K2500 Brake issues

[ricnor]

My 1997 454 Vortec 4x4 auto Sub is fitted with power assist to the brakes from what looks like the power steering system, it is not a vacuum booster. In the past on a couple of occassions when I have really had to hit the brakes my foot has gone right to the floor and only luck and just enough room stopped me from hitting anything.
I suspect that the master cylinder will need replacing or overhauling but the brakes have never given me confidence and I was also wondering if there is anything I can do to help boost the system, is the booster already fitted an issue or do they not go wrong?, if they do go wrong are they rebuildable?
I fitted special disc's to the front a few years ago which don't really seem to have helped but I thought it would be something to try, they are obviously vented but also drilled and grooved. Are there any brake pads I should look out for?
I haven't used the burb for a while so thought I would try to fix some known issues before starting to use it again. TIA.

[777stickman]

This system is called "Hydro-Boost". It is feed from the power steering pump to the brake booster and then to the steering box. From my experience it is a reliable system unless the pump gets weak. In that case the steering would be effected also.

A pedal that goes to the floor on occasion would indicate a master cylinder bypassing internally. Other issues could be air in the system.

[j cAT]

the pedal to floor would mean a new master is required. soft pedal would be air in the system. not getting a good brake effort is usually on these rear drum brakes worn drums. if the shoes are worn at the top and not much at the bottom then the drum is worn out [its too big ]

if the drums are worn make sure you have slack in the emergency brake cable. many adjust this cable to compenste for worn out drums. then when the new shoes and drums are installed the rear brakes will drag.

when first testing out the vehicle easy on the brake pedal you may find that you have alot more stopping power than before.

another cause would be front calipers binding . this would also cause loss of brake effort. with the drums worn you get front end dip when braking.

[ricnor]

Thanks for the quick responses, the pedal is firm not spongy but as I said very occassionally it has gone to the floor, maybe 3 times in a year.
Over here we have to have a test on our vehicles every 12 months and part of the test is to check the brake efficiency on rollers hooked up to gauges. whenever the truck has been tested it passes without issue, they first check that the brakes are not binding by running the front wheels on the rollers without pressing the pedal, if everything is fine they then do one wheel at a time and the readings are fed into a computer, after doing the two fronts individually they then reset the rollers and do a test on both the wheels at the sametime to make sure that one side is not better than the other.
This is then repeated on the rear wheels in the same way but now twice over, one lot for the foot brake and then all over again for the parking brake only.
I will check the rear brake shoes for wear just to see.
The power steering works a treat without hesitation and is nice and light, plus similar to an ordinary vacuum brake booster if I put my foot on the brake pedal and then start the engine the pedal goes down a fraction so to me it would appear that the system is working. (hope this is correct).
I am concerned with the brake going to the floor so think I will get a new master cylinder as a start and see if it makes any difference to the overall braking efficiency of the truck.
As I have said I have never been totally happy with the way the truck brakes but can't believe it is something that can't be cured, it's a big heavy rig not to be able to stamp on the brakes and know you are going to stop

[j cAT]

interesting that where you live they test the braking on each wheel.

problem I have with the testing is are they monitoring the brake fluid pressure and measuring the braking effort. if not then this is not a good test to determine if you have lost braking effort. more pedal pressure would overcome worn brake components like the drums.

on larger transportation vehicles I would measure the braking signal as I was measuring the braking effort , to determine if the braking system was within spec.

with my 2000 silverado replacing the rotors ALL and the brake pads the pedal effort is much less to slow the vehicle down.

[Schurkey]

Originally Posted by ricnor

or do they not go wrong?, if they do go wrong are they rebuildable?

EVERY part on a vehicle can become defective. EVERY part can be rebuilt or replaced.

Originally Posted by ricnor

I fitted special disc's to the front a few years ago which don't really seem to have helped but I thought it would be something to try, they are obviously vented but also drilled and grooved.

Parts stores love to sell drilled/grooved/slotted rotors. USUALLY they're the same junk Communist Chinese rotors sold in the "discount" line, but someone threw them on a mill, and then stuffed them into a fancy box; the resulting profit-margin enhancement can be substantial.

Originally Posted by ricnor

Are there any brake pads I should look out for?

Originally Posted by j cAT

with my 2000 silverado replacing the rotors ALL and the brake pads the pedal effort is much less to slow the vehicle down.

First Guess: Less a matter of the rotors, and more a matter of fresh/better pads.

Discount pads tend to wear rapidly. I paid for "premium ceramic" pads once; couldn't wait to get rid of them. Didn't stop well at all. Wore like iron, I was stuck with them for a decade.

There's a hundred pad formulations; every brand claims to be "the best". Good luck, I don't have a solid answer except to say that I'm satisfied with plain ol' semi-metallic from the moderate-upper end of the price spectrum.

Don't know about your K2500, but my K1500 uses leading/trailing shoes at the rear; I just hate 'em. I believe it's a poor design. I'd much prefer self-energizing shoes with the adjuster link at the bottom, like older vehicles.

[j cAT]

when I replaced the rotors/pads/rear calipers they looked still good. OEM GM PADS . rotors had a smoothed non grooved surface.the rotors where 10 yrs old rust holes on all begining to show.

the replacement rotors/pads/calipers advance auto parts life time warrantee. going on 3 yrs still working great.

with drums these parts are in most cases chinese junk. soft metal/ very soft. also using a higher grade pad of the correct material for the vehicle will determine proper brake effort and min rotor/drum wear.

with the soft metal used today best pay for the higher quality lifetime warrantee. bring in the worn out parts walk out with new total cost a few hours work. even the brake pads are free !

[ricnor]

Originally Posted by j cAT

interesting that where you live they test the braking on each wheel.

problem I have with the testing is are they monitoring the brake fluid pressure and measuring the braking effort. if not then this is not a good test to determine if you have lost braking effort. more pedal pressure would overcome worn brake components like the drums.

on larger transportation vehicles I would measure the braking signal as I was measuring the braking effort , to determine if the braking system was within spec.

with my 2000 silverado replacing the rotors ALL and the brake pads the pedal effort is much less to slow the vehicle down.

Hi, no they are not measuring the brake fluid pressure but the braking efficiency of the road wheels. The test consists of putting both front wheels onto a set of rollers, these then turn at about 2mph or so, the tester pushes the brake pedal down and the force needed to stop the rollers is fed into the computer. The force is measured in kilogrammes I think. As stated each is done individually and then one test for both together so that if one wheel has a lazy caliper it would show up as not exerting the same force or pressure on the rollers as the other side. The test is not great but a fair few cars do fail it (I have loads of problems when I take my 79 vette in for the handbrake test). If the pedal is spongy or low then it is down to the individual tester to flag this up but so long as the pedal doesn't go to the floor and the pressures are good enough (there is a table of pressures to axle weights to define the pass or fail) then it passes.
If you build a kit car over here you have a further test for brakes and that does involve a pressure pad that the tester puts between his foot and the brake pedal to determine the amount of force needed to operate the brakes but that is a one off test never to be repeated if the car passes and is never used on a production car that you buy from a dealer.

[ricnor]

Originally Posted by Schurkey

EVERY part on a vehicle can become defective. EVERY part can be rebuilt or replaced.


Parts stores love to sell drilled/grooved/slotted rotors. USUALLY they're the same junk Communist Chinese rotors sold in the "discount" line, but someone threw them on a mill, and then stuffed them into a fancy box; the resulting profit-margin enhancement can be substantial.




First Guess: Less a matter of the rotors, and more a matter of fresh/better pads.

Discount pads tend to wear rapidly. I paid for "premium ceramic" pads once; couldn't wait to get rid of them. Didn't stop well at all. Wore like iron, I was stuck with them for a decade.

There's a hundred pad formulations; every brand claims to be "the best". Good luck, I don't have a solid answer except to say that I'm satisfied with plain ol' semi-metallic from the moderate-upper end of the price spectrum.

Don't know about your K2500, but my K1500 uses leading/trailing shoes at the rear; I just hate 'em. I believe it's a poor design. I'd much prefer self-energizing shoes with the adjuster link at the bottom, like older vehicles.

My first point was more of a question as to if these parts are know to fail or give issues and if they do are they something that you could get a repair kit for or have to buy it fully assembled

As for the drilled and grooved rotors, yes I see where you are coming from but I was shocked at how poor the brakes felt that I needed to try something, the pads I have been using are probably at the cheaper end of the scale as all the ceramic pads stated that they were not recommended if towing trailers, which I do a fair bit of. I don't know if this is right or wrong so cheap pads have been the order of the day and I do get through a set in about 15000 miles or so.

I don't know what my rear shoes are other than huge, think about 3" wide set up from memory but the last time I looked at them was 8 years ago when I first got the truck. I would suspect that they are leading/trailing as on yor one. I know there is still life in them as there is no squealing or grinding, the test shows them working well via foot brake and the parking brake works really well on hills etc. Maybe I will take a look just to be certain but leaving the occassional foot to the floor issues the foot pedal is firm and does not drop much when pushed before the truck starts to slow, it is just that it never seems to slow "quickly" if you get my meaning and you can often think that you are not going to stop in time (a little like brake fade)

[ricnor]

Originally Posted by j cAT

when I replaced the rotors/pads/rear calipers they looked still good. OEM GM PADS . rotors had a smoothed non grooved surface.the rotors where 10 yrs old rust holes on all begining to show.

the replacement rotors/pads/calipers advance auto parts life time warrantee. going on 3 yrs still working great.

with drums these parts are in most cases chinese junk. soft metal/ very soft. also using a higher grade pad of the correct material for the vehicle will determine proper brake effort and min rotor/drum wear.

with the soft metal used today best pay for the higher quality lifetime warrantee. bring in the worn out parts walk out with new total cost a few hours work. even the brake pads are free !

The rear drums are the original set up and would appear to be fine, however that was a few years ago when I first and last checked them so I will take a look to ensure that the shoes are still ok and that the drums have not worn too much.
Buying parts with a lifetime warrantee would be great but there is the matter of a bit of water between myself and the USofA and I found with my Vette that lifetime warrantee's are not extended outside of the USofA. As I said I got the front disc's because the brakes just didn't feel right and never have, they have never faded on braking but it is a similar feel in that you don't think you are going to stop before hitting something. I certainly wouldn't like to do too many emergency stops as I'm sure it would end in tears.
As I said at the start I haven't used the truck for a while but got myself a Chevy Blazer 4.3l 4x4 to sort of help with the fuel costs and I was going to get rid of the burb but I actually hate the Blazer and so have decided that it has to go and the burb gets back on the road, however I really would like to get the brakes feeling a lot better this time instead of always been worried if they are going to do the job or not.

[Schurkey]

Originally Posted by ricnor

I really would like to get the brakes feeling a lot better this time instead of always been worried if they are going to do the job or not.

1. Replace master cylinder, flush old brake fluid so it runs clear and fresh at each bleeder screw.

2. Adjust rear brakes.

[ricnor]

Originally Posted by Schurkey

1. Replace master cylinder, flush old brake fluid so it runs clear and fresh at each bleeder screw.

2. Adjust rear brakes.

I'm just trying to locate a master cylinder now as it goes along with a set of slightly more expensive brake pads, so the above is basically what I'm going to do and then see what it all feels like from there.
Thanks for everyone's input and I will let you know how it goes.

[j cAT]

Originally Posted by ricnor

I'm just trying to locate a master cylinder now as it goes along with a set of slightly more expensive brake pads, so the above is basically what I'm going to do and then see what it all feels like from there.
Thanks for everyone's input and I will let you know how it goes.

remember if the shoe wear is greater at the top of the shoe the drum is worn. the greater the wear at the top vs the bottom the more the drum is out of spec/worn too much.

on a vehicle of this size the rear drum brakes do alot of brake effort.

I have had issues like this with owners vehicles . the front brakes do most of the braking the rears with drums being worn cause the fronts to make up the difference. that where , if it gets bad enough ,the front rotors get distorted.


I would suck out the brake fluid in the res. new fluid. then push back each front caliper with the bleed screw open to dump out the old piston fluid. then do the bleed proceedure starting from the passenger side rear brake to the driverside rear to the passengerside front to the driverside front.

OLD brake fluid does not compress well. also the brake cylinders/calipers get internal corrosion.

[ricnor]

It's been a while since I last posted anything but I finally got a new master cylinder on the truck and a new set of front pads, replaced the metal brake lines on the rear axle and a section of the front to back line as it was very corroded, bled the system with new fluid. The rear shoes look fine and not worn too much at the tops so the drums would appear to be reasonably ok.
The truck at slow speeds seemed to stop fine BUT I went to take it for a short drive to bed in the pads a little and the feel of the brakes became worse and it's now not good.
I also noticed that the brake warning light which comes on at start up does not now go out.
I removed a small wire connector that goes to the pipe side of the ABS unit and the light comes on when the key is turned to start and then goes off after a few seconds, put the connector back on and the light stays on. Is the ABS unit knackard? could this be why the brakes still feel so bad? Is there a special method for ensuring no air is trapped in the ABS unit. I have bled the brakes three times now with no air coming out at any point and the fluid is clear. The front calipers are free to move and do not bind and the parking brake works great. Starting to loose the will to continue, might pull the engine and scrap the truck if I can't sort it soon.

[maxwedge]

If the system trapped air in the abs the only way to bleed it is using a bi-directional scanner to actuate the solenoids,.