Help I cant Stop!!

[eventytoo]

HI all. I own a 1976 GMC 4x4. I did the resto myself. One thing this truck needs is some better brakes. I replaced all the components when I restored it but this truck dont stop!!!! I drive an 04 silver half all week and I jump in this thing durring the weekend and have darn near plowed a few cars over. I feel like im driven a loaded 18 wheeler. Its that scarry.

Well I would like some help. I need to upgrade the brakes so I dont hirt myself or kill somone in this thing. Yes the stock brakes are in proper order. The rear will lock when I stand on the peddle leaving two black streeks behind me.

I have corrected the rear track width with wheel spacers 2 inch on both side a total of 4 inches in the rear. I did this for looks so both front and rear are the same. I would like to do away with this.

Wheels and tires are 16inch alloys 35 inch tall tires Lots of rotating mass here. I do not want to go with a bigger wheel.

This is my thoughts, Go with a hydro-boost? being im running a cam with 13'' vac at idle. And finding a rear axle out of a newer truck with disks already on it.


Pic

What wolud you do? Whats the hot ticket the makes thease trucks stop?

[CLASSIC87']

I don't have any advice... BUT thats a beautiful truck!!

[Restrorob]

100%..... That's a damn sharp lookin rig right there !!!

[BGRAFX]

I'm lookiing for the same advice. I really didn't expect to see a picture of such a nice truck though. hopefully someone can help before you wreck.

[camshaftgsxr]

OP you say the rear will lock.. but will the front? my 84 is only two wheel drive but it'll lock the front wheels well before the back. the brakes will only slow you at a certain rate, the trick is to have all four wheels at the point just before lock up, all the weight is on the front wheels in a truck and since your rear wheels are locking and the fronts are not i think your front brakes are weak/not working properly, my guess would be check the proportioning valve and the metering valve and see if you can get the front brakes to put more clamping force on the rotors. until you get the fronts to put down max power you'll just lock the rear every time instead of slowing down with the fronts (as the rear assists) i'm not saying your dumb but here is the explaination of how they work (i had to look it up to make sure i wasn't wrong)

http://auto.howstuffworks.com/auto-p...ter-brake2.htm

if this needs to be clairified tell me sometimes what makes sense to me doesn't to others

[FLEET72]

Better front pads + ensure proper proportioning valve function and no air in lines.

http://www.ebcbrakes.com/automotive/...ake_pads.shtml

[LONGHAIR]

Originally Posted by eventytoo

The rear will lock when I stand on the peddle leaving two black streeks behind me.


This is my thoughts, Go with a hydro-boost? being im running a cam with 13'' vac at idle. And finding a rear axle out of a newer truck with disks already on it.

What would you do? Whats the hot ticket the makes thease trucks stop?

With only 13" of vacuum, hydro boost is probably the best bang for the buck thing you could do.....but there is no point to "upgrading" the rears if they already lock-up.

[N2TRUX]

Man, that truck sits nice. Your truck is a perfect example of why I always say drop a short bed and lift a long bed.

Hydro-boost is amazing, but I would also consider some of the big brake conversion kits.

[leegrady]

One of the best looking trucks I've seen. A true inspiration.

I agree with what everybody has written. Esp. about the rears locking up. Thinking too that the fronts are not doing their part in stopping.

If I'm not mistaken the truck has a quick take up master cylinder? If it does like my '81 GMC k2500 maybe the master cylinder is not quickly taking up the gap between pad and rotor.

Just a thought.

Real nice rig.

_____________________

'81 GMC k2500 longbed 350/sm465/corp 14/dana 60
'95 T-bird lx 4.6L w/pi heads
Replica '65 Daytona Coupe stroked 351w/tremec tko/9" detroit locker
'71 Nova x2

[cableguy0]

The first thing is to go back and ensure everything is working properly. Just because parts are new/rebuilt doesnt mean they work properly. Quality control is slim to none in most of the big manufacturers at this point. Is the pedal hard to push? If you hit the brakes a couple times within a short amount of time does the pedal get stiffer? Can you get the fronts to lock up?

[datguysaL]

Camshaftgsxr gots it correct, your rear wheels should not lock up quick, check you pro valve, you should have more braking power in the front than the rear, about 80% front and 20% rear. Thats cuz more weight is at the front. Did u use the correct rotors up front? The HD brake rotors are thicker and if u truck has HD brakes and u used just normal brake rotors, then that could be it. The stock brakes should be enought for thar beast. Could also be just air in the lines.

[eventytoo]

Originally Posted by camshaftgsxr

OP you say the rear will lock.. but will the front? my 84 is only two wheel drive but it'll lock the front wheels well before the back. the brakes will only slow you at a certain rate, the trick is to have all four wheels at the point just before lock up, all the weight is on the front wheels in a truck and since your rear wheels are locking and the fronts are not i think your front brakes are weak/not working properly, my guess would be check the proportioning valve and the metering valve and see if you can get the front brakes to put more clamping force on the rotors. until you get the fronts to put down max power you'll just lock the rear every time instead of slowing down with the fronts (as the rear assists) i'm not saying your dumb but here is the explaination of how they work (i had to look it up to make sure i wasn't wrong)

http://auto.howstuffworks.com/auto-p...ter-brake2.htm

if this needs to be clairified tell me sometimes what makes sense to me doesn't to others

The brakes are set up correctly. Under extreme pedal pressure pushing as hard as I can the rears will lock up. You are correct The fronts seam as if I could have more clamping force on the rotors.

[datguysaL]

It could also just be brake-fade caused by excessive heat up front. usually caused when your rotors dont dissipate heat fast enough.

or could of been contamination of brake pad before installation, ex: grease, fluid, cleaners.

what brake pads are you using up front? ceramic, organic, semimetallic.....

*ceramics are good, but alot of people dont know that they are not always compatible with stock rotors.

[thirdstreettito]

Just do a hydroboost conversion. I've never locked em up. Its like having ABS but the brakes dont pulse. Also, you could do a rear disc conversion also if you wanted to.

[Farmer Mike]

Your 35" tires are overwelming your brakes. Look into braided steel brake lines. They won't swell like the stock rubber lines and will enhance your stopping power.

Call Skyjacker for more info. I'm sure they'll be able to help!

Mike

[ghettoluxury]

Hydro-Boost is the way I went and would never go back on a truck with tires 33" or bigger

[knightowl73]

yeah i lke the truck too. think a new prop valve will fix your problem. had a similar problem in my monte a few years back. plenty clamp in the back , but nothing up front. prop valave turned out to fix it after i had kept changing alot of other stuff. know for a fact though, you can actually feel the difference in your braking power f you upgrade to the braided stainless lines.

[eventytoo]

The lift is skyjacker 4" I went with the braded stinless lines but when I installed the front they where to long. So the new stock rubber ones went back on. The rear worked so I have a stainless "skyjacker" one back there.

I know what you mean by the stainless braded lines have rode snowmobiles with them. So much better same sled same brake setup but only one had rubber the other had stainless.

So it looks like what I need to do is...
1. Stainless brake lines from the frame to the cal up front.

2. New prop block.

3. If that doesnt work go with hydroboost.

Does anyone have a picture or part numbers of the prop block setup they are running. The way it sounds I need an adjustable one ? Or should I just get an replacement from like napa?

The brake pads are Wagner thermo quiets ceramic

[knightowl73]

factory replacement would be fne, and easier to adjust also, because you wont have to like you will (trail and error) on the adjustable. check to see if its the same part number if you happen to need the hydroboost later.

[leegrady]

I'm wrong about the quick take up master cylinder. Your truck is equip. with a conventional master.

I want to write tho' that one should remember that even tho' the truck has heaver tires, therefore heaver un-sprung weight, it is designed to carry a considerable amount of weight in the back. The vin no. tells weight and corresponding braking system equip. with each truck off the line. Not empty, but with a full load.

My humble opinion is that unless you're running a big cam, and suffer from low manifold vacuum the stock brakes will stop that truck no problem. As long as everything is as it should be.

Nothing wrong with hydro-boost, but...

[68Timber]

Originally Posted by leegrady

I'm wrong about the quick take up master cylinder. Your truck is equip. with a conventional master.

I want to write tho' that one should remember that even tho' the truck has heaver tires, therefore heaver un-sprung weight, it is designed to carry a considerable amount of weight in the back. The vin no. tells weight and corresponding braking system equip. with each truck off the line. Not empty, but with a full load.

My humble opinion is that unless you're running a big cam, and suffer from low manifold vacuum the stock brakes will stop that truck no problem. As long as everything is as it should be.

Nothing wrong with hydro-boost, but...

I didn't want to get into this, but I've never run anything but a stock brake system on 73-87's. Yeah, the initial take-up on the brake pedal is "spongy" but it hardens up quick and will lock them all up if everything is in order.

Hence my hesistance to speak up, you said it's all in good factory working condition - something is off but I don't have a clue what it is. But if it was all up to specs it'd never drag the rears.

[spinem]

Originally Posted by datguysaL

It could also just be brake-fade caused by excessive heat up front. usually caused when your rotors dont dissipate heat fast enough.

or could of been contamination of brake pad before installation, ex: grease, fluid, cleaners.

what brake pads are you using up front? ceramic, organic, semimetallic.....

*ceramics are good, but alot of people dont know that they are not always compatible with stock rotors.

Yes, here in cali it got to 115*F, in excessive traffic, my truck gets scary.

Originally Posted by Farmer Mike

Your 35" tires are overwelming your brakes. Look into braided steel brake lines. They won't swell like the stock rubber lines and will enhance your stopping power.

Call Skyjacker for more info. I'm sure they'll be able to help!

Mike

Yes, i agree, the ratios have greatly changed.
Yes, the lines will swell, and after 30+ years of this they get dry, and crack, they you have to prey your E-Brake works....also from experience.

Originally Posted by knightowl73

yeah i lke the truck too. think a new prop valve will fix your problem. had a similar problem in my monte a few years back. plenty clamp in the back , but nothing up front. prop valave turned out to fix it after i had kept changing alot of other stuff. know for a fact though, you can actually feel the difference in your braking power f you upgrade to the braided stainless lines.

Yes, i agree, i did my chevelle (72) /w/ no power, and this helped alot.
Any one know how to adjust our year trucks?

Originally Posted by BRUISER

I didn't want to get into this, but I've never run anything but a stock brake system on 73-87's. Yeah, the initial take-up on the brake pedal is "spongy" but it hardens up quick and will lock them all up if everything is in order.

Hence my hesistance to speak up, you said it's all in good factory working condition - something is off but I don't have a clue what it is. But if it was all up to specs it'd never drag the rears.

---Explained perfectly!

Every old vehicle ive ever owned (had a alot of em...worst was an 68 coronet.) I think something is wrong, proportioning wise....



TO WHOM STARTED THIS THREAD:
-Im surprised no ones mentioned the lmc cross drilled rotors. I dont know of any one running them, but i believe this set up /w/ a nice semi-metallic pad wold do the trick.... if ya have the money steel lines, fresh fluid, full purge.... maybe a new boster.... haha so basically a new system i know.... just some ideas.

[f.monroe]

First let me say this .

That truck is Beautiful !!

Next , I think the hydro boost along with a newer rear axle running factory disc brakes would reeally help out .
Frank

[68Timber]

You've got a brake problem you haven't found yet. I hate to go across the grain here but I also hate to see someone throw money at a problem. The biggest tires I've run on a 73-87 is 33x12.50's and it'd throw you through the windshield if you weren't buckled up.

Your stock brakes should be putting 70 percent or more of the braking power on the front calipers, I don't know the exact percentage. But if you're dragging locked up rears to a stop, your stock brakes are not up to par. If they were, they'd haul it down on 35's no problem.

[leegrady]

Hydroboost can be used on your truck if low manifold vacuum condition exist, because of a high-perf. cam the vacuum booster for the braking systems wont be worth a damn.

This is also why you find hydroboosts on diesels.

Hydroboosters also save space in the engine compartment for bigger engines to be shoe horned in. (Like the twin engine sbc '71 Nova I'm working on.)

Key to our want/need to upgrade: because the hydroboost system does not run on vacuum the brakes will be given the same amount of pressure from the second you step on the pedal to the moment you lift them off. In this respect the hydroboost system is superior to vacuum boost. (However, as with most everything the trade off is that the hydroboost uses horsepower to operate.) But...a hydroboost system does not clamp the calipers or shoes against the drums with any more force than the vacuum boost system.

Clamping force is dictated by the size of the master cylinder piston, the size of the caliper piston, wheel cylinder pistons, and on disc brakes how far from the center line of the axle the caliper is located. Larger diameter rotors move the caliper farther away from the center line, and this in turn produces more leverage to stop the vehicle. (Just like your cheater bar.)

If you want your truck to stop better, all things being equal, four wheel disc brakes by all means, larger diameter vented/drilled rotors, and multiple piston calipers.

I race a lot. Most can't catch me. I brake late into the turns. And remember...Always roll the pedal.