wwinton

Hi Guys, I have had trouble at the last 2 track days with brakes, basically the fronts keep overheating, I just read an ad at Paragon saying this is a common problem and to change the Brake Limiting Valve. http://www.paragon-products.com/product_p/944tblv.htm

My problem is I have an 88 model with ABS and can't find this valve, I have a friend with a non ABS 86 model and his screws straight into the master cylinder and straight to the rear brake line.
Does anyone know if an ABS car has this valve?

ninefiveone

On ABS cars, the valve is in the passenger fender behind the wheel liner.

I have the valve you're talking about but I doubt it will help with your overheating brakes. The valve puts the rears to work a bit more but if you're overheating the fronts, something else is up.

Either you've got pads that aren't suited for track use, your driving style might need adjustment, or you need more cooling to the fronts.

wwinton

Thanks for that, do you know if it is the same one 86 models use in the master cyl?
I am using Performance Friction pads, Z compound. They are suppose to be a road/trackday compound. If my fronts are overheating, that would mean the rears could do some more work wouldn't it, I have noticed that the rears don't even generate much dust at the moment.

ninefiveone

Same valve regardless of abs or non-abs.

Overheating fronts rarely mean the rears need to do more work. You'll get a minor improvement in braking performance by increasing the amount of work the rears do but that's it. Weight transfer to the fronts means adding 5% more braking performance to the rear is going to do precious little on your overheating issue.

How about we start with the basics. How much track experience do you have? Fresh brake fluid? Etc?

CO951

What exactly is happeneding when your brake are overheating? Fade? Soft pedal?

wwinton

Ok, I have a half dozen or so track days up, mostly in 911's. I am a Mechanic and prepared the car before hand with a new set of front rotors/pads, checked the rears, they had about 40% pad left but a little bit of rotor wear. I flushed the brake fluid and put in Motul RBF600. After my first run on our local track, my front pads were melted into the rotors, and the rears just looked the same, I did one more run later in the day (5 laps) and boiled racing fluid. In the meantime while I was contemplating my car I tag teamed with one of my customers 964's and we both drove his car all day without a problem.
Here is a photo of my new front rotor with pad fused to it.

CO951

Does your car have the metal deflectors on the struts to deflect air from the cooling ducts to the back of the rotors? I personally, run a full race pad (Pagid Yellows), which I think would help some also. I use them on the street, too during track season even though the are very noisey and have more dust.

333pg333

Wayne, did Mike come out and measure your brake temps at the track? I still think you've got the wrong pads there. I would also put the 968cs air deflectors on. I think there's another thread going at the moment re these. They do help.

Cory9584

are the brakes releasing ok when you let go of the pedal?

CO951

Yes, I just did this write up on a cheap easy way to install the 968 brake cooling scoops on a 951.
https://rennlist.com/forums/showthre...ferrerid=34737

wwinton

I have the stock air deflectors fitted, the brakes are releasing ok, I have checked to make sure there are no seized pistons in the calipers. I think the thing that has got me the most rattled is that another 951 very similar to mine was running Bendix Ultimate pads, (which are not the greatest), jumping on the brakes at the 100m marker (I was not going anywhere near that deep), and he never had a problem.

Cory9584

id say something is keeping the backs from doing their job then. it might be a good idea to jack up the back and see how well their working

Geneqco

Seems very odd... what bed in procedure did you use when you replaced the pads and rotors?

Geneqco

It looks like you've had a lot of material transfer perhaps before they were properly heat cycled.

wwinton

I did the usual half dozen quick stops from 40 mph until they felt like they were working, I also did a couple of hundred road miles to make sure they were well bed in.