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 1996 GMC Topkick hydro-boost motor stays on
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United States
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Posted - 08/16/2013 :  12:28:44 PM  Show Profile  Visit robert21's Homepage  Reply with Quote
Hey Guys,
we have a 1996 GMC Topkick with a 3116 CAT engine. The problem is the hydro boost motor stays on unless you manually pull up on the brake pedal. We replaced the return spring and even the hydro boost unit - it was ok for about 4 months, then the same problem recurred. We checked the brake pedal mechanism but can not seem to fine anything wrong. I am sure we must be missing something. We have a bungee cord attached to the brake pedal to keep the batteries from going dead. Thank you for your time.
Bob Coholan Skyview Service

Well, it's fixed. It seems GMC did not have a clear listing on the brake pedal return spring part. The CORRECT part is #15688632. The confusion came in because there was no such part listed under this particular vehicles' VIN. Many thanks to 'Nadeem' at Beyer Bros GMC in Fairview, N.J. for going the extra mile and tracking this down for us.
As we say all the time these days .... "It's ALWAYS something!"

thanks for watching / reading / listening and most of all...careing!

Edited by - robert21 on 08/22/2013 2:15:19 PM

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208 Posts

Posted - 08/16/2013 :  12:40:03 PM  Show Profile  Reply with Quote
I've not ever worked on a Top Kick, so this may not directly apply, but that sounds like a faulty or out of adjustment stop light switch to me.
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United States
3424 Posts

Posted - 08/16/2013 :  2:21:02 PM  Show Profile  Reply with Quote
Originally posted by eddo

I've not ever worked on a Top Kick, so this may not directly apply, but that sounds like a faulty or out of adjustment stop light switch to me.

That's what I was thinking. I think these are set up just like a '93 to '03 Chevy/ GMC school bus. I really hate to tell you this, because you have spent so much money on this, but there is a little adjustment lever on the brake light switch that will make it quit. Your brake lights might be coming on when this is out of adjustment too, but not always. If the switch could possibly be bad as well.

Here is a switch like they have, listed on Ebay.

The adjustment I am talking about is the small tab at the base of the longer lever. Just move it until the motor quits. Make sure you didn't move it too far by pressing the brake pedal with the key off to make sure the motor still comes on.

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