my 98 blazer 4.3 4x4auto shudders like a mad man btween 40 60 mph from what ive read it appears the torque converter is constantly locking/unlocking rapidly... other than a tranny service(which i intend on doing anyways) what can be done to fix this. is there an external solenoid or is thisall internal. any advice is welcome p.s. ive added lucas tranny fix(something i read in this forum as a suggestion to someone with a similar problem)

 

shudder is a funny word.
If your tranny was shuddreing, it would be from slippage and that is bad, no tranny service will fix it. Tranny rebuild will fix it, or a new torque converter. However if the torque converter is going out, the tranny shouldn't be too far behind it.Chemicals, or fluid change will not fix a tranny problem (never), they will at best extend the life until you can have it rebuilt.

As for shutter, is it really a shutter or is it a vibration? Say from a tire imbalance?
Search the Do-It-yourself section for a thread on Vibrations, page 3 I believe.

Now for torque converter locking and unlocking. If its doing this your rpms will flucuate as well. Here's the good and bad. Good, most tranny problems are actually engine performance problems. Teh puter adjusts tranny performance based on engine performance. You may not realize you have engine problems, but the computer does and its doing it best to compensate. Let if go long enough and you will get a SES. As for the bad, if it is the tranny, your due for a rebuild. What temp is your temp gage showing when up to operating temp? When was the last time the engine had a tune up? when was the last time you looked at the air filter, or replaced it? Your MAP/MAf may be dirty causing incorrect air readings which causes all sorts of engine perofromance issues.

As for the solinoid, possible and the only way to know for sure is to get it diagnosed by a reputable tranny shop. And thus my recommendation, find a shop you trust and get it diagnosed. A good shop will tell you if its the tranny or engine. Post up what they find out.

 

the reason i suspect torque converter lock/unlock is because i read in another post that while vibrating stepping on the brake or shifting down to third would make it stop if that was the problem proper terminology can be confusing. at 50mph i get a heavy shaking and the speedo even shakes. as soon as i shift in to third its smooth sailing

 

That sounds more like slipage in overdrive than. If it fine in 3rd and other gears I find it unlikely that the torque converter would look and unlock only in overdrive. Im sure this could be possible but it sound more like an issue with overdrive. Does it seem like its shifting up and down between 3rd and overdrive when you are at 50. You should be well into overdrive by 50 I think it starts at like 35 if I remember. You can check this by watching the RPMs when it does this,but remember to watch theroad too.

 

it doesnt seem like slippage the rpms are not jumping but the whole truck shakes like the rear tires are shaped like a stop sign. i checked my ujoints a while ago they seemed fine maybe i need to give my truck a good once over should the rear tires be off the ground when checking ujoints or does it not matter.