I upgraded to 13" Cobras in the front with Cadillac rear disc in the rear, and an adjustable prop valve, with the stock one gutted. the adjustable one is adjusted out as far as it can go, and they still lock up first, why, and how do I stop it?
My rear brakes still lock up before the fronts...
- Thread starter BlackFox5.0
- Start date
stang&2Birds
Founding Member
You could have air in the brake lines. How did you bleed the lines?
You could have bad rear tires. Your struts could be shot, so you get a lot of nose dive.
I'd bet on air. Pressure bleed the system. Tap the rears calipers. You may even have to take them off the bracket and bleed them with the bleed hole at "exactly" 12 O'Clock to get all of the air out. But, often, a GOOD pressure bleeding with a few *gently* taps is all it takes to get air out. I do at least a pint per wheel.
You could have bad rear tires. Your struts could be shot, so you get a lot of nose dive.
I'd bet on air. Pressure bleed the system. Tap the rears calipers. You may even have to take them off the bracket and bleed them with the bleed hole at "exactly" 12 O'Clock to get all of the air out. But, often, a GOOD pressure bleeding with a few *gently* taps is all it takes to get air out. I do at least a pint per wheel.
I have a very good pedal, I already got all the air out of the rear calipers, my struts are still good, they kept going back down when I was trying to hold them up while doing my spindles. I also have stiff springs, and almost no nose dive. Even if I am going under 5mph, they still drag.
I have 245/45 17 tires all around
I have 245/45 17 tires all around
stang&2Birds
Founding Member
custom89stang said:
Actually, you WANT the rears to lock first. Otherwise, YOU DIE!!!!!!!!!!
When the fronts lock, you HAVE NO STEERING and crud for control. Also, the fronts do ~70% of the braking, not 90%.
The fronts do most of the braking in stangs for a number of reasons. But, in trucks/SUV hauling loads, the REAR tires do most of the braking.
stang&2Birds
Founding Member
WTF! See that ad link for SUV in my post above? That's the first time I've noticed something like that.
stang&2Birds said:
Thats true, but I feel like I am not using the full pontential of my front brakes if I have to prevent the rears from locking....
When I went autocrossing with my stock brakes (only 73mm calipers in the front) My rears would lock up when I stopped in the stop box, I don't want that to happen again....
Here is me at the last event.
Mavrick
Founding Member
Your an idiot if you want your rears to lock up first. You dont want them to lock up because then you lose control of the rear and itll come around on you. 2 perfect examples:
Ricers who yank the E-handle to swing the ass around on a corner. Yeah thats something I want to simulate on the highway at 70!!
Motorcycles: Ask any bike rider if he likes it when his rear tire locks up, and he'll laugh at you. Its a great way to ditch the bike and kill yourself.
Please, spreading advice like that will get someone killed. If you dont know for sure, dont answer at all!!
Ricers who yank the E-handle to swing the ass around on a corner. Yeah thats something I want to simulate on the highway at 70!!
Motorcycles: Ask any bike rider if he likes it when his rear tire locks up, and he'll laugh at you. Its a great way to ditch the bike and kill yourself.
Please, spreading advice like that will get someone killed. If you dont know for sure, dont answer at all!!
stang&2Birds
Founding Member
steve1676 said:
Wow, have you *ever* taken a driving course? Or, have you driven much?
As I said, if your fronts lock, YOU DIE! You can NOT steer. You have NO CONTROL! So, YOU DIE!!
I'm talking about Super Basic brake and racing theory/facts that have been known for over 100 years.
Go to amazon.com, there are tons of racing and brake books available. Or, if you can, take a local performance/track handling course.
stang&2Birds
Founding Member
Oh yea, FORD says the same thing with their M2300K Cobra brake upgrade kit. You would think that Ford would know about how to set up the brakes on the Cobra and Cobra R. 
stang&2Birds
Founding Member
BlackFox5.0 said:
That's way many open track and autocross drivers go to ABS. The professionals can also adjust the front rear and side to side brake bias on the fly. The max braking ability differs depending on how much gas is in the tank, the condition of the tires, the condition of the track, etc.
Yea, for MAX braking, you want your rears to lock up "just before" your fronts do. But, for the *normal every day* driver, having the rear lock up sooner gives the driver warning before the fronts lock up.
The same is semi-true for many ABS systems. The Delco system is made to keep the car straight and *in control*. NOT for max braking. It's low cost and "perfect" for the typical driver. On the other hand, the stang/Vette/96+ Fbody cars have an ABS system that is more oriented for performance braking. It also costs much more.
Michael Yount
Mustang Master
C'mon Stangplus2 - you want a setup that will allow you to maximize your braking potential. Ideally, you'd like all 4 to lock up at the same time. That, as you know, is the wonderful thing about ABS - it holds all 4 tire at threshold braking for maximum stopping power. Absent ABS, you want all 4 to lock up at as closely as possible to same time and if you have to err a bit from that, you want the fronts to lock just ahead of the rears. The reason for that is because in cars like ours (and most vehicles other than tractor trailers) the front brakes do the vast majority of the stopping. You want to be able to extract maximum braking from the front brakes - which means you have to be able to hold the fronts at the limit of adhesion -- without the rear's locking and slewing the arse-end around. That means you have to have enough bias be able to lock the fronts without sliding the rear. The original poster is correct - with his current set up, he can't extract maximum stopping power out of the fronts without the backend coming around - and that's the real safety issue here.
I road raced for lots of years (SCCA SW Division Champ in ITC 89 & 91)- every driver has his/her own style, and their own preference for bias. But I never ran across anyone that wanted the rears to lock first - even for trail braking. The rear is so light under heavy braking that it can easily be made to rotate and help turn the car just by turning in under heavy braking. The rears don't have to lock to help with that -- in fact having them lock makes the car too sensitive to trailing throttle oversteer. They should all lock together, or the fronts should lock slightly before the rear.
Who made your proportioning valve? How much of a pressure cut will it take? Perhaps you need another type that will take a larger cut? Just guessing. Oh - you sure you've turned it 'all the way' in the correct direction?
I road raced for lots of years (SCCA SW Division Champ in ITC 89 & 91)- every driver has his/her own style, and their own preference for bias. But I never ran across anyone that wanted the rears to lock first - even for trail braking. The rear is so light under heavy braking that it can easily be made to rotate and help turn the car just by turning in under heavy braking. The rears don't have to lock to help with that -- in fact having them lock makes the car too sensitive to trailing throttle oversteer. They should all lock together, or the fronts should lock slightly before the rear.
Who made your proportioning valve? How much of a pressure cut will it take? Perhaps you need another type that will take a larger cut? Just guessing. Oh - you sure you've turned it 'all the way' in the correct direction?
Michael Yount
Mustang Master
....and, over the years I've been to 4 different driving schools at tracks all over the country (Russell at Sears Point, Panoz at Road Atlanta, Roos at Pocono, Daly at Vegas), and they always have the bias set on the school cars so the fronts lock first.
Yeah, ABS is totally different that our cars. ABS "pumps" the brakes so that you can still steer. Everybody knows that if you dont have ABS, you pump them so that you can steer. First off, hes not on a race track that may require intense braking and the need for power sliding. Secondly, I dont know any racing circuit that requires that you lock up your brakes around every corner. The reason why you dont steer while locking up the brakes is because your not suppose to lock up your brakes. Good pressure or pumping is the norm for street driving, not jamming. The reason why they made ABS is because people jam and cant steer. The solution is not to do that. Tell you what, tomorrow when I get my car dynoed, I'll act stupid and tell the mechanics I want them to adjust my rear brakes so that they lock up.
