I have just ,in the last year, coverted the brakes on my '89 from
abs to standard brakes. The cars has been in the shop for 4 months
being painted. I have been driving it for a week. Today the
brakes became very hard, as if no brake boost. The booster and the
master cylinder are new. The vac hose still has plenty of vac.
Did the new booster fail? I was looking through the book and
noticed the type of hose used between the resevoir and master
cylinder had to be a specific type. I cant remember what it is but
I bet it is not correct. Could this cause this?–
Texarkana Autobahn
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If you have vacuum, with the engine running, at the large (~3/8" ID)
vaccum hose that attaches to the booster vacuum fitting, but a hard
pedal, then likely the booster diaphragm has failed. You can test the
booster diaphragm by putting a vacuum pump (MityVac or the like) on
booster vaccum fitting and seeing if it will hold a vacuum. If you are
using a hand pump like the MityVac, you will have to pump it 5 - 10
times before you see a significant change on the gauge, as there is a
considerable air volume in the booster.
I’m not sure what you are describing as “hose used between the
reservoir and master cylinder.” Are you referring to the vacuum
reservoir or the brake fluid reservoir? If you are referring to a
vacuum hose, any decent brand of vacuum hose (that won’t collapse and
plug the vacuum line) should work. If you are describing a hose that
carries brake fluid from the fluid reservoir to the master cylinder,
then you need a rubber compound that is rated to handle brake fluid,
and I don’t know what that spec is.
Of course, there may be a mechanical problem in the pedal linkage,
booster or master cylinder that is restricting master cylinder travel,
depending upon what was done in the conversion. That would demand close
scrutiny for safety purposes.
George Balthrop, Clifton, VA USA
85 & 89 XJ-S Coupes; 89 XJ40 VDP-----Original Message-----
From: LotusGuy cccmitchell@netzero.com
I have just ,in the last year, coverted the brakes on my '89 from
abs to standard brakes… Today the
brakes became very hard, as if no brake boost. The booster and the
master cylinder are new. The vac hose still has plenty of vac.
Did the new booster fail? I was looking through the book and
noticed the type of hose used between the resevoir and master
cylinder had to be a specific type. I cant remember what it is but
I bet it is not correct. Could this cause this?
AOL now offers free email to everyone. Find out more about what’s free
from AOL at AOL.com.
I replaced everything from the pedal box forward. Simple bolt up
install. When I put a vacuum on it, it will hold a vacuum. When I
depress the pedal, and the engine is running, a have a sucking
noise from the pedal box. I think it is just a bad booster.–
The original message included these comments:
Of course, there may be a mechanical problem in the pedal linkage,
booster or master cylinder that is restricting master cylinder travel,
depending upon what was done in the conversion. That would demand close
scrutiny for safety purposes.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
4
LotusGuy wrote:
I replaced everything from the pedal box forward. Simple bolt up
install. When I put a vacuum on it, it will hold a vacuum. When I
depress the pedal, and the engine is running, a have a sucking noise
from the pedal box.
Yep, that’s a bad booster. I had a similar failure once, but it was
on a Honda – with a carburetor. When you pressed on the brake
pedal, you heard the sucking noise from the footwell and the engine
tried to die. With EFI, the engine won’t try to die – in fact, I
think it’ll try to speed up, just what you need when your brakes
aren’t working!
depress the pedal, and the engine is running, a have a sucking
noise from the pedal box. I think it is just a bad booster.
A few years back I took my booster (servo, whatever) to a local
rebuilder.
He looked at it and said, “That looks just like a Chevy.” I was out of
there in 10 minutes with a rebuilt.
In reply to a message from LotusGuy sent Sat 26 May 2007:
A quick way to test for booster vacuum is to hold your foot on the
brake while starting the engine. If the brake pedal eases down a
bitonce the engine starts, the booster is working. If the pedal
doesn’t move when the engine starts, then it isn’t…–
345 DeSoto
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