Front brakes lock up in panic stop

[Rusty Nail]

Yep.

When the rear ends changed.

 

[JoeR Jr]

If you can lock up the front brakes on dry pavement, I’d say you have a very good working brake system and nothing more.
But that said, either your rear brakes are pulling their weight or not. And IMO it’s pretty easy to feel a vehicle that is stopping only on front brakes.

Id go test the brakes. Do a couple hard stops, see if you can get the back brakes to lock up or not. Heat your brakes up some and see if the drums are hot.

This^^^

It would be a problem if you can't lock your front wheels. You're most likely over-thinking it. Adjust your rear brakes so they're working correctly and see how it goes. ABS became popular because drivers (non-drivers really) without it would lose control of the vehicle in a panic braking situation. ABS allows the vehicle to continue steering when the driver just mashes the brakes and stops driving the car.
I'm not pointing any fingers or making accusations, but if you can lock your wheels, great! If you haven't done so, learn to modulate them so it doesn't happen. It definitely takes practice, and every car without ABS will behave differently.

Joe

 

[curbstone mech]

I remember a guy starting a thread talking about his brakes would not lock up but, he wanted them to. Lol

I think in these trucks if you stomp hard enough (like an emergency)they will lock up because they don't have antilock brakes. But, I'm about 5 beers deep and what do I know. Lol

That's when I do my best thinking

 

[Keith Seymore]

With all this talk back and forth I'd really like to know what the answer really is, I'm genuinely curious. I think in the end the only way we would know for sure would be if someone that was in design on these trucks, were to answer, otherwise it's just going to be what we "think" is right. If memory serves me I'm pretty sure @Keith Seymore was in brake design on these trucks. Maybe he'd be kind enough to tell us if one axle or the other is designed to lock up first in a panic stop.

Wow. A lot of conversation on this one. I hardly know where to begin.

I did do some brake development at the Desert Proving Grounds for a couple years, and full vehicle development (which included brake projects) at the Milford Proving Ground. I was actually a driveline specialist, but my boss (God rest his soul) was a brake guy through and through, and was always trying to recruit me to come over to the "Dark Side".

I guess the only things I would add at this point in the discussion:

a) We never really were looking for "lockup", per say, but trying to balance the front and the rear systems for the threshold of lockup. Not only do you have to tune the system for maximum braking (in order to pass the MVSS requirements, for both ABS on and ABS disabled, at both Curb and GVW, or you are not able to sell vehicles*) but also for comfort (pedal travel, feel and effort - and noise) during normal braking.

b) The balance varies based on overall weight distribution and CG location. Keep in mind brake friction material size (and composition) is not the only variable in balancing the system, but all of those little pieces have an impact, too (distribution valve meter, split and slope, caliper piston diameter, rear brake cylinder size, etc) and are all knobs you can turn.

c) For old school vehicles - I agree with the idea of learning how to modulate the brake pedal yourself. Learn to achieve that threshold of braking on your vehicle. A good driver can beat the stopping distance of an ABS equipped vehicle, because the ABS is tuned to allow for stability during braking, not best stopping distance.

K

*sometimes were were so close to not passing that we would recommend a specific driver run the test (ie, "uh - we need Wayne to drive this one". We would run a series of "development" tests until we got a "pass", then relabel that one as our "validation" test.

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[SirRobyn0]

Wow. A lot of conversation on this one. I hardly know where to begin.

I did do some brake development at the Desert Proving Grounds for a couple years. I was actually a driveline specialist, but my boss (God rest his soul) was a brake guy through and through, and was always trying to recruit me to come over to the "Dark Side".

I guess the only things I would add at this point in the discussion:

a) We never really were looking for "lockup", per say, but trying to balance the front and the rear systems for the threshold of lockup. Not only do you have to tune the system for maximum braking (in order to pass the MVSS requirements, for both ABS on and ABS disabled, at both Curb and GVW, or you are not able to sell vehicles*) but also for comfort (pedal travel, feel and effort - and noise) during normal braking.

b) The balance varies based on overall weight distribution and CG location. Keep in mind brake friction material size (and composition) is not the only variable in balancing the system, but all of those little pieces have an impact, too (distribution valve meter, split and slope, caliper piston diameter, rear brake cylinder size, etc) and are all knobs you can turn.

c) For old school vehicles - I agree with the idea of learning how to modulate the brake pedal yourself. Learn to achieve that threshold of braking on your vehicle. A good driver can beat the stopping distance of an ABS equipped vehicle, because the ABS is tuned to allow for stability during braking, not best stopping distance.

K

*sometimes were were so close to not passing that we would recommend a specific driver run the test (ie, "uh - we need Wayne to drive this one". We would run a series of "development" tests until we got a "pass", then relabel that one as our "validation" test.

You must be registered for see images attach

Thanks Keith, I really appreciate the in-depth reply and inside information we could only otherwise guess at.

 

[Raider L]

@SDJunkMan,

I was stopping on my front brakes for years and didn't know my rear brakes were barely working. I rarely had a lock up situation but if I did whatever happened wasn't that noticeable which end was doing the locking up.

I was regularly rebuilding my rear brakes with new shoes and new spring kits at the same time for years. That is until I had been thinking about it due to a sudden stop was when I happen to notice the back didn't do that much locking up like the front was doing that time. Someone mentioned to me to check the rear rubber brake line. They said that the line will look perfectly normal on the outside but the inside is collapsing.

I changed that brake hose and I couldn't believe the difference. I have disc's in the front and 11" x 2" drums in the rear. The way the proportioning valve is set, the rear always lock up first because they provide the driving force. All things being equal the truck should stop in a straight line. Yeah, like how many times has your square been sideways in a sudden stop? But that's the way it's supposed to work.

Change that rear rubber brake hose.

 

[Raider L]

@WebMonkey,

That's the way I learned to drive in the Army, To brake, let off, brake, etc. If you feel the rear coming around do your sliding on ice trick to steer in the direction of the swerve. In making my remarks about which brakes first was from a mechanic at the local Chevy dealership and I figured he knew and I didn't. His advice was basically to keep your brakes in good working order. If you think you are having a problem get them repaired. I understand that we want to know what's best because we are the ones doing the work.

But like several have said here, try not to stomp but rather a pressured controlled stop. I know that's easier said than done, just do your best to come to a safe stop. Rear locks first, whatever, just don't have a wreak trying to skid your way to a stop.

I'll tell you this, my rears lock up much worse on a wet pavement! I don't know why. I'll just be barely moving and when I apply the brakes the rears lock right up.

 

[AuroraGirl]

My f150 does this but one drum locks before the other. Infact. The other drum doesn’t even stop the tire on ice and full brake application.it spins for a few seconds. From like only 1mph.

Yeah... I’m 22 and learned to pump brakes in my first car! Scary! But it was not an issue I had a car with new brake lines and good material

 

[SDJunkMan]

Yeah, I normally pump the brakes when I can. This time it was to sudden. The good news is that it pulled straight.

You've all given me some good ideas on things to check, unfortunatly I'm fighting a kidney stone this week so probably won't get to it for a few days.

 

[Goldie Driver]

Yeah, I normally pump the brakes when I can. This time it was to sudden. The good news is that it pulled straight.

You've all given me some good ideas on things to check, unfortunatly I'm fighting a kidney stone this week so probably won't get to it for a few days.

I have heard the worst thing, and at the same time the best thing, is when you pass them.



I hope you get better soon!

 

[SDJunkMan]

I have heard the worst thing, and at the same time the best thing, is when you pass them.



I hope you get better soon!

Thanks, I'm definatly looking forward to passing this dam thing, it's doubled me over in pain several times. Luckily it's getting close and the pain has receded some.

 

[Raider L]

@SDJunkMan,

I'll pray for ya' man. What do they do about those things these days? Give you a pill? A long time ago they used sonic waves to bust them up and you'd pass them. I can't imagine having something like that. I don't remember anyone in my family having them.

 

[SDJunkMan]

@SDJunkMan,

I'll pray for ya' man. What do they do about those things these days? Give you a pill? A long time ago they used sonic waves to bust them up and you'd pass them. I can't imagine having something like that. I don't remember anyone in my family having them.

Depends on the size, mine is supposed to be 4 millimeters, you can usually pass one under 5 mm. Larger ones can be busted like you mentioned or surgically removed. They do prescribe Flomax, which supposedly opens things up a little to aid it in passing. You are lucky if you don't have a family history of them, because they are genetic, my dad had them also. Told my son to be prepared

 

[Rusty Nail]

My truck was like this when I first got it. Turned out to be the flex lines collapsing.

Happened to me too. Luckily they are cheap enough