Robyn
01-31-2009, 09:12
The IFS front ends on our GM pickups have some issues that have plagued them from the gitgo.
The anoying tendency to have a pulsing or stuttering brake on one or the other front rotor is the biggy.
I have had 3 mid nineties Burbs that have had this issue and all of them needed a LH Rotor replaced to fix this issue.
All of us seem to agree that we want to buy Made In USA.
That said I always cringe when the box says Mexico, China, Maylasia or ??????????/
I have mentioned before and I will do so again, I used to purchase nothing but top rate NAPA rotors and pads.
I have had several NAPA rotors fail.
Now these never seem to be warped and the runout (As checked with a dial indicator) is always just fine.
The issue I am venturing a guess is the metalurgy and that what is happening is the frictional quality is changing at spots around the rotor due to heat and or water being tossed onto the rotors during or just after a hard braking.
The sudden cooling of the rotor can cause a change in its hardness and with it comes a different coefficient of friction (IN SPOTS)
The Made in China Rotors that I have purchased, so far have never done this.
I have had OEM (GM) stuff that lasted less than a week and were jerking.
Some NAPA stuff lasted less than the life of a set of pads and were toast.
The cheap stuff I have bought are working great and still at it after several sets of pads.
Now, even though I have been through all the training on brakes and understand the technical DOGMA.
Unless I have a rotor thats warped or that the pad has gone too far and ate the surface, I never machine the rotors.
I simple replace the pads with a fresh set and have never had any issues.
I go easy on the brakes for the first few stops and it works fine.
Another area that causes great trepidation is the flange headed bolts that retain the bearing/hub assembly into the housing.
These bolts have a hex head that is very prone to rounding off and if this happens can be a real PITA to get out.
The best solution is to purchase a 15mm impact socket and turn the OD down some so it will fit into the counterbore in the knuckle.
The 12 point sockets, although thin enough to fit will usually slip and or split and then round over the bolt.
I use the Modified 15mm impact with a break bar (1/2" Drive) to get the bolts loose and then remove with a 3/8 drive wratchet and thin socket.
Once out a good cleaning of the threads is in order and always use some neverseaze on the threads when reinstalling.
Generally the bearing assembly will slide right out of the housing once the bolts are removed.
If it does not a slide hammer mounted to the lugs will usually persuade the recalicitrant critter to come out.
Always grease the bore and the sealing ring after cleaning it up.
The older trucks 94 and older have the ABS reluctor inboard of the hub and these can and do fill with crap.
A good blow down of the reluctor and the area with air will clean the notches and help keep the ABS system from getting cranky.
The newer hubs (95 0n) have the reluctor inside the hub so it stays clean.
To my way of thinking, this design should have been a NO BRAINER.
Electronic sensor and reluctor, down in the mud and salt etc. ?????????? :eek:
Another area that needs atttention is the retaining bolts and sleaves that hold the calipers to the mounting.
If these are allowed to get stuck and really crudded up the caliper will not float correctly and the pads will wear unevenly causing other issues including poor braking.
There has also been mentioned the tendency of some trucks to have poor rear brakes.
OHHHHHHHHHHHH YES. This is caused (Usually and if everything in the back is good) by the combination valve which is the little assembly right after the master cylinder and before the ABS 94 and 5 trucks anyway.
This valve assembly also has a little wire hooked to it.
The wire is a ground for the Brake light on the dash which signals that the brake system has a pressure fault either front or back (leak)
The insdie of the valve assembly has a piston and a spring.
The assembly will restrict pressure at a certain point from going to the rear brakes to keep the large drums from locking.
Unfortunately the little valves either came with a poor calibration or over time the spring loses its tension.
GM sells an updated version that will solve this issue.
We used to have two 94 Burbs and one had excellent brakes and would literally squat with very light brake pedal pressure.
The one we still have has always had much more brakes on the forehand and the rears lag a lot.
For many of us that use the rig as a people mover only, the issue is not a biggy.
If you are towing and need all that the brakes can deliver, the updated Combination valve is a good way to go to get those big 13" drums doing their share of the work.
My 94 will show nearly no heat in the drums even after a hard stop.
Only after repeated use will they even get warmed up.
Replacing the Combi valve does require bleeding the system fully.
The ABS brake system has some quirks as to how it should be bled out.
A power bleeder is a real plus to get the system totally air free.
Hope this helps those that have questions about this brake system.
Best
Robyn
The anoying tendency to have a pulsing or stuttering brake on one or the other front rotor is the biggy.
I have had 3 mid nineties Burbs that have had this issue and all of them needed a LH Rotor replaced to fix this issue.
All of us seem to agree that we want to buy Made In USA.
That said I always cringe when the box says Mexico, China, Maylasia or ??????????/
I have mentioned before and I will do so again, I used to purchase nothing but top rate NAPA rotors and pads.
I have had several NAPA rotors fail.
Now these never seem to be warped and the runout (As checked with a dial indicator) is always just fine.
The issue I am venturing a guess is the metalurgy and that what is happening is the frictional quality is changing at spots around the rotor due to heat and or water being tossed onto the rotors during or just after a hard braking.
The sudden cooling of the rotor can cause a change in its hardness and with it comes a different coefficient of friction (IN SPOTS)
The Made in China Rotors that I have purchased, so far have never done this.
I have had OEM (GM) stuff that lasted less than a week and were jerking.
Some NAPA stuff lasted less than the life of a set of pads and were toast.
The cheap stuff I have bought are working great and still at it after several sets of pads.
Now, even though I have been through all the training on brakes and understand the technical DOGMA.
Unless I have a rotor thats warped or that the pad has gone too far and ate the surface, I never machine the rotors.
I simple replace the pads with a fresh set and have never had any issues.
I go easy on the brakes for the first few stops and it works fine.
Another area that causes great trepidation is the flange headed bolts that retain the bearing/hub assembly into the housing.
These bolts have a hex head that is very prone to rounding off and if this happens can be a real PITA to get out.
The best solution is to purchase a 15mm impact socket and turn the OD down some so it will fit into the counterbore in the knuckle.
The 12 point sockets, although thin enough to fit will usually slip and or split and then round over the bolt.
I use the Modified 15mm impact with a break bar (1/2" Drive) to get the bolts loose and then remove with a 3/8 drive wratchet and thin socket.
Once out a good cleaning of the threads is in order and always use some neverseaze on the threads when reinstalling.
Generally the bearing assembly will slide right out of the housing once the bolts are removed.
If it does not a slide hammer mounted to the lugs will usually persuade the recalicitrant critter to come out.
Always grease the bore and the sealing ring after cleaning it up.
The older trucks 94 and older have the ABS reluctor inboard of the hub and these can and do fill with crap.
A good blow down of the reluctor and the area with air will clean the notches and help keep the ABS system from getting cranky.
The newer hubs (95 0n) have the reluctor inside the hub so it stays clean.
To my way of thinking, this design should have been a NO BRAINER.
Electronic sensor and reluctor, down in the mud and salt etc. ?????????? :eek:
Another area that needs atttention is the retaining bolts and sleaves that hold the calipers to the mounting.
If these are allowed to get stuck and really crudded up the caliper will not float correctly and the pads will wear unevenly causing other issues including poor braking.
There has also been mentioned the tendency of some trucks to have poor rear brakes.
OHHHHHHHHHHHH YES. This is caused (Usually and if everything in the back is good) by the combination valve which is the little assembly right after the master cylinder and before the ABS 94 and 5 trucks anyway.
This valve assembly also has a little wire hooked to it.
The wire is a ground for the Brake light on the dash which signals that the brake system has a pressure fault either front or back (leak)
The insdie of the valve assembly has a piston and a spring.
The assembly will restrict pressure at a certain point from going to the rear brakes to keep the large drums from locking.
Unfortunately the little valves either came with a poor calibration or over time the spring loses its tension.
GM sells an updated version that will solve this issue.
We used to have two 94 Burbs and one had excellent brakes and would literally squat with very light brake pedal pressure.
The one we still have has always had much more brakes on the forehand and the rears lag a lot.
For many of us that use the rig as a people mover only, the issue is not a biggy.
If you are towing and need all that the brakes can deliver, the updated Combination valve is a good way to go to get those big 13" drums doing their share of the work.
My 94 will show nearly no heat in the drums even after a hard stop.
Only after repeated use will they even get warmed up.
Replacing the Combi valve does require bleeding the system fully.
The ABS brake system has some quirks as to how it should be bled out.
A power bleeder is a real plus to get the system totally air free.
Hope this helps those that have questions about this brake system.
Best
Robyn