New member needs help! (new booster same issues) (1 Viewer)

[PNW80]

My initial issue started a few weeks ago. While coming down a hill, I hit my brakes to discover a very soft pedal. I pumped a few times, which seemed to build pressure and the brakes functioned so my initial thought was the booster was bad. I pulled over to discover that my back brakes on both sides were smoking. Testing further convinced me that the booster was bad (pump the pedal a few times, builds pressure but engine wants to die).

Fast forward, I have replaced everything in the brake system apart from the hard lines and the master cylinder (which appeared to be relatively new). OEM booster, all new soft hoses, calipers, rotors, pads, bearings, everything in the rear as well.

What I would like to know is: What are the chances I received a defective booster? What else could be the issue (this only happens when the brake pedal is depressed and worsens when you pump the pedal).
Thanks

 

[red mud fj]

Experience my fair share of brake issues, replace a rebuilt booster less then a year old during Cruise Moab so possibly it's the booster.

Recently replaced timing gear gasket, crank shaft seal and valve cover seal. What a major difference eliminating those Vacuum leaks made. Brakeing is very good.

Look for engine vacuum leaks.

 

[ppc]

A booster failure would normally show as a hard pedal. That could also be a vacuum leak in the hose or failed check valve. Brake failure going down hill most likely cause is overheated brakes. The brake fluid can boil producing gas bubbles in the lines. Old brake fluid has absorbed moisture and can lower the boiling point.

If pumping the brakes results in better brakes then there is a good chance the wheel bearings are loose causing the rotors to wobble somewhat pushing the pads outward.

 

[RFB]

I have just done all the above as well, All OEM. if you dont have a speedi bleed or power bleeder borrow or buy one. Also do you still have ABS and LSPV in truck?? I ask because I removed ABS and LSPV several months ago, and brakes were better. And I just did ALL new OEM and then after gravity bleeding, not so great. After using speedi bleed on truck, I fianlly have brakes.

 

[bulax99]

You should probably replace the master cylinder. They are a dual plunger setup so if one starts deteriorating the other will provide some function. One plunger drives the front and the other drives the rear. If one is going out you will get less pressure to the front (sounds like what you are experiencing) and the rears are being overloaded for lack of a better word. The fact that it’s a soft pedal and pumping it a few times brings it back to a firm pedal means that you are getting pressure back to the front. Sometimes brake fluid will seep down the outside of the brake booster (where the MC bolts to the booster) or the fluid will leak inside the booster. Hope this helps.

 

[BILT4ME]

You should probably replace the master cylinder. They are a dual plunger setup so if one starts deteriorating the other will provide some function. One plunger drives the front and the other drives the rear. If one is going out you will get less pressure to the front (sounds like what you are experiencing) and the rears are being overloaded for lack of a better word. The fact that it’s a soft pedal and pumping it a few times brings it back to a firm pedal means that you are getting pressure back to the front. Sometimes brake fluid will seep down the outside of the brake booster (where the MC bolts to the booster) or the fluid will leak inside the booster. Hope this helps.

I doubt its half of the master giving out.

What is more likely the cause for the rear brakes smoking is an improper adjustment of the LSPV (Load Sensing Proportioning Valve) that adjusts pressure to the rear brakes. More pressure as the rear squats, less as the rear raises.

You mentioned they were smoking after coming down hill.

First, DON'T ride your brakes when going downhill. Use the gear shift to downshift and use engine braking. You can safely push the engine to 5000 RPM when engine braking. If you need you brakes, you stab them hard, then let off completely to cool.

If you were pointing downhill, then likely the rear would RAISE which SHOULD lower the amount of pressure to the rear brakes and cause the front brakes to do more work, possibly boiling the fluid in both front AND rear brakes.

A soft pedal leans toward boiling fluid, not the booster. A blown booster USUALLY fails with a hard pedal.

That was a good tip above to check all vacuum lines.

Good Luck!

 

[LINUS]

IDK what yr or how far in you’ve gone - is it possible your smoking rear brakes were the e-brake drum pads, not the discs?

Or have you had the back rotors off or seen clear signs of glazing / heat tempering on the disc portion?

Changing all the parts, did you swap in a LSPV & set the arm wrong so it thinks it needs to work that hard?

Is there a lift on this 80 that you didn’t install youself, so the LSPV could be wrong due to that?

— Just some q’s so we get an idea of yr & mods because situationally that can affect things.