[DeTomaso] Brake Upgrade

Sat Nov 12 18:21:28 EST 2011

When I set the MG up with aftermarket brakes, rotars and MC, I built a
complex spreadsheet calculating everything from pedal length and throw,
psi, pad area, rotor, tire radius and a 100 other things. It is a non
boosted car and I needed to maximize the effort needed for pedal throw. I
needed also to get balance as close as I could because unlike a balance
bar, the more the proportional the more pedal force required as a whole.

With the spread sheet I pretty much nailed the correct Master, rotors,
calipers and balance. Braking is pretty good for a non boosted car.

Gary

>
> There area a number of online resources for those who want to
> theoretically look at their options and play around with rotor to caliper
> sizing to master cylinder sizing. It's also fairly easy and useful in
> retrospect to verify an existing brake setup.
>
> I found a great Excel based spreadsheet when I upgraded my GT40 from hung
> to floor mount pedals and new master cylinders. Tilton  Engineering (the
> pedal assembly manufacturer) also had an online submission and they came
> back with similar recommendations, nothing like a second opinion! The
> effect of the bore of the master cylinder is often overlooked and
> misunderstood in an upgrade (how many times have you heard of just
> switching to a large bore Master?), especially where dual or step bore
> cylinders are used, it's important to match everything to get a system
> that is ballpark in overall braking efficiency and only rely on an
> adjustable proportioning valve for fine tuning.
>
> Julian
>
>> From: detomasoregistry at gmail.com
>> To: MikeLDrew at aol.com; JDeRyke at aol.com; bjbstewart at yahoo.com;
>> detomaso at realbig.com
>> Date: Fri, 11 Nov 2011 15:46:41 -0800
>> Subject: Re: [DeTomaso] Brake Upgrade
>>
>> I'll chime in here, as I'm one of those types Mike refers to below.
>>
>> (Copied from the text below)
>>
>> If you elect to try to piece your own system together with various bits
>> and bobs, you can still achieve success.   You'll probably have to
>> resort
>> to some sort of adjustable valve to do so unless you're smart enough to
>> succesfully calculate the necessary piston sizes front and rear to
>> achieve the
>> desired proportioning
>>
>> I pseudo-pieced together bits and bobs (Bob Byars to be specific).
>>
>> Full details on my brake system (stock calipers and rotors) can be found
>> at the Registry
>> website here:
>>
>> http://www.provamo.com/Members/TechInfo/BrakeMasterUpgrade.asp
>>
>> I tested my stock brakes repeatedly over about 9 months (and two sets of
>> tires -yikes)
>>
>> I replaced the brake master with a "stepped-bore" master from Precision
>> Pro-Formance
>> (Bobby Byars).  I also upgraded the booster with one about 1" larger in
>> diameter at the
>> same time.  I then replaced the stock pressure-limiting (front brake
>> limiting only) with a
>> manual proportioning valve, and also scuttled the stock (brass)
>> distribution block (with
>> the shuttle.)
>>
>> The rotors and calipers stayed the same.  Braking was VASTLY improved.
>> I could adjust the
>> proportioning valve such that the rears locked up first (both unsafe and
>> a scary result),
>> just to know what that was like.  Take my word, you don't want the rears
>> locking up first.
>> The car swerves like you threw out an anchor.  Where you are eventually
>> pointed even with
>> the left and right calipers well matched and balanced is tricky.  But
>> hey us engineers
>> just have to push the limits - right?
>>
>> Then I dialed the proportioning valve in small increments such that the
>> fronts eventually
>> locked up first, and the rears generated very limit heat (or stopping
>> power)  This was
>> over about 10-15 increments.
>>
>> In the end I could have not used the proportioning valve at all, as it
>> was sitting at
>> neutral when in the best setting.
>>
>> Then, having worn out that set of tires (all 4), I moved to my 17" Campy
>> clones with fresh
>> Goodyear tires, and repeated a subset of tests.
>>
>> The end result is what OTHERS say is an impressive brake system (for
>> stock rotors and
>> calipers).  I upgraded to Porterfield pads, and repeated some testing.
>>
>> I used to demo the braking system, until I wore out those 17" tires.
>>
>> Now I'm back to 15" as I have a Drew-like inventory of 15" tires to
>> consume, before I
>> return to the 17"s and new tires.
>>
>> Anyway, I enjoyed the experience of making adjustments, testing, and
>> tuning.
>> I stopped when it was time to move to the track to evaluate repeated and
>> heavy track
>> braking.  Anyone want to fund my tire fund?
>>
>> Chuck
>>
>>
>>
>>
>>
>> In a message dated 11/11/11 13 15 58, JDeRyke at aol.com writes:
>>
>>
>> > 1)- totally remove the stock non-adjustable proportioning valve that
>> > limits
>> > the front brake pressure, so you rely mostly on the toy rear calipers.
>> > Removing this and re-plumbing for full use at both ends allows the
>> decent
>> > stock
>> > front brakes to work to full capacity. This alone improves brake power
>> > markedly and is all some guys decide they need.
>> >
>>
>> This is a complete misconception fueled by a fundamental
>> misunderstanding
>> of how a braking SYSTEM works.   This modification will improve the
>> performance of the front brakes and screw up the performance of the
>> braking SYSTEM as
>> a whole.
>>
>> The original calipers were badly mismatched, front-to-rear.   I have
>> copies
>> of the original braking system DOT certification tests, conducted on
>> hand-built preproduction prototype Panteras (chassis number 1007, 1010,
>> etc.),
>> where the need for the proportioning valve was revealed, and then the
>> braking
>> improved once they were fitted.
>>
>> Brakes need to be properly balanced front-to-rear.   Especially in a
>> mid-engined car with extensive weight on the back end, and even more
>> especially in
>> one fitted with aftermarket wheels and tires (where typically the
>> difference in front-to-rear tire width is even greater than stock, and
>> thus the need
>> for rear braking is greater than stock), it's crucial that the back
>> brakes
>> contribute their fair share to the overall stopping scheme.
>>
>> The stock proportioning valve is actually a pressure reduction valve.
>> It
>> is designed to reduce front line pressure, relative to rear line
>> pressure,
>> so that the front and rear brakes are properly balanced.
>>
>> If you remove this valve entirely, as Jack recommends (again and again),
>> what you are left with is overly-sensitive front brakes.   To the
>> ignorant,
>> this is an 'improvement', because for a given amount of leg pressure
>> applied
>> to the pedal, there is a greater apparent braking effect.   As long as
>> you
>> are just driving around normally and not attempting to actually stop the
>> car
>> with any sort of vigor, this can feel like 'good' brakes.   It's quite
>> true
>> that a car so-modified will stop with less effort when coming to a stop
>> sign,
>> etc.
>>
>> However, what this modification has done is actually to disable the rear
>> brakes!   That is, the front brakes are now so sensitive, relative to
>> the
>> rears, that when pedal pressure is increased, the front brakes simply
>> lock up
>> and the tires slide, while the rear brakes are hardly doing anything.
>>
>> Real-world performance braking (track work etc.) will reveal that cars
>> with
>> such a modification have substantially LESS overall stopping power,
>> because
>> they are relying almost entirely on their front brakes.   This also will
>> lead to rapid overheating of the front brakes and resultant fall-off in
>> braking performance (which is what Brent experienced I believe, as I
>> think a
>> previous owner of his car followed Jack's advice).
>>
>> If the stock pressure reduction valve is removed for any reason (on a
>> stock
>> braking system), then it should be replaced with an adjustable
>> proportioning valve.   Initally the valve should be plumbed wide-open
>> (no restriction),
>> then real-world testing should be conducted with progressive adjustment,
>> and
>> repeated hard stops.   A hand-held heat gun (thermometer) can be useful,
>> as
>> rotor temps will give an indication of braking performance--if your
>> front
>> rotors are hot and your rears are not, you don't have enough rear brake
>> bias.
>>
>>
>> Eventually you'll go too far and the rear brakes will lock up first;
>> then
>> back off the valve so that the fronts lock up first BUT the rears are
>> still
>> doing their fair share of the work.   Too much rear brake bias is
>> dangerous;
>> if the rear brakes lock up, the car can easily go out of control.   So
>> the
>> front brakes should always lock up first--but not excessively so.
>>
>> Jack's advice regarding brake vacuum is quite valid.   If your power
>> booster is blown out, or if you have insufficient vacuum to operate the
>> power
>> brakes, the brakes won't work well at all.   Some cars can have great
>> braking
>> effect with no power assist (the Ferrari F40 is such an example), but
>> this is
>> achieved through proper engineering--typically the pedal is much longer,
>> so
>> the leg has a much greater mechanical advantage over the master
>> cylinder.
>>
>> A properly functioning Pantera brake system, equipped with performance
>> pads
>> but no other upgrades, should be able to lock up all four wheels.
>> Sadly,
>> many Panteras are suffering from some form of deterioration and this
>> can't
>> be achieved.   Rather than trying to band-aid the system, the
>> responsible
>> thing to do is identify the actual source of the problem so that the
>> stock
>> (which is to say, quite good) brake performance can be restored.
>>
>> All bets are off when aftermarket systems are installed.   Ideally, the
>> vendor will have done his homework, and front-to-rear proportioning will
>> be
>> handled via different piston sizes in the calipers (my Wilwood system
>> from
>> Dennis Quella has four calipers that externally are identical, but
>> differ in the
>> sizes of the pistons on the front versus rear calipers for just that
>> reason).   If you elect to try to piece your own system together with
>> various bits
>> and bobs, you can still achieve success.   You'll probably have to
>> resort
>> to some sort of adjustable valve to do so unless you're smart enough to
>> succesfully calculate the necessary piston sizes front and rear to
>> achieve the
>> desired proportioning (which I most emphatically am not!).
>>
>> Mike
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