[Shop-talk] Brake issue on mason dump

[John Innis]

Does your truck have a vacuum booster, air booster, or hydroboost?  I am
guessing by the age and type it is a hydroboost.  If so, check and possibly
change your power steering fluid.  The problem could be there, in the ABS
unit or the master cylinder.  Also check that the brake warning light will
come on at bulb test.  If not, fix that and then see if it is coming on
when you drive the truck.  I had a similar issue with my 99 2500 that ended
up being the front wheel speed sensors.  Took a long time and a visit to a
very smart old timer to figure that one out.  But what was happening was at
speed, the sensors were working fine.  When I got below about 15mph, they
would cut out intermittently and the ABS would kick in, but only just a
bit, so that I didn't hear the pump run.  It felt like spongy brakes, was
really the ABS being dumb.  Confirmed the problem by disabling the ABS pump
and driving for a few days.  Fix was to replace both front hubs.  Not too
expensive, but very labor intensive.

On Tue, Jul 17, 2018 at 1:19 PM, <eric at megageek.com> wrote:

> Last year, the brake line on my '98 GMC 3500 mason dump developed a leak.
> I replaced the line, bled the brakes (BTW, the rear of a 3500 with a
> duellie is IMPOSSIBLE to bleed) and everything was fine.
>
> I've been using the truck infrequently without any issues (loaded and
> unloaded.) It's always garage kept.  Today, I had it loaded with scrap
> (just over a ton from the scale readout).  I was going down the highway for
> about 10 miles at speed.  At the exit ramp, the brakes felt spongy and the
> truck wasn't stopping normally.  Then, all of a sudden, I felt a jolt and
> the brakes worked normally.  I got out and checked and there was nothing
> that I could see wrong.  The rest of the trip they were fine.  I even ended
> up going down a 15% grade with the load and no issues.
>
> Question, what do I need to check?  What could have happened.  I can only
> think that maybe the booster pump wasn't working at first, then it kicked
> in.  (if that is even possible?)
>
> I'm stumped, but I'd love to know that this truck is safe for the next big
> load.
>
> Thanks.
>
>
> Sent from my Commodore 64 on a 2400 Baud Modem.
> Tech Viper
> "Be as beneficent as the sun or the sea, but if your rights as a rational
> being are trenched on, die on the first inch of your territory." Ralph
> Waldo Emerson
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