Brakes

[Vulnavia]

2006 chevy 3500 express van. 194000 miles, daily driver and tow vehicle.
Problem: Every so often, go to brake and the pedal is rock hard, really hard as in won't move for a split second followed by a split second of, I will call it a "gap" the pedal moves a very small amount to normal pedal and brake feel.
Any ideas before I take it in?

Thanks,
Will

[billtebbutt]

Master cylinder would be my guess. Sounds like the piston gets "hung up", or perhaps the linkage between the pedal and the MC has developed wear or a "groove" that shouldn't be there.

In any event, get it in the shop asap!

cheers,
BT

[Apexcarver]

I would say booster actually. one thing to be very cautious about is the possibility of a master leaking into the booster and hydraulically locking the booster.

The hard pedal is indicative of loss of the assist provided by the booster, there is a lot to unpack diagnosing if its the internal membrane of the booster or something regarding vacuum supply though.

With that age/mileage, I would seriously consider just loading the parts shotgun with a new master and booster just to refresh a system that isnt a good territory to have a failure on your tow pig.

[DaveW]

I would say booster actually. ...
The hard pedal is indicative of loss of the assist provided by the booster...

Booster makes sense, especially with the comment on split-second delay. Does this happen randomly, or only on startup after a long rest? Knowing that may narrow the possibilities.

It could be that the check valve (or some other hose connection) that lets air be sucked out and seals the vacuum into the booster is leaking.

[Vulnavia]

Taking it in Monday.

Thanks for the thoughts and replies.

Will

[Vulnavia]

Its random and infrequent. Drove 220 miles yesterday and didn't happen at all.

Will

[Garey Guzman]

With it being random and infrequent, it may be difficult for the Tech to diagnose.

First thing to note is if this is a mechanical lock vs. hydraulic lock. IOW, does the pedal stop like it hit a stop or did it stop like more "squishy" like when you push the pedal before starting the van? The first may indicate a pedal assembly or linkage issue while the latter would indicate something else.

If brake fluid level in master cylinder reservoir is ok, don't need to worry about fluid in the booster. You'd have to refill the reservoir a couple times to fill the booster!

Maybe try pushing the pedal different ways while idling in the driveway in park. If it's a linkage issue, perhaps you can change the angle your foot hits the pedal to see it you can duplicate. Without a way to duplicate, it may be returned NDF, unless this is a chevy thing that the tech has seen before.

[mikey]

Is this a hydroboost or vacuum boost system?

my 2005 3500 pickup does the same thing. I've replaced the hydro booster and it got better but still get a weird random "kickback" feel sometimes.