| Can booster hold vacuum and not boost [message #324732] |
Mon, 09 October 2017 08:01  |
Tilerpep
Messages: 404
Registered: June 2013
Location: Raleigh, NC
Karma: 7
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Senior Member |
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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
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| Re: Can booster hold vacuum and not boost [message #324740 is a reply to message #324732] |
Mon, 09 October 2017 10:42  |
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wally
Messages: 643
Registered: August 2004
Location: Omaha Nebraska
Karma: 5
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Tilerpep wrote on Mon, 09 October 2017 08:01Big 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
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| Re: Can booster hold vacuum and not boost [message #324743 is a reply to message #324740] |
Mon, 09 October 2017 11:48 |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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Senior Member |
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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
2012 Phoenix Cruiser model 2552
KA4CSG
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| Re: Can booster hold vacuum and not boost [message #326121 is a reply to message #324732] |
Fri, 17 November 2017 19:06 |
Tilerpep
Messages: 404
Registered: June 2013
Location: Raleigh, NC
Karma: 7
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Senior Member |
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Well, chalk this one up to "just because you just put that part on, doesn't mean it's good" category.
I went around the neighborhood several times over a few weeks to check things and hope the pads would bed or some other self correcting thing. Noticed the front of the brake booster getting wet after third trip. Yep, the input/back of the master cylinder was leaking. Put another one on and voila, high pedal, confident brakes. If it hadn't leaked to go with the functional problem I would have chased my tail for who knows how long.
To add more facts as a cautionary tale: it was a Raybestos unit that had sat in the coach, uninstalled (dry) for a few years from PO. It looked fine, buy maybe it got a little humidity/rust in the bore that then tore up the seals when I bled and installed it. who knows.
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
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