Brakes Are Stiff, If Pumped (1 Viewer)

[Shahram]

I searched, and found a thread with a similar problem, but no definitive solution. Maybe I'm using the wrong terminology...

My wife said that when she was backing out of our driveway, the brakes felt stiff and she couldn't stop no matter how hard she stepped on the pedal. I just figured she was a goofy broad, so I responded with "Yo, whatevah" and went back to watching Serpico.

Then it happened to me.

The brakes seem all right, but if pumped, become very stiff and non-responsive. The brake pedal doesn't go to the floor, quite the opposite, you could jam all your weight on the thing, and for a few seconds, they're stiff as a board, then they loosen and the brakes work fine. They also seem stiff when the truck is first started, ie, in the morning when backing out of the driveway.

This is a new development. I have not done any work or mods to the truck in almost a year, and didn't have this problem.

Before I go out and start giving my mechanic ideas, what are your opinions?

Thanks for any and all advice!

 

[Brian894X4]

Sounds to me like a leak in the brake vacuum booster system. If you had no boost, the brakes would be extremely hard to press on. You have some boost, but after pressing the pedle down a few times, you use up your reserve and the boost goes away, until the engine can overcome the leak again and provide enough vacuum to the booster. When you first start it up, the booster is not retaining vaccum due to the leak and so it takes it a few seconds for the booster to work.

I'm no expert, but but that's what I think. Try doing a search for Vacuum booster or brake booster and you should come up with some more info.

There should be a vacuum hose that runs from the intake manifold to the booster, which is the big round thing behind the brake master cylinder on the driver's side engine fire wall. The first thing I'd do is check that hose and make sure it was on tight at both ends and didn't have any leaks or cracks in it. I'll bet you got a leak with that hose. Either it rubbed on something, cracked or one of the ends is split or coming loose.

Beyond, if my guess is correct, you may need to replace the booster itself as the leak may be inside the booster.

Good luck.

 

[matt60/80]

What he said. What you described happened to me a few months ago and I replaced the booster, problem solved.YNiuz

 

[mainemike]

what was the temperature (outside air temp)? I have that problem ONLY when it is below zero. After a warm up period, maybe up to 10 minutes, or as soon as 2, the brakes work fine. Dealer thinks it is the check valve (part of the booster) but is having trouble sourcing one (MrT backorder). The FSM doesn't show the check valve as a separate part, but the dealer claims they can get it for about $50. The assumption is, since it happens ONLY at sub-zero temps, that the check valve is holding moisture and freezing.

So, for me, the problem remains unresolved...

 

[peepers]

tooooooooooootally the booster. any progress?

 

[Shahram]

what was the temperature (outside air temp)? I have that problem ONLY when it is below zero....

I live in Los Angeles. It's winter, so....yeah, it was like 80º. Sub-zero? Good God, man, run away!

tooooooooooootally the booster. any progress?

None yet. First, I gotta get my fat tush off the couch and check for leaks. I'll keep ya posted.

Thanks for all the advice!!!

 

[Shahram]

No apparent leaks in the hoses surrounding the booster, no sucking sounds except those expected to come from my wallet. Brought it in to the mechanic for inspection.

Thanks again.

 

[turbocruiser]

No apparent leaks in the hoses surrounding the booster, no sucking sounds except those expected to come from my wallet. Brought it in to the mechanic for inspection.

Thanks again.

Any update yet?

 

[Arya Ebrahimi]

I've had the same sort of problem, but always when first driving and when the pads are cold. Always attributed it to the pads not being warmed up yet. I wonder if maybe I have a slight leak in my vacuum.

 

[NaterGator]

In the future if this leak is bad enough to fuss with your idle speed a bit you can try spraying a bit of propane around suspect areas to see if it changes your idle. Sucking the propane in through the leak balances out the AF ratio a bit more and the idle settles down again.

It sounds like the only symptom is crappy break booting though

 

[TX_TLC]

Shahram -

Did you ever get around to replacing your booster?

 

[mainemike]

FWIW: dealer replaced the check valve alone ($60 part - not shown in the FSM) which sits between the booster and MC, and so far no problems with the frozen, stiff-pedal brake problem. Way cheaper and easier than replacing the booster or MC!!

 

[Shahram]

Shahram -

Did you ever get around to replacing your booster?

Sorry it's taken so long.

Yes, I did replace my booster. Three times. First time, I had it rebuilt, and it worked like a charm for a day or two, then started to stiffen up little by little. A week later, it was hissing and stiff again. My mechanic said that the diaphragm was blown, so he sent it out to be rebuilt again. After he re-installed it, he blew the second diaphragm on the road test. He sent it out to be rebuilt yet a third time. It lasted about a month, then was back to its old tricks again. Brought it back to the mechanic, who ordered a new OEM booster. It's been on two weeks and works fine.

Now to get rid of that CEL...