brakes bleeding S1 4.2

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#1 brakes bleeding S1 4.2

Post by cooper66 » Sun Jan 05, 2020 6:39 pm


It is definitely a newbie question, nevertheless this is my first intervention on the braking system, and I cannot bleed the front calipers short summary :
-new master vac
-new master cylinder
-restored calipers (tested)
-new brake lines (tested with compressed air and no leaks)

I implemented by the Haynes the following brake pipes :


I respected the order and started by the rear calipers, with manual bleeding (one at the brake pedal and the second bleeding at the caliper). Result is ok brake pedal is hard => issue is for the front calipers, impossible the get fluid out of the bleeding nipples and even if nipples are opened the pedal stay hard.

Any idea ? I'm stuck here ...


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Location: Australia

#2 Re: brakes bleeding S1 4.2

Post by abowie » Sun Jan 05, 2020 10:47 pm

1. Use a syringe to try to squirt fluid from the reservoir hose into the front circuit with the front caliper bleeder open.
Note that the front and rear systems are entirely separate and so make sure you are squirting the fluid in from the correct reservoir hose.
If this works, do both sides and then try your pedal again. ... ringe.html

2. Sometimes with initial bleeding the shuttle in the tandem slave cylinder (L in your diagram) can get pushed too far forward and prevent fluid entering the front system. Try putting fluid under pressure into the caliper via the bleed nipple to see if you can move it back, then try 1 again.

3. Check that there is actually a hole in the booster for the fluid to come out. Seriously.

881824, 1E21538. 889457..oops. Jezza the V12 XJS race car.
Adelaide, Australia

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#3 Re: brakes bleeding S1 4.2

Post by Springer » Sun Jan 12, 2020 4:02 pm

Maybe a stupid question but since the front caliper has its own master cylinder. Are you sure you got the mechanical connection from the pedal box to the cylinders correct?
Can you actual see it is pressure on the master cylinder to the front calipers?
If it is and you can open bleeders on both sides and the pedal it still hard I would have looked at the master cylinder first.
Restauration project of a serie 1 1963 model OTS now running proudly

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