Master cylinder for discs

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Master cylinder for discs

Postby Asolepius » Mon Mar 19, 2012 8:40 am

At long last I have just bought a disc brake kit on eBay. I have the entire front suspension from a 1500 Midget, with discs, hubs, calipers etc. Now to put it on my Mark 1. I realise I need a 3/4 inch master cylinder. I have already had the 7/8 master sleeved with stainless, and have a spare that I was planning to have sleeved down to 3/4. I will need the 3/4 piston of course. I have read at http://www.brakecylinder.com/spridgetbrakes.htm that the 3/4 pistons are different (apart from being smaller of course), but would I get away with turning down a 7/8 piston? I could buy a new 3/4 cylinder but that would not be stainless sleeved and these things do corrode badly without it. I have a 1275 clutch and the pedal pressure is fine so no real need to go down to 3/4 for that.

Any thoughts?
Les Rose, Salisbury, UK
1959 Sprite, owned since 1978
Asolepius
1098cc
 
Posts: 489
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Re: Master cylinder for discs

Postby Talonaer » Mon Mar 19, 2012 5:03 pm

Best guy to talk to is Gerage of http://gerardsgarage.com/ who also regularly posts over at Britishcarforum.

I have got exactly what your going through but I am going to give it a go with the dual 7/8 and deal with the extra pedal pressure required. To deal with the difference in valves I will take the residual valve out of the 7/8 and put a 10psi wilwood valve on the rear brake line.

The thing to remember is that whilst the fronts change to discs...the rears change from single to dual piston drums...

Keep us posted with how you get on! There were a few 3/4 cylinders on ebay the other month that I missed out on otherwise I would have used the pistons from one of them (they're as rare as rocking horse ****).
Talonaer
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Re: Master cylinder for discs

Postby Asolepius » Tue Mar 20, 2012 4:36 am

One of the reasons to change is to reduce the pedal pressure with the drums. I am using alloy drums on the front and fade is not a problem, but the disc brake cars I have driven all have lighter pedals. I was thinking about fitting bigger drums - Austin A40 Mk II, Riley 1.5 or Wolseley 1500. Some of the 1500s had 9" drums, and I was toying with the idea of using 9" alloy drums from the back of a Datsun 240Z. Some of the Morgan boys use those. They would need some machining of course, and so would the backplates. I have seen a Frogeye with Riley 1.5 drums and the installation looks quite neat.

Anyway, I got the discs for only GBP70 including all suspension bits and A/R bar. My kingpins need restoring anyway and the Midget ones are claimed to be OK. So I am just left with the master cylinder work. If someone could post precise dimensions for the 3/4 piston I could make one up on the lathe. I will then get the spare cylinder sleeved, 3/4 for brakes and 7/8 for clutch, and all should be well.

I suspect that modern friction material without asbestos has less grip, so you have to push harder to stop. Either that or I am just getting old!
Les Rose, Salisbury, UK
1959 Sprite, owned since 1978
Asolepius
1098cc
 
Posts: 489
Joined: Tue Jan 25, 2005 6:50 am
Location: Salisbury, UK

Re: Master cylinder for discs

Postby Talonaer » Tue Mar 20, 2012 2:37 pm

Keep us in the loop with how you get one would you? If you can easily make pistons up on a lathe life gets alot easier (been meaning to learn how to use one for awhile now: got one sat in the back on the barn).

The riley 1.5 and disc set up was first used on the Sebring sprites I think and used a girling master cylinder set up.
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Re: Master cylinder for discs

Postby Asolepius » Tue Apr 03, 2012 8:24 am

I have now collected the 1500 front suspension kit, and the discs, bushes and bearings seem good. Now to dismantle, and get the lot blast cleaned and powder coated. Also got 1500 rear backplates complete with cylinders etc. But new cylinders were so cheap that it's not worth my time restoring the old ones. 3/4 master cylinder piston on its way to me from across the pond. Would be nice to get it all done in time for the 30th June track day.
Les Rose, Salisbury, UK
1959 Sprite, owned since 1978
Asolepius
1098cc
 
Posts: 489
Joined: Tue Jan 25, 2005 6:50 am
Location: Salisbury, UK

Re: Master cylinder for discs

Postby Asolepius » Mon Apr 16, 2012 5:27 am

The parts have now been stripped - more seized bolts than I have ever encountered! But the gas torch and lots of penetrating oil did the job, although I did have to drill out the cotter pins. The good news is that the discs and pads appear virtually unused, the hub bearings are excellent, as are the fulcrum pins and swivel pin bushes. The calipers are rusty but good inside. But the swivel pins themselves are badly corroded and probably beyond redemption. I have toyed with the idea of turning them down in the lathe and fitting a sleeve. There is no Speedi-Sleeve available that would work, and they seem to be intended for lip seals not bearing surfaces. Maybe I should start another thread for this as it's getting off-topic! I think I'll end up using my existing Mark 1 swivel pins, assuming they are the same size.

The master cylinder piston arrived - thanks Richard. I'll be off to the machinist next to get the cylinder sleeved.
Les Rose, Salisbury, UK
1959 Sprite, owned since 1978
Asolepius
1098cc
 
Posts: 489
Joined: Tue Jan 25, 2005 6:50 am
Location: Salisbury, UK


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