I recently noticed this problem a few days ago. While I'm driving around (usually on highways) my blazer will jerk randomly as if a gear was slipping then catching or binding up with an audible single 'clunk' sound. It feels like it is coming from the rear. I've noticed it to occur when maintaining a constant RPM. Can Anyone shed some light on what may be the issue?

 

do you have a tach? can you tell if its the rpm dropping out?

i had a similar issue. thought it was the trans then started thinking it was a misfire. sounded like the timing was dropping out. started replacing everything, coil, full tune up, distributor, then for the heck of it i replaced the computer and problem solved. trucks ran great ever since.

but its hard to diagnose a problem without seeing it ya know. all those parts i had laying around so it didnt cost me nothing to swap stuff around

 

sounds like a rear diff issue

 

there's no change in RPM's when it happens. Just had the truck in the shop the other day b/c the timing was off, somehow it got set back so the timing is fine.

 

I don't know what you mean about your timing getting set back. Your timing is non adjustable and is controlled by the PCM it is either on or if it is off You might have some PCM issues. Just my thought.

 

the distributor base timing was set incorrectly

 

You do not set base timing as there is no adjustment besides the 1 tooth method...

Have you tested your fuel pressure? Leak down?

It sounds like a dead miss while cruising...

 

There IS a base setting for the timming, your mechanic will do that then the computer will adjust from there.