Is the radiator air dam a high pressure area on third gen F body?

Hey guys, without getting too long winded, I have a 92 Trans Am with C4 13 inch brakes and 18x10 inch wheels. Everything is in good condition with braided lines, decent pads, Motul 600 fluid, etc.

Long story short, I'm boiling brake fluid after 15-20 minutes of HPDE time. Like, literally boiling to the point where steam pours out of the master cylinder cap and the fluid breaks down to basically water. Flushing the fluid brings it back to 100%, until I boil them again.

So Im adding brake ducts before the next track day. I prefer not to change the look of the car too much, so I'm trying to do this subtle and clean.

Is the lower air dam that feeds the radiator a high pressure area? It seems like it'd have to be if it's intended to catch enough air to feed the radiator, right? Can I mount the ducts there or am I wasting my time?

Alternatively, I could remove the fog lights/turn signals and mount them there, but it's a street car and I really like the look of them, so I don't want to if I don't have to. But I will if necessary.

Pics for clicks.

here's the airdam

Yes, it should be a relatively high pressure area.  Of course, the question is always really "is it higher pressure than the area I'm trying to feed air to?"  But I think that'd probably be the case as well.

I wonder if it might be easier to first try some of those A-arm clip on deflectors (Like GRM did with these) but it does sound like you need a fair bit of cooling....

First, nice GTA. I have a '91 'vert.

I think it's definitely a high pressure area. But my question would be, do you want to take away air meant for the radiator/engine cooling when there is already a deficit of that air? I think the foglight/turn signal area is the better option. Having said that, it's obviously it's going to be much more difficult to package with the bumper bar and such. I swapped to projector foglights from a '99 denali and run LED strips for turn signals but never got around to running the brake ducts themselves.

BA5 said:

Yes, it should be a relatively high pressure area.  Of course, the question is always really "is it higher pressure than the area I'm trying to feed air to?"  But I think that'd probably be the case as well.

I wonder if it might be easier to first try some of those A-arm clip on deflectors (Like GRM did with these) but it does sound like you need a fair bit of cooling....

Those ducts are GENUIS. That is absolutely brilliant. I'll check those out.

ian sane said:

First, nice GTA. I have a '91 'vert.

I think it's definitely a high pressure area. But my question would be, do you want to take away air meant for the radiator/engine cooling when there is already a deficit of that air? I think the foglight/turn signal area is the better option. Having said that, it's obviously it's going to be much more difficult to package with the bumper bar and such. I swapped to projector foglights from a '99 denali and run LED strips for turn signals but never got around to running the brake ducts themselves.

Thanks man. I appreciate it.

I know I'm gambling taking away some engine air, but believe it or not, the engine never runs close to overheating on track. I have an adjustable fan controller running both factory fans, and not once has it ever went past the 220 I have them set to. Worst case I could always remove the ducts and put a new air dam back under there, so I'm willing to try it.

Im certainly willing to cut the crash bar and trim stuff to put them in the fog light holes if necessary, but I like the practicality of them and don't want to mod the exterior if I don't have to.

Im hoping to end up with a street car than can survive 5-6 track days a year rather than a track car that is miserable to live with on the street.

I tried those Porsche ducts back a decade or so ago and never found a good way to adhere them while retaining a shape that would scoop air correctly. The steering stop location means they would either be crunched at full lock or not mounted very close to the wheel. YMMV, obviously.

The Denali foglights didn't seem crazy out of place (to me) and put out way more light being a projector design.

Whatever you do, post up the process or the finished products. I love seeing a good thirdgen around.

ian sane said:

I tried those Porsche ducts back a decade or so ago and never found a good way to adhere them while retaining a shape that would scoop air correctly. The steering stop location means they would either be crunched at full lock or not mounted very close to the wheel. YMMV, obviously.

The Denali foglights didn't seem crazy out of place (to me) and put out way more light being a projector design.

Whatever you do, post up the process or the finished products. I love seeing a good thirdgen around.

I'll post up some pics of the outcome man. It's a niceish GTA in presentable condition and I'm trying to keep it clean and not modified too crazy. It's a sentimental car to me otherwise I'd just start cutting away for the vents.

The brake ducting parts are already on the way, so I'll give them a try first. 

Here is a closer pic of what it currently looks like.

Without knowing more information it sounds to me like you have a problem where brake ducts MAY mask the symptom but probably won't fix the problem. The heat you've described seems way out of line for a 20 minute HPDE session.

Are you running slicks and very aggressive pads or are you using the treaded street tires shown in the undercarriage pic when you're on track?

Were any changes made to the rear brakes or are they stock? If stock, were any changes made to balance the system when the C4 front setup was installed?

Is there a brake line very close to the exhaust system? Any possibility a heat shield was removed somewhere? Are the rotors on the correct side of the car?

Are you sure the brakes aren't dragging all of the time?

NOT A TA said:

Without knowing more information it sounds to me like you have a problem where brake ducts MAY mask the symptom but probably won't fix the problem. The heat you've described seems way out of line for a 20 minute HPDE session.

Are you running slicks and very aggressive pads or are you using the treaded street tires shown in the undercarriage pic when you're on track?

Were any changes made to the rear brakes or are they stock? If stock, were any changes made to balance the system when the C4 front setup was installed?

Is there a brake line very close to the exhaust system? Any possibility a heat shield was removed somewhere? Are the rotors on the correct side of the car?

Are you sure the brakes aren't dragging all of the time?

 

 

 

I've definitely never had a car boil fluid to the point it's steam until this one.

I tracked it on street tires and street pads, on 18x10 square setup wheels.

The brake kit was installed by the previous owner, so I don't know every detail. The rear is original rear discs and calipers.

Under hard braking, the front tires can be made to lock up. I've never felt the rear tires lockup. There doesn't appear to be any change to the proportioning valve that I can see.

Under hood is bone stock L98 with factory exhaust manifolds and a cat back exhaust. There doesn't appear to be any heat shields missing. I have had it on a lift and can feel no wheel dragging or sticking. I'm also careful not to drive with my foot on the brakes.

I just went out and double checked, and your right, the front rotors appear to be on the wrong sides. The vanes are pointed the wrong way. I'm not sure how I didn't catch that before. Could the rotors alone cause that much heat buildup?

Hhere is the brake line under hood

Directional rotors on the wrong side sure isn't helping your situation as they are meant to increase cooling flow through the rotor by spinning in the correct direction. 

The air "duct" or "deflector" doesn't need to be anything fancy. I made some out of simple ABS plastic that I cut to clear the wheel and hang low. Bent the the top and inboard edge to make a bit of scoop and screwed it right to the front edge of the A arm. Think of it like the radiator air dam...it just hangs down into air under the car to build a high pressure area that will push up towards the brakes. I made mine hang low and let them self clearance against the road.

While it looks like you have plenty of clearance to the brake lines from the manifolds what are the under hood temps getting to? Could be more of an ambient under hood temp problem than a proximity one. I struggled with coolant and air intake temps (engine air drawn from under hood) but not brakes (my lines are much farther away from the exhaust). Hood vents was big drop in temps. I later added a 3rd hood vent and fender vents for even more drop in temps. Not to mention a bump in front grip levels at speed. Venting the fenders should also help lower the pressure around the tire which should help improve any brake cooling you do as well.

If you experienced that much heat in the brake system while running treaded street tires without the tires getting so greasy from overheating that you were under steering into every corner on track something is wrong with the brake system.  The challenge is to figure out what. While I first looked at this thread because I have a big interest in aerodynamics and would be happy to offer possibilities for brake ducts I think you might be better off to start a new thread with a title regarding brake fluid overheating during entry level HPDE sessions. That might give you a lot more eyes on your problem and therefore more suggestions for things to look at. 

IF, after getting the brake system operating properly you find you get to a point that you're running wide sticky tires and aggressive pads and you're having heat issues, revisit the idea of adding brake ducting to keep the brake pads in their ideal operating range by bumping this thread up to the top.

I don't know if having rotors on the wrong side of the car can cause that much heat build up. BUT, we have a brake engineer here on the forum "angrycorvair" who might know and would likely respond to a thread with  overheating brake fluid  in the title. This forums features are primitive compared to most forums, so there's no easy way to attract his or other folk knowledgeable about brake systems attention to this thread.

If you're not familiar with it, there's a forum called   thirdgen.org   where you may find some useful info about cars that have had the C4 front upgrade. I would think the C4 upgrade should actually reduce temps due to the additional mass in the front rotors (during 20 min HPDE sessions) which leads me to believe something is wrong somewhere. It might be something simple like rotors on the wrong side or non functional rear brakes but you'll need to go through the process of checking to be sure things are assembled and adjusted correctly along with any possible modifications necessary to incorporate the C4 fronts such as a different master cylinder, combination valve removal,  and/or a rear bias valve.  

Have you inspected the front and rear pads for glazing? IIRC the rear calipers are adjustable and require the parking brake cables to be adjusted correctly for the calipers to perform correctly. If the rear calipers aren't adjusted correctly the system (as a whole) won't function properly and you'd likely have a long pedal (press farther than it feels like you should before brakes grab).  Run the car with the rear off the ground and tested the rear brakes?

Do you have a laser guided temp gun? If so drive the car out on the street and see what's getting hot.

Although Asphalt_Gundum and I've mentioned a few things in our posts here I do think a thread with a title that will get the attention of brake experts will bring more things for you to check.

here are some things i'd look at:

• verify the front brakes aren't dragging when they get hot
• make a sheetmetal shield to protect brake lines / prop valve / booster and master from exhaust manifold radiant heat
• remove OE prop valve and install adjustable prop valve, then adjust it to move more work to the rear brakes

do you see heat damage to the tie rod or ball joint boots?

I think you guys are onto something here. The laser thermometer idea is brilliant. 

I don't know if this is enough information to extrapolate an answer from, but I just did 15 minutes of street driving with three hard full stops from 60, and after the last stop, the front rotor measured 405 degrees, and the rear rotors measured 205-220. I know the front brakes do more work, but shouldn't they be closer in temps than that? Also, if they got that hot after 15 easy minutes of street driving with only three quick stops, theres no telling how hot they got at the track. 

I'm wrenching this afternoon, I'll post back what I find in the inspection.

Here is the condition of the rear caliper. I don't see anything obvious aside from some blueing on the rear rotor. Also, the handbrake is weak. It only grabs at full up, and just barely. Could that be related?

That's a pretty big temp difference. Sounds like your front calipers may be dragging when they get a little heat into them.

I don't see anything wrong with that rear. If your park brake doesn't engage until the top of the handle travel, it is possible that your rear caliper pistons are not adjusted out properly. they should adjust automatically with use. 

Asphalt_Gundam said:

While it looks like you have plenty of clearance to the brake lines from the manifolds what are the under hood temps getting to? Could be more of an ambient under hood temp problem than a proximity one. I struggled with coolant and air intake temps (engine air drawn from under hood) but not brakes (my lines are much farther away from the exhaust). Hood vents was big drop in temps. I later added a 3rd hood vent and fender vents for even more drop in temps. Not to mention a bump in front grip levels at speed. Venting the fenders should also help lower the pressure around the tire which should help improve any brake cooling you do as well.

That's a good idea, I hadn't considered under hood temps. The car doesn't show any symptoms of high under hood heat, except for the 95 degree plus summer months in stop and go traffic, then the power steering fluid will start to cook. But that seems to be common on 3rd gens so I hadn't thought much into it.  I have a remote thermometer with a wired probe, I'll test it out and see what the temps are like.

In reply to NOT A TA :

Your post made me inspect the parking brakes, and what I found was the driver side parking brake is working normally, but the passenger side parking brake isn't working at all. The adjustment screw for the end plate adjustment was already stripped, so I can't do anything with it without tearing it apart.

But driving it around and doing some hard stops, both rear calipers were the same temps, suggesting they were braking equally? 

They are the 90-92 PBR calipers, with no adjustment in the parking brake cables.

I did find a thread on 3rd gen.org where guys are swapping out the spring inside the proportioning valve with a 3 dollar spring from Grainger to give some more rear brake bias.

I think I'll try that next before jumping straight to the adjustable wilwood and see what effect it has. 

If the handbrake only functions at full up,  the self adjusters in the calipers may not be functional any more. If that's the case then the rear pads have to move too far before the pads contact the rotors which can cause a couple of issues.

Those look like the PBR calipers that were used on the higher end 88-92 Camaro and Firebird models which were also referred to as part of the 1-LE upgrade. Do some research and learn how to push the piston back into the caliper, manually adjust the caliper, correct park cable adjustment, and how to maintain the calipers since you'll be tracking the car.

Does the inside of the rotor look the same? If the caliper isn't sliding properly or the piston isn't able to move properly the brake may not be functioning properly even though one or both sides of the rotor may be shiny. The rotor looks almost too "perfect" like someone installed new pads and rotors at some point but the caliper wasn't/isn't functioning properly and the pads are just gliding along. Pads may be glazed. I'd pull the calipers and check them out. Make sure the piston is free, caliper pins are lubed to slide freely and if the flex lines to the calipers and from the body to the axle haven't been replaced do it while you're in there, they may be 30 years old.

I was making dinner while occasionally typing my post and missed AC's post and a couple of your posts. You need to have the park brake working correctly for both wheels to have the rest of the system operate correctly.

My stepson had an '88 GTA.  He installed an under drive pulley which caused engine temps to go up during hot summer days. Any chance someone put one on your car?

Sorry for the delay, work yesterday wiped me out. 

There are no underdrive pulleys or anything I can spot on the engine. Everything related to the engine appears to be bone stock.

They are indeed PBR calipers. And I learned that the driver side parking brake is engaging, the passenger side is not. The pads move when the handle is pulled, but the arm is too far back and they don't contact the rotor when the parking brake is applied. They do however, seem to grab fine with the brake pedal.

I have the later style parking brake assembly with no adjustment built in the cable.

I'm working on getting the parking brake working on that caliper now.

I went on and ordered the stronger spring for the proportioning valve. For three bucks, I'll throw it in there for gits and shiggles just to see what happens.

Ill update the thread with the results this weekend, I appreciate all of the help.

IIRC the caliper itself can be manually adjusted and when the park brake cable is installed you should only have about 1/8" gap between the cable end and bracket.

The spring change in the proportioning valve part of the combination valve might act as a band aid by keeping the rear line pressure higher when the pedal is released so I'd get both rear calipers adjusted properly and the parking brake cables in place before trying the spring thing. I've heard cases where folks think the spring change helps with pad knock back or when swapping from drums to discs in the rear without swapping to a disc/disc master and combination valve but have no personal experience with it. This is AngryCorvair's territory since he's an actual brake engineer.

AC can also probably explain better as to why it's so important to have the rear calipers adjusted properly. I know from working on 1st, 2nd, and 3rd gen F bodies that if the late 2nd gen through third gen rear calipers aren't adjusted properly the brakes "suck" and the pedal feel changes as well as the overall performance of the system. He knows the technical reasons why.

I have a new bias valve I won't be using I could sell ya cheap if/when ya get to that point if you're interested. I have a 2nd gen I've installed 14" Baers all around on and decided to use twin master cylinders with a cable operated bias bar I can control from the drivers seat. So I won't need the simple inline bias valve I'd gotten before deciding on using the twins.