Hard brake pedal in mornings

[slyhog022056]

Hey people, I am having a brake problem and no one seems to know what is wrong. To start with I have a new vacuum pump, showing 24 inches of vacuum, new brake booster. pads, rotors, calipers, shoes and drums less than 20k miles. System has been flushed and bled 3 times. Rear ABS is completely bypassed.
In the mornings when the temp is below about 60* My brake pedal is so stiff it takes everything i have to get it to stop with both feet. After i drive 5 miles or so and get some heat into the system the brakes are alright. Any ideas would be appreciated. I am out of ideas of my own and so are the 3 different national big brake places i have taken it too.

 

[snicklas]

How quickly does the vacuum build? Ours does the same thing, the vacuum pump is "lazy" as I call it. The pump will pull a good vacuum, just not quickly.... Vacuum should build very quickly. If it climbs to 24 slowly, over several seconds, there is an issue. It should "jump" to the 24 you are seeing, not build to 24.....

Also, just because the vacuum pump is new doesn't mean it's not bad... We had another member have that issue recently.

 

[DaveBen]

Lazy, as you call it, could mean a leaky line or fitting. Just saying.

 

[snicklas]

True... But on mine direct to the pump, it's slow.....

Big thing is, and I've been caught with this also, that

New = Good

I've been bit assuming the new out of the box part I installed is good.

OP.... Dave makes a very good point, test connected directly to the pump, if that appears good, work away from the pump and find the leak.

 

[Thewespaul]

I had a similar issue and went through two vacuum pumps and ended up pulling a used one off a parts engine that worked perfect.

 

[hesutton]

As posted above, there is either a leak (could be vacuum hose under the hood or in the dash somewhere, the new booster, or somewhere else) or a poor pump.

Had the same issue with my '86 crew cab. Had a weak pump and cracked line in the dash.

Heath

 

[slyhog022056]

How quickly does the vacuum build? Ours does the same thing, the vacuum pump is "lazy" as I call it. The pump will pull a good vacuum, just not quickly.... Vacuum should build very quickly. If it climbs to 24 slowly, over several seconds, there is an issue. It should "jump" to the 24 you are seeing, not build to 24.....

Also, just because the vacuum pump is new doesn't mean it's not bad... We had another member have that issue recently.

it only takes about 3 or 4 seconds to get to full vacuum. gauge is direct off of the vacuum pump. I guess i will check to see if the vacuum hose to the booster has a pinhole in it but why would this only be a problem on cool mornings?? There isnt anything but the brake booster ran off of it. the vacuum limes to the dash controls isnt hooked into the vacuum system, straight from the pump to brake booster.

 

[Thewespaul]

If youre getting that reading directly off the pump I would get new pump, does it take that long hot or cold?

 

[slyhog022056]

It doesnt matter hot or cold, the gauge right in front of me during cranking since i have to crank it over 5 revs and use glow plug to start it anyway.

 

[snicklas]

3 to 4 seconds is too long..... it should be almost instant......

Cold, the rubber in the pump will shrink slightly (it's just a diaphragm pump) and the hole will be slightly bigger when it's cold...

 

[madpogue]

It can't be direct from the pump to the booster if you also have a gauge. Try taking the gauge out of the picture and running a brand new piece of hose from the pump to the booster. If still no boost, and you feel suction on the hose, it's gotta be the booster.

 

[slyhog022056]

sounds loghical to me but today at work i was checking the line to the booster pulled it off and pressurized it with air to check for leaks, no leak but found out real quick the hose had separated internally, the insides were collapsed and even blowing through it by mouth it would collapse and block flow. will replace hose tonight and get another vacuum pump this weekend, no telling how much of the hose insides are in the vacuum pump.