later you have some recourse. When I'm not towing anything it shifts the same in or out of tow mode.

 

[Chris B.]

quote:

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Originally posted by Bob Woods:
I have a 2002 GMC Sierra and it doesn't shift harder in tow mode, it just shifts at higher rpm's and speeds. Hard shifts on these transmissions lead to bigger problems. If you don't get it fixed make sure you have it documented so when it fails later you have some recourse. When I'm not towing anything it shifts the same in or out of tow mode.

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Bob, how do you know that hard shifts might give me problems later?

 

[Bob Woods]

Chris, Do a Google search for "4L60E hard shifts" plus hard shifts are like popping the clutch and thats bad for mechanical parts too.

 

[Chris B.]

Thanks Bob. The more I think of it the more I think I'm going to have them fix it the way it was before.

 

[Bob Woods]

I don't blame you, GM is the same company that tells us knocks (piston slap) on start up is alright. Yet I keep hearing about GM owners getting new engines paid for by GM.

 

[JWRENCH]

I also had a '02 GMC and it shifted only slightly harder and at a higher rpm in T/H mode. Actually the difference should be in the programming not the transmission. I could take my Predator programmer and make my tow/haul shifts very mushy if I wanted to.

Hard shifting due to higher fluid volume (shift kit)is ok, but if it's through high pressure it will soon take its toll. I know a lot of the guys I've talked to at the ls1tech site have found that out the hard way.