Brake Booster => Combo Valvetorhome

[donald w. miller]

Hi Scott,

I got excited over this one.

Looked and my 75 book shows a dual master cylinder with front and rear lines
running back to the proportioning valve.

This indicates it is redundant system and you should always have either
front or rear when the other fails.

Whew ....... dodged another bullet.

Cheers,

Don and Margaret Miller
1975 Glennbrook in pieces
Shenandoah Valley of Virginia

>
>So therefore, I'm NOT correct in thinking or hoping that we have this
>independence. If we get a leak somewhere, we have no brakes except for
cable
>driven rear emergency brakes, right? If yes/ that sucks! If yes/ can
>anything be done to upgrade to newer two part master cylinder?
>
>Scott Adohen
>

 

[bartz paul]

Don:

I don't believe you can claim it's a redundant system, which infers a backup
system. They are two separate circuits (i. e. front brakes and rear
brakes).

You can say that if one chamber leaks/looses fluid, then the other should
still afford some degree (either the front or the rear, but not both
circuit's) of braking capability.

Also, slap yourself silly , say "combination" and not "proportioning"
valve.

Paul Bartz

From: Donald W. Miller [mailto:millerdw]
Sent: Friday, March 05, 1999 3:29 PM
Subject: Re: GMC: Brake Booster => Combo Valvetorhome

Hi Scott,

I got excited over this one.

Looked and my 75 book shows a dual master cylinder with front and rear lines
running back to the proportioning valve.

This indicates it is redundant system and you should always have either
front or rear when the other fails.

Whew ....... dodged another bullet.

So therefore, I'm NOT correct in thinking or hoping that we have this
independence. If we get a leak somewhere, we have no brakes except for
cable driven rear emergency brakes, right? If yes/ that sucks! If yes/
can anything be done to upgrade to newer two part master cylinder?

Scott Adohen

 

[bartz paul]

Emery:

If you have access to the Brake Handbook, by Fred Puhn, he says the
combination valve is commonly installed in American vehicles having front
disc and rear drum brakes. Its purpose is to overcome the time delay
inherent in the application of the mechanical linkage components inside the
brake drum vs. the front brake calipers once the brake pedal is activated.

Paul Bartz

From: EMERYSTORA [mailto:EMERYSTORA]
Sent: Friday, March 05, 1999 4:19 PM
Subject: Re: GMC: RE: Brake Booster => Combo Valvetorhome

say "combination" and not "proportioning" valve.

Either is correct. I believe that you'll find more mechanics using
"proportioning valve" than use the term "combination valve" even though the
GMC manual does say combination.

My dad had a garage with mechanics when I was a kid, 1950-60's. I recall
the term proportioning from that time.

 

[donald w. miller]

Gosh Paul,

I almost failed the third grade because I couldn't spell combination, so I
avoid that word as much as I can. Even now as I type it, I get a nervous
tic.

OK, the GM manual does call it a combination valve. Guess I'll have to go
along, since that is the official word bestowed upon us by some high ranking
GMCMH technical writer.

I even understand why he named it so, for it seems to be a combination of :

1. A proportioning valve (ooops, bite my tongue)
2. A failure switch
3. Maybe some yet to be discovered stuff
inside if someone ever opens one up.

I used redundant to mean "two separate systems" since the question was one
or two.

Your definition seems to be "a backup system".

My library is in storage while we live in this tiny apartment, and our cheap
dictionary only defines redundant as "excess" or "superfluous" or "wordy".
None describes my GMC's brakes, except I'll get plenty "wordy" if they fail.

Regardless of word usage, perhaps we agree front and rear brake
systems are almost independent and almost isolated from one another and you
probably will have some limited braking ability remaining if either the
front or rear system fails.

On the other hand, If that single brake pedal snaps off under your foot or
the "O" ring in that "valve thing" fails simultaneous with a front or rear
brake system failure, you better have a hard working guardian angel and
a good insurance policy.

Semantically yours,

Don Miller
75 Glennbrook
Shenandoah Valley of Virginia

>Don:
>
>I don't believe you can claim it's a redundant system, which infers a
backup
>system. They are two separate circuits (i. e. front brakes and rear
>brakes).
>
>You can say that if one chamber leaks/looses fluid, then the other should
>still afford some degree (either the front or the rear, but not both
>circuit's) of braking capability.
>
>Also, slap yourself silly , say "combination" and not "proportioning"
>valve.
>
> Paul Bartz