psalt

The reason your suggested procedure is meaningless should be obvious, but apparently beyond your understanding. When you press on the brake pedal any "slack" or " excessive distance between the pad and rotor" disappears. When you change the pads, it is also obvious that the pistons need to be retracted, because the replacement pads are thicker than the worn pads. If you were to insert a piece of wood that is thinner than the new pad and press the pedal, you would have to manually retract the pistons to replace the pad, and you would wind up in the same state before the "procedure". If you were to insert a piece of wood that was thicker, the pistons would remain further back in the caliper. In either case, you have accomplished nothing and the "slack" would be automatically taken up when you pumped the pedal before attempting to bled the system which is SOP when you replace the pads. To me, your suggestion is similar to a witch dotor rubbing chicken organs over a sick patient and claiming it did something. I am sorry if you find the facts disturbing, but they should be obvious if you take a minute and consider how the system works.

Paul

theiceman

autobonrun

Most of Psalts posts are of an arrogant flaming nature, not intended to educate but to "pose". You are doing the right thing.

Good on you ..

I know he is going to respond to this and then we will just let the thread hang for people to read and judge for themselves as neither of us will respond..

psalt

Yes, if there is a reasoned explanation for the necessity to "fit brake pads tightly in a caliper using a block of wood", I would like to hear it. So far there is none, just heresay. Iceman, you cannot claim to have read most of my posts unless you were a member of the original 911 Rennlist mailing list. Perhaps you can search the archives if you are interested. My only interest in this thread is debunking an erroneous suggestion, which should be obvious to anyone with training and experience with brake systems. You should try the same.

Alan Herod

In answer to your question, 'How do I know my brakes are OK after bleeding?' I use an IR pyrometer to compare temperature readings if all else seems to be in order. The results are consistent whether taken after a track session or after a few brake tests on the street. Generally they may help you confirm what you felt; but, they may identify an anomaly. The cheap IR pyrometer seems to be perfectly adequate for the task and provide consistent numbers. Side to side should be about the same and fronts should be significantly hotter then the rears.

psalt

I also find an IR pyrometer to be very useful, especially in finding dragging calipers. The book for my Raytek say 3C or 5F difference side to side indicates a problem, but I think this is unrealistic for a road car. What do you consider abnormal side to side ? I don't know how you would detect air in the system unless you had a library of previous readings under exact conditions and something like pedal pressure to compare it to ? Are you saying the historical temperatures would be higher if the bleeding didn't work ?

Paul

Alan Herod

As an example, at Summit Point, December 2, ambient temp 29 - 37F, my temps were 373 front and 282 rear. This front to rear variation was consistent with previous readings. Two days before the event my student had encountered trouble bleeding his right front brake, and was not satisfied with his result. Predictably, his car was pulling to the left under hard braking. His right front temp was approx 70 degrees less then his left front or closer to the temp of his rear brakes. His pyrometer temps indicated approx 100F less then mine. We were both using PF97s (he was using my take-offs) and new ATE Blue.

I find the results are repeatable on the street or the track; its just that external conditions will have a larger apparent effect on the readings. Unfortunately, I was not able to check his other car after his last event; because it was not until we were changing his transmission that I noticed his rear rotors still appeared to be new.

At this point I am only worrying about relative temperature for a given day. I also need to add better cooling to the fronts.

psalt

I agree, relative temperatures and a history make a good indicator. You would need an awfully large sample to get a meaningful absolute reading and there are many variables. I have seen over 500F on 911's with a frozen front caliper. A stuck caliper can easily boil the fluid after a short highway drive and a history of IR readings can see it coming. Having driven many miles in early single circuit equipped cars, boiling the fluid at speed is not an experience I would recommend.

I have never found it difficult to feel air through the pedal response, but I have been doing it for 30 years. An IR reading could be helpful for someone with no experience, but since the MFG recommends at least threes full stops at speed for a standard road test, measuring the distance may give you the same result if you don't have the instrument. A race track is a different environment. I also use my IR thermometer on engines. The plug and exhaust port temperatures are useful in tuning and setting up programmable EFI systems.

Paul

dshepp806

psalt states: The reason your suggested procedure is meaningless should be obvious, but apparently beyond your understanding.

Now why the hell would you make such a comment about his "ability to understand"?

Completely uncalled for.

Your brake information is good and welcomed....but this type of bullsheeit is way off base.

...maybe Clive is dead on with his observations, no?


geeeze,



Doyle

MUSSBERGER

Son of OC Ben?

theiceman

Gee Doyle where did you dig up this thread ? :-)

Psalt has been gone ages .. (thank god ) . Don't be testing the P-gods . he might come back.

PS going to the track tomorrow, have a good one guys ..

old man neri

You....at the track? Surely you jest. Which track anyways?