break-in period for brakes?

[plumbcut]

I just redid all the brakes on my truck (77 K25).. with discs all around, I had all 4 rotors turned, replaced the master cylinder & vacuum booster, and cleaned up all the pads & calipers which are fairly new already... braking performance isnt what it was before...

the master cylinder I put on was a new raybestos unit.. the two MC's i had on the truck previously were rebuilt (at least the second one was, for sure) GM's... It had very very sensitive brakes and I liked it .. now it seems like it just a regular old half ton with old brakes.. its a struggle to make it lock up or stop quickly.. i re-bled the entire system. Is there a break in time for rotors & pads? Will performance come back w/ time?

Anybody completely removed that factory prop. valve from their trucks? Its new too and Im thinking it aint doing me any favors with the 4 wheel discs that the truck has. Its REALLY hard to bleed the rear...


If I were to eliminate it, whats the best way to continue the hydraulic lines through that junction?

just looking for some ideas... thanks

pc

[86dieselburb]

I have heard of people using a proportioning valve from an 80's vette. It's designed for 4 wheel disc brakes. I'm probably going this route when I convert my 14ff to discs.

[Destructo]

factory valve will not work with your disc brakes, thats your problem, you will need one from a different vehicle or an adjustable. I suggest picking up an adjustable from summit or something, their not too expensive.

[plumbcut]

let me clarify-- i didnt just install the rear disc brakes, I did that a couple years ago... What I DID just do was swap masters and had the rotors turned.. my main question is if there is a wear in time for old pads w/ freshly turned rotors.. (long shot......)

if not, im not real satisfied with the new MC...

pc

[DrMaserati]

There shouldn't be a wear-in period. They should feel right from the start. Without more info, I would say your problem is most likely with the M/C.

Is the new M/C the same as the previous ones? You need a M/C designed for 4-wheel discs for the brakes to work properly. Here is a link to a page on master cylinders at Master Power Brakes. Their site has a wealth of information about brakes explained in layman's terms. Even if this is not your problem, you are likely to find a solution there somewhere.

http://www.mpbrakes.com/masters.htm

Here is one of the comments you will find there: "If you attempt to use a disc/drum master on a four wheel disc system you will get poor rear brake function and experience a spongy brake pedal with a long pedal travel."

A disc/disc system generally incorporates a combination valve, which combines metering and proportioning valves into one unit. If you're still using the valve that was in your original disc/drum system, that could also be contributing to the problem.

Good luck,
JP

[DennyB]

Did you bench bleed the master cylinder?
There may be air in one of the chambers.

Is the pedal firm or spongy?
If its spongy there is air in the line/MC some where.
If you didnt bench bleed the MC then I would remove and bench bleed it while its sitting level.

If the pedal is nice and firm then we need to look into other options.

[N2TRUX]

Although your pads are not new, they still need to be aclimated to the rotors. The process of "bedding" the brakes puts pad material on the rotor surface.

From another thread-

You need to read this info on -Bedding in new pads and rotors It makes a huge difference in how your brakes will perform....