Touchy braking from speed - anyone?

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Last Flight Out

Last Flight Out

Joined
Feb 15, 2022
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Atlanta, GA
Figured I was ask the collective here....Have an 81 US Spec and all original drive line and brake setup (orig booster). Over the years I have added things like 4Plus front bumper, 33" BFGs and new suspension. So the weight has gone up a bit - I am estimating around 4100-4200lbs now with factory hardtop. About to add a Warn EVO10 on the front. This leads me to my braking performance...

Recently (especially after new tires), I have noticed that when braking a bit more aggressively (I'm not speeding, but maybe coming down a hill for example with a lot of weight), I have locked up when coming to a more aggressive stop around 45mph or so. A couple of times the 40 had locked up and skidded (those T/A's make a hell of an amazing noise). Not out of control....but has caught me off guard like twice now.

Is this common when you have just more weight on a lifted truck and larger tires and coming to more aggressive stops? Or is there a way I can adjust brakes so that they are not so touchy? Not even sure this is recommended or even a safe thing to do.

Hit me back with some knowledge (please).

IMG_4137.webp
 
3_puppies said:
you state locked up
is that front, rear or all 4 wheels?
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this.
If it is your rears first that's actually OK they will lock up before the fronts because the weight shift in breaking. There are ways to broaden the gap between the rears locking up and the front locking up as well by making sure the breaks are setup correctly and the brake booster is proportioning correctly.
We all need to remember that there are still vehicles out there that do not have ABS so there are now 4 generations of drivers that may have no idea how to panic break anymore.
 
1MOA said:
this.
If it is your rears first that's actually OK they will lock up before the fronts because the weight shift in breaking. There are ways to broaden the gap between the rears locking up and the front locking up as well by making sure the breaks are setup correctly and the brake booster is proportioning correctly.
We all need to remember that there are still vehicles out there that do not have ABS so there are now 4 generations of drivers that may have no idea how to panic break anymore.
Click to expand...
Makes sense.
 
My front disc brakes were locking up on my farm truck and I discovered the rears were not engaging. Way out of adjustment and a seized wheel cylinder on one side. (Front disc rear drum.) It felt like I was jamming on the brakes at the slightest touch. I fixed and adjusted the rears and all is fine.

Your mileage may vary.
 
Hugh Heifer said:
My front disc brakes were locking up on my farm truck and I discovered the rears were not engaging. Way out of adjustment and a seized wheel cylinder on one side. (Front disc rear drum.) It felt like I was jamming on the brakes at the slightest touch. I fixed and adjusted the rears and all is fine.

Your mileage may vary.
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Thanks. I’ll take a look at adjusting per the FSM.
 
Rears for $2000
Proport valve is likely gummed up with trash.
Remove and replace it.
 
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I would put an adjustable prop valve on the rear, because the factory preset is usually irrelevant once the rig has been lifted and accessorized. And it will continue to be adjustable as you continue to modify.
 
I would also look at your tire contact patch. If the tires are over inflated the patch shrinks. It will also shrink if you are running wider tires on skinny rims. Lowering the pressure some will increase the contact patch size giving the tires more grip and delay lockup. Don't go to far in letting the air out as you will loose contact patch, riding more on the outer edges. It's all a balancing act.
 
B y r o n said:
I would also look at your tire contact patch. If the tires are over inflated the patch shrinks. It will also shrink if you are running wider tires on skinny rims. Lowering the pressure some will increase the contact patch size giving the tires more grip and delay lockup. Don't go to far in letting the air out as you will loose contact patch, riding more on the outer edges. It's all a balancing act.
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An excellent point! Too often overlooked. People are too quick to go with ‘recommended’ psi.
 
65swb45 said:
I would put an adjustable prop valve on the rear, because the factory preset is usually irrelevant once the rig has been lifted and accessorized. And it will continue to be adjustable as you continue to modify.
Click to expand...
Great idea. Do you recommend a specific one for an 81 setup?

And yes did a chalk test a few months ago and got the pressure dialed in. First thing I’m gonna do before even thinking about a proportion valve is I’m going to check the rear adjustments by lifting up the rear of the truck and just spinning the rear tires to see if there’s any drag on them right now. My hypothesis is the fronts are locking up and the rears aren’t as grippy, but I really don’t know until I do this first.
 
if the rear locks up it will usually cause the rear to go sideways. very dangerous. might also look to make sure you don't have brake fluid leaking on the shoes as that will cause them to be grabby and lock up. just because its not leaking externally doesn't mean it hasn't started soaking the lining yet.
 
Gotta40 said:
if the rear locks up it will usually cause the rear to go sideways. very dangerous. might also look to make sure you don't have brake fluid leaking on the shoes as that will cause them to be grabby and lock up. just because its not leaking externally doesn't mean it hasn't started soaking the lining yet.
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I don’t have any leaks…
 
Just a thought - how new are your wheel cylinders? A piston can seize, not move so the extra pressure/fluid goes elsewhere and locks that wheel - make all the cylinders are working. The old wheel cylinder adjusters had tapered slots that faced downward towards the axle - this helped keep the shoes centered. New ones, they lazily cut the slot flat - so no centering help.
Check that the drums are still round, and the shoes are wearing evenly and still attached.
 
charliemeyer007 said:
Just a thought - how new are your wheel cylinders? A piston can seize, not move so the extra pressure/fluid goes elsewhere and locks that wheel - make all the cylinders are working. The old wheel cylinder adjusters had tapered slots that faced downward towards the axle - this helped keep the shoes centered. New ones, they lazily cut the slot flat - so no centering help.
Check that the drums are still round, and the shoes are wearing evenly and still attached.
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Charlie, it’s an ‘81. Different components. Much more like modern brakes, with a single overhead cylinder that almost never seizes.
 
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