I posted this in the Bravada forum but thought it was worth posting in the Blazer forum.

I have a 1999 Bravada I bought used 3 weeks ago with 62k miles. It was a replacement for my 1997 Bravada with 205k miles.

The 1999 had the front chatter problem associated with not having blue autotrac II in the transfer case. Below is the mistake I made:

Made a huge mistake. I changed out the front differential fluid instead of the transfer case fluid. I put trac II fluid in the front differential.

Funny thing- this corrected the problem. But for how long and at what cost. After discovering my error I immediately went to GM and got the front differential lube ($15 a container and it took 3 containers). and also picked up more trac II for the transfer case.

I discovered the transfer case did have blue fluid in it.After changing both fluids, the Bravada does not have the chatter problem. The Bravada did have the chatter problem prior to putting trac II in the front differential. This is very concerning that putting blue trac II in the front differential also corrected the chatter problem.

A few thoughts-

Old fluid in the front differential can also cause the chatter problem commonly identified as a transfer case/ autotrac II problem

Autotrac II may need to be replaced on a regular basis in the transfer case.

Guess I will be changing the front differential fluid soon to make sure all the autotrac II is flushed out. Another $45 to the local GM dealer. The bottle for the front differential stated it was GM's advanced product and the [art number is different from what the owners manual states- the parts guy stated this is a newer lube developed for better performance.