N600 master cylinder check valves

[Greg Prentice]

Hello all.
I have removed the booster and sent it to Karps for rebuild.
I plumbed the master cylinder outlet direct to front brakes.
First road test was fine more effort to brake but ok.
Second  test the front started binding again.
Got home relieved brake pressure at master cylinder outlet and brakes released immediately&..
I will remove the check valve and thoroughly clean again&.
Anyone know why these check valves are needed?
MCs on other cars do not have them&.
Thanks.

[dereks600]

Here is my take but it might be wrong... There are two different check valves (see pics on this forum under albums/ Derek's N600 project ; they are the only pics in there)    Flow to the brakes occurs by lifting the check valve against the spring and off the seat.  Reverse flow back to the master occurs by lifting the small rubber disc inside the check valve.  This small rubber disc would provide resistance to reverse flow and a small residual pressure. Where the check valve seals is the difference between the two check valves.  One has a small notch in the sealing ridge where it contacts the seat.  This notch would allow a low volume free reverse flow.
    In general, drum brakes need some residual pressure to reduce pedal travel and application time.  When I assembled mine, I put the check valve with the notch on the front brakes so there was no residual pressure and the one without the notch on the rear.  It seemed to work fine that way.
   As of a couple years ago, you could still purchase one of the check valves from the dealer, I think it was the one with the notch but I'm not sure.  I figure in a pinch either one could be modified by either filling the notch or cutting a notch.

[Bill]

Take a look at the bleed back hole in the master cylinder. �If you have the master off already they are under the hoses coming from the brake fluid reservoir.� The very small hole is under both the hose going to the front and rear parts of the master cylinder. �Some times this small bleed back hold gets clogged preventing the fluid to bleed back. �By opening the line or bleed screw to any of the cylinders or calipers you are releasing the fluid just like the bleed back hole does. �
Caution: remove the master cylinder pistons so you don’t cause damage to the cups by sticking something into the bleed back hole.
Bill
�

[Greg Prentice]

Thanks for input&
I believe the flow is opposite from below&&the flow going to the brakes lifts the rubber disc inside the check valve and return flow pushes down on the return spring or through the notch&

[Greg Prentice]

Thanks Bill.
I have disassembled the master cylinder to try to understand the problem.
Fig 11C-14 in the sedan service manual show 2 ports in each connection for the reservoir.
One is the ‘inlet’ port and one is the ‘compensating port.
I found the inlet port clear – but the compensating port does not appear to be drilled through.
Fig 11C-3 in the manual show these 2 holes in the cross section. The compensating port is shown with a counterbore with a very small hole drilled through.
The counterbore is present but the drill through is not. It does not appear to be blocked by dirt.
Neither the front brake circuit or rear brake circuit has a drill through for the compensating port.
Has anyone noticed same on their MC ?

[Greg Prentice]

I drilled out the compensating holes with a small drill bit…
Reassembled, bled and roadtested.
Brakes no longer bind at all…..
From:
Greg Prentice
Sent:
Tuesday, August 14, 2018 10:04 PM
To:
'anzhonda600owners@yahoogroups.com'
Subject:
RE: [anzhonda600owners] N600 master cylinder check valves [2 Attachments]
Thanks Bill.
I have disassembled the master cylinder to try to understand the problem.
Fig 11C-14 in the sedan service manual show 2 ports in each connection for the reservoir.
One is the ‘inlet’ port and one is the ‘compensating port.
I found the inlet port clear – but the compensating port does not appear to be drilled through.
Fig 11C-3 in the manual show these 2 holes in the cross section. The compensating port is shown with a counterbore with a very small hole drilled through.
The counterbore is present but the drill through is not. It does not appear to be blocked by dirt.
Neither the front brake circuit or rear brake circuit has a drill through for the compensating port.
Has anyone noticed same on their MC ?

[Bill]

Over time the bleed back hole will clog, and there must have been some bleed back because it would release after a while. �DOT3 will corrode (or exfoliate) aluminum over time and these master cylinders are cast aluminum. �Solidified DOT3 also looks like aluminum or white residue filling the port. �I normally unblock them with a dentists root canal hand drill. �But the result is the same.
Gland it worked.
Bill