The next symptom I am addressing on my son's project car is related to breaking.

After driving the car for about 15 minutes, the car does not roll freely. It seems like the breaks are on.

I have determined that it is the front brakes. They are both applying and not releasing. I can open the bleeder and the breaks release, so I don't think its a mechanical problem with the breaks themselves.

Could it be something to do with the ABS? How do I go about troubleshooting this?

Any help would be appreciated. :-)

 

Could be:
1) The front calipers are hanging up and not sliding as they should. Make sure they are free and able to slide.
2) Your rubber hoses (frame to caliper) could be collapsing internally, not allowing the fluid pressure to release.
3) The brake system may need to be bled (yeah, I really meant to say that).

 

The braking is just fine until I drive for a few minutes. I think the calipers are releasing just fine. I removed the ABS relay and the problem was the same, so its not the ABS (thank goodness). I have ordered the flex lines for the front and will replace them tomorrow. Any suggestions on making them easy to replace? :-)

 

+1 on what he said

Your ABS system has a Isolation and a dump valve. That means it can turn off adding pressure from the master cylinder to the caliper and it can dump that pressure. It cannot force pressure into the caliper or make pressure stay there. In fact if you don’t feel it pulsing it has no effect on your braking. The condition you described has been around a lot longer than any ABS systems. If you are trying to turn the wheel with your hands it can be caused by the caliper seal getting hard. If it is something you are sure you can feel when you drive then it is the hoses. Like I said it is very common but a lot more so in a car that has not had its brake fluid changed. I have seen cars pull into the shop and once the car was on the oil dry/concrete the front tire would just lock up. That made it tuff to get them on the lift.
If you take the car to a good shop they will advise you to rebuild/replace calipers, hoses and flush the brake fluid. They may suggest doing the rear wheel cylinder/calipers if there is a lot of moisture in the brake fluid.

 

Woot! I think its fixed! I replaced the front flex hoses, and bled the brakes. There was moisture in the fluid at the calipers. My first two test drive showed no brake drag, and very little heat generated at the wheels. I'll need to drive it more to make sure, but it has dramatically improved.

Thanks so much for all your advice!

 

You should flush the brake fluid and replace the front and rear calipers. Brake fluid absorbs moisture it is not possible to just have water in one part of the brake system. Right now you brake system will be prone to brake fluid boiling which can reduce Braking up to 50%.

 

^ Good point, but he did say he flushed the calipers. Let's hope common sense kicked in when he bled the first yucky one, and at the very least bled them all.
Any time I bleed the brakes, I take my syringe, suck the old fluid from the reservoir, clean the crud out real well, and replace with new.
Kinda pointless running a reservoir full of old contaminated fluid through while bleeding.

 

I did bleed them all, but I'm also replacing the calipers tomorrow. The flex lines seemed to help a bit, but the problem persisted.

 

The same thing that causes the lines to fail will cause your calipers pistons to rust and bind. Also small chunks of the old hose can make it way to the caliper. All those times you bled your calipers before you put the new hose you where pushing little bit of fail hose into the caliper. A mechainc should never offer to replace a hose without servicing the calipers unless the reason for the hose replacment is external damage.

Don't skimp on the brake fluid. If you not going to flush the system then run enough brake fluid thru it that you get clean fluid from all 4 wheels. I use a cheap vacuum based bleeder system.

 

The problem was the calipers. I also bled lost of fluid through the calipers. :-) Thanks for the advice. At least its fixed now.