Can booster hold vacuum and not boost

[tyler]

Big update! The 78 Royale I got in January went around the block for the first time since April! Gas thanks in...now tuning and drivability.

I replaced almost everything on the bakes from the mc to the rear wheels. Mc, new lines, new rubber lines front and rear, new shoes pads, calipers.
But it still took two feet on the pedal a few times. The vacuum booster looks original, holds a vacuum over time (it hisses when i pull of the one way
valve) but the pedal feel indicates no real boost. I have an uninstalled metric booster from the P.O., but don't want to trade for the slow leak and
figment problem to the mc that Dave lenzi has said can happen if this one is not the problem.

Also, i did not change the valve thing by driver wheel. Seems to me that if fluid flowed to bleed brakes, that valve isn't constricting. Include the
info in case i may be wrong

--
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC

 

[wally anderson]

> Big update! The 78 Royale I got in January went around the block for the first time since April! Gas thanks in...now tuning and drivability.
>
> I replaced almost everything on the bakes from the mc to the rear wheels. Mc, new lines, new rubber lines front and rear, new shoes pads,
> calipers. But it still took two feet on the pedal a few times. The vacuum booster looks original, holds a vacuum over time (it hisses when i pull of
> the one way valve) but the pedal feel indicates no real boost. I have an uninstalled metric booster from the P.O., but don't want to trade for the
> slow leak and figment problem to the mc that Dave lenzi has said can happen if this one is not the problem.
>
> Also, i did not change the valve thing by driver wheel. Seems to me that if fluid flowed to bleed brakes, that valve isn't constricting. Include
> the info in case i may be wrong

On vehicle booster testing is described on page 5-37 of a service manual. I can send you a page scan, Pm with your email. Can't get the darn thing to
copy paste on here.
--
Wally Anderson
Omaha NE
75 Glenbrook
Megasquirt III injection
Bob Stone hydroBOOOOST
Manny reaction arm system
Branscombe Kelsey Hayes park brake
http://wallyandsue.blogspot.com/

 

[thomas phipps]

The little OEM iron brake valve that you did not replace can be the source of many varied problems. If you do not have one, get the brass one to
replace it. The iron valve can rust into permanent position and appear to be okay, but the internal valve will not slide and do it's job. At least
push the pin on the front of the valve and see if it moves. No movement, it's toast.
Your description of the problem sounds like air in the lines.
Tom, MS II
--
1975 GMC Avion
KA4CSG

 

[Jim Hupy]

When you have exhausted all the remedies but one, and still have the
problem, it pretty much tells you where to look next. The original
distribution valve is made for combination disc/drum systems. If you have
rusty crud in your master cylinder, you will have it in the distribution
valve also. If it is frozen up, replace it. It is a pain in the a##, and
you will twist off at least one brake line, but, that is the nature of the
beast.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

The little OEM iron brake valve that you did not replace can be the source
of many varied problems. If you do not have one, get the brass one to
replace it. The iron valve can rust into permanent position and appear to
be okay, but the internal valve will not slide and do it's job. At least
push the pin on the front of the valve and see if it moves. No movement,
it's toast.
Your description of the problem sounds like air in the lines.
Tom, MS II
--
1975 GMC Avion
KA4CSG

_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org