blew out a trans cooler line...now slipping in 3rd gear..'99suburban
 

HELP!!
The wife was driving our 1999 suburban and a trans cooler line blew. she didnt realize it until it stopped moving under its own power. So i go and add fluid to it. replace the line, thoroughly check the fluid level (its correct) and now when it hits third gear the engine just runs away and nothing happens. play with the throttle a bit and it will grab third but something is up. would running it really down on fluid, i added 5.5 qts, kill third gear or take out a transmission?
its got 4wd and has the 5.7 motor.

the things has been flawless for years now this...and to take out a trans for a simple line would really suck.

I'd check the tranny fluid again to make sure there's enuf in it.

i agree with ya there...checking auto trans is such a PITA...the fluid is so pale and i guess the stuff is slightly moving around in there.. and ya gotta check it while its running....but it sure looked full

I have a '94 with the heaver duty 4L80E transmission as it is a factory build for towing. Despite the heavier duty transmission, it has been rebuilt a total of twice since 1994. Seems like it is probably time for a rebuild. on your '99, especially running it while it was low on fluid does not help it at all.

It sounds like low pressure to the third gear band actuator, causing it to slip. When you said playing with the throttle sometimes caused it to engage, that's what I thought of.

If the trans was working good before, I doubt that you completely wore the third gear band so fast.

Maybe there is some debris lodged in the valve body third gear passages because when it went low debris moved around in the trans.

First, double-check the level (using the proper procedure for your tranny). Then if it's really ok, time to take it to a reputable trans shop who could diagnose the problem. NOT the type of shop that just says "time for a rebuild".

Steve

02Sub,
That seems to make sense. the vehicle has about 115k miles so relatively low for its year.
Yeah a "rebuild" or new will be pricey.

it was working fine before the "incident"...thats what is so strange....but running it down that low on fluid cannot be a good thing thats fer sure.

the fluid should not be pale. it should be bright red. What type and brand of fluid did you put in?

It's DEXRON III...just not a dark color like motor oil..and 51 yr old eyes! lol