Brakes help please

[SMOKEDYA]

I installed my 93 cobra MC and line locks and adjutable proportioning valve on my 89.I already had 4 wheel disc.Now the pedal is hard topush and it barly stops!Even after i fooled with the proportioning valve. Any ideas?peace











john

 

[ironhead498]

What booster are you using?

If it's still the stock booster for the stock rear drum set up...that's probably the the culprit.

I used the booster and master cyclinder out of a 95GT.

Check this link out...it has pretty much anything you would want to know about this topic.

87-93  Ford Fox Body Mustang Brake Upgrades

 

[SMOKEDYA]

I have been doing a little research since i posted this,and i was thinking it could be the adjustment rod in the booster?I did or thought iadjuted it correctly per mm's instructions.But i could be off?I will try to adjust it in some and try that?I do have the stock 89 booster tho.peace






john

 

[SMOKEDYA]

Well i turned the rod on the booster in some tonight and that helped alot,so i will remove the m/c tomorrow again and turn it in more.peace









john

 

[Rick 91GT]

Bench bleed the master cylinder....

 

[Mustang5L5]

Be careful ypu don't adjust it top far out. What you are doing is shortening the stroke slightly, but too much may cause the brakes tp start to drag.

What is you full combo again? What fromt and rear brakes? You might need to swap to the SN95 booster if you find pedal effort is much too high.

 

[SMOKEDYA]

Bench bleed the master cylinder....

Yes sir i did!

Be careful ypu don't adjust it top far out. What you are doing is shortening the stroke slightly, but too much may cause the brakes tp start to drag.

What is you full combo again? What fromt and rear brakes? You might need to swap to the SN95 booster if you find pedal effort is much too high.

Ok i will watch that.I have OEM 03 cobras front and OEM 94+ cobra rears,93 cobra M/C and a summit proprtioning valve.Before i did the mc and valve the brakes were soft but stopped good.....peace












john

 

[Mustang5L5]

I have the same setup as you...but I'm using the sn95 booster

 

[ironhead498]

I have the same brake set-up also. With the 95 Boster and MC the pedal is firm, not overly firm, but the harder you push the harder is stops.

Just wondering.....but what route did you take for modifying the stock proportioning valve?

I used the MM kit that does away with the stock PV all together, and just have the PV for the rear brakes.

 

[Noobz347]

subscribing....

I'd always thought it was a no-no to reuse the Fox GT booster. Interested in seeing how this turns out as I have an 86 and pretty much everything I've read says it's a HUGE PITA to install the larger booster.

I'm not fond of the idea of having to beat and bang on the strut towers to get the damned booster to fit.

 

[SMOKEDYA]

I have the same brake set-up also. With the 95 Boster and MC the pedal is firm, not overly firm, but the harder you push the harder is stops.

Just wondering.....but what route did you take for modifying the stock proportioning valve?

I used the MM kit that does away with the stock PV all together, and just have the PV for the rear brakes.

What do you mean?I order the 3-2 conversion from MM and they say to keep the stock valve.

peace









john

 

[Mustang5L5]

Honestly...I think you'll have to change the booster.

If you don't want to, you'll need a smaller mc to compensate.....like 94-95 cobra mc (15/16")

 

[ironhead498]

Just as long as you did the modification to the stock PV you're fine. They also sell a kit that comes with couplers and you completley do away with stock PV. Just one less thing in the engine bay.

http://www.maximummotorsports.com/s...age=product_info&cPath=49_145&products_id=688

 

[ironhead498]

I'd always thought it was a no-no to reuse the Fox GT booster. Interested in seeing how this turns out as I have an 86 and pretty much everything I've read says it's a HUGE PITA to install the larger booster.

I'm not fond of the idea of having to beat and bang on the strut towers to get the damned booster to fit.

I think I've read where if you use the 93 Cobra MC you can get away with using the stock booster. Maybe if it was on a car with a stock motor and good vacum. I cant see where it would work real well on a car with a lumpy cam.

As far as installing the sn95 booster goes...it did take a little massaging of the strut tower, but you can't see it once the booster is in place. I also had to take off the upper intake manifold, and you have to elongate one of the mounting holes in the firewall to get it to mount up.
All in all it only took a couple of hours from start to finish to change out the booster. I had oringinaly tried without changing the booster because of the horor stories I had also heard, but it realy wasn't that bad.

 

[SMOKEDYA]

Just as long as you did the modification to the stock PV you're fine. They also sell a kit that comes with couplers and you completley do away with stock PV. Just one less thing in the engine bay.

Brake Proportioning Valve Eliminator kit, 1987-93 [MMBAK-6] : Maximum Motorsports, the Latemodel Mustang Performance Suspension Leader!

So with that eleminator kit in the link they are useing those 2 unions to attach the fronts and the rears together instead of running them threw the stock proportioning valve?I would like to see the install instructions that come with that part.peace




john

 

[SMOKEDYA]

Ok just found the instructions on their site.WOW they want $20 for 2 fittings that cost .30 each peace







john

 

[Noobz347]

Honestly...I think you'll have to change the booster.

If you don't want to, you'll need a smaller mc to compensate.....like 94-95 cobra mc (15/16")

5L5... this makes no sense to me. A LARGER MC would increase the mechanical advantage and make things easier on the brake booster. How does this compute?

I think I've read where if you use the 93 Cobra MC you can get away with using the stock booster. Maybe if it was on a car with a stock motor and good vacum. I cant see where it would work real well on a car with a lumpy cam.

As far as installing the sn95 booster goes...it did take a little massaging of the strut tower, but you can't see it once the booster is in place. I also had to take off the upper intake manifold, and you have to elongate one of the mounting holes in the firewall to get it to mount up.
All in all it only took a couple of hours from start to finish to change out the booster. I had oringinaly tried without changing the booster because of the horor stories I had also heard, but it realy wasn't that bad.

Two questions: (ok, it ended up being three)

What did you use to, "massage"?
Did it change the geometry of the tower at all?
You said you changed the booster because of horror stories. Does that imply that the stock booster was working well for you initially? How confident were you of that booster in the event of an emergency braking requirement?


thx

 

[Mustang5L5]

5L5... this makes no sense to me. A LARGER MC would increase the mechanical advantage and make things easier on the brake booster. How does this compute?

Because it's highly dependant on the ratio of the piston area of the master cylinder vs the slave cylinders (calipers)

A larger MC pushes more fluid. Drum brakes require very little fluid to operate so when adding rear disks brakes, a larger bore MC must be used.

But too large of a bore will push a lot of fluid so the pedal distance will be shorter since more fluid moves. As a result, pedal will also be harder. A smaller bore pushes less fluid, but as a result the pedal stroke needs to be longer to operate the pistons properly.

Given the same calipers, downsizing the MC bore will make pedal effort easier, but require a longer stroke. upsizing the MC will make pedal effort firmer, but require less distance overal of pedal travel.

So choosing an MC requires a little bit of thought. Just putting a larger bore MC on won't give you a good pedal. There are 4 disk brake MC's, all 1/16" bore differences. There is no "universal" MC that will work with all disk setups

 

[ironhead498]

What did you use to, "massage"?
Did it change the geometry of the tower at all?
You said you changed the booster because of horror stories. Does that imply that the stock booster was working well for you initially? How confident were you of that booster in the event of an emergency braking requirement?


thx

To massage the tower I use a hammer and a block of wood. It only needs a little clearancing in order to get the boster in place. Once it's up tight to the firewall there is room for the booster, but getting in place is where the clearence is tight. I realy don't think it changed any geometry at all.

I originaly didn't change the booster and used the stock one, and you had to stand on the pedal to get it to stop. I hadn't changed the booster cause I was hoping that I could get away without it. As far as an emergency stop with the foxbody booster and sn95 MC all I can say is GOOD LUCK. I drove around the block twice and pulled it back in the garage to change the booster.

 

[Mustang5L5]

Kinda what I did. Tried to go without the booster..one trip around the block and i went home and changed it.

I didn't do any massaging. I slotted the firewall holes, cut the studs down about 1/2" and it slid in without hitting the strut tower at all. Difference in stopping was night and day