71-73 Swag

  • New T-Shirt Design (Also coffee mugs and posters!) – read more!
  • Mach 1 Key Tags available (almost gone!) – read more
  • Convertible Key Tags available (limited supply) – read more
  • Coupe Key Tags available (only a few left) – read more

  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Brake Problems.
#1
I have had a spongy brake pedal for the last 5 years and its starting to annoy me that the brakes barely work on my car. A few years ago I switched out the master cylinder because it was leaking out of the cap and out the back, but once I installed the new one it did the exact same thing. Just yesterday I pulled the master cylinder and bench bled it to make sure it was done properly, and then I bled each wheel. None of the wheels seemed to have any air in the lines. I cannot find any leaks anywhere in the lines, the only thing that leaks is that master cylinder out of the cap and from the back where it bolts to the booster. I just don't understand whats going on. I'm thinking maybe something is wrong with the proportioning valve or the booster? Is the master cylinder bad?

The back brakes seem to be OK, and doing there job, but the front brakes barely do anything unless I push the spongey pedal all the way to the floor. I am on the verge of buying an entirely new system, lines, mc, everything.

[Image: 25rnz1y.jpg]

~Buddy
  Reply
#2
Try replacing the master Cyl again. They are cheap and easy to replace. If it is leaking from where it bolts to the booster it is certainly bad.


'Mike'
73 Convertible - 351C/4V CC heads/4bolt/forged flat tops/comp 270/rhodes/mallory unilite/tri-power/hookers/glasspacks/c6/3.50 limited slip/Gear Vendors/Global West sub frames, strut rods and shelby style traction bars/ Rear sway bar/tilt steering (not original)

Pics of modifications included in:
  Reply
#3
will e;32213 Wrote:Try replacing the master Cyl again. They are cheap and easy to replace. If it is leaking from where it bolts to the booster it is certainly bad.

Yeah that is what I am thinking.

[Image: 25rnz1y.jpg]

~Buddy
  Reply
#4
Before you do that how about trying this. Be sure that all fittings are tight. Level the car and be sure your reseviour is full. Open all bleeders until you just see fluid emerge(usally about a half turn). Let the car sit for 24 hours.
This will gravity bleed some of the air out.
Close all bleeders. Then 1 at a time starting at the passenger rear, Have someone in the car. You crack the bleeder. Have them slowly push the pedal to the floor and hold it there until you close the bleeder tight. If you got some air out repeat again.Check your level and do the same to driver side rear, passenger front lastly driver front. Be sure they don't let the pedal move until you tell them OK the bleeder is closed and don't let them pump the pedal. Just 1 push and hold for each bleeder.
By the way, the reseviour is not supposed to be full to the top. It should be 1/4 to 1/2 below the top with new brakes and all the air removed. Hope this helps

[Image: 2rr7aiv.png]

Just cruising along minding our own business when BAM!!! The LAWS show up.
  Reply
#5
have you checked the length of your push rod on booster plunger?

If the push rod is somehow too short, you will have to push the pedal to the floor to stop the car.

check pedal height tolerance. can you pull the pedal back like its not coming fully back up?

to check the pushrod the master will need to come off, you then have to build a gauge based on the manual specs to measure the push rod height and make sure its correct.

this will also depend on how original the parts are, if you have an aftermarket master or booster this will throw off the measurements.

now leaking cap can be an issue as well. why is your cap leaking? you need to look into that.

if the master is leaking out the back that is not a good sign, that would indicate damage to the O ring seals on the pushrod, the master should not be leaking anything anywhere.

now as first talked about if the push rod adjustment on the booster is too long that can damage the master and cause a seal failure.

based on the leakage you are getting i would replace the master with a new one make sure it matches OEM spec. they sell a lot of masters that claim to fit the 71-73 mustang so you have to be careful.

once bench bled or vaccum bled, i would inspect the booster make sure its holding vacuum correctly you can use a hand vaccum pump to check it, and check the pushrod length(it is adjustable with a Acorn nut on the stud.) you also want to check pedal height.

if somebody swapped in the wrong bracket from a manual brakes car it will cause all kinds of brake problems.

the key is first getting all the right components together then make sure whats on the car is correct.

as far as the prop valve.
the proportional valve only effects the pressure to the rear drum brakes line.
if you have Disc brakes the front brake lines get full pressure no restriction.
the valve only works on the bottom intermediary line that runs to the rear drum brakes.

now if you can bleed the rear brakes that means they are getting pressure.
same with the front if fluid squirts out of the bleeder when you press the pedal then i would start looking into the master and the geometry of the linkages that activate the master cylinder.

  Reply
#6
It looks like I'm going to order a new master cylinder, they are cheap enough. I did take the MC off and the fluid has really crusted up the rod and the rubber gasket/seal behind the MC. Looks like fluid has made its way all inside the booster and its real nasty in there. Its the original booster so its more than likely leaking.


I have not checked the pushrod length but I will.


EDIT: I went to the car wash earlier today (yes ive been driving the car around regardless of brake issues) and sprayed off around the master cylinder and booster. Its pretty clear now that the only place its leaking is from around the cap, NOT from the backside. It was just running down before and made it look that way. I can't pull the pedal up so its coming all the way back up. When I press the pedal it has about 1/2 inch of play. I can see when I press the pedal it forces fluid out of the cap. Why would it do that? Maybe the brake lines are clogged up and the fluid doesn't have anywhere to go but out the cap? I can try getting a new cap but I get the feeling its going to do the same thing.

I'm thinking I might just get a new master, new front brake lines, and maybe even new front calipers.

[Image: 25rnz1y.jpg]

~Buddy
  Reply
#7
If the booster is original you probably don't have a push rod issue. Be very careful to get the right vacuum booster master cylinder set up. I replaced my set up for my Chevelle from an online company (trying to save a buck) and spent 2 weeks altering firewall brackets and waiting on a heim joint to get it right. Spend your money wisely, your time is worth something too!

[Image: 2rr7aiv.png]

Just cruising along minding our own business when BAM!!! The LAWS show up.
  Reply
#8
markmel;32222 Wrote:If the booster is original you probably don't have a push rod issue. Be very careful to get the right vacuum booster master cylinder set up. I replaced my set up for my Chevelle from an online company (trying to save a buck) and spent 2 weeks altering firewall brackets and waiting on a heim joint to get it right. Spend your money wisely, your time is worth something too!

Yes I think im just going to do the master first since it is relatively cheap. If I do end up getting a booster too it will be from a place I can trust, like from a vendor on this site or a place like yearone.




Attached Files
.jpg   185292_10150255455837523_600367522_7590972_1796349_n.jpg (Size: 78.67 KB / Downloads: 210)

[Image: 25rnz1y.jpg]

~Buddy
  Reply
#9
A vacuum check will tell you if you need a booster. Good luck
markmel;32226 Wrote:A vacuum check will tell you if you need a booster. Good luck

After reading your edit that it's FORCING fluid out the cover you probably need to check your calipers and see if they are froze up.
The boot in the cover is intended to only make up the difference between new pads with a full system and pad wear. If you topped off the reseviour when the pads were worn out this may be the problem.
So in a nut shell. The easiest way to trouble shoot your problem is:
1. Put all new pads on with the master cylinder cover off.
2. If when you compress the front calipers to install new pads it forces fluid out, you probably had too much fluid in the system.
3. If #2 is true buy a new cover aftere you've replaced your pads (sounds like that may be where the air is coming from) and do a bleed the way I noted earlier. I doubt the problem is much more than that.[/u]
markmel;32226 Wrote:A vacuum check will tell you if you need a booster. Good luck
[u]
markmel;32226 Wrote:A vacuum check will tell you if you need a booster. Good luck

After reading your edit that it's FORCING fluid out the cover you probably need to check your calipers and see if they are froze up.
The boot in the cover is intended to only make up the difference between new pads with a full system and pad wear. If you topped off the reseviour when the pads were worn out this may be the problem.
So in a nut shell. The easiest way to trouble shoot your problem is:
Rocketfoot, How did everything end up underlined? Did I fatfinger something?
What did I do that got everything underlined? Fat finger something or what? Rocketfoot help me out here.
1. Put all new pads on with the master cylinder cover off.
2. If when you compress the front calipers to install new pads it forces fluid out, you probably had too much fluid in the system.
3. If #2 is true buy a new cover aftere you've replaced your pads (sounds like that may be where the air is coming from) and do a bleed the way I noted earlier. I doubt the problem is much more than that.


[Image: 2rr7aiv.png]

Just cruising along minding our own business when BAM!!! The LAWS show up.
  Reply
#10
Fix leaks first to be sure but what is your vacuum at idle and during operation?

Seems you have power brakes and of course vacuum effects operation. I know you are knowledgeable and know this but sometimes we can't see the forest for the trees.

73 conv. 460, D0VE large valve heads, Performer RPM manifold, Voodoo 227/233 cam, Holley 950 HP carb, C6 trans, 3.25 trak-loc.
  Reply
Share Thread:  


Possibly Related Threads...
Thread Author Replies Views Last Post
  Lincoln Continental brake swap ? avarageerod 9 333 02-07-2018, 03:50 PM
Last Post: mustang7173
  Location of parking brake light switch Spechti 11 4,265 02-05-2018, 08:10 AM
Last Post: eddyw
  Brake Discrotor upgrade worth it ? Robsweden 22 662 02-04-2018, 11:53 AM
Last Post: Carolina_Mountain_Mustangs
runninpony PARKING BRAKE CABLE NOT A T5 7 683 01-04-2018, 01:09 PM
Last Post: Hemikiller
  Front disc brake swap master cylinder? Horsin' Around 10 524 12-18-2017, 09:58 PM
Last Post: imusa76
  firewall hacked for pwr brake conversion??? scgamecock 13 721 12-16-2017, 03:37 PM
Last Post: johnwanzel
  Parking Brake Cables cheezsnake 19 1,139 09-17-2017, 03:02 PM
Last Post: cheezsnake
runninpony Brake Register for 9 inch Ford small Bearing Axle mustang7173 8 815 09-07-2017, 11:05 AM
Last Post: Carolina_Mountain_Mustangs



Users browsing this thread: 1 Guest(s)