<div dir="ltr">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. <br></div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Jul 17, 2018 at 1:19 PM, <span dir="ltr"><<a href="mailto:eric@megageek.com" target="_blank">eric@megageek.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><font size="2" face="sans-serif">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.</font>
<br>
<br><font size="2" face="sans-serif">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.</font>
<br>
<br><font size="2" face="sans-serif">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?)</font>
<br>
<br><font size="2" face="sans-serif">I'm stumped, but I'd love to know that
this truck is safe for the next big load.</font>
<br>
<br><font size="2" face="sans-serif">Thanks.</font>
<br><font size="2" face="sans-serif"><br>
<br>
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