| Author |
Message |
    
Jason Stables
New User
Username: jase
Post Number: 3
Registered: 06-2025
| | Posted on Monday, 09 February, 2026 - 16:51: |    |
Hi
So, I have an odd brake pump problem hoping someone has had similar and can point me in right direction
76 Corniche
I put a rebuild kit (springs and O-rings) in hydraulic pump and refitted
Have ZERO pressure on gauge, removed high pressure line and directed pump outlet into clear container
Zero flow????
Suspected an air lock, so I sucked couple hundred mls fluid through pump with big syringe
Tried again, still zero flow !!
Removed new reservoir filter to check for blockage is perfectly clean
Hose reservoir to pump is new and perfect
Started engine and looked in open reservoir can see pump backflowing in fluid ?
(remember at this stage my pump is flowing (or not) into container, so this isn’t forward flow though system)
Putting my finger over reservoir outlet hole, fluid is moving back and forth (not sucking like it should be)
OK surely something isn’t together correctly in pump
Removed pump disassembled and checked assembly and all looks fine
Was a tiny scratch in check valve face, so lapped in with grinding compound (not perfect but is 99%)
Reassembled, refitted to car and retested, is same (no flow)
Something’s not correct but I can’t work out what
Any clues before I go insane??
For context
Problem first occurred at end of brake system refresh (replaced all flexible hoses, cleaned reservoir, replaced reservoir filters, rebuilt all callipers)
Was bleeding system when lost all pressure on one circuit ???
Attached pressure gauge to confirm circuit had zero pressure ☹
Suspected broken pushrod (or possibly spring)
Sourced parts removed brake pump to find pushrod intact and no broken springs???
Put the rebuild kit (springs and O-rings) through pump while it was apart anyway and refitted
Zero, nothing, simple job but it’s driving me crazy
Anyone?? |
Brian Vogel
Grand Master
Username: guyslp
Post Number: 3459
Registered: 06-2009
| | Posted on Tuesday, 10 February, 2026 - 01:13: | |
Have you looked at the condition (or tried to rebuild) your accumulator control valves? Even if the pump were working perfectly, if something's wrong there, the entire "orchestration" of the system goes kerflooie, as the ACV is the conductor.
Definitely start by checking the pressure at the bleed screw on the ACV itself.
If fluid is at least circulating back to the reservoir, there should be a noticeable "bump" in the fluid above the return port when that's happening. Your overall description makes me thing that the ACV is somehow stuck in bypass mode rather than cycling between charge and bypass mode as it should.
Brian |
Geoff Wootton
Grand Master
Username: dounraey
Post Number: 2372
Registered: 05-2012
| | Posted on Tuesday, 10 February, 2026 - 02:56: | |
Another possibility is you have a worn camshaft lobe that's preventing the pushrod from rising to it's full extent, meaning the pump is being severely compromised. It's worth checking. |
Jason Stables
New User
Username: jase
Post Number: 4
Registered: 06-2025
| | Posted on Tuesday, 10 February, 2026 - 05:45: | |
hi Brian
right now the pump isn't connected to the ACV (or circuit) the high pressure output from pump is redirected to clear bottle
I almost pulled ACV to strip it down before I realised it wasn't getting ANY fluid
the bump you mention is pronounced (x times larger than normal) and over the outlet port (as in where filter should be) the other circuit has the normal pump over return port (easy to compare, no memory involved)
hi Geoff
not saying cam isn't worn (i didn't measure the lift) but pushrod is moving what appears to be normal amount, I'm not talking no flow here, I have zero flow, even badly worn pump, leaking check valve and worn lobe should push some fluid ??
I shall remove pump again, something must be installed wrongly
thanks
Jase |
Jason Stables
New User
Username: jase
Post Number: 5
Registered: 06-2025
| | Posted on Tuesday, 10 February, 2026 - 16:33: | |
So, I pulled the pump out again, disassembled, checked assembly (order) was correct, inspected closely with magnifying glass, reassembled, refitted & started engine (with discharge still into container) still nothing !!
pulled pump off engine again, checked pushrod again, roughly checked pushrod stroke (cam lobe) OK
disassembled pump again, inspected again and reassembled again and refitted started engine again still nothing !!!!!
crazy, these pumps really are a very simple thing, why wont it pump !!!
after a lot of head scratching (maybe a little swearing) I had idea to start engine while pulling a vacuum on the pump discharge
bingo, flow started, measured flow looks good
connected pump discharge back to car (connect high pressure line) start engine 1000psi almost immediately climbed to 2300-2400 as expected
all I can think is it had the mother of all airlocks ??
anyway, system is perfect now, very happy ………now (wasn’t before)
accumulator pressures are good
maybe this can be a lesson for the next guy |
Mark Aldridge
Frequent User
Username: mark_aldridge
Post Number: 904
Registered: 10-2008
| | Posted on Tuesday, 10 February, 2026 - 20:45: | |
Jason, have you cleaned the filters in the fluid tank, and have these collapsed ( very common). Mark |
Jason Stables
New User
Username: jase
Post Number: 6
Registered: 06-2025
| | Posted on Wednesday, 11 February, 2026 - 05:45: | |
hi Mark
better than that the filters were replaced (new)
thanks
Jase |
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