I have a 94 Blazer with the 5.7 litre engine. It has 188000 miles on it and up until a few weeks ago no issues with the transmission. At low speeds it seems to be searching between low and second gear, but at higher speeds it will shift out fine all the way through Overdrive and recently i noticed that the speedometer is not working sometimes when driving at low speeds. I only use the truck for driving around hunting club. I was going to have the transmission serviced but was told it was not a good idea on a vehicle with this many miles. I have checked the fluid and it is brown so I know the fluid needs at the least changing. My question is do I just need to drain the fluid and replace it or do I need to replace the filter too taking the chance of messing up anything? It has 4wheel drive and all seems to be fine when the engine is running at higher rpms, but just has the issue at lower speeds and cruising around the woods. Could it be a vaccuum line or modjulator valve? A new transmission would probably cost more than the vehicle is worth so i am hoping it is a minor issue. If anyone has some troubleshooting ideas to try out, please let me know.

 

Well, if it's anything like the one I just did, a piston wore out and let the band slip which engages 2nd gear. A possibility of what is going on. When you are turning higher RPMs you'll be producing more pressure which will let the band clamp harder so it wont slip.

My guess would be that you should plan on it not working in the next month or two. Until then it'll just slip until it hits 3rd gear. But it'll eventually run enough filings through everywhere and start breaking down more parts.

 

I'm not sure if your blazer has this but there might be a vehicle speed sencor on the tail shart of the transfer case and that will make your transmission act like its gone .It will also mess with your speedometer , this part went on my blazer .