I bought a 93 mustang with front brakes upgraded to those of a 99. whenever i press the brakes with any force the front brakes lock up and slide. im not slamming the brakes. this has been a major issue as i track the car and its getting dangerous on the street as well. we tried replacing the pads, calipers, lines, and master cylinder. my uncle, a mechanic, took a look at the car and said there is a line coming from the side of the master cylinder, to the proportion valve, and then to the front left and rear brakes, and there is another line straight from the bottom of the master cylinder to the front right (my lefts and rights might be backwards). i have no idea if thats the stock configuration, but it sounds off to me. i have no idea whats wrong with it but im going to the track in a month and i need to get it figured out. any help is appreciated, thank you. and if this is in the wrong section sorry, i wasnt sure seeing as the brakes are from a 99.
Brake Locking Issue
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stang&2Birds
Founding Member
First, welcome to STANGNET! 
Yup, correct section!
Okay, let's start with basics.
1) WE NEED PICTURES! Front brakes, back brakes, lines, prop valves, Master Cylinder, lint in the ash tray. Well, maybe the last one isn't really needed.
Use photobucket/etc. Since you're a newbie, post the url as:
photobucket DOT COM / whatever
Don't worry, we'll figure it out.
2) What do you mean by "99" brakes? Verses the 94-98 GT brakes. I know what it means, but do you.
3) What do you have for the rear brakes???
4) Do you have an aftermarket proportional valve? If so, what type, and do you know the setting.
5) Do you know if they did the correct thing and "gutted" the prop valve?
BTW, a good reference for upgrading to sn95 brakes is from FRPP:
(it's for the M2300K kit - Cobra brakes, but there's a lot in common)
http://www.fordracingparts.com/download/instructionsheets/FordInstShtM-2300-K.pdf
Yup, correct section!
Okay, let's start with basics.
1) WE NEED PICTURES!
Front brakes, back brakes, lines, prop valves, Master Cylinder, lint in the ash tray. Well, maybe the last one isn't really needed. Use photobucket/etc. Since you're a newbie, post the url as:
photobucket DOT COM / whatever
Don't worry, we'll figure it out.
2) What do you mean by "99" brakes? Verses the 94-98 GT brakes. I know what it means, but do you.
3) What do you have for the rear brakes???
4) Do you have an aftermarket proportional valve? If so, what type, and do you know the setting.
5) Do you know if they did the correct thing and "gutted" the prop valve?
BTW, a good reference for upgrading to sn95 brakes is from FRPP:
(it's for the M2300K kit - Cobra brakes, but there's a lot in common)
http://www.fordracingparts.com/download/instructionsheets/FordInstShtM-2300-K.pdf
stang&2Birds
Founding Member
BTW, what do you mean by "track the car". Do you mean quarter mile, circle track, HPDE, oval, etc?
For me, track means for "real handling".
For me, track means for "real handling".
Thanks for the response. I'm his Dad and I just posted the same question after he did. I should have read the new posts first. I didn't know he knew about stang.net. I guess like father, like son!
I'm not sure photos will help. The brake system is a stock 93 set-up, except the previous owner added 99 to 04 front brakes when they did the 5 lug conversion. The rear brakes are drum brakes. The proportioning valve is stock. Please read my post for more information. And what the heck do you mean by "did they do the correct thing and gutted the proportioning valve?"
Thanks for any help.
P.S. Scott try and watch your typing and punctuation!
I'm not sure photos will help. The brake system is a stock 93 set-up, except the previous owner added 99 to 04 front brakes when they did the 5 lug conversion. The rear brakes are drum brakes. The proportioning valve is stock. Please read my post for more information. And what the heck do you mean by "did they do the correct thing and gutted the proportioning valve?"
Thanks for any help.
P.S. Scott try and watch your typing and punctuation!
stang&2Birds
Founding Member
I still want to see pictures of how they did the lines from the MC to the prop valve, and then out of the prop valve.
From the posts (no pictures, so a lot of assumptions!):
1) You can not use the POS 87-93 MC on an sn95 setup.
2) What did they use for the rear? I forget the 5-lug drums.
3) A 94-98 GT front brake is way too much braking for drum brakes. A 99+ GT caliper makes it that much more "worse" in terms of braking ability (front to back).
4) An OEM prop valve is custom tuned for each car and each brake setup. Just because someone slaps on some brake upgrade, don't touch the bias, and they "don't get killed after driving it 10 feet", does not mean that it's correct.
5) I strongly suggest going to a 94/94 MC, gut the Prop valve, add a proportioning valve (start at the setting FRPP suggests, and tune from there for your setup).
6) The 87-93 MC and prop valve setup has to be one of the most asinine brake setup ever done. It was done for cost reasons. Still, it never should have been allowed! Going with big front brakes just makes the always present imbalance in the front brakes in a stock 87-93 setup much worse.
From the posts (no pictures, so a lot of assumptions!):
1) You can not use the POS 87-93 MC on an sn95 setup.
2) What did they use for the rear? I forget the 5-lug drums.
3) A 94-98 GT front brake is way too much braking for drum brakes. A 99+ GT caliper makes it that much more "worse" in terms of braking ability (front to back).
4) An OEM prop valve is custom tuned for each car and each brake setup. Just because someone slaps on some brake upgrade, don't touch the bias, and they "don't get killed after driving it 10 feet", does not mean that it's correct.
5) I strongly suggest going to a 94/94 MC, gut the Prop valve, add a proportioning valve (start at the setting FRPP suggests, and tune from there for your setup).
6) The 87-93 MC and prop valve setup has to be one of the most asinine brake setup ever done. It was done for cost reasons. Still, it never should have been allowed! Going with big front brakes just makes the always present imbalance in the front brakes in a stock 87-93 setup much worse.
stang&2Birds
Founding Member
IMHO, those rear drums will die/fade very quickly. Plus, drums are horrible for side to side constancy. Add in an 87-93 ******ed up front brake setup. and each brake "does it's own thing and not very consistently".
It would be best to go with the sn95 rear disks. Plenty of options, and it's not very expensive anymore. Plus, they work with 15" sn95 rims.
Yes, it is possible to do HPDE with a stock POS Fox brake setup. But, IMHO, I'd suggest it for a very beginner only.
Regardless, I worry more about getting the brake system to some reasonable setup.
I'll shoot you some photos of the brake line set-up as soon as I get the car back. I agree that the proportioning valve is probably the culprit. We have big 99+ disc brakes on the front and a stock 93 braking system. We recently bought the car and only knew it had a 5 lug conversion. When we bought the car, I bought new Hawk racing pads for my son's first track event and the new ones were tiny compared to the pads that were on the car. That's when I figured out the PO had upgraded the brakes. I think that is why they sold the car as cheap as they did, because they don't work. I just don't want to go backwards as far as the braking capacity. I think we probably need to scrap the stock proportioning valve. I just don't know how to do it. I have a 99 GT that I carry to the track for HPDE events and it has anti-lock brakes. I don't think we want to go there with this car. I thought about just putting individual, aftermarket, adjustable proportioning valve on each corner and working it out. I was just hoping that there was a better way that someone else had done.
Thanks for all you advice!
Thanks for all you advice!
stang&2Birds
Founding Member
WOW, I read it quickly and just noticed that the first letter in the post was capitalized! Lucky!
Here's a good life lesson: If someone doesn't care about spelling, punctuation, and grammar when asking a question in a forum, then they often get ignored by many people - me included!
Let's talk "Get a Clue".
If you don't care enough to take the time and effort in asking and submitting a question, they WHY should someone else take their time and effort to help you???At work, I deal a lot with sending/getting/reading emails - most of them are very technical. There's a time when quick short emails are appropriate. Still, for me, 99% of the time, I use formal grammar and structures.
I agree about the drum brakes. They are marginal at best and not what we eventually want for the car. I recently put a IRS cobra rear under my 99 so I have a stock 99 full rear with the brakes, etc. that is sitting on the floor of my shop. I would love to put the entire set-up under the 93 LX, or just the rear disc brakes. Still, does that change the proportioning valve issue? Plus, I believe the 99 rear is wider than the 93 rear. We are running 17" rims so the size doesn't matter. I got parts, I just don't know what ones to use!
Thanks!
Ben
Thanks!
Ben
stang&2Birds
Founding Member
Read the FRPP M2300K install manual.
As long as you can make brake lines, it's not bad!
IMHO, the worse part can be getting the prop valve out! Mine had every brake line rusted to the fitting. So, every brake line broke! That's common in New England because of the snow and salt used on the roads. My best
friend use the Stang as a DD (winter included of course) for ~10 years until he sold it to me.
You gut the Prop valve. You can but the plug online for ~$10.
You put in a 94/95 MC.
You make some brake lines from the MC to Prop Valve, prop valve to front brake lines.
You add an adjustable prop valve near on the rear brake line on the passenger side, next to the firewall. There's a union there already. Just put the adj prop valve at that place.
Again, the FRPP instruction go over all of the above, and in a pretty good write up. Now, that is.
When I did it, the M2300K install instructions where basically "Take out old stuff. Put in new stuff". I went by the M2300K install article on the "other site" and called FRPP a few times for things that still weren't clear.
stang&2Birds
Founding Member
The 99+ rear is too long. Even sn95 rear axles makes it tight. You can go with stick rear axles and an sn95 rear disk setup by using the North Race Cars adapter plates. Many people do the 5-lug upgrade that way.
IMHO, as long as you can get that small bolt out that is inside the rear diff, and do not turn the axles, it's not hard at all to yank/replace the axles at all. Even if the fill bolt is rusted, you can get a new back plate with a fill hole.
We will give that a try. It seems doable! I just wasn't sure if there was an easy fix with the existing parts. But from what you have told me the factory set-up is garbage. It didn't make sense to me. I will research putting my 99 rear brakes on the rear, so we only have to do this once.
Thanks again.
Thanks again.
stang&2Birds
Founding Member
Found it:
North Race Cars makes the adapter plates:
http://www.northracecars.com/5lugSN95reardisc.html
http://www.northracecars.com/Brakes.html
BTW, this is the bolt/pin to be careful with.
Once cover is off, remove the 5/16” bolt that holds the big pin in the center of the traction lock unit. Remove pin once free.
IMHO, I'd hit it with a little heat if it doesn't not want to come free with only a little force. They do make a special kit to drill and remove that bolt if it breaks. But, IMHO, you don't even want to think about that method.
North Race Cars makes the adapter plates:
http://www.northracecars.com/5lugSN95reardisc.html
http://www.northracecars.com/Brakes.html
BTW, this is the bolt/pin to be careful with.
Once cover is off, remove the 5/16” bolt that holds the big pin in the center of the traction lock unit. Remove pin once free.
IMHO, I'd hit it with a little heat if it doesn't not want to come free with only a little force. They do make a special kit to drill and remove that bolt if it breaks. But, IMHO, you don't even want to think about that method.
Sounds like soneone just installed the calipers and never made any prop valve or mc changes.
Stock brake setup on the mustang has one line direct to drivers caliper and then the pass caliper and rear brakes feed directly off the prop valve.
There really isn't an ideal MC for the brake setup you have. Shirt term solution is to gut the factory prop vavle and install and adjustable.
Of course, that's not the most ideal setup, but it's source of your issue
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Stock brake setup on the mustang has one line direct to drivers caliper and then the pass caliper and rear brakes feed directly off the prop valve.
There really isn't an ideal MC for the brake setup you have. Shirt term solution is to gut the factory prop vavle and install and adjustable.
Of course, that's not the most ideal setup, but it's source of your issue
Sent from my iPhone 4S using Tapatalk
Since there are only two lines leaving the proportioning valve, I guess once we gut the valve, I would then put the new, adjustable, proportioning valve on the line to the rear brakes. The drivers side would still come from the MC. Do I still need to replace the MC with a 94/95 model? We just replaced the existing one with a new 93 unit. Thanks for all the help. This is just a weird set-up.
Unfortunately I'm on vacation so my little spreadsheet is inaccessible. But you MC selection should be proportional to the fluid increase of the front calipers. Under sizing the mC can create and overly sensitive condition while too large a bore may result in needing a bit of leg muscle to stop.
What are your ultimate plans? Do you want rear disks?
Sent from my iPhone 4S using Tapatalk
What are your ultimate plans? Do you want rear disks?
Sent from my iPhone 4S using Tapatalk
I have a set of 99 rear disc brakes I want to use. I now intend to buy the north race car brackets. So what MC do I use and as important at this moment, how do I gut the proportioning valve? Do I just drill it out? I want to do that first and then add the rear disc brakes immediately after.
Thanks for all the help!
Thanks for all the help!
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