94 s10 blazer kicking in and out of overdrive

My S10 blazer is kicking out of overdrive even at 75mph. All the other gears work fine and has no slipping. I can't find what to adjust to help overdrive. Does this model shift with vacuum or is it electronic? I'm affraid my transmission clutches are failing, but if there is an adjustment, I would like to try it! Thanks!

All electronic for o/d, a trans capable scanner will see why this is happening.

The "94" Trans work off of Vacuum and your CMU. I was have the same trouble. I didn't have any error codes. So, here is what I found. Directly to the rear of the Plenum. You have a vacuum outlet that connects to a 4 way check valve "T". This "T" valve handles your AC baffels, emission, and trans. My Check Valve was leaking from the diafram. I replaced it and it was in top shape. Hopefully thats all it is for you. The other thing you mite want to check is your trans fluid. It should be pink to light red in color. If the trans fluid is dirty then your filter will restrick the flow and can cause it to drop out os overdrive.

Thanks! I don't have any error codes either. I will check out the T valve. I think I remember seeing it just beside the distributor cap, is that correct?





The "94" Trans work off of Vacuum and your CMU. I was have the same trouble. I didn't have any error codes. So, here is what I found. Directly to the rear of the Plenum. You have a vacuum outlet that connects to a 4 way check valve "T". This "T" valve handles your AC baffels, emission, and trans. My Check Valve was leaking from the diafram. I replaced it and it was in top shape. Hopefully thats all it is for you. The other thing you mite want to check is your trans fluid. It should be pink to light red in color. If the trans fluid is dirty then your filter will restrick the flow and can cause it to drop out os overdrive.

Thats the one!!!!!!!!! Good luck........

I have this same problem on a '92 S-10 Blazer, mostly anyway. The vents take a long time to switch between def/vent/floor/etc if they decide to switch at all.
I've also been told that my problems shifting the truck between 2wd and 4wd might be vacuum related (people with different year Blazers). 2->4 works fine, but getting back out of 4wheel into 2wheel varies.. sometimes it goes right away, sometimes it takes minutes.

My question is if that valve is in the same place on a '92.

I also have lost high gear (D and OD) recently, though at first I assumed the tranny had just seen its day (150K+ miles). Is the '92 tranny vacuum-controlled for D and OD?

Would be really great if that valve being replaced would solve almost all the problems with my Blazer. Then I could spend the money on the exhaust instead of an expensive (used, to boot) transmission replacement.

Sorry if I ramble, been a long day of searching and calling shops to ask opinions on the transmission. Vacuum leak was always secondary in my mind until I read here that the tranny might be vacuum-controlled too.

I have this same problem on a '92 S-10 Blazer, mostly anyway. The vents take a long time to switch between def/vent/floor/etc if they decide to switch at all.
I've also been told that my problems shifting the truck between 2wd and 4wd might be vacuum related (people with different year Blazers). 2->4 works fine, but getting back out of 4wheel into 2wheel varies.. sometimes it goes right away, sometimes it takes minutes.

My question is if that valve is in the same place on a '92.

I also have lost high gear (D and OD) recently, though at first I assumed the tranny had just seen its day (150K+ miles). Is the '92 tranny vacuum-controlled for D and OD?

Would be really great if that valve being replaced would solve almost all the problems with my Blazer. Then I could spend the money on the exhaust instead of an expensive (used, to boot) transmission replacement.

Sorry if I ramble, been a long day of searching and calling shops to ask opinions on the transmission. Vacuum leak was always secondary in my mind until I read here that the tranny might be vacuum-controlled too.

First of all, this valve should take care of your vent trouble, and maybe your trans problem. But your trans trouble sounds a little more complex. When was the last time you serviced your trans. (Fuild & Filter replacement)? This could be part of your trouble also. If you replaced the valve, trans fluid and filter and the trouble continues. You probably need to replace one of your solonids inside your trans. I'm not a trans specialist, but you can check this thread for more info on transmissinons. Good Luck..........

The trouble I experienced was the converter locking and unlocking on the highway. Replacing rotten vacuum lines cured what ailed it.