Booster with 4-wheel disc brakes

[steveg]

I've ordered the Lockheed single-line booster from Tom's. Will be installing it with my new Toyota calipers.

Later on when I add the Jag-caliper rear disc conversion, I was planning on adding a dual master cylinder, such as Welch or Wilwood.

Is the car likely to brake satisfactorily with unboosted rears and boosted fronts?

 

[Lotuswins]

Hi Steve,

This is a very good question. I'm not sure I'm qualified to answer it, but I can comment based on my mods to the Europa. The differences between disk and drum brakes are often misunderstood. The drum brake, as it is normally configured, is self energized, like having an internal amplifier. This is why modest pressure is needed for drums versus a higher pressure needed for disks. I have converted to rear disks on the Europa, but have removed both boosters on the car since it weighs so little (1600lbs), and even with the more aggressive brake pads it is marginal as a lot of pedal pressure is required to stop in a panic, or on a track day at the end of the straight. I have a 7/8 inch diameter M/C on the car, up from a .700 one which gave too much travel and a spongy feel to the pedal. Now it behaves much better with a firm pedal and acceptable travel, but again, it takes more pressure to stop in a panic or threshold situation.

With the heavier Healey, moving to rear disks will require more volume to engage the the disks, and if you put a M/C in to provide sufficient volume, the pressure won't be suffient to give acceptable braking force. So, in my opinion, you will have to have a booster for the rear disks. Also, hopefully, the caliper pistons area and disk diameters are calculated to provide a proportional amount of braking compared to the front disks and the weight distribution of the car. I put in an adjustable brake bias regulator in the rear circuit so I could adjust it in case the rears got too much pressure (not good on track day).

I hope this helps.

 

[John Turney]

I have the Denis Welch front and rear discs on my 100-6 and a Nissan B-210 dual circuit MC with no booster. Works just fine.

 

[dougie]

Like John, I also have 4-wheel disc brakes and no booster. In fact most of us racing big Healeys don't use boosters. Jeremy Welch likes them, but I don't see the need. Plus their too way heavy. I use a Wilwood 1" tandem MC and an adjustable bias at the rear. I think it's personal preference on how you like your pedal to feel. Mines firm, and does take some muscle under heavy braking.

https://www.wilwood.com/MasterCylinders/MasterCylinderProd.aspx?itemno=260-7563

 

[steveg]

John,
Can you post a picture of the B210 MC in situ?

 

[HealeyRick]

Hi Steve,

Just to throw out something for discussion. Unless your car is being track driven, are rear discs really necessary? Most of the heavy lifting of braking is going to be done by the front brakes and the Toyota calipers should give you some improvements there. And at some point, no matter how much we improve our brakes, stopping distances will be ultimately dependent on how wide and sticky the tires are that transmit the braking force to the ground. And most Healeys tires aren't particularly too wide, nor too sticky. I'd be the last to dissuade someone from making mods to their Healey, but I'm just wondering if the cost/benefit of rear discs is worthwhile on the street?

 

[steveg]

I already have the rear discs, adapters and Jag calipers. Since the whole car is performance art anyway, I'm interested in the rear discs for esthetic reasons - the car's more pukka with 4-wheel discs.

 

[HealeyRick]

I already have the rear discs, adapters and Jag calipers. Since the whole car is performance art anyway, I'm interested in the rear discs for esthetic reasons - the car's more pukka with 4-wheel discs.

I like that term, "performance art". I totally understand. Press on!

 

[Bob_Spidell]

Hi Steve,

Just to throw out something for discussion. Unless your car is being track driven, are rear discs really necessary? Most of the heavy lifting of braking is going to be done by the front brakes and the Toyota calipers should give you some improvements there. And at some point, no matter how much we improve our brakes, stopping distances will be ultimately dependent on how wide and sticky the tires are that transmit the braking force to the ground. And most Healeys tires aren't particularly too wide, nor too sticky. I'd be the last to dissuade someone from making mods to their Healey, but I'm just wondering if the cost/benefit of rear discs is worthwhile on the street?

IMO, no. If your brakes are effective enough to lock up the wheels then tires are the determining factor in stopping distance (as you point out). All-wheel disk brakes are better on the track, but how many 'street' cars go from max acceleration to max deceleration repeatedly in even 'spirited' driving? Otherwise, if the rear brakes are adequate to keep the rear end from coming around they are probably sufficient. I also don't see much advantage for drilled and/or slotted disks in street driving. Newer pads aren't as susceptible to outgassing and the holes can cause fractures of the disk. Braided SS lines sound like a worthwhile upgrade, however (have heard the braid can chafe the liner, though).

I have found that pad compound makes a difference. I replaced 'stock' pads--organic Raybestos IIRC--with some Ferodo pads and and the brakes became noticeably more effective. I didn't expect that, or I might have made some 60-0 stopping distance tests to measure the difference.

 

[steveg]

Thanks to everyone for the informed discussion - all useful points!

 

[dougie]

I already have the rear discs, adapters and Jag calipers. Since the whole car is performance art anyway, I'm interested in the rear discs for esthetic reasons - the car's more pukka with 4-wheel discs.

There pretty sexy too...

https:// DSC09450 by dougescriva, on Flickr

 

[John Turney]

John,
Can you post a picture of the B210 MC in situ?

It's almost impossible to see with the ITG air filter in place. It bolts in place of the stock Girling MC that comes on a BN4, which has an integral reservoir. The B210 MC has two reservoirs, one for each circuit, that are clamped to the MC. There are 2 brake lines coming off the bottom of the MC, one for the front and one for the rears. I found that, to get the lines to seal, I had to install a short (12") line from each of the MC fittings up to place where I could get a wrench on a coupling to attach to the lines that went the rest of the way. I installed the short sections to the MC before installing the MC in place.

The forward port and reservoir go to the rears and the rear port goes to the front calipers. Balance is achieved by a slight delay in engaging the rears compared to the fronts.

This was a setup that was suggested in a now-ancient book on racing British sports cars. I've misplaced the book now or I would pass along the name.

As for performance art, if you saw the condition of the drum brakes that were on the car when I got it, these make the difference between moving art and stationary art. They were that bad. As a plus, 4-wheel disc brakes were an option on BN4s.

 

[Lotuswins]

John, the book is "Vintage Racing British Sports Cars" by Terry Jackson published by Robert Bentley Publishers in 1990. It gives setups by vintage racers for many cars. Did you install a bias adjuster in the rear circuit as they recommend? Are you able to lock the fronts in the dry? and in the rain, not lock the rears first? just curious.

 

[John Turney]

Thanks for remembering the name. I think my copy is buried in my BIL's garage. No, I didn't install a bias adjustment as I don't race. With Denis Welch's help in choosing appropriate pads, it seems as though the balance is ok for normal driving. I haven't intentionally tried locking either front or rear wheels, although my wife might tell you about some heavy braking I did on our last outing.