transmission surging in overdrive.

[broken_line]

i have a 87 s10 blazer and it will shift in and out of over drive really easily, if im going 65 it wont do it, but around 50 or so into the wind it will go up and down every 5 seconds it will also do this from 2nd to 3rd gear.. i was thinking it either needs fluid changed. or the torque converter is messed up as it shifts 5 times.. and its a 4 speed. it is also a little low on fluid. also surging immediatly goes away when brake is held down just enough for tail lights to come on (was told it locks converter out or something when brakes are applied) fluid color is red and smells normal not toasted like a buddies truck.

and ideas?? thanks!

[Deer_Assassin]

Best thing to do would be to pull the pan,change the fluid and filter, and go from there. The solenoid on those trannies can get hung up also.It controls the lock up on the converter. What motor is in the truck,how many miles,etc?

[broken_line]

it has a 2.8l v6 has 140k on it with 28" tires.

[Macgyver55]

or the torque converter is messed up as it shifts 5 times.. and its a 4 speed.

The last shift you feel is the converter locking up. The brake kight switch is also used to unlock the converter and/or disengage the cruise control if you have it.

By any chance have you worked on the cables or adjustments of them at the throttle body?

This transmission uses a cable (throttle valve cable)to determine the need for a down shift.

My guess would be that that the throttle position (at 50 mph into the wind) is right on the edge of where it needs to shift. Larger tire size can change the rpm at any given speed, so readjusting the cable will change the speed or throttle opening higher or lower.

One thing for sure is that proper adjustment is very important to the survival of your transmission. Driving it long term while shifting up and down will take it out sooner than later. If necessary, downshift it into drive rather than overdrive when it happens.

[Scott K]

What Mac said

[broken_line]

dropped the pan today and there was a little bit of sludge on the magnet, 1 tiny peiece of brass but other wise the pan was shiney inside, filter was black. oil hald dark red half pink didnt smell burnt and the cruise does not work at all. so could the TPS be shot? changing the fluid shure makes a mess!!

it looks as if the filter had never been changed out.

i was told to throw some trans tune in there when i get it all back together.. good idea?

[Whoaru99]

I'm not a believer of putting in additives for the most part.

If it were me, and it hadn't been changed forever, I'd probably change it again in short order...couple hundred miles maybe.

[jeffreyd]

i agree with last post, dont add anything, make sure you put the right fluid back in and replace the filter. Run a couple hundred miles and make the mess again, now you know what not to do to keep it from spilling. I usually take all the bolts out leave one in the middle front and one in the back of the pan, loosen the back one slowly and let her drain then carefully take the front bolt out and spill it everywhere. replace filter and oring and go back together. good luck