Break compensator

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toplessexpat
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Your car is a: 1976 Spider 1800
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Re: Break compensator

Post by toplessexpat »

Nanonevol wrote:
By lowering the car, you've raised the spring rates and the car sits much more level during braking, yes even really hard braking.
Does that apply to cut spring lowering or only upgraded spring lowering?
Either has an impact. Cutting the spring alters the geometry between the axle and the bottom of the car. As the compensator works on the relationship between the two, then it's impacted.

Not altering the compensator set up at all, and shortening the springs, is going to mean that the compensator doesn't "come on" (i.e. restrict the flow of brake fluid so the brakes don't lock up).
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Nanonevol
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Your car is a: 1977 Fiat 124 Spider
Location: Medway, Massachusetts

Re: Break compensator

Post by Nanonevol »

Oh, and I thought it just looked cool. Seriously though I'm thinking more of the cornering when lowering the car. A previous owner removed my brake compensator (I can spell brake but not compensater) and I honestly doubt I'll replace it. Priorities.
1977 Fiat Spider
1985 Jaguar XJ6
1967 Triumph Bonneville (hard-tail chopper)
1966 BSA Lightning
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toplessexpat
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Joined: Fri Aug 31, 2012 2:29 am
Your car is a: 1976 Spider 1800
Location: Houston, TX

Re: Break compensator

Post by toplessexpat »

Handling is definitely improved by lowering / stiffening. I'd recommend using lowering springs, not simply cutting into stock springs.

For $30 you can fit a nice shiny new compensator.. and be assured you've got the safety device that Fiat intended you to have.

a
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KevAndAndi
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Your car is a: 1981 Fiat Spider 2000
Location: Chatham, NJ

Re: Break compensator

Post by KevAndAndi »

Leaving aside for a moment the question of whether it's a good idea to remove stock safety equipment: Here's a thought experiment.

Scenario:

Car with the Wilwood big brake upgrade installed on the front. Stock brakes in the rear. Bypassed compensator. Car is not "lowered", but it is not particularly high, either; it has big bumpers.

Questions:

Will the upgraded front brakes make it more, or less, likely that the rear brakes will lock up?

Will the new front brakes make the car nose dive more than the stock brakes did?

Will the greater force of the modern 4-piston calipers and larger rotors effectively act as a "compensator", assuring that the stock rear brakes won't lock up?
Kevin
1981 Spider 2000
So Cal Mark

Re: Break compensator

Post by So Cal Mark »

during our stopping tests with either of our front kits with bypassed compensator, the rear brakes never locked up. This was under extreme braking to measure stopping distance.
We did the same thing on cars when we developed the rear big brake kit. No lockup from the rear brakes under extreme braking with the compensator bypassed
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bradartigue
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Your car is a: 1970 Sport Spider
Location: Atlanta, GA

Re: Break compensator

Post by bradartigue »

So Cal Mark wrote:during our stopping tests with either of our front kits with bypassed compensator, the rear brakes never locked up. This was under extreme braking to measure stopping distance.
We did the same thing on cars when we developed the rear big brake kit. No lockup from the rear brakes under extreme braking with the compensator bypassed
In other words, it works fine so long as you lower the car and buy your brake kits.
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toplessexpat
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Re: Break compensator

Post by toplessexpat »

KevAndAndi wrote: +snip+
Will the greater force of the modern 4-piston calipers and larger rotors effectively act as a "compensator", assuring that the stock rear brakes won't lock up?
Experience wise - I don't know.

Logically.... The new brakes give a greater capacity to the front end to slow down, and therefore dip. The dipping of the front end rotates the geometry of the rear axle to the body activating the compensator (in a stock setup). With no compensator, as the front dips the back end would lighten downward force on the rear axle... So logic tells me that in certain conditions it would be more likely to lock if it did not have a compensator than if it did.
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DieselSpider
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Your car is a: 1978 124 Spider with Isuzu Turbo Diesel

Re: Break compensator

Post by DieselSpider »

Yes if you modify the bias so much that the fronts lock before the back so that you don't get much rear braking proportionally until the fronts are almost locked then yes the rear compensator is moot however then the rear brakes serve little purpose in normal use except to provide for the parking brake. That could pose a problem at times when driving on public streets in real world situations.

The basic rule of thumb is to stay within 5% of the original bias to keep a car balanced and to maintain compensation for dynamic bias changes. It is a balancing act which needs to be vetted out differently on a daily driver compared to a car that's only driven on dry roads or a race track. The compensator valve makes for a more universal approach providing braking that is tuned for a variety of road conditions and bias loads while eliminating it leaves you a compromise with the brakes tuned more for panic braking or wet roads or trunk loaded or trunk unloaded, etc but not self compensating for all/most. The compromise that fits someone who never drives in traffic or on wet/dusty roads or never varies how the car is loaded will be different than for the daily driver that sees a variety of traffic, weather, road conditions or loading situations not to mention the personal preferences of the driver.

Interesting read and calculator:
http://www.tceperformanceproducts.com/bias-calculator/

Bottom line is one size does not fit all and good working properly adjusted compensated bias brakes fit more situations then fixed bias brakes. One has to make an informed decision as to which approach is the better fit for how and where they will be driving the car.
So Cal Mark

Re: Break compensator

Post by So Cal Mark »

big brakes and lowering is not required. We've easily installed over a hundred bypass hoses on both stock and lowered cars without any issues. But hey, if you like longer stopping distances don't consider the change.
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toplessexpat
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Re: Break compensator

Post by toplessexpat »

Mark - is it really that clear a tradeoff? (i.e. Shorter Stopping Distance vs Safer Stopping)?

Some thoughts:

Putting on big brake kits etc, certainly improve the stopping power of the car. The nose will dip more just as if you jammed on the stock brakes hard you would dip more too.

A lot of the time the compensator doesn't really do much, big brakes or otherwise. Where the compensator is useful is when you've got your foot hard on the brakes (stock or big), the nose is dipping hard, weight is off the back axle, and it's breaking loose a bit.....
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bradartigue
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Re: Break compensator

Post by bradartigue »

So Cal Mark wrote:big brakes and lowering is not required. We've easily installed over a hundred bypass hoses on both stock and lowered cars without any issues. But hey, if you like longer stopping distances don't consider the change.
Depends on what you define as an "issue". This is like saying "we removed the airbags on over 100 cars and no one died." But hey, if you like trading off balanced braking for insignificantly shorter stopping distance, don't consider the change.

That's enough for me on this thread, I keep saying the same thing over and over - it's too easy to do it right. At least the defense attorneys can review this thread when that one issue does occur.
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KevAndAndi
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Re: Break compensator

Post by KevAndAndi »

DieselSpider wrote:Yes if you modify the bias so much that the fronts lock before the back so that you don't get much rear braking proportionally until the fronts are almost locked then yes the rear compensator is moot however then the rear brakes serve little purpose in normal use except to provide for the parking brake. That could pose a problem at times when driving on public streets in real world situations.
Perhaps obviously, my "thought experiment" questions were not entirely academic. I have the Wilwood big brake kit and intend to install it this winter. I also have an uninstalled compensator bypass hose. Any reluctance on my part to preserve the compensator stems from the fact that I suspect, as you do, that it would be "moot", in which case it could actually be considered a potential liability, e.g., as a possible source of brake fluid leaks. Might it be better to simplify by removing a part rather than preserve it, when it likely has no benefit? That's what I'm struggling with.

(In a similar situation, though less related to safety, I decided to preserve the throttle body heater, replacing the cover with Mark's billet aluminum version. The car will never be driven in cold temperatures, obviating the need to keep the throttle plate from freezing, but the new plate has a bleed screw which helps burp the cooling system, so net-net, it's a plus.)

I guess one solution to the potential problem you raise is to replace the aged compensator and buy Mark's rear brake kit. :o
Kevin
1981 Spider 2000
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toplessexpat
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Joined: Fri Aug 31, 2012 2:29 am
Your car is a: 1976 Spider 1800
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Re: Break compensator

Post by toplessexpat »

Kevin - it won't be moot. Keep it. Install the big brakes on the front. The compensator will continue doing its job. If you lower the car, adjust the compensator appropriately. It will still be doing the same job - albeit less frequently.
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So Cal Mark

Re: Break compensator

Post by So Cal Mark »

wow, you really like to twist words and conjure up situations. Insignificant stopping distance? HAHA, you really should drive a car with the brake upgrades and see the difference. I'll be happy to do a side-by-side comparison. Let's drive 40 mph at a brick wall with a predetermined braking point. Your car will end up quite a bit shorter in length than mine when the test is over.
The bottom line is if you're happy with 50 year old braking technology, keep your car just as it is.
DieselSpider
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Your car is a: 1978 124 Spider with Isuzu Turbo Diesel

Re: Break compensator

Post by DieselSpider »

So Cal Mark wrote:wow, you really like to twist words and conjure up situations. Insignificant stopping distance? HAHA, you really should drive a car with the brake upgrades and see the difference. I'll be happy to do a side-by-side comparison. Let's drive 40 mph at a brick wall with a predetermined braking point. Your car will end up quite a bit shorter in length than mine when the test is over.
The bottom line is if you're happy with 50 year old braking technology, keep your car just as it is.
You also have to compare on a roadway during accident avoidance maneuvers and in other real world situations. Brakes have to be balanced for more than a statically loaded car performing a straight line panic stop on a smooth level roadway, brick wall aside. Brake mods do have to be vetted out in multiple real world scenarios not just tested for one specific situation. Last thing you want to have is the rear brakes still grabbing like the rear axle is fully laden while bleeding off speed to make a corner. The sides or rear of the car could end up messed up by a tree stopping you well before you get to the brick wall.

If you found a compromise that works well enough for all situations that is grand and probably took a lot of trial and error effort. I am only pointing out that people just can't start slapping on mods to the braking system or remove components without giving serious thought to balancing the system for the variety of driving conditions they are going to face on the road.

Brakes that work safely only when driving straight ahead can be as bad or worse than having no brakes in certain driving conditions. One does have to look before they leap and be cautious about over improving the brakes on just one end of the car and creating an imbalanced system.
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