No brakes, pedal rock soild...

[chumwon]

Hello everyone, looking for some advice from the guru's on this dumb old vacuum brake system. Couple months ago i had the vacuum pump seize up and give me the stiff pedal, replaced the pump, back to normal (sub-par but it is as old as me).

Now within the last few days when the truck is cold and first moving the pedal is rock hard but is back to normal by the first stop sign (thankfully!) It's been consistently doing that the last couple days until today the pedal was rock hard 95% of the time an the one time it is soft again after a second pump its back to hard again. While it sits running i can get it to pump once but goes rock ******* the second pump. Belt, tensioner, and pulley are all in good shape. Do I have a bad diaphragm in the pump? Maybe the booster? Or possibly as little as a bad vacuum line? Thanks in advance everyone!

 

[Thewespaul]

Sounds a vacuum problem, I would start there.

 

[laserjock]

Probably a vacuum leak. May be why the last pump died. You should have like 20" of Hg vacuum I believe to have a good pedal. It may not be low enough to turn the light on but poor enough to have bad brakes.

 

[chumwon]

Alright sounds like I'll be checking lines tomorrow then! I don't have any dash lights on but i also think most the bulbs are shook loose..

 

[snicklas]

Don't rule out the new pump either....... on our 92, if the ambient temperature is cooler... like in the 50's and lower, the vacuum pump is lazy.... it has not been replaced, but it takes several seconds for the red BRAKE light on the dash to go off. It will also do the 1 good pedal, then stiff. Once the pump warms up it gets better, but is still lazy...... it's on the list to replace.......

Just remember, 92 is a transition year for the IDI, early build dates (pre 03/92) is a V-Belt setup. After is serpentine. Can be fun when ordering replacements.

 

[Garbage_Mechan]

1st find out if the pump is making vacuum. Carrefully pull the rubber line off and connect a vacuum gauge to the pump (nothing else connected) After starting the engine, it should go to about 25" of vacuum in seconds. If your gauge connection is tight, it should stay at the same reading for a while with the engine off.

If this is OK, then reconnect the booster with the gauge connected to the tee mounted on the fenderwell and everything else connected as normal. After starting the engine the vacuum should rise to the same reading after a minute or so. If not it is either the booster, a hose or connection. To check the booster to see if it is why the vacuum is not rising, run engine reved up for a while and then shut off and stick your head under dash listening for vacuum sound around the pushrod going thhrough firewall.
Sometimes a failing booster will stop leaking if you hold the pedal ever so slightly depressed.

Bottom line if you prove the pump is making vac and you prove out the hose and connections are not leaking, it has to be the booster.


Do not trust the Vacuum switch that turns on the warning light. I have seen more that do not work than do.

 

[pelky350]

There isn't too much that's ran by the vacumme on these trucks but do the test, some placac s of interest would be the vacuumed block on the fire wall where everything ran by vacuums go through, vent flap for heating system, booster, and safety switch and if you have cruise control I belive that is also ran by vacumme but I'm not sure as I don't have cruise. When my booster went bad I could hear it leaking when truck was at idle with head buy pedals under dash. Always make sure belts and good and properly tensioned as well!

 

[chumwon]

I have noticed a hissing noise down by the brake pedal while braking but haven't tried once the truck was off. Mine is the serpentine style and I just swapped the tensioner cause I though she was a little weak an dressed the belt aswell. I'll be getting the vacuum gauge out today an do a little more digging to see what I can come up with. Thank you gentlemen!

 

[laserjock]

Hissing by the brake pedal is likely your booster. I'd go through the rest of the system to be sure since it's cheap and easy.

 

[chumwon]

Hissing by the brake pedal is likely your booster. I'd go through the rest of the system to be sure since it's cheap and easy.

Roger that, I'll still go through the vacuum tests first but I'm thinking it probably is the old booster. Hoping that's not to terrible to do on the ole girl, but id be thrilled if my brakes were a little better afterwards!

 

[chumwon]

Well after a little testing with the vacuum gauge I came up with 17 in at the pump and maybe 12 at the booster... soo from what you guys are saying my newish pump isn't producing...stinking reman..

 

[snicklas]

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[laserjock]

And you've probably got a leak somewhere if it's that much lower at the booster than at the pump.

 

[chumwon]

And you've probably got a leak somewhere if it's that much lower at the booster than at the pump.

Yeah that's kinda what I was afraid of.. it's always had a softer pedal then I'd like but couldn't bleed it out soo in guessing it's a slight vacuum leak. And maybe in a perfect world fixing my vacuum issue may bring my cruise control back to life! Thanks again everyone!!

 

[Thewespaul]

Hydroboost!