Cold weather means stiff brakes

[fatherdoug]

Lately, I have been having to stand on the brakes to make them stop the truck, but only when the outside temp is below freezing. This only occurs when I first start the truck. The colder the weather, the more I have to stand on the brakes. As the engine warms up, it no longer becomes a problem, or, if the temp is above freezing, the brakes act as they should.

Could this be condensation in the brake fluid? The brake booster hasn't been changed in the 8 years I have owned the truck, but the master cylinder has been replaced, not recently though. The truck is a '78 F-150 4WD, with power brakes.

 

[DNFXDLI]

The brake fluid might have absorbed some moisture...the diaphragm might be stiffening up...the vacuum line might be contracting and leaking...that's about the only thoughts I have.

 

[Beach66Bum]

I agree with Duncan. I would start with the easiest and change the fluid and bleed the brakes. Don't think it would be the BB, your brakes are not fading or losing pressure.

 

[fatherdoug]

Thank You Duncan, Roy. I will take a look at replacing the fluid.

 

[DNFXDLI]

Doug...check the vacuum line(s) first...there could be a split which gets worse from contraction in the cold.

 

[mm_0_mm]

maybe the vacuum line to the booster is getting small cracks that open up when cold, allowing a vacuum leak until the engine warms up the rubber?

 

[DNFXDLI]

maybe the vacuum line to the booster is getting small cracks that open up when cold, allowing a vacuum leak until the engine warms up the rubber?

Great minds....

 

[fatherdoug]

Great minds....

Thank You, Great Minds. I did cut a chunk of hose off of the end where it connects to the booster and reinserted the hose onto the booster. That made no difference. I did find the vacuum tree at the back of the engine was loose, and tightened that up also. I will get some new hose and run from the tree to the booster.

 

[LEB Ben]

Vacuum issues would cause the brakes to get mushy, would it not? My thought is either moisture in system or an old rubber part either hardening or collapsing/constricting due to the temp. I've seen old rubber lines from the caliper look perfectly fine externally, but internally are breaking down and inhibit flow.

 

[m78]

Also check the vacuum lines for moisture. The air could bubble by when thawed , yet not get by whiile frozen.

 

[fatherdoug]

Also check the vacuum lines for moisture. The air could bubble by when thawed , yet not get by whiile frozen.

Thanks Ben, Mark. I don't do well with brake issues, so this could be a nightmare for me.

 

[bucks77ford]

You can also get a "hard pedal" from possible Booster failure. Many times there is a vacuum leak somewhere and the booster doesn't get enough vacuum pressure to fully function giving you the hard pedal. As the engine warms up things expand and the vacuum leak may seal itself and then things function as normal. It may not have to do with the booster itself, but somewhere in the vacuum system. If there is no sign of vac leak, than it could be the booster. But, at least start with making sure all vac lines are sealed and re bleed the brakes. IF those things don't help, than it could be the booster needs replacing.

an obstruction of some sort would cause the hard pedal too as mentioned which should be fixed with re bleeding.

 

[fatherdoug]

I hope it's not the "B" word. I looked for one of those a couple of years ago, and I seem to remember trying to locate a booster for a truck with factory cruise, and came up empty.???????? I'll have to look again, after I check some vacuum lines, etc. Thanks, Buck.

 

[bucks77ford]

Ya, I wouldn't go the trouble of replacing the booster until all other avenues have been driven.

 

[DNFXDLI]

Vacuum issues would cause the brakes to get mushy, would it not? My thought is either moisture in system or an old rubber part either hardening or collapsing/constricting due to the temp. I've seen old rubber lines from the caliper look perfectly fine externally, but internally are breaking down and inhibit flow.

Loss of vacuum makes them hard...you are losing your vacuum assist. Just like when you get a cam that makes no vacuum at idle, you need a reservoir so you have more than a couple of applications before the pedal gets stiff.

 

[bucks77ford]

Another thing to think about would be that the booster check valve isn't working properly when it's cold.

 

[SuperCab]

Loss of vacuum makes them hard...you are losing your vacuum assist. Just like when you get a cam that makes no vacuum at idle, you need a reservoir so you have more than a couple of applications before the pedal gets stiff.

x2. Not to pick on Ben, but for future reference, a bad booster make the brakes seem hard due to no assist. Mushy usually means air in the system or bad Master Cylinder or drum brakes being not adjusted tightly enough can also feel mushy.


Also x2 on a bad check valve sticking when it's cold. That's one of the first things that came to my mind...

 

[fatherdoug]

Another thing to think about would be that the booster check valve isn't working properly when it's cold.

x2. Not to pick on Ben, but for future reference, a bad booster make the brakes seem hard due to no assist. Mushy usually means air in the system or bad Master Cylinder or drum brakes being not adjusted tightly enough can also feel mushy.


Also x2 on a bad check valve sticking when it's cold. That's one of the first things that came to my mind...

Is the check valve what the vacuum hose attaches to on the booster?

 

[SuperCab]

Yes, the check valve is the little plastic critter on the booster side of the vacuum line.

 

[fatherdoug]

Thanks, Matt. That would be an easy fix!