Rear brakes locking up before fronts

[myf16]

1996 XLT 4WD. I just replaced my stock tires with 31x10.5x15 mud tires and I replaced the rear pads with ceramics (Wagner ThermoQuiet QC667). Now when I mash the brake pedal the rears lock up way before the fronts.

I probably have semi-metallic pads on the front but I'm not sure. I'm thinking step 1 is to replace the front pads with ceramics matching the new rears. Or should I switch the rears to something else?

 

[J_C]

Was this an extreme braking test, do you feel the rear are locking up too easy or the front have a problem? I'd take the front wheels off and inspect them. Usually ceramics don't grab as well as semi-metallic and brake bias is on the front wheels, but if your front are degraded badly enough then I could see there being an imbalance towards rear bias.

What was involved with changing the rear pads? Did you bleed the lines and maybe they're now at 100% but there's air in the front lines?

It should be fairly easy to tell if the front are semi-metallic because those cause black buildup on the wheels.

Yes I would replace the front with ceramic when the time comes, which may be now if your front rotors are worn unevenly and need replaced too.

Also try not to mash the brakes too hard while you're breaking in new pads. I assume the old rotors looked good or where they turned (lathed) or replaced too?

Heh, come to think of it I'm also assuming a '96 has rotors instead of drums, but on Rock Auto I see both the choices of drums and rotors for the rear. If they are drums, did you adjust in the pad adjuster screw enough and make sure it all went together correctly?

 

[myf16]

I mashed the pedal pretty hard but the amount of braking I got before lockup did not seem extreme. So maybe the fronts are weak. Or maybe the mud tires just don't give good braking performance.

Rears are discs and I did not have the rotors machined or bleed the lines. I just replaced the pads.

 

[J_C]

Even if the mudders have poor braking traction, you do have them on all 4 wheels so that factor should cancel out, right?

I suppose it could also be that if you have a loose rear end, maybe worn shocks, no load, the rear could lock up first, or a combination of several factors but I'd start by assessing the front brakes.

Keep in mind that mine has ABS so an owner of one without ABS may give better vehicle specific advice on lockups.

 

[J_C]

Come to think of it, do you have no ABS, rear (only) ABS, or 4 wheel ABS? If you have ABS is your ABS dash light momentarily coming on when the vehicle is started, indicating the bulb works, then bulb turning off, indicating it "thinks" ABS is working?

 

[myf16]

No ABS at all on this vehicle. I wish I had it.

Edit much later: Oops it does have 2-channel ABS, which has no reported faults. I'm pleasantly surprised that the vehicle had ABS after all.

 

[J_C]

^ If you did, that module is one of the potential failure points causing rear lockup on vehicles with ABS, and can cost $700+ to fix.

I don't know the state of the vehicle overall, what brake work has been done when if ever, but it's about at the age where if it's never been done, it could be time for new front brake hoses, as they can be come restrictive inside even if no cracks on the outside, and new hard lines too if they're rusty to the point of flaky scale.

Fortunately front brake hoses probably only cost around $12 each on Rock Auto, but if the lines are rusted, swapping them can be an exercise in finesse if you don't want to do the lines too. This is the type of thing that can cost only a little to DIY, or over 5X as much at a shop.

I'm stating these things if the rotors look good. If they don't, I'd change them and the pads first.

 

[myf16]

I replaced the front pads with ceramics matching the new rears and the brakes now behave normally, although the mud tires are quite short on road grip. They lock up a lot sooner than the road tires did.

 

[J_C]

Yeah, each tire for its purpose. AT tires trade off road contact for recesses.