Braking Stiff only when Applied Urgently

[snicklas]

You may have a "lazy" vacuum pump. The one on my 92 (previous truck) was this way. It would do something very similar to what your are describing. It would give 1 or 2 boosts and then get behind. When it really showed the issue was leaving the driveway. Fire up the truck, back out and maneuver to leave, sometimes the last time you would hit the brakes, the pedal would start to get hard. Also, if it was cold (air temperature) it would take a few seconds to build vacuum at startup. Connected straight to the booster, it would do this. I'd say the pump should help a lot.

When I've had boosters fail, when you would apply the brakes, you would get a loud swoosh sound from the booster. Not all fail this way, but the ones I've had fail, failed this way.

 

[Thewespaul]

If you have stiff brakes without assist, and it stops well when the assist is there ignore the hydraulic side of the brakes. It’s working fine, which means the prop valve (which really isn’t much of a prop valve in these trucks) is fine as well.

Focus on the vacuum side of things, you’ve ruled the booster out by replacing it, so if you have the pump directly to the booster and you are still having issues... we know the booster isn’t the issue, that leaves the pump.

 

[Cubey]

Puling the vacuum pump pulley requires a special puller tool. Autozone rents it for like $40, return for full rebate.

The O'Reilly rental one wouldn't fit my pulley. I had to buy a $75 kit at Napa that does fit. Still cheaper than paying a shop.

 

[faaiish]

Will the vacumn pump effect the cruise control too. Brakes work great but I turn on cruise control and it will work and take the pedal and about 30 seconds later let go and stop working. A few minutes later it will work again for a couple of seconds if I dont turn it off. New to this, if I should have started a new thread I am sorry.

 

[chillman88]

Will the vacumn pump effect the cruise control too. Brakes work great but I turn on cruise control and it will work and take the pedal and about 30 seconds later let go and stop working. A few minutes later it will work again for a couple of seconds if I dont turn it off. New to this, if I should have started a new thread I am sorry.

Yes, the cruise control is vacuum operated in these trucks.

 

[snicklas]

Will the vacumn pump effect the cruise control too. Brakes work great but I turn on cruise control and it will work and take the pedal and about 30 seconds later let go and stop working. A few minutes later it will work again for a couple of seconds if I dont turn it off. New to this, if I should have started a new thread I am sorry.

Yes, 91 down is vacuum operated. It's the black can over by the brake booster with the cable that goes over toward the engine.

92 up is an electronic cruise control, it's mounted in the same area, but is a smaller rectangular box.

If you need additional troubleshooting help, please start a new thread.

 

[Macrobb]

92 up is an electronic cruise control, it's mounted in the same area, but is a smaller rectangular box.

I have a '92 OBS F-250 which has the vacuum cruise control. My '93 has the electronic cruise control.

 

[Thewespaul]

92.5 and up

 

[snicklas]

Thank you fellas!!! Wonder if it was the same time they made the v to serp belt change. Seems like they mad the body change, then other changes shortly after. A lot of changed in 2.5 model years.

 

[Thewespaul]

I believe so, but I have seen a low mile service truck with an obs body, v belts, and the newer style cc. I don’t think the changes were cut and dry for the obs trucks, lots of leftover inventory probably

 

[IDIBRONCO]

Like I wanted the flux capacitor next.

You should have got that first. If it works off of 1.21 gigawatts, then surely it would hold up to a 3G alternator.

 

[MICHAEL MICHAUD]

Well guys. I got the tool. Replaced the vac pump in ten mins. The brakes work so good that a suitcase slammed me in the back of the head. Worth it.

Ready for the trip home now. Thanks for all the help and tips

My cruise control is also electronic.

Ill post an update when im home on the build thread.

Thank you!

 

[corrado9184]

That's good news! Wish it had worked on my truck like that.

Watch out for them suit cases!

 

[Thewespaul]

That's good news! Wish it had worked on my truck like that.

Watch out for them suit cases!

Just because you replaced the pump doesn’t mean you have a good pump. I went through three parts store pumps for my personal truck before I pulled one of a engine core that worked way better. Just food for thought

 

[MICHAEL MICHAUD]

Just because you replaced the pump doesn’t mean you have a good pump. I went through three parts store pumps for my personal truck before I pulled one of a engine core that worked way better. Just food for thought

I bought a brand new one from summit. But i will absolutely maintain a safe distance and be weary.

Oh yes i see you were talking to corrado. I meant to tell him that as well! Change out your pump again haha! Mine was absolutely a vac issue and I could tell by the way it worked and then didnt.

Good luck. 80 bucks from summit right now for brand new no core.