Some of you receiving this may not know me personally. I race a Lotus 61
formula Ford with HSR-West and CSRG. I discovered something purely by accident
last night on the Lotus concerning the brakes. I'm passing the information
along to you; the vintage racer, Lotus racer or race enthusiast. If it does
not apply to your brake system then press the delete key. If you are involved
with vintage racing I ask that you forward this to anyone who may be affected
so they may check their car.
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I was explaining to a friend last night how brake biasing works. Since I had
the Lotus 'undressed' it was a simple task to show him how the brake balance
bar, when turned left or right would change the distance from the centerline
of the brake pedal to the centerline of the master cylinder pushrod; thus
changing the mechanical advantage (and leverage) on the specific master
cylinder, which would change the effective amount of braking on the front or
rear of the car. Without thinking about it I took hold of the balance bar and
slid it back and forth within the brake pedal bushing! That was not good(!!),
and further analysis became a high priority during my prep for the next race.
This afternoon I removed the brake pedal from the car. Refer to photo's # 2,
3, 4. As you can see, the only thing that held the balance bar bearing
centered in the pedal bushing was grit, grime, rust and corrosion!
Devising a cure was simple enough... after doing so I dropped by my machine
shop to run my theory by them. They were in agreement, so back home, and got
to work.
The outside surface of the bearing that supports the balance bar; I ground an
indentation on it that would later accept a locking screw. Refer to photo #9.
Next, I drilled the center of the brake pedal bushing, then welded on a grade
8, 1/4"-20 nut. Refer to photo's #11, 12. I inserted a set screw with a lock
nut on it. I reassembled the brake pedal then tightened the set screw and lock
nut. The end result is the balance bar works as it should.
In studying the 'floating' balance bar bearing it looks like this would have
no affect on brake bias. This is not a correct assumption for, although you
have the same distance from the balance bar fulcrum (bearing) to the master
cylinder pushrods, you are still potentially changing the distance from brake
pedal centerline, which is potentially changing the cosine angle of the pedal
centerline and master cylinder centerline. Also, not 'pinning' the balance bar
has the undesireable effect of the bias balance potentially changing from one
brake application to the next.
If you do nothing, and your balance bar bushing is moving back and forth, your
brakes will still work! However, the bias will be potentially changing all the
time.
Again, feel free to forward this to anyone who may potentially be affected or
publish it in any club or marque newsletters. Any commercial publications,
while this is not copyrighted, I do ask that you notify me of publication.
Thank you, and safe racing!!
Carl McLelland
Lotus 61M/FF/79
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