On way home from City all was well on car… few miles into return trip home the hydraulic brake assist dissapeared, abruptly.
Stopped after about 25 miles of mashing foot to floor to stop the car, I found no leaks under hood and green mineral oil reservoir looks OK as did the levels in the dual master cylinder… No unusual noises from the radial hydraulic pump (engine idling nice) or any unusual noises.
My suspicion is on the of solenoids (two) on the aluminum valve body are not operating and is remaining CLOSED…
Relays under passenger panel to check or Volts on solenoids??
?? Any thoughts?
It sure seems electrical
When the system failed to pump up I seem to recall I removed the cover from the relay and manually triggered the pump to run, I think the low pressure switch had failed. I just had to remember to reach under the dash to close the points after a brake application. A replacement LP switch fixed that problem
This 1989 XJ6 has the radial mechanical pump but maybe the LP switch on accumulator is not closing on the valve body assembly and letting the pressure charge up?.. I have voltage at the yellow connector plug (plus volts on white slate wire and negative volts on yellow and black wire) to the valve body…
I have a LED monitor between WHITE and SLATE wire positive and YELLOW and BLACK wire negative that seems to indicate the LOW pressure switch is connected… though and LED monitor (I installed on yellow connector) does not mean there is enough current to operate the LOAD solenoid (LOAD is name on JAG schematic for one of 3 solenoids) .
Still donw know what happened to brakes. Thoughts?
super…great idea… JAGLOVERS is super helpful for all JAG owners… will check OHMS on 3 solenoids tomorrow and check wiring on what I believe for 89 is only a single LOW PRESSURE switch mounted on same aluminum assembly as the accumulator sphere…
Any ideas?
Hi there, I had exactly the same problem with my 1990 XJ40. Turned out it was an in line fuse in the footwell. Took about 10 minutes to locate and replace for a couple of dollars. Hope this helps.
Thanks for the help. Wish I had a 90 they did use an electric hydraulic pump… not so on
88-89 XJ40 they used an engine driven radial 3 piston mini pump bolted to front of
engine… but rest of 88-89 system is fairly complicated…
Additional Data
Car off checked the 2 switches on the accumulator sphere assembly one was open (Yellow Black wire & Black–CHARGE) the other closed (Yellow Red wire and Black–LOW PRESSURE) at the GREEN Amphenol connector.All seems normal as per posts on Jaglovers and schematics.
Plugged green connector back together…
Disconnected YELLOW connector to Girling valve body
The Charge Solenoid measured 30 ohms. All looks normal.
Started Car, foot on brake, no power assist no normal pedal drop, still low pressure
warning on dash VCM and of course no power assist.
Stopped engine left KEY on
Mechanics Stethoscope on CHARGE solenoid (top of assembly towards front of car) ,
alternately disconnected its POWER–YELLOW connector, on off, on off,— (it was getting
12 volts) --we years back installed charge volts monitor LED & resistor on this connector
it was nicely light up—
Stethoscope on CHARGE solenoid I could hear a small but distinct CLICK inside as I opened
and closed the power to it. Again it seems OK.
On Green connector SHORTED Yellow Black wire to Black wire CHARGE switch-- still LOW PRESSURE warning on dash VCM
Reading mores posts. It appears sudden loss of power assist could be.
Charge valve not opening or its clogged
Hydraulic BOOST at master cylinder its SPOOL VALVE my be stuck allowing high pressure
fluid to pass right through the booster and not getting any booster boost (BB to Jagmen).
Removing Charge solenoid may be next step look for micro dirt.
I have a brand new hydraulic booster… maybe Ill swap lines temporary leave the old
booster mechanically connected (seems complicated to release its front clevis connection)
but swap the 2 hydraulic lines to new booster and see if LOW PRESSURE on dashboard VCM
goes away. That would tell me it is the spool valve…
Not sure why I could not just block the High Pressure lied to the booster with say a
cap??? and see if it then builds pressure and turns off the dashboard LOW PRESSURE
warning.
I have a Waken pressure gauge maybe check for high pressure at inlet but not sure If I
have the proper connector…
Anyone tried just blocking the boosters HPressure line and see of the LOW PRESSURE
warning goes away??
“Hi there, I had exactly the same problem with my 1990 XJ40. Turned out it was an in line fuse in the footwell. Took about 10 minutes to locate and replace for a couple of dollars.”
Thanks for the help. Wish I had a 90 they did use an electric hydraulic pump… not so on 88-89 XJ40 they used an engine driven radial 3 piston mini pump bolted to front of engine… but rest of 88-89 system is fairly complicated…
Additional Data
Car off checked the 2 switches on the accumulator sphere assembly one was open the other closed at the GREEN Amphenol connector.All seems normal as per posts on Jaglovers.
Plugged green connector back together…
Disconnected YELLOW connector to Girling valve body
The Charge Solenoid measured 30 ohms. All looks normal.
Started Car, foot on brake, no power assist no normal pedal drop, still low pressure warning on dash VCM and of course no power assist.
Stopped engine left KEY on
Mechanics Stethoscope on CHARGE solenoid (top of assembly towards front of car) , alternately disconnected its POWER–YELLOW connector, on off, on off,— (it was getting 12 volts) --we years back installed charge volts monitor LED & resistor on this connector it was nicely glowing red—
Stethoscope on CHARGE solenoid I could hear a small but distinct CLICK inside as I opened and closed the power to it. Again it seems OK.
Reading mores posts. It appears sudden loss of power assist could be.
Charge valve not opening or its clogged
Hydraulic BOOST at master cylinder its SPOOL VALVE my be stuck allowing high pressure fluid to pass right through the booster and not getting any booster boost (BB to Jagmen).
Removing Charge solenoid may be next step look for micro dirt.
I have a brand new hydraulic booster… maybe Ill swap lines temporary leave the old booster mechanically connected (seems complicated to release its front clevis connection) but swap the 2 hydraulic lines to new booster and see if LOW PRESSURE on dashboard VCM goes away. That would tell me if it’s the spool valve…
Not sure why I could not just block the High Pressure lied to the booster with say a cap??? and see if it then builds pressure and turns off the dashboard LOW PRESSURE warning.
I have a Waken pressure gauge maybe check for high pressure at inlet but not sure If I have the proper connector…
Anyone tried just blocking the boosters HPressure line and see of the LOW PRESSURE warning goes away??