I bought my 4x4 1998 blazer less than a year ago. I starting having some issues about 2 months ago but they are getting worse. While driving down the road between 40-70MPH the rps drop 200-300 and kick back up and it keeps going. When the problem was first noticed it would only happen when in drive and going up hills. now it will do it while in 3rd gear and drive, and it happens on flat road and hills. The transmission is making a humming sound once I get to 40MPH, the faster I go the loader it gets, but the tone of the humming doesn't seem to change. When I get to about 70MPH and the humming stops. When I tap the breaks while the rpm's are surging it doesn't seem to help. I noticed the issues started shortly after I had the seals on the front and the rear of the drive shaft replaced since they were leaking. The cruise control stopped working and the truck pulls to the left while driving down the road. What could be causing this? I'd like to avoid huge costs so any help will be greatly appreciated. I'm going to attempt to attach a video and hopefully it helps.

Trans help needed, 98 blazer - YouTube

 

Check your fluid level and see if it's a brownish color.

 

It's a little brown, smells burnt, going in Monday night for new fluid filter change. but could that cause all these problems?

 

It's possible, mine had similar symptoms right before I needed my transmission rebuilt.

 

I hope it's not at the point it needs to be rebuild, don't have the funds for that.

 

Honestly, I'd start saving cause I didn't and all of the sudden it went out. I mean it could be fine but you never know.

 

i have this problem now for 2 days at 40 mph only under light load , any suggestion?
if its the torque converter can i keep driving it at least i dont want it to break down ?

 

It's that type of part that may last 2 days or two years it really depends.

 

i did the transmission flush and there is no more shudder i was getting it at exactly 65km/h or 40 mph , the shop replaced all 12 liters/quarts

 

Bad tranny fluid can cause ALL sorts of odd problems in any vehicle. Worst I ever saw it was in a Subaru I had once. I replaced the transmission fluid and the differential fluid. It was burnt so bad my buddies standing 10 feet away could smell it, they thought I was using a lighter underneath and caught something on fire.

Once replaced my torque bind was gone and the tranny was quiet as a cave.