Need a brake expert
 

I have been using Search function but nothing I find seems exactly like my problem. Truck is a k10 that has had K20 running gear installed and this just started. Brakes are vacuum boosted power brakes. Problem is: Drive approximately 8 miles on freeway. Truck becomes increasingly sluggish, finally pull over and Rt front brake is smoking. Brake pedal rock hard. Wait approximately 45-60 minutes problem clears and truck drives fine. Drive on surface streets and some freeway approximately 25-30 miles no trouble. Next day drive approximately 9 miles on freeway. Truck becomes sluggish and brake pedal gets rock hard again. Wait 45 minutes and problem cleared. This truck has: New (re-man) calipers, new front brake hoses, new master cylinder and vacuum booster. Any ideas, suggestions opinions?

Re: Need abrake expert
 

Could be the pushrod between the m/c and booster is set up too long.

Re: Need abrake expert
 

defective reman caliper on that side and the heat is building up in the system and expanding the fluid ? ? ?

Re: Need abrake expert
 

Is metal brake line run any where near hot exhaust ? Maybe the brake line/fluid is getting hot and expanding and causing that caliper to "activate" ?

Re: Need abrake expert
 

Most issues like this I’ve come across are usually a sticky caliper. Take it apart, grind clean and make sure it isn’t binding.

Re: Need abrake expert
 

It does sound like you have a caliper dragging but that indeed could be caused by the rod between the booster and the M/C.

I had a similar thing happen to me after I had completely rebuilt my brake system. Although I discovered it before driving any real distance or before it got hot, my pedal became very sensitive (worked like air brakes) then the truck wouldn't move for a while.

After going over everything, I discovered that I had the adjusting rod under the dash a little too tight. Backed it off a little and haven't had a problem since.

Re: Need abrake expert
 

You can also have a clogged rubber line between the frame rail and the caliper if they are original.

Re: Need abrake expert
 

Thanks for all of the replies. Right now I am thinking sticky caliper and will look for this when I get time. However, I would lik to know more about the rod between the booster and MC. If I recall correctly, It was a solid rod. Do these come in different sizes or are adjustable ones made?

Re: Need abrake expert
 

I thought they were all adjustable. Research shows I’m wrong.
A test to see if the pushrod is too long might be to just loosen the m/c and slip some shims in too hold it forward while you test.

Re: Need abrake expert
 

Geezer. I may wind up trying that. I will look at the caliper first and then at the push rod. if it is not calipers. Of course, If it is too long, where am I going to get one that is correct? Does any one sell adjustable length rods?

Re: Need abrake expert
 

Geezer. I may wind up trying that. I will look at the caliper first and then at the push rod. if it is not calipers. Of course, If it is too long, where am I going to get one that is correct? Does any one sell adjustable length rods?

Re: Need abrake expert
 

Who makes your m/c and booster?
Where they a matched set?
You might need to wait until you test.
I’ve found some on summit or jeg’s But it depends on the manufacturer.

Re: Need abrake expert
 

Geez. Thanks for the info. Sorry to be so long replying but my computer developed a bad power supply (I hope that's all It is) and the only access I have is to use wife's until I get a new one. She writes and so is using it constantly. Probably won't get to the truck again until tomorrow or Saturday. Then I will look at caliper first and take it from there. MC and booster were (I believe) from Rock Auto as a set I will look for more info today. Just to be clear, we are talking about the push rod that goes between the booster and the MC not the one from the pedal to the booster. Right? One other question. If the problem was at the MC wouldn't it affect all wheels equally or at least the front or back in pairs? Later. "She who must be obeyed" wants her computer back.

Re: Need abrake expert
 

The best way to figure out what is going on with that brake is to drive it until it does its thing then open the bleeder on that caliper. If it blows off pressure and the wheel turns easy after that it is in the hose or line. If it doesn't change then it is in the caliper.

Re: Need abrake expert
 

Checked up on my Rock Auto purchase records I bought the MC and booster separately, not as a set. Pretty sure I used the push rod from the old MC/booster assembly.

Re: Need a brake expert
 

I like forums, and I like searches within them. A couple of weeks ago I had the privilege of spending over an hour on the interstate moving only a couple of feet every few minutes due to a wreck ahead. After a while I noticed the truck was not coasting when I released the clutch. Later it got harder and harder to make the truck move, and it was very obviously dragging. When traffic started moving I went to the shoulder and went maybe a mile at around 10 mph. I then stopped, and a hand on each hub cap easily identified driver side front as very warm, other three not warm. I presumed a front caliper problem, so I replaced both. A drive around the block announced: Not fixed! I then came to the forum, and here I find advice for someone who had the same problem before me. Opening the bleeder screw, as suggested in post #14, released the caliper, so I now suspect the flexible hoses. I used to be good about changing them around every 10 years, but my record shows I last changed them in 2014. I will order new ones tomorrow.