ATF recommendation for a worn trans, 98 GMC

[Rachael]

My 98 Suburban with 185K (w/ the 4L60) has always done a lot of towing... still tows several times a year... and now when I pull out of park the truck kind of bangs into gear. The 1-2 shift is also pretty hard if I am not super careful. The fluid/ filter is about 9 months old and I'm going to change it again. It was AAP store brand dex/ merc. The transmission has been doing this for about a year without really getting worse, so I think it still has some life left in it.

What easily available ATFs are nice and thick for my feeble transmission? It is mostly a utility vehicle so it will probably be doing some more towing in the future (It actually shifts perfect without fail when it's pulling something ???). I was also thinking about running some Seafoam Trans Tune before I drain the fluid. Is that a good idea too?

 

[Chris Meutsch]

Does it do it only when cold or all the time with the banging?

Perhaps a high-mileage ATF?

 

[SteveSRT8]

you probably have a stuck pressure regulator, it's a common thing in those trans. I've seen it occur in the updated 4L65-E as well.

Get some Dex VI, any brand is excellent, but I usually buy the Valvoline as it's full synth.

It's a great upgrade, fully backwards compatible.

I would be VERY careful with the additives. I'm not a fan.

 

[CourierDriver]

go to Napa,,,get the product called Lubeguard, only one recommended by the OEMs,,make sure u get the bottle that is for GM for sure, this stuff is a miracle worker and look them up on the internet for sure,,,I use it in my one ton van,,shifts better and reduces friction and heat, but I also put on an oversized transmission cooler for heavy loads.

 

[sciphi]

Valvoline Maxlife ATF. It's worked good things on my Buick's transmission.

 

[Rachael]

It does it cold and hot, but probably a little worse when cold.

I am especially curious as to which brand of ATF is thickest, as I thought that might help it hold together a little better. I have always used the Lucas trans fix product to thicken the fluid, but from what I have been reading about Lucas products on this site I don't think I want to use it anymore.

 

[unDummy]

Flush your transmission with a quality ATF. Don't use any additives.
Any high mileage ATF, full synthetic Dex/Merc, or any DexronVI can be used.

 

[EricF]

I have yet to actually verify this.. but a GM Parts guy told me when that happens the throttle position sensor is at fault, and it won't generate a code.
he said that the computer is misreading the throttle valve so the transmission bangs into gear.

What he said makes sense.. but I've yet to try it out / verify it.

 

[SteveSRT8]

the reason it does it worse when cold is the pressure in the unit is higher when cold than hot.

The LAST guy I would believe is a stealership mechanic. Go to a local rebuilder who does those trans every day.

 

[Rachael]

Is there any resource that has the viscosity ratings for each of the popular fluids? tried a search and couldn't find anything... like which is thickest: castrol high mileage, or Valvoline MaxLife? those are the two that are most available to me in high mileage form.

 

[bmwtechguy]

Sounds like a broken accumulator spring. The accumulator is a hydraulic "cushion" to prevent banging into gears. Does it also bang into reverse? If so, then I would be more suspect of high line pressure.

 

[Rachael]

yes it definitely bangs into reverse. I don't even make enough money in two months to pay for a rebuild, so that's out of the question. When the trans finally goes, I will save up a couple hundred bucks for a JY replacement and put it in myself. I am just look for a good fluid/ filter combo that might help it last a little longer. Unless, of course, there is a way to fix it myself with no transmission experience aside from taking them in and out... is there a simple way to reduce line pressure if that seems to be the problem?

 

[SteveSRT8]

Originally Posted By: SteveSRT8
you probably have a stuck pressure regulator, it's a common thing in those trans. I've seen it occur in the updated 4L65-E as well.

 

[Rachael]

hmm okay, did some research on that and it looks like there's a transgo shift kit that's supposed to solve this exact problem, and be easy to install as well!! Guess i will try that. thinking i will go with castrol high mileage fluid.

 

[cronk]

Originally Posted By: EricF
I have yet to actually verify this.. but a GM Parts guy told me when that happens the throttle position sensor is at fault, and it won't generate a code.
he said that the computer is misreading the throttle valve so the transmission bangs into gear.

What he said makes sense.. but I've yet to try it out / verify it.


This was the problem with my 93 c1500 when I first got it a couple years ago, slammed form 1-2 like it had a shift kit.
$30 for a throttle position sensor and it shifts like new.
That was the older throttle body injected engine, don't know if it would cause that issue on a newer truck.

 

[cronk]

Also I would recommend Maxlife ATF.
Its working great in mine!

 

[cchase]

Originally Posted By: cronk
Originally Posted By: EricF
I have yet to actually verify this.. but a GM Parts guy told me when that happens the throttle position sensor is at fault, and it won't generate a code.
he said that the computer is misreading the throttle valve so the transmission bangs into gear.

What he said makes sense.. but I've yet to try it out / verify it.


This was the problem with my 93 c1500 when I first got it a couple years ago, slammed form 1-2 like it had a shift kit.
$30 for a throttle position sensor and it shifts like new.
That was the older throttle body injected engine, don't know if it would cause that issue on a newer truck.


I have to laugh at reading this because it happened to me as well. It did throw a code though when the TPS went, so if the truck isn't throwing a code the TPS is likely fine.

 

[Boss302fan]

Maxlife at Walmart...It will work great for your application and may help within a few hundred miles.