Dual Brake System

[higgins]

I'm thinking about converting my Longbridge model from a single to a dual circuit brake system.

Does anyone have any advice?

Is there an alternative master cylinder to the expensive Healey one?

Would it also be necessary to instal a brake servo?

Any help/advice would be useful

 

[Randy Forbes]

That's a very good idea; if I was to embark on such a project, I'd start with an MGB master cylinder circa 1968-1974 US-spec (w/out servo).

Similarly, the one for a US-spec MGC, but I'll bet it costs an arm & a leg (maybe both arms...).

Naturally, there'd be Asian units available, but it might be harder to determine individual bore sizes, plus the need for Metric pipe connections.

 

[BUNDYRUM]

Hello higgins, I did it to a BN1 back in the early 1980's. I used 2 3000 type master cylinders with BN1 type reservoirs. Obviously a 6 cylinder car is different from a 4 cylinder car but it is possible. DWR has a dual circuit system available.
Best regards,
bundyrum.

 

[dougie]

Higgins -

I replaced the stock Girling system on my '57 Longbridge 100-6 MM
racer with this Wilwood dual-circuit system. It was a direct replacement, no cutting or fabrication needed, just run an addition brake line. I have 4-wheel disc with a bias valve and this system works well under race conditions.

https://www.hrpworld.com/client_images/ecommerce/client_39/products/pdf_5232_1.pdf

Dougie

 

[Randy Forbes]

Dougie, would you set it up any differently if you were still running rear drums (and 3000 MKI fr discs); would you still want to plumb in an adjustable bias valve?

I'm going to <span style="font-style: italic">hope</span> that master cylinder in your link will fit my car, as I narrowed the LH scuttle brace right up to the edge of the original m/c, so I could fit a 1-3/4" air filter on the 3rd 45DCOE.

Higgins, thanks for getting the ball rolling, as this is a very practical upgrade.

 

[BUNDYRUM]

Hello Randy Forbes, if you're fitting the dual circuit system having the adjustable bias valve would be good. Discs generally need a greater line pressure and because of this you would overcome the pressure needed for the rear drums and end up with the drums working (ie locking) and yet the discs would not. For a street car the other way of doing it is to reduce the rear lining area but this is done with a lot of testing. Basically you start by having your brake shoes relined with material all the way along the shoe. Then you reduce the length by removing say 1/2 inch of lining material from each end on all 4 shoes till you get a happy balance (meaning the rear wheels don't lock up anymore). This is a lot of work but if you like doing this kind of thing it can be interesting.
Best regards,
bundyrum.

 

[dougie]

Randy - I would still run a bias for the same reason stated by Bundyrum above. It was an easy install the small dial on the valve enters just behind the front passengers seat.

Dougie

 

[Randy Forbes]

Thanks guys, I am going to move this to the top of my "to do" list.

I've driven cars where the brakes have failed before, but I was much younger, and I suspect my reflexes were a tad faster then too...

 

[HealeyPassion]

Dougie, how's the dual master working out? What Wilwood did you use... I don't see it on the link. How did you dial it in?
Thanks!

 

[dougie]

Dougie, how's the dual master working out? What Wilwood did you use... I don't see it on the link. How did you dial it in?
Thanks!

My dual brake system works terrific, very happy with its performance still. Here's Wilwood Master Cylinder I installed.

Wilwood Disc Brakes 260-7563 Wilwood Combination Remote Tandem Master Cylinders | Summit Racing

Free Shipping - Wilwood Combination Remote Tandem Master Cylinders with qualifying orders of $109. Shop Master Cylinders at Summit Racing.

www.summitracing.com

 

[HealeyPassion]

I see you went with a 1" bore rather than a 7/8"... is the pedal pressure more? ... or less? How does it compare to a stock Healey?

Thanks!

 

[John Turney]

The M/C bore is also dependent on what calipers are used. I have Girling 16PB calipers in front and Jaguar Girling 14 (IIRC) calipers in the rear. My M/C is similar to Dougie's with a 3/4" bore. It's a Nissan.

 

[steveg]

I'm using a Fiat 3/4" dual remote-reservoir master cylinder. The 3/4" works fine without a booster with the Toyota 4 piston calipers.

IMO one would need at least a .70" or 11/16" MC to avoid excessive pedal travel. I also think on an earrlier car, one could build a system without a booster, then add one later on if pedal pressure was too great.

Edit: it would also be interesting to find out whether the newer 4 pot aluminum calipers take as much pedal pressure as the Girlings. My Toyotas evidently have a self-servo action because one set of pistons is smaller than the other.

 

[HealeyPassion]

My British car mechanic friend does not like the finicky vacuum assist used on Healeys...and since I've never had a Healey with assist...and never thought it was too hard ... don't plan on an assist on this one.

 

[dougie]

I don't use a booster as well. The pedal pressure is is right where I like it, strong and to the point. There's a little travel, but not as much as my BJ8 street car with the booster. It's just the different between a race car and a street car.

 

[steveg]

One of my friends (BN6-4 wheel discs) originally ran the 5/8" MC and disliked the longer travel - he switched to the Girling .70" MC and likes the travel better and says the pedal pressure's not too much greater.

 

[HealeyPassion]

I'm using a Fiat 3/4" dual remote-reservoir master cylinder. The 3/4" works fine without a booster with the Toyota 4 piston calipers.

IMO one would need at least a .70" or 11/16" MC to avoid excessive pedal travel. I also think on an earrlier car, one could build a system without a booster, then add one later on if pedal pressure was too great.

Edit: it would also be interesting to find out whether the newer 4 pot aluminum calipers take as much pedal pressure as the Girlings. My Toyotas evidently have a self-servo action because one set of pistons is smaller than the other.

Steve,
I'm using the Fosseway Performance 4 piston calipers.... which have 30% more piston area than my original BJ7's. So, I'm needing to factor that into the whole process. The rears are, at this point, still drums, albeit they have been radius match to maximize performance. Of course, I'll need to use a balance valve to get the correct front/rear pressures regardless of what is pushing them.

 

[Randy_Gay]

I used a Raybestos MC39087 Master from a 73 Datsun 1200 - 11/16". Worked fine with BJ8 discs up front and drum rears.

 

[HealeyPassion]

Initial installation of my Wilwood dual master cylinder (they call it a "tandem") was completed last Friday. As you may have guessed it wasn't a simple bolt on. After conversations with Wilwood guys I learned that my Healey pedal ratio (3.83) was not a good match for the Wilwood dual master cylinder. Based on the Fosseway 4-piston caliper size that I'll be using, their recommendation was Wilwood's 260-14241 (7/8") unit. They told me that a more acceptable pedal ratio was in the 6 to 7:1 range. So, that's what I've done.... changed the pedal ratio... which also required repositioning of the master cylinder. There's more to do, but where it's mounted now gives me a pedal ratio of 6.64 and allows full travel of the pushrod in the MC (important for safety).