Brake weirdness

Been working on my own cars a long time, but this is a first. I put new pads on the front of my '98 SR5 (4X4 V6 auto), and also flushed the system with new, never-before-opened Dot 3 brake fluid. Bled everything until all the bubbles were out. Adjusted the rear shoes (which still had some life left on them). Ever since, the brakes have been mushy when the truck is cold. Vague feel and you need lots of leg to stop. But when it warms up, they perform very well with 'normal' pressure. I rebled the system but no further bubbles came out. Anybody have a similar problem and/or have insights? Thanks!

 

What is your Ambient air Temperature ??

you say after it warms up your brakes are normal? The pedal feel changes ?

Is this with the truck parked till the engine temperature is up to operating temp?

Truck is driven till Engine temperature is at operating temp??

 

Any info on the pads? Unlikely but the pads COULD have bad cold performance.

I would say to bleed the system again. Some times small bubbles are captured or emulsified and a second bleeding removes them

 

Do you have ABS? When you say you flushed the system- how did you go about that? Could you have introduced more air into the system on accident by letting the MC go dry?

I am huge fan of the motiv power bleeder. Not necessarily the universal adaptor for our trucks, but the system overall. I never had great results bleeding my brakes the old fashioned way, especially having to rely on someone else to pump the pedal at the right time, etc.. I got myself a motiv kit when I did my rear axle rebuild and the results were clearly better.

 

Original brake lines?....ever been replaced......

 

It is the fact that when the vehicle warms up .

Braking action becomes normal at least to the OP.

 

Thanks for all the replies. I will try to answer all the Qs.

* What it SEEMS like is that the brakes start working 'right' when the engine warms up. When I start and for about the first 5+ minutes, the pedal is very spongy. The brakes do stop the truck, but spongy and require a fair amount of leg pressure. No matter how many times I depress the pedal in that first 5 mins (thinking I'm heating and/or drying the pads), it doesn't correct until - again, it very much seems - like the engine is warm. Once that happens, the brakes are good the rest of the day. (Weird, huh?)

* I got one of those MOTIV bleeder things years ago, and really liked it when I used it last. Of course, I cannot for the life of me find it in the garage. So I bled the brakes with a little 'kit' I got consisting of a clear tube with a one-way valve thingie in the middle. It allows fluid to go only one way and does not allow any to be sucked back. I put the correct end on the bleeder, with the other end in a bottle that already had some fluid in it. I started at the right rear, bled (by pushing brake pedal) until clear fluid was coming out. (Oh, and sucked as much old fluid out of brake reservoir, refilling with new before I started.) Then went to LR, RF and LF, in that order. Twice. I never let the fluid get so low in the reservoir that it could have sucked air.

* The brake lines are original. Never had a prob with them or the brakes before.

* No ABS.

* I replaced the pads because they wore through on one side, buggering up the rotor. So I had the rotors turned, also. Before that, I did not have this problem. So its definitely something I did (or didn't do right).

* The brake pads are ceramic. I got them through Rockauto. I threw away the box so don't remember the brand.

* Temperature-wise, I did this brake job 3 weeks or a month ago. Out here in CA, it was still hotter than Hades - high 90s to over 100. (Did the job in morning before it heated up.) It is currently in the 60s and raining. None of this seems to have any influence on the problem one way or the other.

 

Could definitely be the pads having crappy initial bite or air in the system. Those are the 2 things you changed so I'd start with a rebleed since it's cheaper, but you might want to do some better pads, ceramic's are hit and miss for bite, usually miss.

Powerstop does Z36 pads for the 1g's. You definitely won't have any bite issues with those. Z23's are an upgrade from factory as well, but I would definitely recommend the Z36 if you've added any weight or bigger tires or offroad it.

 

Did you follow any break-in / bed in procedure? If you damaged the rotor (from contacting the pad) they probably should have been replaced, not turned. I've given up on turning the parts store bought rotors, they just don't last the second time. I also highly suggest the Akebono (

$59 ACT436 Proact Ultra Premium Ceramic Disc Brake Pad kit, GREY

ACT436 are what I have) pads. Much better than the parts store brands.

 

What I question is the mushy pedal to the engine warms up!!

If you had Air in the brake lines Warming the Engine would not change the pedal feel

Poor pad contact( for what ever reason) would give you the hard brake application pressure not the mushy soft pedal

A vacuum leak to the booster that something expands and seals at operating temperature .

By chance did you get your calipers on upside down?? The bleeder valve is at the top!

I must agree this is a strange one

 

did you bleed the Brake Proportioning Valve located on the rear of the truck, this might be were you have air in the system. Just my 2 cents worth.

 

A valid point but warming up the truck would not cause any change in air in the brake system.

That is what makes this so strange.

I had given thought to new bad brake fluid but again warming the truck would not effect that either.