Classic Mustangs List Archive

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Mail From: Walt Boeninger (email redacted)

Matt.


[from "matt roman"]
>Hey Tony, not being a brake expert at all, tell me what the safety benefit
>of a dual master cylinder is. At first I thought it would be that if if you
>had a sudden leak in one of the lines , lets say a rear line let go, then
>you would have full use of the front brakes.
>But if I remember correctly, when bleeding the brakes, the pedal will go
>completely to the floor if any one of the bleeder valves is open (same as a
>line rupturing.) Am I over looking something?

Let me quote part of my posting yesterday:

The thing that saves you is the differential shuttle valve.
When one side looses pressure, the shuttle gets forced by the
pressure in the good side, and blocks the distribution to the
bad side. During bleeding, you are not (hopefully) pushing
hard enough to actually displace the shuttle. I have seen a
shuttle (67 style) that was so sensitive to pressure that the
lines all had to be full of fluid for it to *not* move while
bleeding using the brake pedal. I always use suction to
bleed so never have the risk of screwing up the shuttle valve.
In this instance, using a vacuum bleeder was the only effective
Way to get the thing bled, plus we had to remove the front fitting
on the distribution block and manually push the shuttle back to the
center.

So during bleeding you will get the pedal to the floor.
But not, hopefully, during a failure....

I have only experienced one brake failure while driving, in my
69 Mach I. I lost the master cylinder. The pedal nearly went to
the floor, i was able to pull over and stop. then the BRAKE WARNING
light came on. It needed that final stomp on the pedal. The
BRAKE WARNING light can only come on *after* you've already felt
the pedal go long. You can lose all the fliud in one end, but
until you hit the pedal, the light won't come on. So it's not a
warning light, it's a FAIL light.

-------
Regards

Walt Boeninger - Nor Cal SAAC 67 GT500 | 67 Shelby T-A #31
norcal-saac.org 71 Boss 351 | 97 5.0 Explorer
mailtoemail redacted) 99 C5 Hdtp | 86 Mustang GT

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This read-only message was archived from a public mail list.
Mail From: matt roman (email redacted)

This explains alot. Thanks for the education Walt.


>From: (email redacted) (Walt Boeninger)
>Reply-To: (email redacted)
>To: (email redacted)
>Subject: Re: [CM] Dual master upgrade...Cheap saf
>Date: Wed, 12 Jul 2000 10:12:19 PDT
>
>Matt.
>
>
>[from "matt roman"]
> >Hey Tony, not being a brake expert at all, tell me what the safety
>benefit
> >of a dual master cylinder is. At first I thought it would be that if if
>you
> >had a sudden leak in one of the lines , lets say a rear line let go, then
> >you would have full use of the front brakes.
> >But if I remember correctly, when bleeding the brakes, the pedal will go
> >completely to the floor if any one of the bleeder valves is open (same as
>a
> >line rupturing.) Am I over looking something?
>
>Let me quote part of my posting yesterday:
>
> The thing that saves you is the differential shuttle valve.
> When one side looses pressure, the shuttle gets forced by the
> pressure in the good side, and blocks the distribution to the
> bad side. During bleeding, you are not (hopefully) pushing
> hard enough to actually displace the shuttle. I have seen a
> shuttle (67 style) that was so sensitive to pressure that the
> lines all had to be full of fluid for it to *not* move while
> bleeding using the brake pedal. I always use suction to
> bleed so never have the risk of screwing up the shuttle valve.
> In this instance, using a vacuum bleeder was the only effective
> Way to get the thing bled, plus we had to remove the front fitting
> on the distribution block and manually push the shuttle back to the
> center.
>
>So during bleeding you will get the pedal to the floor.
>But not, hopefully, during a failure....
>
>I have only experienced one brake failure while driving, in my
>69 Mach I. I lost the master cylinder. The pedal nearly went to
>the floor, i was able to pull over and stop. then the BRAKE WARNING
>light came on. It needed that final stomp on the pedal. The
>BRAKE WARNING light can only come on *after* you've already felt
>the pedal go long. You can lose all the fliud in one end, but
>until you hit the pedal, the light won't come on. So it's not a
>warning light, it's a FAIL light.
>
>-------
>Regards
>
>Walt Boeninger - Nor Cal SAAC 67 GT500 | 67 Shelby T-A #31
>norcal-saac.org 71 Boss 351 | 97 5.0 Explorer
>mailtoemail redacted) 99 C5 Hdtp | 86 Mustang GT
>
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>mix.twistedpair.ca/mailman/listinfo/classic-mustangs

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Mail From: Keven Coates (email redacted)

> > bad side. During bleeding, you are not (hopefully) pushing
> > hard enough to actually displace the shuttle.

I have a tool that screws into the brake light sensor fitting on the shuttle
valve that will keep it centered during brake bleeding. It's nothing more
than a threaded rod that has a nib on it to forcefully retain the shuttle
valve in it's middle position. My father had it, and I have no idea where
he got it, but it would be easy to duplicate.

Yes, I've had a brake failure as well, and the light is truly a "fail light"
I didn't even reconnect it. It's worthless. If I have a brake problem I
can feel it, usually long before it fails.

One thing to keep in mind during a failure is once the pedal goes to the
floor, you can pump it again (if you have time). This will hopefully pull
the pressure up enough to slow you down so you can pull over. Sometimes
just hitting the pedal once to the floor won't do it with a bad leak.

Thanks.

Best Regards,
Keven D. Coates
Internet Audio Group


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Mail From: Walt Boeninger (email redacted)

[from "Keven Coates"]
>> > bad side. During bleeding, you are not (hopefully) pushing
>> > hard enough to actually displace the shuttle.
>
>I have a tool that screws into the brake light sensor fitting on the shuttle
>valve that will keep it centered during brake bleeding. It's nothing more
>than a threaded rod that has a nib on it to forcefully retain the shuttle
>valve in it's middle position. My father had it, and I have no idea where
>he got it, but it would be easy to duplicate.

Now that would have come in handy for my buddy! I've never heard
of it. Wonder if it's something someone homemade...great idea...
I'm usre it's not mentioned in the 67 Shop Manual..I've read it
many times. I'm gonna look right now...

-------
Regards

Walt Boeninger - Nor Cal SAAC 67 GT500 | 67 Shelby T-A #31
norcal-saac.org 71 Boss 351 | 97 5.0 Explorer
mailtoemail redacted) 99 C5 Hdtp | 86 Mustang GT

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