The truck belongs to my brother-in-law in Crescent City, Ca.  The truck is a 2002 Quad Cab, 4x4, automatic transmission with approximately 170,000 miles on the truck.  Every thing is stock.

 

The problem:  After about every 20 or 30 brake applications the brake pedal gets hard and there is no power assist.  As soon as he releases the pedal, everything is back to normal.  He took the truck to a shop.  The guy who runs the shop is a very knowledgeable man and his business has an excellent reputation..  He asked if the power steering worked when the event occurred.   My brother-in-law said that he didn't notice anything with the steering, but his focus was on stopping the truck..  The shop could not make the event re-occur.  No codes were set.  After discussion between the shop owner and my brother-in-law, it was determined to replace the hydra-boost with a remanufactured one.   

 

On the first long trip after the repair, the same event occurred twice again.  This time my brother-in-law did not release the brake pedal until after he tested the steering to see if the power steering was working normally.  It was.

 

Any ideas on the cause?  

 

- John

Only thing I can think of is the spool valve has an issue. You can get a Pirate Jack rebuild kit and rebuild the hydro booster. Then you can see what's going on.

Since the hydro booster was replaced, wouldn't the spool valve be a different valve?  I am always suspicious when a component gets replaced and the problem symptoms don't change.  That usually tells me that the original component did not fail.  Usually.  

 

A couple of questions:

 

Could a malfunction in the antilock brake system cause a intermittent hard pedal symptom?  If so, wouldn't a code be set?

 

Could  an intermittent blockage of return line flow from the hydro booster cause a hard pedal symptom?

 

This particular problem kind of baffles me.

 

- John

My truck had a sticking power steer relief valve, easy enough to inspect, I know this fault doesn't really point to the relief but it is really easy to check and rule out.

 

Also you say the hydroboost has been replaced.... that in my experience doesn't automatically mean the new part is any better than the old nowadays, was the booster/accumulator changed also.

If you still have the old unit Pirate Jacks kit is MIUSA and good quality

If the return was plugged I would figure it would apply the brakes being it can't release pressure. I still think spool valve being its not applying pressure to assist with braking. Maybe the pump but steering would be affected being heavy. Could be the inlet is plugged but I would figure steering again would be affect being its daisy chained to the steering.