Brake master cylinder help needed

[Alan c]

I'm a member of many years who has been otherwise occupied with other projects of the 2 wheeled type for a good while (so my apologies for lack of interaction with club). I have however kept my Marlin C417 LFF on the road all this time until a few months ago when my brake master cylinder gave up due to bore corrosion and new seals did not fix it. Here is where help is needed:

1. It had a Ford servo with Master Cylinder No 6118138 (Lucas/Girling 74066315) off a 82 to 88 2.3D Sierra. I searched extensively for a new one all out of stock and suspect no longer made.
2. I got a newer near identical one and machined servo to cylinder flange to make it fit, but I cannot get brakes to bleed - even my local garage tried with pressure bleeder. (we cant see any faults with new one in fact got 2 and both the same)
3. After months of strips, rebuilds and re bleeds I am at a dead end.

Can anybody give me advice and direction on what I may have missed and what new available assembly options (including servo) are likely to fit my pedal box (from doners or kit car suppliers - with least disruption/effort)

Marlin Cabrio running a 2 litre pinto engine

[greyV8pete]

The dual circuit tandem master cylinder must be bench bled off the vehicle first. It’s the only way to get all the air out. I rigged up a caulk gun frame to provide controlled pressure on the piston. Photo shows the Mk1 jig with a piece of packing where the cartridge normally fits. The round flange on the operating rod has to be removed and a plastic cap fitted to protect the bore. The frame is gripped in the vice so the master cylinder can be fitted and removed without damage. I say Mk1 jig because in the event the pipes were not needed. It is only necessary to put a small amount of brake fluid in the inlets holes* and then make small in and out movements of the piston until all the air bubbles cease to appear in the inlet holes when the piston is released. You then need to fit blanking plugs to all the ports to prevent fluid loss while you refit the master cylinder. Then remove the plugs and fit the pipes one at a time. Then fill the reservoir and bleed the system normally.

Note* My Hunter has a remote reservoir which is not connected in the photo. If you have a standard Sierra reservoir only part fill it so you can easily watch for air bubbles.
IMG_0904.jpg

[andyf]

What Pete describes is standard practice for dual circuit master cylinders. I have used a vacuum bleeding pump successfully without pre-priming the pump, just for the record.

[Alan c]

Thanks for the replies. I did try with a vacuum bleeder but maybe did not give it enough time to pull air from as far as the master cylinder. I also put a pressure feed on the top cap but again maybe did not fully clear the air. Now heading off to the set up the rig shown, Thanks again.

[Alan c]

I'm not quite sure what you refer to here could you elaborate please. "The round flange on the operating rod has to be removed and a plastic cap fitted to protect the bore"

[greyV8pete]

Thanks for the replies. I did try with a vacuum bleeder but maybe did not give it enough time to pull air from as far as the master cylinder. I also put a pressure feed on the top cap but again maybe did not fully clear the air. Now heading off to the set up the rig shown, Thanks again.

Yes I have tried both of these techniques in the past but it only seems to work after replacing a caliper or other brake component. With a new empty master cylinder the method I described is the only way to coax all the small air bubbles out of the master cylinder. The difference is a rock solid pedal rather than just a “firm” pedal.

[greyV8pete]

I'm not quite sure what you refer to here could you elaborate please. "The round flange on the operating rod has to be removed and a plastic cap fitted to protect the bore"

I was describing the mods required to the orange caulk gun. It normally has a round flat washer / flange that pushes on the cartridge when used for its intended purpose. When removed it leaves a rather ragged end to the metal operating rod. I put a plastic cap over mine to protect the bore of the master cylinder from damage.

[Alan c]

I was describing the mods required to the orange caulk gun. It normally has a round flat washer / flange that pushes on the cartridge when used for its intended purpose. When removed it leaves a rather ragged end to the metal operating rod. I put a plastic cap over mine to protect the bore of the master cylinder from damage.

Penny dropped thank you

[A_Hogg]

I've never had a problem bleeding dual circuit cylinders - maybe I'm just lucky. I've also come across the various you tube video's for bench bleeding and if that works for you I'm all for it. These days I must admit to using a vacuum bleeder as I then don't have to wait for assistance !