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Author Topic:   Brake experts needed
Mpcoluv
Gearhead

Posts: 1278
From: Charlotte NC usa
Registered: Apr 2001

posted 07-26-2001 10:28 AM     Click Here to See the Profile for Mpcoluv   Click Here to Email Mpcoluv     Edit/Delete Message   Reply w/Quote
Hi guys I need the help of a brake system expert.
I have converted my '69 stang to rear disk brakes using '85 Eldorado calipers and the rotor from an 85 t-bird.
The problem is that I can't get a good pedal. I have bled the brakes numerous times, including with the bleeder screw pointing straight up.
I am still using my '78 granada manual disk master cylinder. Is this the problem? Do I need to go to an aftermarket mastercylinder?
If so, what have you guys had success with?

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69maverick
Moderator

Posts: 1455
From: Thomaston,CT.
Registered: Jan 2001

posted 07-26-2001 01:46 PM     Click Here to See the Profile for 69maverick   Click Here to Email 69maverick     Edit/Delete Message   Reply w/Quote
I haven't done what you did but I think you need a perportioning valve? The other thing I was thinking about is Volume of fluid,Do you have enough? You may have to use larger lines?

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jkilroy
Gearhead

Posts: 1808
From: Vicksburg, MS
Registered: Dec 99

posted 07-26-2001 02:25 PM     Click Here to See the Profile for jkilroy   Click Here to Email jkilroy     Edit/Delete Message   Reply w/Quote
Whats the bore size on that master? You might not be getting enough volume. You can try a master from a late 80's lincoln, which has a 1 1/8 bore. The other upside is that they are aluminum and weight about 1/4 of the iron ones.

------------------
Jay Kilroy
68' Fastback GT 390
"No such thing as a cam thats too big"

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Doc
Gearhead

Posts: 466
From: Redwood City, Ca. USA
Registered: Jan 2001

posted 07-26-2001 03:36 PM     Click Here to See the Profile for Doc   Click Here to Email Doc     Edit/Delete Message   Reply w/Quote
On some systems I've had to use 2 methods of bleeding, the one we all do "pump up and open the bleeder" and "open the bleeder then push the pedal down and close the bleeder". The second one will many times unseat an air pocket that somehow escapes the first one over and over. You should be able to get a good pedal even if the system isn't balanced and won't work well. Please understand I'm not saying yours is not right, just that even if it weren't you should still get a good pedal.

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Mpcoluv
Gearhead

Posts: 1278
From: Charlotte NC usa
Registered: Apr 2001

posted 07-26-2001 03:59 PM     Click Here to See the Profile for Mpcoluv   Click Here to Email Mpcoluv     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by 69maverick:
I haven't done what you did but I think you need a perportioning valve? The other thing I was thinking about is Volume of fluid,Do you have enough? You may have to use larger lines?

I have a Wilwood proportioning valve mounted under the back seat much like shown in the Boss 302 chassis book.
I don't think the brake line size is my problem...

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Mpcoluv
Gearhead

Posts: 1278
From: Charlotte NC usa
Registered: Apr 2001

posted 07-26-2001 04:02 PM     Click Here to See the Profile for Mpcoluv   Click Here to Email Mpcoluv     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by jkilroy:
Whats the bore size on that master? You might not be getting enough volume. You can try a master from a late 80's lincoln, which has a 1 1/8 bore. The other upside is that they are aluminum and weight about 1/4 of the iron ones.



Is the lincoln master cylinder bore size too large to use as a manual master cylinder?
NPD sells a Moog master cylinder with a 1" bore for use with 4 wheel disk brakes. It was used on 82-89 town cars from what I gather.
My current master cylinder is a 7/8" bore.

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Gary Ferringer
Journeyman

Posts: 59
From: Kennerdell,Pa.
Registered: Feb 2001

posted 07-26-2001 06:58 PM     Click Here to See the Profile for Gary Ferringer   Click Here to Email Gary Ferringer     Edit/Delete Message   Reply w/Quote
Am I correct by assuming that you have 4 wheel disc brakes? If so, you need a 4 wheel disc master cylinder. The volume in the reservoir will not be enough for the rear disc brakes in a standard disc/drum master cylinder.

On my Capri, which has the factory discs on the front, and Lincoln Versailles 9 ? rearend and disc brake system in back , I used a master cylinder from a mid ?80?s Lincoln Continental with 4 wheel discs. I think, but am not certain,that this is the same as was used on the SVO Mustangs of that era.

It works quite well. The pedal is very firm,and does require some muscle power to push it since the bore is quite large for a manual system,but it stops my car in a hurry at the end of a run,and I am confident it would work as well on the street. In fact the friend that bought my ?68 Mustang is using the same master cylinder in it after he converted it to 4 wheel discs,and he says it works quite well once you get used to it. I?m sure it works a heck of a lot better than it did when I had it,it had 4 wheel drum brakes then.

As far as the bleeding troubles, it could be a lot of things. A leak in a fitting, a different bleeding method might be needed, the brake lines might be higher than the master cylinder, maybe the master cylinder itself might be bad. If it is old or used,maybe it is pretty well spent. And don?t assume that if it is new, that it will be good. We wasted several days when we were getting Dad?s ?72 Pinto ready this spring trying to get the brakes to bleed, to no avail. Over a gallon of brake fluid later,we took the thing off, and exchanged it for a different one, and in 10 minutes the brakes were bled.

I should also add that it was really tough to get mine to bleed as well, but this was a completely dry system at startup, and it takes a lot of messing around to get all the air out. Doing it completely alone doesn?t help either. You might want to rig up a pressure bleeding apparatus. This will save a lot of time,and will be a lot more effective than the old pump and bleed method. It doesn?t have to be anything fancy. A tire pump, and a modified master cylinder cap will do in a pinch.

------------------
'85 Capri
Cleveland powered
carburetted
6.95 1/8th
@94 1/2 MPH
1.49 60 ft.

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Gary Ferringer
Journeyman

Posts: 59
From: Kennerdell,Pa.
Registered: Feb 2001

posted 07-26-2001 07:06 PM     Click Here to See the Profile for Gary Ferringer   Click Here to Email Gary Ferringer     Edit/Delete Message   Reply w/Quote
Also,before I forget, the disc/drum system contains a residual pressure valve for the rear drum brakes,I'm not sure if it is in the master cylinder,or in the stock combination valve, but whichever it is,you absolutely do not want it in a disc/disc system. It will cause the brakes to drag all the time on that particular axle.

------------------
'85 Capri
Cleveland powered
carburetted
6.95 1/8th
@94 1/2 MPH
1.49 60 ft.

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Mpcoluv
Gearhead

Posts: 1278
From: Charlotte NC usa
Registered: Apr 2001

posted 07-26-2001 08:45 PM     Click Here to See the Profile for Mpcoluv   Click Here to Email Mpcoluv     Edit/Delete Message   Reply w/Quote
What is the bore size for the SVO master cylinder?
What year SVO should I look for?

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