'02 4dr 4wd with 153k miles; yesterday driving on highway at 70mph or so, after about 20 minutes into a 60 minute trip had 5-7 occurrences where it felt like I drove over a very rough section of road or got hit with a blast of high winds...neither of which were present. The occurrence lasted for less than a second, engine RPM never varied, just a brief shudder. This has happened before, but only once or twice during same trip...and then all fine for several trips. Yesterday was the worse.
Got off highway after about 45 minutes onto surface streets and all was fine again.
Have check trans fluid and is fine, had fuel...and like I said, RPM never varied so I do not think it is engine missing. No Check Engine Light either.

Was wondering if this is first signs of transmission going out?

Any thoughts?

Thanks

 

After more searching, sounds like this is likely the torque converter unlocking / re-locking...

Again any thoughts??

 

Mine did the same thing or something very similar. It started out mild and gradually got worse over a year. I was told it could have been many things from an axle going bad up to tranny going bad. I had gotten tired of wrenching on it and just sold it. Mine was a 2002 ZR2 Blazer. I had previously replaced the shift solenoids a couple of years earlier and had an itch to do the others as well but didn't. So bottom line is I never found out what was really wrong. About 6 months after I sold it I saw it posted for sale saying it had tranny issues. He sold it and it has been seen around town though. Sorry I didn't answer your question but I would like to know as well what the problem is.

 

Sounds like you might have case of TCC (Torque converter clutch) shudder.
To verify you will need to either
A) when you feel the shudder slightly apply the gas to see if it gets worse & depress the brake pedal to illuminate the brake lights, but not enough to apply the brakes. (You will be 2 footing the gas and brake.) This will unlock the TCC and the shudder will go away. keep in mind that this maneuver is the when the ignition is requesting the most output from the coils to the sparkplug's and is misdiagnosed as TCC shudder and is actually bad plug wires.
B) scan the vehicle for codes, you should come up with a P1870 code TCC slip. you will need a better than a $200 code reader to do this. If you look at transmission data for the TCC you will see a slip speed if it goes beyond 200 RPMs of slip it will set the code. If under 200 RPMS of slip it will not set the code but you may feel the slip as a shudder while the computer tries to ramp up the apply pressures to clamp the TC clutch for the slip.
Depending on severity, the fix for this is.
1) install a bottle of "shudder fix" from your local parts house for $8-$12. short lived but works.
2) To install a 1" piece of 1/4" brake line tubing in the TCC apply valve to block its movement. turns the PWM (pulse width modulated) TCC apply into a On/Off apply or
3) Techpack Fitzall makes a replacement valve for the TCC apply that you can replace or
4) Transgo has a shift kit available with a new valve to install in same location. Comes with much better instructions too. (this is available on eBay with all the gaskets required for $50-$75, if not PM me)
5) replace the valve body and/or torque converter
6) overhaul the transmission complete with a new converter.
As a retired transmission rebuilder option 3 was my choice and only did not fix it with TCC slip/ P1870 code 1 time.

 

Just a quick update; made the same exact drive the next day and nothing.
I did check the trans fluid again and this time in better lighting; level was good, but color of fluid seemed to be more brown than red. Since it has been quite some time since I changed filter/fluid going to get busy and do that.

I will try the brake/gas pedal procedure next time it does the shudder.

Thanks