Dual circuit conversion with ATE master cylinder problems

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ted698
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Dual circuit conversion with ATE master cylinder problems

Post by ted698 » Mon Apr 01, 2019 8:51 pm

Bought a AHSchofields master cylinder conversion kit for my stock 67 (was single circuit) which uses a ATE late bay with servo MC.
A couple of things, when fitted and pushrod adjusted to 1mm play the pedal only goes down halfway with no pipes connected, as if I’m reaching the end of the MC travel way before the end of the pedal stroke... is this normal?
When all plumbed in and bled with an ezibleed I have a good pedal but can stand on the brakes and just coast to a stop.... this is with a new VWJim servo installed too! So somethings not right.... I’d expect it to stand on its nose! also if I press the brake pedal hard enough it goes halfway, then clunks and goes a bit further.... you can feel it mechanically through the pedal, which definitely feels odd.... I’m wondering if I have a faulty MC...?
The MC has 5 ports all on one plane, 4 to the sides and one on the very end. The end one is blanked, I’m using the LH ports to run into the servo inputs, the RH ports have blanking plugs in them. The rear most port is to front brakes, front port (nearest pushrod) is to rear brakes. The ones in the pictures all have an angled port at the rear, mine doesn’t... also is it right that the front ‘collar’ moves into the MC when pushing pedal?... I’m guessing this is attached the front piston.
Any ideas?
Brakes all worked perfectly before I removed the single circuit.... :roll:


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Re: Dual circuit conversion with ATE master cylinder problems

Post by ted698 » Mon Apr 01, 2019 9:02 pm

Pics
8303E744-DED2-47E3-BCB4-87395A4E6836.jpeg
563C3DB0-E337-4141-8B50-A8148199F380.jpeg
97F2647D-7C99-4533-A4F5-5DBCC4FF4B1C.jpeg

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vwJim
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Re: Dual circuit conversion with ATE master cylinder problems

Post by vwJim » Mon Apr 01, 2019 9:59 pm

The m/c action certainly doesn't sound right. But also your brake pipes need improving as you've got the rear pipe unsupported lengths of copper pipe.
Supplying quality in house designed items plus parts from SyncLink, Kennedy Clutches, & CB Performance. Also fitting service including modifications & mechanical upgrades.


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Re: Dual circuit conversion with ATE master cylinder problems

Post by ted698 » Mon Apr 08, 2019 4:21 pm

For anyone interested I sorted the brake bleeding in the end - the clunk in the pedal stroke - ie it would go halfway then clunk and go a bit more - I worked out was the front piston hitting the rear piston in the master cylinder - i.e doing exactly what it is designed to do - if one circuit fails the piston travels forwards connects with second piston and pushes the fluid.

This told me I had a lot of trapped air somewhere - and I surmised this was actually in the master cylinder itself - now I've always heard of people 'bench bleeding' master cylinders and always thought it was a load of old rowlocks - but I was desperate & broken :x: :lol: (repeated brake bleeding with little result does this to a man!) So I took off the MC and made a bleeding tray... I placed an old 1ltr brake fluid bottle on its side and cut the very top/side off it - so I had a deep open tray - I put the MC in it and filled it with fluid right to the brim, I left the full reservoir in place, and had 2 of the ports already blanked off anyway - I pumped the piston in and out using my fingers and got absolutely *loads* of air out of it by moving/rotating it around a bit in the bath of fluid without the orifices breaking the surface- it took a good few pumps before both open orifices were pumping clear fluid without any micro bubbles in it. (the good thing about doing this in a bath of fluid is it sucks back in good fluid when the piston goes back)
I then put my fingers over the two open ports and holding it as upright as I could (open ports to the top), I managed to re-connect my brake lines without tilting it too much - (my long lines were useful for this!) and re-bolted it back in place, and quickly re-bled again with the easibleed - absolutely perfect now - the pedal is rock solid.

So today's lesson is 'bench bleeding' is a thing and it does work! :bounce: Why this MC would not bleed properly through normal methods I don't know - but submerging it in a bath of fluid and manually pumping it definitely worked for me... as well as the usual tips of 'sealing' the bleed nipple threads by packing around them with grease, and also when using the easi-bleed let it flow a little then give the pedal a gentle pump or two on each wheel, just to make sure you move the fluid well through the system.

Ideas stolen from: (especially the second procedure which I modified slightly, as I kept my reservoir in place)
http://www.vw-resource.com/bench_bleed.html
http://www.vw-resource.com/alternate.html

Cheers, TED

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Re: Dual circuit conversion with ATE master cylinder problems

Post by vwJim » Mon Apr 08, 2019 7:12 pm

:cheers:
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Re: Dual circuit conversion with ATE master cylinder problems

Post by flatbeat » Fri Apr 12, 2019 11:46 am

It’s a mystery why MC’s trap air....but they do!!! It’s a common and frustrating problem so well sorted.
Packed a few belongings and headed out to Pirates Cove. In my buddy’s old grey Kombi we rolled until the gas got low.....

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