Author Topic: 68 brake issue  (Read 1025 times)

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Offline sah62

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Re: 68 brake issue
« Reply #15 on: February 11, 2019, 06:02:39 am »
My LF.  Reckon I got them on wrong.   I'll swap them out tomorrow, everything will probably work just fine.

If the bleeder is pointing up you almost certainly have an air pocket in the caliper that can't be bled out. Good luck with the swap - it should make an improvement.
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Offline RoyceP

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Re: 68 brake issue
« Reply #16 on: February 11, 2019, 09:42:00 am »
Classic backwards caliper install. Whoever is telling you they need to face upwards is wrong.


My LF.  Reckon I got them on wrong.   I'll swap them out tomorrow, everything will probably work just fine.
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Offline Coralsnake

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Re: 68 brake issue
« Reply #17 on: February 13, 2019, 02:19:59 pm »
Winning!

Offline 67428GT500

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Re: 68 brake issue
« Reply #18 on: February 13, 2019, 04:17:35 pm »
Can you take a picture of the distrubution/proporting vavle and post?
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Offline smines80

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Re: 68 brake issue
« Reply #19 on: February 17, 2019, 02:14:08 pm »
Got it fixed guys, all thanks to Teeling.  The shuttle valve in the distribution block wasnt centered.  Opened up the LR bleeder, pushed the pedal until I could see the shuttle valve centered, then closed that bleeder.  Now got pressure to the LF to hold the rotor!

Offline sah62

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Re: 68 brake issue
« Reply #20 on: February 17, 2019, 03:10:17 pm »
Got it fixed guys, all thanks to Teeling.  The shuttle valve in the distribution block wasnt centered.  Opened up the LR bleeder, pushed the pedal until I could see the shuttle valve centered, then closed that bleeder.  Now got pressure to the LF to hold the rotor!

An off-center piston shouldn't cause the problem you described. It should cause the brake warning lamp on your dish to be lit, but that's it. On the other hand, it's hard to argue with success...
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Offline 67428GT500

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Re: 68 brake issue
« Reply #21 on: February 17, 2019, 04:10:18 pm »
Isn't that what we've been discussing for days in PM. You're welcome. 
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Offline smines80

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Re: 68 brake issue
« Reply #22 on: February 17, 2019, 07:39:29 pm »
67428GT500, no you were telling me to center the proportioning valve.  It was the shuttle valve in the block that was off centered.  And as far as me having this issue, when I shouldnt have.  Who know's, were talking about a new reproduction distribution block and probably made in China.  May not work exactly like one build by Ford in 1968.  It sure was fun driving it out of the garage today.  Hasnt done that in over 30 years! 

Offline 67428GT500

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Re: 68 brake issue
« Reply #23 on: February 17, 2019, 08:23:06 pm »
Yes, the pin floats front to rear as the pressure is disproportionate from front to rear of the master cylinder. That is a safety feature if there is a loss of fluid to either the front of rear system. Hence the reason the light/circuit was completed on the switch. That block is the proportioning valve.  I explained that, hence the reason for the tool to lock the valve centered.  The small tubular valve isn't a proportioning valve that is a part of that assembly, but a pressure differential. It holds a slight amount of residual pressure in the line to the rear brakes.

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Online 70cj428

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Re: 68 brake issue
« Reply #24 on: February 17, 2019, 10:40:47 pm »
Quote
An off-center piston shouldn't cause the problem you described. It should cause the brake warning lamp on your dish to be lit, but that's it. On the other hand, it's hard to argue with success...

+1 , If I'm Not Mistaken .... (My standard disclaimer), the shuttle valve in the distribution block on a 67-69 mustang shouldn't effect brake pressure at all, all it does is light the light when a pressure differential between the front and rear brake systems is detected. Scott (sah62) is definitely the resident expert on these valves and blocks as he's probably still seeing "O" rings in his sleep after developing the rebuild kits..

Quote
The small tubular valve isn't a proportioning valve that is a part of that assembly, but a pressure differential. It holds a slight amount of residual pressure in the line to the rear brakes.

Actually, the round (tubular) valve in series with the rear brake line that's clamped on the mounting bracket is the proportioning valve on a 68 or 69 Mustang. ( the same valve is clamped to the rear rail by the back tire on a 67, it can be anywhere in the line to the back brakes. ) The residual pressure valve(s) you mentioned are located just behind the seats where the lines connect in the master cylinder body.

If I had to guess, you probably bled out some residual air while trying to center the shuttle valve. Whatever you did that actually fixed it, be glad it's fixed. I just played hell trying to bleed the fronts on a 70 mach 1, it ended up being a defective Chinese master cylinder .....

JMHO, John
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Offline RoyceP

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Re: 68 brake issue
« Reply #25 on: February 18, 2019, 10:14:49 am »
Correct, the centering of the indicator light switch is what turns the idiot light off. That has zero effect on the brakes or bleeding them properly. Until you fix the swapped calipers you won't be able to bleed the brakes properly.

The proportioning valve restricts flow to the rear brakes but allows full flow for fluid returning to the master cylinder when the pedal is released. There are no residual valves in the '68 brake system.


Quote
An off-center piston shouldn't cause the problem you described. It should cause the brake warning lamp on your dish to be lit, but that's it. On the other hand, it's hard to argue with success...

+1 , If I'm Not Mistaken .... (My standard disclaimer), the shuttle valve in the distribution block on a 67-69 mustang shouldn't effect brake pressure at all, all it does is light the light when a pressure differential between the front and rear brake systems is detected. Scott (sah62) is definitely the resident expert on these valves and blocks as he's probably still seeing "O" rings in his sleep after developing the rebuild kits..

Quote
The small tubular valve isn't a proportioning valve that is a part of that assembly, but a pressure differential. It holds a slight amount of residual pressure in the line to the rear brakes.

Actually, the round (tubular) valve in series with the rear brake line that's clamped on the mounting bracket is the proportioning valve on a 68 or 69 Mustang. ( the same valve is clamped to the rear rail by the back tire on a 67, it can be anywhere in the line to the back brakes. ) The residual pressure valve(s) you mentioned are located just behind the seats where the lines connect in the master cylinder body.

If I had to guess, you probably bled out some residual air while trying to center the shuttle valve. Whatever you did that actually fixed it, be glad it's fixed. I just played hell trying to bleed the fronts on a 70 mach 1, it ended up being a defective Chinese master cylinder .....

JMHO, John
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Offline smines80

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Re: 68 brake issue
« Reply #26 on: February 18, 2019, 01:48:34 pm »
The four brakes bleed just fine, even with the front calipers installed wrong.  Swapping them didnt fix the low pressure issue I had with the LF.  Getting the shuttle valve back to center did.  And if the shuttle valve in the block has nothing to do with bleeding or pressure, why is there a special tool to hold the shuttle valve in center, while you bleed the brakes?  Some of y'all think you know everything and cant admit "geez I didnt know that".  I'm done with this thread, I appreciate the help from those that did try.         

Offline RoyceP

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Re: 68 brake issue
« Reply #27 on: February 18, 2019, 03:07:49 pm »
Holding it in the center turns the light off. The switch - it is not a "shuttle valve" - doesn't have any effect on the brakes at all. You need to hold it in place while bleeding the brakes so that the light will be off when you are done. Bleeding the brakes makes the switch turn on because it thinks there is a differential pressure failure.

The four brakes bleed just fine, even with the front calipers installed wrong.  Swapping them didnt fix the low pressure issue I had with the LF.  Getting the shuttle valve back to center did.  And if the shuttle valve in the block has nothing to do with bleeding or pressure, why is there a special tool to hold the shuttle valve in center, while you bleed the brakes?  Some of y'all think you know everything and cant admit "geez I didnt know that".  I'm done with this thread, I appreciate the help from those that did try.       
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Offline 69cobrajetrugae2

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Re: 68 brake issue
« Reply #28 on: February 18, 2019, 04:40:59 pm »
+1 Royce.

Bleeding brakes on our cars is a non issue to most of us because we understand what's happening.

That tool is silly and useless unless a customer insists on buying one, then the customer is always right.

I never thought a qualified person would have a problem with bleeding brakes.

Here is how I've always charged a dry brake system.

Fill up the reservoir and cap it.

Crack the passenger rear bleeder valve and attach a tube to a coffee can.

Reach down and slowly depress and release the brake pedal a few times.  Don't bury it to the floorboard, just a couple of inches!

Wait a half hour or until brake fluid is witnessed in the coffee can then I repeat the process on the drivers rear, passenger front, and lastly the drivers front brakes.

Using the assistant pumping the pedal can warp and damage seals because trapped air under 1200 PSI can be forced through a seal which is designed to retain brake fluid.

Online 70cj428

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Re: 68 brake issue
« Reply #29 on: February 18, 2019, 06:06:20 pm »
Quote
Swapping them didnt fix the low pressure issue I had with the LF.  Getting the shuttle valve back to center did.  And if the shuttle valve in the block has nothing to do with bleeding or pressure, why is there a special tool to hold the shuttle valve in center, while you bleed the brakes?  Some of y'all think you know everything and cant admit "geez I didnt know that". 

The special tool avoids the unpleasant, time consuming , messy situation of recentering the valve by bleeding the opposing side of the system. Aside from being messy, it's hard to determine which side the valve is shifted to, so centering it can be a real hassle. By removing the switch, and installing the tool, the problem is solved....

I kinda thought that this thread was going to go this way, and I had thought about just keeping my mouth shut. However, these threads live on forever (Theoretically) and a lot of others with the same issue may reference this thread for years to come so accurate info is important. Fortunately, this forum isn't like facebook that has more than it's share of mental midgets. There's a ton of Knowledge here, from guys with 30-40 years of experience with these cars, including several engineers  (some who actually did developmental work on these cars when they were new.) (Scott, who's answer you don't agree with, has probably disassembled and analyzed dozens of these valves developing the kits to rebuild them)

Another way to look at this is that ford would never design the system to limit the pressure to just one front wheel in the event of a hydraulic failure, the result would be an asymmetric application of braking force and the car darting right or left when you hit the brakes just when you needed all the braking help you could get.

I'd be the first to admit "geez I didnt know that" If I wasn't confident of my answers   ( If I wasn't confidant of an answer, I wouldn't offer any advice in the first place....)  Get to know some of the guys on here before you question there intelligence....

JMHO, John

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70 "Q" code Mach1, Grabber Green / White, Auto,AC
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