Brakes Not As Good As They Should Be

[ron86]

My SVO sat for 8 years (93-01). When I began restoring it last year, I had to replace the master cylinder. The brakes are good but not good enough. If I STAND on the pedal, I get a brief little chirp from one or more wheels. Braking is straight but barely adequate. I did the test on the power booster...passed based on shop manual. The fluid is clean synthetic; rebuilt calipers all around; performance friction pads. Any ideas?

[SVOeric]

Performance friction pads from autozone ?

they aren't the greatest pads..

I'm a little confused on your times....

How many miles have you driven since it sat??
did you turn the rotors after the car sat??
when did you rebuild the calipers?

[svobud]

I've never had to replace one...but...isn't the master cyl a SVO specific part? And if so, did you use a SVO specific master cyl or one for a regular FOX Mustang?

[ron86]

I have put on approximately 3000 miles since I brought it out of storage. The rotors were all turned and the calipers were purchased rebuilt units.

I have generally been happy with PF pads in the past...huh.

Does anyone know if the master cylinder is SVO specific...I don't think it is.

Anyone else have any ideas?

[SVOeric]

the SVO master-cyl is different from stock mustangs..

I know this for a fact, as I thought Iwas going to have to buy one a couple of weeks ago, and I had checked prices on them.

did you also replace the lines on the master-cyl to the prop-valve, because I believe the fittings were different sizes, but I'm not positive on that one...

oh yea.. those PF pads are ok, as long as you dont try to auto-x with them. I run them on my daily driver truck..

[ron86]

I'll check my paperwork but I must have gotten the SVO specific unit because everything fit fine. The brakes work...I would just expect them to totally lock up if I stand on them (not that this is a desireable condition). I was wondering if there was an adjustment that needs to be made to increase braking pressure. I know there is an adjustment that can be done to the brake booster but this was not replaced.

[SVOeric]

the only adjustment on the booster is for pedal height, and wont really make any difference in braking performance..

there are no other adjustments I know of... make sure you have all the air out of the system...
I heard from someone (can't remember who) that used synthetic brake fluid that they bleed the brakes, drove the car for a week, then bled them again, and it made a big difference..

They said it was like the air didn't want to push to the front like it did with regular fluid.

[ron86]

I'll try bleeding again but the pedal is very stiff.

How about the proportioning valve?

Thanks Eric

[svono50]

Ron, From what I have heard/read it sounds like you may still have air in your master cylinder or just an incorrect master cylinder. The proceedure for bench bleeding a master cylinder sounds very daunting and tough to get right the first try w/o the proper equipment. There a lots of places for air bubbles to get trapped in there.

You may also need to go back and verify you got the right master cylinder (i.e.- correct piston diameter). If you have the incorrect one you would either get a soft/long movement or hard/short movement of the brake pedal. Here is a website that has a lot of useful Mustang brake info:

http://svo73mm.cjb.net/

Another thing to ask, were your new/rebuilt front calipers 73mm piston units? If they were V8 fare with smaller pistons you would end up with a very stiff pedal. Just some more ideas.

[ron86]

UPDATE

I confirmed that I have 73mm calipers (replaced them with rebuilt units) and the correct master cylinder. I bled the system again and braking is improved (enough pedal pressure will induce a front lockup). However, the pedal travel seems to vary and I often need to push the brake pedal twice to get good brake pressure (less pedal travel). I fear that I still have air in the system (probably the master cylinder). I did not bench bleed the master cylinder. Is is possible that air is still trapped in the master cylinder after 16 months and 3000 miles (and many attempts to bleed). Also, an old post on the "other board" says that this condition was solved by adjusting of the brake booster rod length?!?

Thanks,

Ron

[SVOeric]

adjusting the rod length will only fix the problem if the the pedal is always low .. if you pump the brakes, and the pedal comes up, then you do have air in the system.

Air can be very hard to get out.  when I did my svo, I bled the brakes, and drove the car a bit for about a month, then bled them again.  I went through alomst a full quart bottle of fluid, but I finally got all the air out. (now I have to change the prop valve, and will have to go through it all again)

If you look in the product review section, you will see a couple of reviews for something called a speed bleeder.  They are pretty cheap, and I plan to pick up a couple of these myself, just to play with.. .but they shound like they work really well.

 

[ron86]

Thanks Eric,

I ordered the speedbleeders. I'm also thinking about pulling my master cylinder to bench bleed.

Ron

[svono50]

Ron,

Based on your description, you definitely still have air in the system. From the conversations I have listened to in the past, you almost always have to bench bleed the master cylinder before installing to ensure there isn't any air in it. Luckily I haven't had to cross this bridge yet (knocking on wood!). Good luck and let us know how it goes.

[Eyelawdoc]

Having read through this thread, it definitely sounds like you have air in the system, probably because the master cylinder was not bled first.

It is very easy to do, you don't even have to take it out of the car. Just disconnect the brake lines at the master cylinder and reconnect a short line from each of the 2 output ports that loops back into the respective front and rear reservoirs. Now get inside and pump the pedal slowly 8-10 times or until air stops bubbling out of the ends of the lines submerged in the reservoirs.

At this point, your master cylinder bleed is complete. Reconnect the brake lines and bleed the rest of the system in the usual fashion.

[turbizzy]

SVO master cylinder

Ok, im sorry for such a late reply to this thread and i don't know if this has already been answered but i heard that the master cylinder for the SVO is specific and the same for the 93 cobra. Also from what i have heard, these are still available at any autoparts stores or Ford.