Brakes locking up!

mike65

On the way home tonight my brakes started locking up (after several perfectly drama-free braking moments) When I got to my destination after two more incidents, I checked the discs, the back ones were barly tepid the fronts HOT! This may be how thay always are (was suprised how cool the rear ones were). I'm not loosing fluid. Unfortunatly I could'nt tell which side was locking or if both were (which seems unlikely).

Any ideas, I should add I had new discs, pads and the capilier on the drivers side replaced a couple of weeks ago.

Mike.

Integra

hmmm, not too sure.... Might be seized calipers, or maybe the brake pedal.... the fronts will always be hotter

Seanie M

What kind of a car is it Mike? Has it got ABS?

mike65

Oh yeah sorry, no ABS and is a Merc 190e.

Mike.

Seanie M

No ABS.... then it sounds like a mechanical fault. If it had ABS I would then assume a more technical, but software based, breaking system, but as you have none, its got to be a mechanical issue.

One thing I would try out - get to a car wash, and try as best you can to get your wheels as clean as possible. Then, over the next few days, monitor the amount of kevlar breakdust depositing on your rims. I think you will know if it looks excessive within a short time, that would indicate that even your breaks neutral, or resting position, is rubbing off your disks, indicating perhaps a slack adjuster of the shoes, or added pressure behind them (too much break fluid in the little resevoir?).

Probably put it into the back of your mind the kind of driving you were doing up to the point of your breaks locking up again, if they do - speed bumps? bad pot holes you went through? surface water? unusual breaking procedure? Might shed a clue IF it appears regular.

I am not a mechanic at all, but logic would tell me to keep an eye on these things... then to go to a garage if it gets worse (but it can be a random event too, you know).

Seanie.

mike65

I wondered if a disk had become contiminated with something I splashed through. I let the car roll "at rest" to see if the brakes were grabbing without applying pressure, the car moved freely. Tomorrow I'll use the journey to work to try some braking tests (the Outer Ring Road is empty when I'm on it!) to try and isolate which side side is locking and what kind of pressure I have to use to get a lock-up.

Mike.

Darwin

I had a very similar probelm to this with a new car some time back - the brakes were grabbing intermittently (and boy did the front discs heat up). It turned out the spring in the brake pedal was faulty and needed replacing. Good luck finding the fault...

junkyard

You should buy a BMW Mike.;) When did you change the brake fluid last? You might have one of the brake calipers trying to seize up but you'd notice a pull to the left or the right when you brake.

mike65

The 'new' caliper is in fact off a scrapped car. Maybe its playing up though I'm slightly suprised it did'nt show itself earlier if it is faulty.

Mike.

greglo23

one thing you could check is if the brake fluid is returning to the master cylinder. open the bleed screw a half turn and fluid should run out fairly freely. if not you may have a damaged flexible hose. the internal diameter is very small in the hose and if the hose is crimped too hard it damages it and the fluid cant return to the master cylinder causing the brakes to overheat. the fluid is going down the hose under pedal pressure but the only thing sending it back is the internal rubber seal in the caliper which tends to pull back the piston on release of pressure. this can also happen with old hoses which start to break up inside.

mike65

You mean the bleed on each brake calliper (like I say I'm not sure which side is the problem at this point)?

Mike.

greglo23

try each of the fronts and you should see fluid trickle out in a steady flow almost straight away. if not i'd suspect the hoses.

AMurphy

mike65 wrote:

On the way home tonight my brakes started locking up (after several perfectly drama-free braking moments) When I got to my destination after two more incidents, I checked the discs, the back ones were barly tepid the fronts HOT! This may be how thay always are (was suprised how cool the rear ones were). I'm not loosing fluid. Unfortunatly I could'nt tell which side was locking or if both were (which seems unlikely).

Any ideas, I should add I had new discs, pads and the capilier on the drivers side replaced a couple of weeks ago.

Mike.

Odd that you canot tell which is locking, just so as we are on the same page here, when you say "locking" you mean when you initially apply the brakes, they grab and one or several wheels lock and skid, If so that should be easy to figure out which wheels.
Or do you mean, after braking, the brakes appear to be still applied and dragging the acceleration down.

The front will typically be hotter than the rears, given they do most of the braking, hence ventilated and larger in front on most cars.

a) however, if one is "roasting" while the opposite side is hot or warn, you have a sticking (closed) calliper.
Or b) if one is cold while the other hot, the cold one is sticking open and the other doing all the work.
Easy to figure out the sticking one, jack up that wheel, spin it while your beautiful assistant applies the brake reasonably hard. If it does not release on lifting the foot, you have condition a, if it does not stop at all you have condition b.

Given you say you had one replaced, I'd check it is tight, but free to slide on its guides. If for some reason it is loose and tilts, it may "wedge", hence lock the wheel.
Why was it necessary to replace all the components on that side anyway?.

A warped disk, can "jam" and lock, but that is pretty easy to pickup as there is a pulse in the steering on light application of the brakes.

Is the foot pressure required to lock them the same as the pressure used previously to simply stop. or is there a requirement for additionial foot force to get reasonable braking?.

If a lot more foot force is required for normal braking, you may be correct in that your rears are not doing much of the work, hence your front ones are at the skidding point.

and to find out which side/corner is locking, locate a carpark with a hard, but gravel or packed sand surface and break until a skid develops, then check the marks.

mike65

Phew! Thanks for all that, the locking was indeed a grab not a failure to release.

The parts were replaced cos the disk on the drivers side had developed a small warp, caused by the old calliper. So I decided to replace the lot. The brakes were both equally hot last night. The amount of braking force applied by me was as normal. This morning on the commute I used a quiet dual carraigeway to "force the issue" but blow me down they would'nt lock up even when forceing the car to a stop. I tried the same on the way home and only managed a slight "slippage" at aboput 10 mph due to the damp surface. The brake fluid was cool when I checked it afterwards.

I begining to wonder if I drove through something which caused the trouble until it dried off. Tomorrow I have a free day and will do some checking for residue, for binding, for how freely the fluid runs from the calliper joints...

Mike.

AMurphy

mike65 wrote:

.....

I begining to wonder if I drove through something which caused the trouble until it dried off. Tomorrow I have a free day and will do some checking for residue, for binding, for how freely the fluid runs from the calliper joints...

Mike.

Seens normal enough from the last description.

Could be, but what. got a new tyre fitted and the sticker was left on the tyre?.
Diesel at a pump,
Road paint?.

or something leaky ahead of you.... like mine?.:D

mike65

I had just driven past the exit to a constuction site, needless to say the road is covered in a layer of mud from the trucks coming and going.

I was in the car for about an hour today round town and the ring road and nothing happened, I checked the disks they were clean except for a black smudge on one section of the drivers front disk which may or may not have been the culprit (impossible to tell really).

Mike.

AMurphy

Mud/clay is slippery when wet, that's for sure.
Black smudge on disk. could be a trick of the light or reflection.
Also, you mentioned you got these replacement parts in a junk yard. If they did not store the parts indoors & disassembled, there may have been an oxide spot formed between the pads and the stationary disk. This leaves some pitting, it should fade with time.
otherwise, some grease monkey left a greasy paw print on your disk when fitting, however that would have presented itself sooner and be gone by now and if you had sufficient grease, your brakes would have faded and be simply poor.

mike65

The disks and pads were new the calliper old.

Mike.

Gary ITR

I had the same problem in one of my cars... It was the brke master cylinder seizing up.

AMurphy

mike65 wrote:

The disks and pads were new the calliper old.

Mike.

In that case, I might veer towards "trick of the light" for the moment. If it is breaking normally, just keep an eye on it, I'd expect any surface roughness that may cause this to wear off in a few weeks.
New disks come with a anti-rust coating, but I usually wash this off with hot water and soap, and blow and dry inthe oven. Don't know what was done at your end.. Anyway, I'd do nothing for now, just monitor the situation. make sure there is no leaking oil or slide greas getting on things, make sure everything is tight, all the springs, etc are in place and carry on.

stratos

Off thread a bit I know.
but the abs on my car caught me out the first time.
Being used to cadence braking, as the just before wheel lock up I eased of the brake, just as the abs begins to vibrate the pedal, frightened my foot off the pedal the first time.
It happened on my approach to a roundabout at high speed, which put me in a bit deeper than would have liked.
If your old school and drive with abs go somewhere quiet and get used to it.

AMurphy

I though he indicated somewhere there was no ABS on the vehicle.

Anyway, you are correct, some ABS systems can hammer like hell when they go off. you'd think you had square metal wheels on the car.

others can be very silent, so silent, you have no clue the ABS is the reason you are not stopping.

but a good idea to go somewhere slippery, gravel/mud/wetgrass and try them out in advance.