Dual circuit brakes for 100/4 Bn1

[LuckyLuke]

Dual circuit brakes for 100/4 Bn1

I like to convert my BN1 to dual – circuit brakes. Does anyone have experience? what master cylinder could be used best?

Thanks

 

[GregW]

Hi Luke,
I haven’t done that myself. I know Denis Welsh sells parts for that. I believe Cape International does also, but there catalog seems to be offline.

 

[LuckyLuke]

Thanks, I found the one from Denis Welch. I may try to build a convesrion my self since I do not care about the adjustment. Rolf

 

[Randy_Gay]

Luke,
I'm working on one using a Datsun 1200 Master. Can't say how it works yet, though.

 

[LuckyLuke]

Keep me posted,

I'm planning a trip to the junkyard to see what could fit with the same piston diameter.

 

[LuckyLuke]

Does anyone else have experience with a conversion for dual circuit brakes??

 

[dougie]

Luke,

I just completed a conversion on my '57 100-6 MM vintage racer this year. I found a Wildwood system that was a direct replacement for the stock Girling master cylinder. I installed this after my first race of the season and having to "double pump" going into every corner (not good).
Simple installation and now I can out brake most cars of my size in our grid.

https://www.streetperformance.com/part/wilwood-engineering/brake-master-cylinder/665424-260-7563.html

Dougie

 

[GregW]

Hi Dougie,
What else do you have brake-wise? I know the 4 disc brakes. Do you have a booster also? Wasn't the original MC a 5/8" bore? I'd think the 1" bore Wilwood would need a fair effort from the leg muscles. Thanks.


P.S. Oh, did you need a proportioning valve for the rear circuit?

 

[dougie]

Greg,

I do have a proportioning valve at the rear and no booster. I thought about the idea, but the pedal pressure is not too bad, I didn't the additional weight of the booster. My front calipers are a 4-pot system from Coopercraft in the U.K. I'm pretty happy with the whole system under race conditions.

www.coopercraft.co.uk

Dougie

 

[Randy Forbes]

Does anyone else have experience with a conversion for dual circuit brakes??

No experience, per se, but I wouldn't rule out using the MGB dual circuit M/C from the 68-75 model years. I don't know the specs offhand (and I'm about 1000 miles away from my manuals as I type this) but I would think the MGB would have similarly sized components to the Healey. Period Triumphs (though I personally wouldn't admit to using Triumph parts on my Healey...) would be another possible source.

Are you also converting to front disc brakes, or keeping the twin leading shoe drum type?

Dougie: thanks for the link on the twin-circuit M/C, splitting the brakes on my car has been on my mind for some time. Unfortuately, due to narrowing my pedal-box area to allow an air filter for my 3rd Weber, I couldn't make use of an adjustable bias three (3) M/C setup. On the "double-pump" you know, it can take a very long time (and several sessions) to completly bleed ALL the air out of a fresh disc brake installation. There's no doubt in my mind that you have done several bleeds already, but you may still have enough air trapped that accounts for the second pump. Have you done the math on cylinder displacement; volume of calipers vs discharge of M/C? Aother one of the benefits of the three (3) M/C setup (including the clutch, of course) is being able to fine-tune the separate requirments of each end of the car. :wink:

 

[terp83]

Hi Luke:

Back in the 1990's a member of the North Texas Austin-Healey Club was a regular contributor to CHATTER, as the monthly magazine of the AHCA was then known. In the May, 1995 issue, at pages 21 and 22, he detailed his conversion to a dual-circuit brake system on his 1962 BT7 tri-carb, which he raced.

The master cylinder used by him was a 3/4" bore diameter unit from a Fiat Spyder (Fiat part #793298). He also noted that a Nissan master cylinder will work, but wasn't sure from what model. I have read elsewhere that another enthusiast has used one from a Nissan/Datsun 810.

The system requires separate reserviors, and Fred also installed a proportioning valve at a place in line to the rear brakes where he could make adjustments on the fly.

The article also includes a template for a bracket which keeps the stock pushrod mated to the new master cylinder.

Using Fred's article as guide, in 1997 I installed a dual-piston master cylinder in my Healey (also a 1962 BT7 tri-carb). A friend who then owned a Fiat Spyder and works at Autozone helped me order a suitable master cylinder (NAPA part #4739135; 1997 price: $31.99). This tandem master cylinder has two outlet ports off the back piston (for a separate line to each of the front brakes) and a single outlet port off the front piston for the rear brakes. Each piston has a single inlet port from the fluid reservior. I used the stock reservior for the front inlet (rear brakes) and a nylon reservior purchased from Pegasus for the rear inlet (front brakes). I also purchased a proportioning valve but located it in the engine compartment. Because of the offset of the master cylinder, I had to cut a small notch in one of the structural braces to allow one of the outlet lines to clear.

I tried to keep existing lines wherever possible so that the system could easily be returned to stock.

I still am running this system today and consider it an improvement over the stock system. I haven't had to replace or rebuild anything in the system. Earlier this year, I replaced the stock flexible hoses with stainless steel ones, and the pedal feel is much improved.

All this being said I have virtually no experience with BN1's but know that there are some differences in those early systems and that of the BT7's. I hope that this helps.

Jerry

 

[LuckyLuke]

Thanks for the advice!
I'm trying to change as little as possible on the mounting of the cylinder to keep the car somewhat original.

The drums are no safety issue to me. Drum brakes are as good as the liners. Keeping everything adjusted right and avoiding 3rd world liners I have always been happy with drum brakes for European bikes and cars. I do not know if this is true for American Cars.

Still hoping to find someone that did the conversion on an BN1 or BN2. I know bolt on solutions are availabe for the 6 cyilnder AH.

 

[GregW]

I do have a proportioning valve at the rear and no booster. I thought about the idea, but the pedal pressure is not too bad, I didn't the additional weight of the booster.

Sitting here after some sleep and sipping coffee, I realize what I said. With either dual or tandom M/Cs, you'd need <span style="font-weight: bold">two</span> boosters, one for each line.

 

[healeynut]

you don't want a booster on a dual circuit system because then you have to put two boosters on the car. Have a look at any MGC and you'll see what I mean.

 

[GregW]

With either dual or tandom M/Cs, you'd need <span style="font-weight: bold">two</span> boosters, one for each line.

you don't want a booster on a dual circuit system because then you have to put two boosters on the car.

Ummmm, isn't that what I said?

 

[healeynut]

Greg -

Sorry, was looking at an earlier post of yours. Or if you want you can accuse me of early onset senility and repeating everything you said. Either way works...

 

[GregW]

I'll forget about it if you buy the beer next time you're in L.A.