Problem with Brakes? Hydroboost? Need Help!!

[rizzos442]

I had this same problem until I flipped my hydroboost unit upside down. MY problem was that the power steering pump didn't have enough power to get the hydraulics to the hydroboost unit in its normal, upright configuration. Once flipped, the problem was completely gone. It humms every once in a while but that is it.
I also run a manual now and if that were to happen to me, I would FREAK! I would be sooo pissed and if I hit something, not to mention how dangerous it would be on the street. I would NOT drive your ride until you resolve the problem.

[toofun]

Who recommended that you flip the unit? Also how did you know the pump was not supplying enough pressure??

Thanks
Mark

[toofun]

OK, PLEASE ALLOW ME TO CLARIFY THIS RIGHT OFF THE BAT.. THIS BRAKE PROBLEM WAS PRE EXISTING BEFORE I EVEN HAD THE HYDROBOOST. I am in NO WAY BLAMING THE HYDROBOOST UNIT OR PAUL IN ANY WAY. If people interpreted this to be the case. PLEASE DO NOT TAKE IT THAT WAY, IT WAS NOT MY INTENTION!! My apologies to Paul or anyone else that may have misinterpreted this post to mean that I was bashing or blaming the Hydroboost unit. It is an exceptional piece of equipment.

Regards,

Mark
TOOFUN

[Hydratech®]

The history behind this particular Camaro's braking issues are such that this problem has existed all along, well before any of the above listed mods were performed. With that being said, let's take a closer look at items that are not on the list, as this is going to go a long way towards getting this strange problem resolved. At first glance, conventional wisdoms would have you believe that we are dealing with a master cylinder problem, though this condition has manifested itself even after the MC has been swapped out. So what else could possibly be at fault to produce such a concern? There are many possible alternate causes:

* My first thoughts here are to believe that the issues will ultimately be found to be front steering knuckle / spindle / wheel bearing related. ??? How? A substantial intermittent drop in pedal height during brake apply indicates that either the master cylinder isn't building or holding pressure correctly, or that the hydromechanical items downstream of the MC are not responding to these pressures correctly. With the MC being swapped out with no improvement observed, there is a higher probability that the MC is not at fault. Ok, so now what? I'm willing to bet that the caliper pistons are being pushed back in during certain maneuvers, which upon the next brake apply causes an alarming lack of response in the braking actions (called caliper knockback in the industry). Mark has indicated that this problem seems to manifest itself more when backing up in reverse, which bolsters my theory. How in the world does this bolster the theory? Most wheel alignment specs call for a certain measure of toe in, meaning that the tires are actually pointed inward ever so slightly - maybe a 1/16 or even up to 1/8 of an inch. As you are rolling forward, this provides a very slight amount of steering linkage / gear / tire preload to maintain a very positive and tight feel in the steering response. When you throw it into reverse, the tires will actually shift in the opposite directions ever so slightly (barely even visually perceivable). Ok, so what does all of this mean? Here are the most likely causes for steering knuckle related "caliper knockback":

* Wrong wheel bearing installed (wrong part number, visually very close and easy to miss)

* Severely worn spindle shaft

* Wrong bearing races installed into the rotors

* Severly worn rotors (bearing races loose in the rotors)

* Wheel bearing simply radically out of adjustment (not likely but possible)

The above listed items can cause the rotor to move in relation to the spindle quite a bit, which under certain circumstances will push the caliper pistons back in quite a bit = the next time you hit the brakes you will find the pedal heading towards the floor before any braking actions occur. Here is an interesting article regarding caliper knockback (courtesy of StopTech Inc): http://www.stoptech.com/tech_info/wp_knockback.shtml While this article speaks more of hard racing maneuvers, the basic tech behind what we are discussing IS relevant, though manifesting per different reasons.

The only other potential issue that comes to mind is that a brake line is too close to an exhaust header pipe, and the fluid is possibly boiling (though the line would have to be just about touching the header and the exhaust temps would have to be very high).

There are obviously many many other issues that *could* be at fault, though I'm hedging my bets based upon my experience that the front steering knuckles are the most likely culprits. Here is what I recommend:

* Jack the vehicle up securely onto some jack stands (shake test the vehicle while up on the stands / lift before performing any further operations to insure your safety).

* Remove the front wheels.

* Carefully visually inspect the steering knuckles for any visually obvious signs of troubles before disassembly.

* Remove the front calipers from their mounting to the spindle, though leave the flex hoses connected. Do not allow the calipers to hang from the flex hoses, so rest them on top of the upper control arms while working.

* With the calipers removed, firmly grab the rotors and see if you can get them to "clunk" at all in relation to the spindles. If so, then we are definitely on the right track.

* Remove the rotors from the spindles and then clean the spindle shafts very thoroughly to prep them for careful inspection.

* Put the rotors on a work bench and remove the grease seals and wheel bearings. Do this in such a way that insures you can re-install the same bearings back into the same bearing races (as they have worn together). Why? Mismatching the wheel bearings into different bearing races can induce accelerated wear...

* Very thoroughly clean the brake rotors, bearing races, and wheel bearings using a solvent of your choice / parts washer.

* Carefully inspect the races installed into the rotors to make sure that they aren't loose inside of their seats in the rotors. If you find a loose bearing race, discard the brake rotor and obtain a proper replacement.

* Carefully inspect the wheel bearings for any visual wear, pitting, blueing or galling - replace as needed.

* Take the bearings and test fit them onto the spindle shafts. They should be an ultra precise fit onto the spindle shafts. Without any grease, they may even be difficult to slide into place. What I'm hoping you will find here is an incorrect bearing that is very sloppy on the spindle shaft, or nothing wrong with the bearing though heavily worn shaft = same difference either way.

* If you have not yet conclusively discovered a problem, lube the bearings and races with some light spray lube (WD40 or equivalent) and then temporarily re-assemble the rotors back onto the spindles. (grease will potentially mask a bearing problem, which is why I suggest you use the WD40). Torque the spindle nuts down 2-4 ft. lbs. then firmly grasp the rotors and see if you can get any "clunk" out of them (which would indicate that the problem is "right there" in your hands. I have seen worn or incorrect bearing / race combos torque down properly, yet still have play or slop as assembled for various reasons.

* I would also be inclined to test the spindle shafts while the rotors are off, as this is now an "old car", and you may be shocked to find that spindle shaft itself may actually be loose in the spindle (!) (very rare, though I have seen it)

* Inspect the brake pads and the areas that they contact, as a worn in step could be hanging up a brake pad at times, then pop out of the groove it is stuck in to cause this pedal loss condition.

Summary: You have replaced just about everything else in the brake system, and therefore I'm hedging a strong bet that you will likely find the gremlin(s) in the front steering knuckles. The only other issue that comes to mind is a brake line resting on an exhaust pipe somewhere...

Spend a couple of hours very carefully inspecting the front spindle / brake assemblies and report back your findings / success!


BTW - you state that you have to pull the pedal back up with your foot when this happens. This actually provides a strong diagnostic clue! The hydraulic brake assist units do not have a very strong return spring inside of them, and therefore count on the force of the master cylinder to push the assist unit back to its rest position when you release the brakes (like a manual brake setup would). This essentially tells me that you are indeed definitely experiencing a pressure loss somewhere downstream of the master cylinder, which happens to fit my above theory perfectly. Also, the orientation of the assist unit (right side up vs upside down) is irrelevant...