Brakes are locking up with Very little pressure applied to pedal

[bushcat]

My datsun truck 1981 started to skid when applying the brakes. I don't have to push on the pedal hard for the brakes to lock. I read this could be do to a faulty master brake cylinder. Anybody else experience this? Is that part hard to replace?

[banzai510(hainz)]

I had maybe a year old mastercyl from China or taiwain and. It would pump up everytime I pushed on the pedal and had to release the bleed screw to get pressure down and get home. It did this 2 times and then I changed it and was ok.

 

You have a 81 so I assume it has self adjusting brakes maybe this is a issue???

 

Or you got new drums and they are not turned if made in china. as most are not round from factory and drum will get hot.

 

Hard?

As John Wayne said Life is hard, Life is harder if your stupid. So I think its ez to change. brake nut wench and bleeding brakes

[Roadster-ka]

Check for free play at master cylinder.

[datzenmike]

Raise the rear wheels.... are they free to spin by hand??? if not, have your used you parking brake (e brake) recently?

[Lockleaf]

Which brakes lock up? Front or rear?

[datzenmike]

Good, I ASSumed it was the rears.

[datzenmike]

Well if the fronts, with care, feel the rim and see if they are hot. You may notice hot brake smell, like burning clutch.

 

 

If only one is overly hot then the caliper is not releasing. Could be seized or just stuck. Sometimes just removing the caliper and retracting the piston with a large C clamp fixes it. Be sure to install and pump the brakes several times to force the piston back out against the pads.

 

If both are overly hot then pressure is trapped in the front lines and are not releasing. As mentioned this could be from lack of 'free play' at the pedal. Push the brake pedal down with your thumb. You should have about 1/16" or a couple of mm of travel before there is firm resistance.

[bushcat]

They don't seem to be hot and I don't get a burning brake smell. Just the smell from the tires skidding on the asphalt :). I'll try raising the rear wheels and spinning by them by hand. I have used the parking brake recently, I use it all the time because it's a manual. No free play that I can notice at the master cylinder. Would I test this by just trying to wiggle it back and forth? If so, very little to no movement at all. No new brakes recently. How would I tell which wheels are locking up?

[Lockleaf]

Have someone watch you drive by. Hit the brakes. The wheels that lock up will stop rolling and skid. Watch for that.

[bushcat]

Have someone watch you drive by. Hit the brakes. The wheels that lock up will stop rolling and skid. Watch for that.

OK, thanks. I'll try that and report back.

[wayno]

I bet it is the rear brakes, and the whole truck feels like it just broke something from the noise it makes when it locks up.

One of mine does this also, I try to remember to pump the brakes hard when I start it, then the first time I touch them I touch them lightly, after that I don't have any issues the rest of the day.

[scooter]

Contaminated rear brake shoes can make them grabby, ive also have had this phenomenon that wayno has with the 620 and a bunch of other drum braked vehicles.

[bushcat]

So, pumping the brakes really hard before driving seem to solve the issue. If that solves the issue, what could it be?

[wayno]

So, pumping the brakes really hard before driving seem to solve the issue. If that solves the issue, what could it be?

I have no idea why it is doing it myself, don't drive mine enough to worry about dealing with it, it only happens to me the first drive of that day, once I get it to stop doing it, I have no more issues that day, sounds like you had it happen in the middle of a drive, I have never had that happen so far, only on the first drive of the day, and only the first few times I use the brakes, then I am good after that.

It's really strange too, only the backs lock up, I am barely even touching the pedal, and I don't feel the front brakes working at all, but it is stressful to me when it happens, as the whole truck makes a loud noise like someone hit the cab with a hammer, by the way mine is a Ranchero type truck, the box and cab are connected, so maybe mine isn't isolated from the frame all that well, so the noise in mine might be louder in the cab than it is in your cab when it happens.