Hard Brake Pedal But Poor Braking

[Von Hayek]

I have been battling poor braking for a while now, to the point where I have just been throwing parts at it. The symptom is that I have a much too hard brake pedal but poor stopping power. I cannot like up the tires if I want too, and when on a very steep descent, I sometimes have use two feet on the pedal just to keep from the truck from moving and the pedal occasionally bottoms out under such situations.

I have replaced the front calipers and the master cylinder. I have bypassed the LSPV and have a manual proportioning valve. I have adjusted the rear drums.

The only reason I have never replaced the power booster is that it seems to pass the tests in the manual. Pedal goes down after stopping the engine. With the engine off, the pedal hits the stop on the first push, but rises afterward.

Any advice would be appreciated.

 

[OSS]

Replaced the rotors, pads, drums & shoes?. Glazed rotors & drums won't stop anything.

 

[Cruiser Corps]

Sounds like a booster to me.

 

[RustyNailJustin]

Sounds like a booster to me.

yep

 

[Michael Hanson]

HI, Booster. Mike

 

[morganism]

Was the Master replaced without adjusting the throw length? There is an adjustable nut on that rod....

 

[Von Hayek]

Was the Master replaced without adjusting the throw length? There is an adjustable nut on that rod....

The master was replaced without adjusting the throw. Could that cause a hard pedal?

One more tidbit, I went to test the check valve and when I pulled the line off of the booster, there was still vacuum on the line. This was 30 minutes after I shut the truck off.

 

[Kleatus]

The master was replaced without adjusting the throw. Could that cause a hard pedal?

One more tidbit, I went to test the check valve and when I pulled the line off of the booster, there was still vacuum on the line. This was 30 minutes after I shut the truck off.

Don't let that fool you - you can have a booster that holds vacuum, right until you press the brake pedal. I had one in my 62 do just that.

 

[Von Hayek]

Don't let that fool you - you can have a booster that holds vacuum, right until you press the brake pedal. I had one in my 62 do just that.

Good to know. New booster going in with a push from @Cruiser Corps. Thanks for the advice folks. I'll give an update.

 

[Cruiser Corps]

I hope that push is right!

I don’t want any death threats if I am wrong. Lol

I think we are in the right track.

Take care
Mike

 

[Von Hayek]

Nah, would never blame anyone for some honest advice.

 

[morganism]

do you have your old MC still? You want to measure how far the rod sticks out the back to the Booster....

 

[Von Hayek]

do you have your old MC still? You want to measure how far the rod sticks out the back to the Booster....

I don't have the old master, and I did not want to post this and confuse the situation but--the previous master cylinder was not original--it was for a 4Runner. So, someone had clearly upgraded the brakes at some point. However, before I knew that, I had replaced the front calipers with stock units. So after replacing both the master cylinder and the calipers, I should be back to a stock configuration.

 

[unklwedy]

One other thing to check , Plugged vacuum port at intake manifold.

 

[lcwizard]

There's more than one thing that can go wrong with a booster and there are a couple easy tests you can do in the truck
to diagnose.
Sometimes you can pass or seem to pass one but fail another

Test the check valve by starting the truck and running it for a few minutes to let vacuum stabilize. Press the brake pedal and hold.
Shut the vehicle off. If the pedal rises within a few seconds you've got a bad check valve. It shouldn't rise for about 30 seconds. The rise
is very apparent and will push your foot back noticeably.

Second test is, with the key off, you pump the pedal 3 or 4 times and hold, then start the truck. The pedal should sink.
If it doesn't then it's not working properly. Vacuum accumulates in the booster when the engine runs.
There is a rubber diaphragm that separates the engine side from the pedal side.
A valve at the vacuum hose from the engine that introduces vacuum. Another valve at the pedal opens
when you push the pedal allowing air into the booster at pedal side or the diaphragm . When air is introduced at the
pedal side it creates a pressure differential allowing engine side of the diaphragm, with the vacuum, to contract and push on
master cylinder.

If either valve isn't working properly or has a leak or if the
diaphragm has a leak, the booster will not work correctly

Last test, run the car for a few minutes then shut it down. Pump the pedal a few times. With each pump the pedal should rise.

There's probably even more tests that people use but these should catch most of the ills