FFaust

Excellent write-up Dennis

CT03911

Thanks FFaust.
Ran Lime Rock on Monday. The original temp strips STILL have not registered at all, the 466-554F ones.
All I managed to do after VIR was clean the car, did not have the wheels off to swap temp strips out before LRP.
I actually thought I might register a temp at LRP, it being a shorter circuit.
I could see one rotor's temp paint and it apperars to be in the 1000 degree F range color. That is consistent with what Rick Moroso saw at VIR on his rotors on his '99 Vette GTR.
Neither of us had any change in temp strips.
I will get the wheels off before the next track day and post up more pics and replace the strips with a lower temp one.
For now it does appear the calipers stay below 466F at VIR and LRP, rotors around 1000-1100F.
(April temps, Cup ducts, stainless lines, Motul 600, CCW 14 wheels, ATE front and OEM rear rotors)

CT03911

Finally yanked the wheels off for a better look. There was no registered temp on the caliper strips so I replaced them with lower range strips for the next three days at Lime Rock Park.
The rotors are more interesting right now, as I could see more with the wheels off.
I "borrowed" the rotor temp paint from Rick Moroso and so I do not have the temp chart with me as I write this. I will update it.
The rears clearly heated up and changed the paint color but not by much, as reported before. It is super high temp paint.
Look at the fronts though.
Two completely different temps from inside to outside of the rotor.

I wonder if others are seeing this, race shops etc?

I cannot imagine this is optimal as the pads have to react to two different temps from inside to out.

We'll see what happens over the next three days.

I cannot tell from the paint bottle chart to the rotor EXACTLY what temp range the inside vs outside of the rotor got to. The temp chart colors make it a hard call. The paint is advertised as "Six distinct color changes signal temps below 299° C (571° F), 300° C (572° F), 351° C (663° F), 431° C (807° F), 526° C (980° F), and over 671° C (1240° F)".

There is a lot to learn here for me. I was assuming the inside of the rotors was way cooler because of the ducts. Now, not so sure looking at the color chart.
The fact that they differ is intriguing though.

KOAN

great info. Thanks for keeping us up on what you are discovering.

CT03911

Chuck, how's the mod to your windshield doing? All better I hope?

KOAN

Yes, after VIR, I decided that a strategic upgrade was in order. I now have an intact windshield that I can see through. Haven't had a chance to track test or record any data, but my seat of the pants impression is that it will be an improvement. I'll be at Mid Ohio with NNJRPCA in a few weeks, and can't wait.

CT03911

A windshield protection layer and tearoff sure keeps those new windshields pretty. I have had one for three years and think they are worth it.
They won't stop even a piece of gravel smacking a chip, as I found out a few years ago, and never what you had (obviously) but they do keep the crazing and sandblasting down.
Mid-season I pull off the tear-off and replace it.

FFaust

Any info on the tearoff or "protection layer"?

CT03911

IMO, windshield protection is a good way to go IF you have a new windshield or one in nice shape.

I use The Tear Off Guys.

A few years back I tried installing them myself and got average results. Usually lifting at some corner, etc.

Like painting and drywall mudding, somewhat of an art form. I have a full front windscreen protection layer and run a tearoff on that and a banner on top.

I find with a banner I do not need a tinted helmet visor. The tearoff gets replaced mid-season, the bottom protection layer is like new.

FFaust

Thanks,

BoostBuggy

Dennis, nice job and nice write up. I did want to add a few things here I think will help for others that try to do this....

First, regarding when one should do this, it really depends on the temps your calipers are seeing and has little or nothing to do with the rotor temps other than when rotor temps are higher, the caliper temps tend to be higher also. If you're tracking the car (particularly if you are tracking the car "hard") you should always have temp strips on the calipers. The caliper are far more heat sensitive than the rotors. The temps registering on the temp strips will be approximately 100 F lower than what the pressure seals (O-Rings) and brake fluid are seeing. With that in mind you do not want to see caliper temps in excess of 300 F. Why is this? The EDPM material the pressure seals are made out of have a max temp rating of 398 F. When the pressure seals are subject to temps in excess of 398 F the durometer (hardness) and elasticity of the seals begin to change. And not for the better! Other than providing a seal for the brake fluid/pressure, the O-Rings are what draw the pistons back into the caliper when pressure is released. The channel the O-Ring sits in has a 5 degree slant to it. So when the pressure is applied and the piston extends it (for lack of a abetter way to put it) "rolls" the O-Ring just a tiny bit. And then when pressure is released, the elasticity of the O-Ring pulls the piston back into the bore. Consequently if the O-Ring(s) begin to harden, i.e. lose their elasticity, they also begin to lose their ability to pull the piston back. Then you get pistons that stick and hold the pad against the rotor creating undue heat, wear, etc. You get the picture I'm sure.

Second, in terms of sourcing parts, you can find Brembo parts from many different sources. Folks that typically have them in stock in all sizes (and will not give you sh_t aboutthem being Porsche sizes) are Pro-Systems, Hoerr Racing Products, Truechoice, Paragon Products, Pro Race Store and many others (just Google "Brembo Dust Boots") Additionally the Stoptech parts will work also. The Stoptech dust boots are a medium grey as opposed to the black of the Brembo boots. Personally I feel the Stoptech dust boots are a bit more fragile and will rip in the "bellows" area easier than the Brembo boots but there are also less expensive. The Stoptech O-Rings are for all intents and purposes the same as the Brembo so no issues there. And the ST's are also, once again, less expensive than the Brembo boots.

For the 6 Piston calipers Gen 1 (996) the pistons sizes are (f) 38/32/28 and (r) 30/28. the 997 6 piston calipers are different with (f) 32/30/28 and (r) 34/34. For the 4 piston calipers, all 951S, 928 S4, 928 GTS, 993, Big Reds were (f) 44/36 and (r) 30/28 with the exception of the 993 which was 34/30 standard, 28/28 turbo and 36/34 Carrera RS (if I have read the PET correctly) Of the monoblock calipers the (f) are either 40/36 or 44/36. Monoblock (r) were 30/28 almost completely across the board with no variations I can find other than the rear 4 piston calipers that go with the 6 piston front.

When rebuilding it is advisable to use Dow Corning #111 silicone lube on the O-Rings prior to placing into the bore. Not every one does this. For example I know Alcon and the IndyCar teams simply use brake fluid to lube the seals. However Pro-Systems recommends the Dow Corning lube. I have used it on every caliper rebuild and never had an issue. Can't really tell you the pros/cons of using/not using the Dow Corning lube but I know Pro-Systems did A LOT of rebuilding for top NASCAR teams. NASCAR has some SERIOUS brake temp issues so I chosse to go with Pro-Systems recommendation.

Someone in the thread mentioned corrosion coming from H20 in the brake fluid. This would not be the case as brake fluid contains corrosion inhibitors. If the H20 in brake fluid could corrode the pistons or calipers it would have corroded the steel brake lines first.

I would suggest keeping an eye on the dust boots. If you rip or burn up a dust boot I would be most concerned about getting crap into the bore and scratching the bore. You don't want a scratched bore as that would mean replacing the caliper. I don't recommend sanding the bore as you mind remove just enough material as to case the caliper to leak. The tolerances are VERY tight.

To pop the pistons I made a little tool that works wonders. I have pics and video but will have to upload them a bit later.

I hope this has been helpful.....

mjb

^^ I finished my rebuild a month or so ago and agree with your points here.

A lot of this has already been detailed in this thread but let me add my .02 summary to the good stuff already written:
- Use a tool of some sort to depress the brake pedal and close the circuit before removing the calipers. I used a swifter mop (mop end wrapped with a towel) wedged between the seat and the pedal. Prevents excess fluid leakage.
- cap off the brake lines with the plastic/rubber vacum caps available from any auto store or online. An assortment of them is cheap and you'll find the right size.
- Brembo dust boots seem to be a bit higher quality versus StopTech and I would go with those as mentioned above.
- I changed out the o-rings only on the front calipers as they certainly get hotter than the rear. The old o-rings looked and felt fine but it's probably difficult to determine their elasticity just by feel. Anyway, figured it would be better to change the fronts out. However, just new dust boots for the rear.
- As Dennis said above (and thanks Dennis for your excellent write up and advice on the phone) the difficult part is devising a "shim" strategy for popping the pistons out using an air compressor(40-60 PSI seemed to work for me). You want them to all come out evenly and it's a bit of a PITA. I fashioned a backstop out of wood for the front and rear caliper, and did a kind of 2 phase operation to get them to come out evenly, and far enough to remove by hand. Hopefully this will be less time consuming the next time now that I'm a bit further up the learning curve and have the shim jigs.
And yes, make sure to cover the calipers with a towel or rags when you're popping the pistons out with the compressed air as brake fluid will spew everywhere.
- clean everything up nicely, lube up the o-rings, pistons, bore, etc.( I just used brake fluid which works fine and is often recommended in the various online DIYs) I mildly used a c-clamp to pull the pistons in EVENLY once they were inserted properly - they should draw in nice and smoothly. Insert dust boots and you're ready to reinstall the calipers.
- The ceramic "buttons" capping the pistons where all in good shape and never came off. I guess this has been a problem for some folks.
- Of course, you'll need to do a good brake fluid flush to make sure all the air is out of the system.

My take is that depending on how much you track your car it's a good idea to at least change your dust boots once a year. I suppose if I did, say 10-15 DE days a year I wouldn't bother with the o-rings on a yearly schedule (adds a lot to the job). Maybe every other year or so, and even that might be unnecessary, but probably worth the effort.

BoostBuggy

Here's a short video I made to demonstrate how to pop the pistons for a caliper rebuild

I have drawings for this caliper tool and similar toos for most of the other Porsche calipers (front and rear.) If there is an interest I can make them available as PDF files for download.

CT03911

I read autokurl and mjb's feedback which was great. I can add a little more info now too.
After putting on the Thermax #7 temp strips (390-450F) in two different locations and running at Lime Rock two days they do not register a temp reading. One of those days it was 95 degrees out.
I will pull the strips and put on the #6 strip (330-380F) in two locations.

One of my initial interests was to determine if my brakes ever got to the Motul 600 fluid temp. Autokurl suggests around the seal area could be 100 degrees hotter than where a temp strip is normally placed. I do not doubt that really, but do wonder how that was measured.

All I know definatively now is:

My calipers where I can measure them do not even get to 390F.
My rotors register two very different temps inside to outside.
Our GT3 dust seals get toasted and many of us need to replace them.

The block autokurl fashioned is nice. If he does provide the PDF and we can make this block out of some material other than metal, it would be a very neat tool to have.

Genesis (maker of the rotor paint) never answered my email regarding how to interpret the rotor temp paint color changes. As I said before, the color chart on the bottle differs from the one on a supplied paper color chart.

There seems to be little the 996 GT3 community can do to get equal cooling on the rotors. It is what it is and may not be a big deal, pads seem to wear fairly evenly so far for me and many of us flip them to keep them even.

I looked at my pads pretty critically after my re-build and 6 track days on new pads. Pad taper seemed virtually nonexistant.
Either the rebuild of the caliper helped the pistons "work" better or flipping pads at six days is earlier than I have ever done before and seems like a good point to flip pads to keep them really close in wear.

My brakes always feel better after a few track days if I bleed them. They just do. I am still trying to prove or disprove if the caliper gets near the boiling point of Motul 600 but it sure does not seem like they do- I can't get a temp strip to even read 390 so far.

I am betting the #6 strips (330-380) will register something but that is a lot cooler than Motul 600 can handle. So what is up then? I am left wondering if the actual brake line is near the rotor enough that it is the area that gets hot enough to boil.

You guys running SRF are probably laughing at all this but I just want to know what temp my brakes are at, not guess. I like a really stiff brake pedal. So far a quick squirt of a bleed at all four corners feels a little better next time out. Does SRF feel the same- just a little better with a bleed than before?

serickson

I have place non-reversing temperature dots 340-380F & 390-435F on my calipers. I positioned my indicators on the outside front of each caliper on each side of the Porsche decal. Ran Mid-Ohio (outside temp 85) and Road America (outside temp 75) in both cases neither of my indicators registered. I recently switched to Castrol SRF from ATE, not sure it was really necessary. I confirmed that my indicators work by placing one on a spoon and exposed it to an open flame, the color went from Silver/White to black in the correct order(not sure the temp but they did activate).