1st Gen RX-7 Brake Questions

[CaptainWho]

Hi guys, we had a sort of a strange brake failure this weekend at Kershaw, and I thought I'd see what you folks thought about it.

For background, I replaced the pads on all four corners, and the bearings and rotors on the front at the beginning of this season. At the end of March, we ran two 14-lap (30 minute) SARRC races at Kershaw. Still plenty of meat on the pads, rotors look good, no issues with the feel.

This weekend, the brakes are fine during practice. A couple of hours later, they're fine at the beginning of qualifying. Have to drive off track to avoid a spin, which tears the brake duct on the RF severely. A few laps later the marshals meatball us for dragging (the brake duct) and we examine the RF corner.

It's boiling the grease, so we let it cool, replace the brake duct, and repack the bearings. In the process we forget to torque the lug nuts. So, about fifteen minutes into the forty-five minute race, the RF gets a bad vibration. Bring the car in, fix the lug nuts, go back out, no problems. Finish the race, everything is good. Sit through impound, then back to the paddock, all still good.

An hour later, go to put the car on the trailer, brakes are soft and pedal just keeps going. Load up. Stop on the way home and notice that there's a puddle of brake fluid around the RF tire. I guess the seals are gone. Overnight about halfway home, and almost all of the brake fluid has leaked out overnight. Finish the trip home, notice that now there's a puddle of brake fluid around the LF tire, too.

This seems strange to us. It's easy to understand the RF failing, after the extra heat it endured while the brake duct was damaged. Though it is a little perplexing that it survived the race, the loose lug nuts, and everything else, and only went bad sitting in the paddock waiting to be trailered.

It's really confusing that the LF went, too, though. Especially that it didn't show any evidence of having blown until so long after being loaded and so long after the RF showed (really) obvious evidence of being blown.

Any thoughts or suggestions would be greatly appreciated.

I'm going to replace the calipers, then rebuild the take offs to keep as spares. I'm wondering if I need to be looking at other stuff, too.

[Daryl DeArman]

Did you use a different type of brake fluid this time?

[sirchadd]

I would inspect all the calipers, may have got the brake fluid too hot. Brake fluid can buiild up moisture and in extreme braking that occurs racing you can acually boil the fliud. I would check all the calipers, if the fluid got hot enough the seals may have been soft upon loading the car, as the system cools and the seals around the calipers cool then the seals are no longer expanded they tighten around the caliper pistons and do not seal to the housing. May be why you didn't notice it till later. Although it could be something else. I would check the seals and pistions on the caliper, and empty the system of the old brake fluid, flush it through with new till crystal clear. That would be my approach to start.

[JeffYoung]

Doug, I am unfortunately an expert on brake caliper seal failures. E-mail me at [email protected] and we can talk more.

However, I can say this here -- I have had the failure you describe happen to me MANY times. The brakes will be ok during the race, I'll get off track and hours later the calipers start to leak.

What I think is happening, at least on my car, is that the caliper, rotor and fluid actually stay cool during the race due to ducting, or cool "enough" anyway. BUT, when you come in and park the car, the things sit there and heat soak. They aren't getting any cool air through the ducts and the iron calipers (mine are anyway, and I suspect yours are too) are retaining a tremendous amount of heat. I've gotten readings of 500 degrees plus on teh calipers as much as 10-15 minutes after exiting the track.

So, a number of things you can do to help. Some are illegal, or of questionable legality. These include brake fluid recirculators (possibly legal under the "brake circuitry may be revised rule"), titanium insulating shims on the back of teh brake pads to keep heat from transferring to the pistons and seals (possibly legal under the "brake pads are free rule"), heat sinks for your pads (same) and ceramic coatings for your pistons (not legal under any theory I can come up with). All work to insulate your caliper seals from the heat source -- the pads and rotors.

However, the best thing I have found to deal with this situation is a TRUE cool down lap, meaning don't touch the brakes. This will singificantly reduce your caliper temps and avoid the heat soak that happens after you come in. If you have decent enough ducting to keep the calipers cool during the race, you should be able to spend 3-4 minutes on a cool down lap working those ducts to get the caliper temps down. You can also extend the cool down lap some by driving a bit through the paddock before stopping.

Again, I'm almost positive you are experience the "heat soak" seal failure that I see regularly on my woefully underbraked car.

Jeff

[tlyttle43]

Doug -

I've had the problem you describe happen a few times on my IT7, also. I think it's just cumulative heat-related abuse of the seals. It really is more of a cosmetic issue, at least initially, as I've found the brakes still work fine after the seeping starts. But anything that involves leaking brake fluid is not something to leave unattended. Replacing the seals fixes the problem for a year of two, then you get to do it again when the seeping reappears.


Tom Lyttle

[JeffYoung]

Or for a race or two, if you happen to be dumb enough to drive an ITS Triumph...lol....

Good runs this weekend Tom. Fun racing with you.

[tlyttle43]

Jeff -

At least I got to watch you out the windshield this time, instead of watching you rocket by my rear window at 90 mph. like last time at Kershaw!


Tom Lyttle

[JeffYoung]

Amen Tom, that one spooked me. Wrecking my car is one thing, wrecking others due to a stupid part failure is another.

Doug, sorry to thread jack. Do e-mail me if you want to chat on this. As Tom says, it just happens over time, sometimes the time is shorter depending on the car you drive.

If you have never rebuilt a caliper, you are in for a treat! LOL...actually, it's not that bad. Just use compressed air to pop the pistons out, clean everything with brake fluid, lubricate the seals with fluid before installing, lubricate the pistons and be sure to push them straight into the bores or they may tear the seals.

Hell, on an RX7, it might actually just be cheaper to buy new calipers....

[NutDriverRighty]

Speaking for Doug, I think that we'll get new (rebuilt) calipers and then rebuild our leaking ones as spares. Thank goodness that this didn't happen during the race. Some guy in an ITS Triumph almost took out half the.............oopps...........sorry, Jeff! ;-)
We had a brake failure at last year's Memorial Monster, but it was a master cylinder issue then. If we keep going at this rate, we'll have a new car soon!

Scott "the other nut" Franklin

[tom_sprecher]

Let me know where you find rebuilt rear calipers as MazdaSpeed lists them as no longer available so I bought a couple of seal kits instead. Fronts you can still get and at $70 each (including the $20 core charge) are a steal.

For rotors I think Frozen were the cheapest I could find at $86 for fronts and & $98 for rears.

[ddewhurst]

Doug, do your brake ducts force all the air through the center of the vented brake rotor or do your rotors just blow air at the inside of the rotor surface? Since I installed MazdaMotorSports brake ducts where ALL air is forced through the vented brake rotor. I have NEVER had an issue with brake heat. NEVER had any seal failure of ANY kind.

Brembo front rotors can be purchased for less than $40.00 each TRUE BREMBO rototrs & not some knock off copies in a Brembo box. A person can do their own Cyro with a series of trips to your 600* F cooking oven & into the home freeser. Never had a rotor failure. From my experiences with tracks in the CenDiv/Midwest Div. Blackhawk Farm is one of the worst tracks for eating brakes.

I also have installed speed bleeders in all 4 calipers & a speed bleeder in the line from the master cylinder to the rear brakes. One men (or women) job. After we bleed the rears we have a half pedal that is HARD. When we bleed the front we DO NOT push ALL the air out of the front lines/calipers because the front piston will not do it's full travel because the pedal will stop at half stroke because the rear lines are fluid solid. OPEN the speed bleeder in the master cylinder to the rear brakes line & with a short line attached to the speed bleeder & into the master cylinder you will now have full travel of the front master cyliner piston during front brake bleeding & you will get rid of ALL the air in the front brake system. ;)

Jeff's stuff relative to keeping heat out of the calipers works. I could add a couple more ideas but I don't do illegal stuff. :o

[tom_sprecher]

Brembo front rotors can be purchased for less than $40.00 each TRUE BREMBO rototrs & not some knock off copies in a Brembo box. [/b]
Where? All I can find run about $65-$70. Do tell.


I also have installed speed bleeders in all 4 calipers & a speed bleeder in the line from the master cylinder to the rear brakes.[/b]
What type of fitting did you use and whose speed bleeders? My wife would appreciate any help she can get when it comes to pumping brakes.

Thanks,

[CaptainWho]

Thanks for all of the suggestions, guys. Jeff, I'll be in touch via email in a day or two. If nothing else, to commisserate. :D

The plan right now is definitely to replace the calipers then rebuild the old ones for spares. They seem to run from about $45 each on up to the more than $275 each that Mazdaspeed wants! I'm going to get some cheaper ones than the Mazdaspeed ones.

Don't have speed bleed valves in this car but had them in our previous IT7 car, and am definitely considering putting them in the new calipers. With a bleeder bottle that stays hooked to the nipple on the bleed valve, I don't have problems bleeding alone now, I just end up using more brake fluid than necessary to get the job done.

The ducts on our brakes right now do not force the air into the vent holes of the rotors. They force air onto the inside "face" of the rotor. This has never been a problem in the past, even with much higher ambient temperatures, and even through some other "duct disconnect" events, notably one at Road Atlanta's turn one.

I'm going to consider the Mazdaspeed units David mentions, but I'm not over the moon about it. July at Road Atlanta and June at Lowe's were both quite a bit hotter than last weekend at Kershaw. I'm starting to think this is not so much an episodic failure as a long-term maintenance item that didn't get the attention it deserved.

Tom, I get what you're saying, but this was in no way cosmetic. Well, it might be after the brake fluid gets finished taking the paint off the trailer. :D No, when I trailered the car, the pedal didn't stop moving, no matter what I did, but I did have a little brakes to stop on the trailer, thank God. At that point, there was no "sign" from the brake fluid yet. About two hours later, there was an obvious puddle on the trailer and the MC was down about 1/4" from where it was when we went out for the race. The next morning, about 10 hours later, there was only about 1/4" left in the MC and a trail of brake fluid down the pavement next to the trailer and a puddle around the LF tire, too. Right now, I don't think it'd stop withough gravity or an immovable object. I'm trying to figure out how I'm going to get it into the garage without taking out the laundry room.

The more I read what you folks are telling me, and review my own experience, the more I think this was a "programmed" failure, as all service/replace items will eventually experience if not serviced/replaced. Only God knows how long ago these calipers were last rebuilt. Some time before we bought the car three years and six or eight events ago. We had no real idea just how much to be concerned about this or what the interval might look like. We're in this to drive, not to work on the cars, and we're not mechanical geniuses. :D

It's really sounding like we need to rebuild the calipers every two-three years or so, and keep a spare set in the bins, just in case. That's not a hardship. It's a little surprising, though. We've bought and run two different IT7 cars, from two different people. In both cases, replacement front rotors, and rear rotors, in one case, were included in the parts package that accompanied the car. But neither has included any calipers or caliper rebuild kits. So we didn't expect it to be a "couple of year" wear item.

We have developed quite a few friendships within the SEDiv IT7 community, and this is the first we're hearing about caliper failures. Maybe this isn't a surprising failure. Maybe it was just time, based on how long ago the previous owner's serviced the calipers and everyone else does them as a matter of course, since they know more than we do about it. But we have no idea, since we're really new at this. :D

It's not a problem, just unexpected. Part of our learning process. Add to the notebook: "Rebuild calipers every two seasons or 10 events", do it, and note the last time it was done.

[ddewhurst]

***Where? All I can find run about $65-$70. Do tell.***

Tom, the locally owned store WAS Arrow Auto. One of two brothers that ran the store owned the building & he sold the building to incoming donut store guy. Auto store GONE........ I'll ask Doug the other owner for a place to purchase Brembo rotors & get back to you. You could also go on the Brembo site, get their number & call asking where in your area to purchase them.

***What type of fitting did you use and whose speed bleeders?***

Man., now yer really pressing it. I don&#39;t have a clue any more. The speed bleeders were the exact thread for the calipers & the Tee for the master cylinder speed bleeder was also the exact metric size from above mentioned defunk Arrow Auto & MAYBE the speed bleeders came from Pegasus. < maybe, they do know how to charge. :o

[JeffYoung]

Doug, for me anyway, it&#39;s not outside air temp that causes the problem, it is the brake caliper and rotor temps caused by the type of track involved. I have no brake issues at Roebling regardless of the air temp, I always do at CMP. VIR is somewhere in the middle.

Part of the deal maybe (it was for me) that you didn&#39;t experience failures in the past because you weren&#39;t using the brakes as much. As you get more experience and use the brake harder (I did), it becomes more of an issue.

I&#39;ll look for your e-mail.

[tom_sprecher]

The plan right now is definitely to replace the calipers then rebuild the old ones for spares. They seem to run from about $45 each on up to the more than $275 each that Mazdaspeed wants! I&#39;m going to get some cheaper ones than the Mazdaspeed ones.[/b]

I am waiting for this order from Mazdaspeed.

Product # Product Description Qty Ext Price
FA18-49-240 SEAL KIT CALIPER RR 2.00 39.90
FAY7-33-99ZR REMAN, CALIPER, LT 1.00 70.40
FAY7-33-98ZR REMAN, CALIPER, RT 1.00 70.40

Total amount: 205.43 plus $16 for shipping.

The $275 must be the price for NEW calipers. Also, after looking into some other universal online parts suppliers you can still get rebuilt rear calipers from them.

[Eagle7]

What type of fitting did you use and whose speed bleeders? [/b]

I just ordered from these guys - http://www.speedbleeder.com/

[CaptainWho]

Well, as it turned out, my fears about having enough brakes to untrailer and get into the garage were unfounded. I finally got time to go over to the storage lot Sunday and refilled the master cylinder (there was less than 0.25" of fluid still in it). Pumped the brake pedal two or three times and had a hard pedal. Trailered home and the pedal was still hard and less than an ounce of fresh leakage. Drove right into the garage with plenty of pedal left.

So now I get to replace the calipers and rebuild the take offs. Hope I don&#39;t have any parts left when I do the rebuild. :-)

[Mike Cox]

[quote]

Brembo front rotors can be purchased for less than $40.00 each TRUE BREMBO rototrs & not some knock off copies in a Brembo box. A person can do their own Cyro with a series of trips to your 600* F cooking oven & into the home freeser. Never had a rotor failure. From my experiences with tracks in the CenDiv/Midwest Div. Blackhawk Farm is one of the worst tracks for eating brakes./quote]


Yep, There you go again David, Giving away all my secrets.



One quick question about your brake problem and a couple thoughts:

are the pistons on your front calipers notched to releave any superheating of the air inside the cup?
(on my car they are and I have a second 3" line blowing directly on the caliper to help keep it cool too. My primary 3" line blows on the bearing hub area and that cools both sides of the brake rotor evenly)

put two 1/4" x 1/4" notches on the piston surface exactly opposite each other where it touches the brake pad. this will releave any air build up inside the cup.

The most benefitial thing I have found on the IT7 braking system is do not ride your brakes into the corner. Go in deep, hit them hard and then get away from the brake peddle. The longer your foot is on that red peddle the more heat you build and I have found deep braking actually works better and I have eliminated a lot of braking issues by doing that.

Secondly, I don;t know how close your competition is. If you are racing hard and trying to stay in line, you are not getting enough air flow on the calipers and rotors (experience speaking here) and you may find that the next corner when you need to hit the brakes hard, nothing happens. (of course the guy in front of has good brakes so you can always use his to slow you down) I tend to move around a bit, even in the draft, sticking my nose out to get a bit of air into the brakes and radiator.

THese are just a few thoughts to ponder and I hope you have a good time.


Now David , I should get a royalty every time you tell somebody about my oven/ freezer trick. (A cold Bud will do just fine)

Mike

[ddewhurst]

Mike, if I told some people face to face what you passed on IN DETAIL WHAT WORKS they would have that "deer in the headlights look". Or someone would say where is the rule that makes that legal. I wouldn&#39;t have the hart to ask them how they would inspect in a protest process to prove legal or illegal. ;) Hey, that Bud thing may never come about because I don&#39;t come South for races. Maybe one of these years I&#39;ll come WATCH at the ARRC. The Runoffs would work if you ever do that.

[lateapex911]

Mike, how do you get so many ducts to your brakes?

[Mike Cox]

Hey Jake,

well I started off with one male and one female duck and they just..................damn it, now I&#39;m giving away another secret

The spoiler design I use has an opening under the turn signal on each side (79 body) so I run my primary to my hub off those hoses. I then designed a secondary hose that is mounted on each side of my oil cooler box that picks up the excess air and routes it to my calipers.

My setup up front is unique because I have designed a dedicated air box to force air thru the oil cooler (oil cooler is mounted under the cross tube) and then under the radiator(instead of thru it). there is a splitter on top of the oil cooler box that directs the air into the radiator without turbulance and splitters on each side to direct the excess air on each side thru the pickups for my caliper ducts.

The air box and the splitters are all made of a space age material (tin) and is very pricy (3 trips to the emergency room for bad cuts) but I rarely get to 190 water temp and 210 oil temp and I have never had a problem of overcooking the brakes with this setup.

Mike

[Tak]

One other brake tip for gen 1&#39;s...rebuild both rear calipers at the same time. If one rear caliper works better than the other, you will set your rear bias based on one caliper, with sub-optimal braking on the other. The result is that the fronts end up carrying the extra bake load (and heat). I&#39;ve been able to put a half a turn more rear brake bias on the car with fresh rear calipers (and 3 years between rebuilds...)

Tak