Hydroboost

[jhenderson]

I'm experiencing a strange problem. When I first start my truck, the brake pedal is fine, but when I back up and turn the steering wheel the pedal goes a little soft. I have always found a bad hydroboost to give a hard pedal. Could low flow from the power steering pump give a soft pedal? After the initial low pedal the brakes are fine, unless I have to perform some tight maneuvering, then I may or may not get the low pedal again. One or to pumps and it's fine again. The problem seems related to steering input at low engine speed. I don't want to throw parts at the problem .

 

[AH64ID]

Since the brake boost does come off the power steering pump your issue could be the pump itself.

Have you ever changed the fluid?

I know when I changed mine a couple years ago it made a big difference in performance from the pump, the ATF in the PS pump is probably the single most neglected item on the pickup.

http://forum.mopar1973man.com/threads/1298-Power-Steering-Flush-on-a-3rd-Gen.?highlight=

 

[jhenderson]

I changed the flid when I replaced the steering box, a short time ago.

 

[AH64ID]

Then I would guess it's the pump.

 

[jhenderson]

What bothers me is that I always thought low pressure or low flow caused a hard pedal, not a soft one.

 

[ata]

It sounds to me like you might have some air still in the system. Jack the front end up off the ground start the engine and turn the steering wheel left and right from lock to lock lots of times and then check the fluid level and for bubbles. With the engine OFF.

 

[sag2]

Make sure the calipers are not contacting anything when turning full lock. Many years ago there were a couple of models that the steering stops were not positioned correctly on. The caliper contacted the frame/body and allowed the piston to be pushed into the caliper slightly. You then had to make a brake application or two to get the pads pushed back against the rotor.

 

[jhenderson]

330,000 miles. I don't think anything has started to move calipers at this point. Maybe I'm jumping to conclusions. I'm going to look at the master. I've been thinking hydroboost or pump because I opened the system when I changed the steering box. Could be I'm looking for zebras when I should be looking for a horse.

 

[Got HO?]

Check your front hubs for play. If you have movement when turning, the rotors will push the pads back in the calipers and give you increased pedal travel until they are seated again. At that mileage, a master cylinder failing on one circuit is also a possibility.

 

[jhenderson]

I put my truck up on the lift tonight. All of my caliper hardware is badly worn, but the worst problem is 2 broken caliper mounting bolts on the right rear. I imagine that's my biggest problem. I'll drill them out and tap them for a temp fix until I can get a new mount. The mount is worn where the caliper rides, and I assume this led to the broken bolts. Thanks for all of the ideas and help. Getting other opinions always helps me think. Jeff

 

[sag2]

They sell aftermarket oversize thread caliper bolts. Google it and you should be able to come up with some if you know the thread size and pin diameter. O'Reilly's and Autozone usually stock them.

 

[jhenderson]

My main concern is the wear on the caliper slides. I'm pretty sure this is what led to the broken bolts. I'm going to weld up and machine the worn areas for now. The I'll source new mounts.

 

[jhenderson]

I'm back up and running. Everything is back to normal. The inner diameter of the wheel itself was holding the caliper on the rotor With the caliper no longer bolted to the bracket, going back and then forward moved the caliper away from the mount and allowed one end of the pads to turn towards the wheel and off of the rotor. This allowed the pad to flex and give me the soft pedal. Coincidence had me thinking it had something to do with power steering pump or hydroboost. Just because I turned the steering at the same time, I ASSUMED it had caused the problem. At my age I should have known better. Always start with the basics.