Brakes

[riva]

After first starting my truck the brakes will be real touchy. But after a mile or two they seem to require a heavy foot to get the same stopping force.



What could be causing this boost assist decrease. My idle is not changing!



thanks

jimbo. :-{}

 

[Posm]

I don't know, but mine does the same thing on the first two or three stops of the day.

 

[Doc Tinker]

It sounds to me like your hydraulic pressure is dropping when the system gets warmed up. You might need a new power steering/hydraboost pump.



Doc

 

[Matt42]

Originally posted by riva

After first starting my truck the brakes will be real touchy. But after a mile or two they seem to require a heavy foot to get the same stopping force.



What could be causing this boost assist decrease. My idle is not changing!



thanks

jimbo. :-{}

Here's a long shot: Try emptying the brake fluid reservoir, and cleaning the plastic part with a lint-free cloth. Then refill, flush and bleed the whole system with non-synthetic (!!!) Dot 3/4 fluid. The symptoms that you describe could (maybe) be caused by wet fluid, caused by a few years of use in humid conditions. On the other hand, fade is also likely. Touchiness can be caused by damp linings that dry after a few uses.



Was your truck subject to the recall for the oil check valve in the vacuum line? If yes, was it done?



FWIW, YMMV, etc.

 

[GeoVeo]

riva,

Your comment, the brakes will be real touchy sounds like damp linings, as Matt suggested, is causing this. Mine do this at times as well, but only when the humidity is up.



Also as Matt suggested, flushing your brake system is a good idea. Some suggest this should be performed about every two years. Brake fluid is hygroscopic and absorbs moisture which reduces the boiling point, leading to brake fade and causes corrosion as well. There are various brake fluid test methods, some that measure the moisture content by actually raising the fluid to the boiling point, some that read the conductivity, and some use a "test strip". Here's a link that has some testers: Phoenix Systems

 

[Joe Mc]

Synthetic

I understand the synthetic is more moisture resistant than regular. Not sure if we can/should use in ours. Anyone know either way?

 

[Matt42]

I don't use synthetic brake fluid. I do use Castrol LMA. When the stuff was new on the market, LMA stood for Low Moisture Absorbtion. I used it initially because it wouldn't eat the British-made rubber parts on Fiat brakes (don't ask). Castrol LMA comes in DOT 4. Valvoline (I think) sells something that they say is a synthetic base. I have never used it and probably won't until I am I know ow it will mix with LMA or regular fluid.



Silicone based brake fluids reportedly don't absorb any moisture at all. They will not mix with regular brake fluid, and changing over requires flushing. Some idiot had added syunthetic fluid to the brake system of a used Grand Wagoneer I bought. It took some effort to get it all cleaned out. In the presence of regular fluid, the silicone fluid took on the rheological attributes of snot.



I have general reluctance to use brake fluids that don't absorb any moisture because they don't absorb moisture. I know that sounds like a circular objection. Consider that regular brake fluid boils at about 350F. (Remember that plain water boils at 212F. ) As it absorbs water, that boiling point slowly drops. The water seems to work its way to the wheel cylinders. (Maybe it just acts that way. ) Brake fluid with a little water in it is still useful, but really needs to be flushed due to the low boiling point and corrosion potential.



Water will get in through humidity, condensation, and so on. However, if the brake fluid absorbs NO water, the water that gets in can coalesce into a small blob. When that occurs, the effective boiling point of the fluid is 212F. That negates tha very high boiling point of the silicone fluid. Do I have first hand knowledge of this? No. It is what I was told--by several sources--when I was thinking of trying the stuff.



In racing applications, brake bleeding is frequent and regular, and the water blob does not become a problem.



When did you last bleed your brakes? I went close to six years.

 

[dan_gilson]

I had this happen once. What had happened was the dealer over greased the front end and some of the excess got on the right rotor. Warped it before I found out what was wrong.



Get a can of brake cleaner and spray the pad and the rotors. Give it a try and if it does not work at least you have ruled out one possibility and for less than $5.