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Old 09-19-2007, 04:47 PM
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348 Brakes

Does anyone know if my 1990 348ts has an adjustable brake apportioning valve, to adjust the braking bias front to rear? It seem that my front brakes are a bit too grabby with a new type of pad that I am using, and the front pads did wear about 40% more that the rears on the last change. Any info would be appreciated... Thanks!
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Old 09-19-2007, 05:37 PM
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I can't comment on the prop valve, but if the brakes are feeling grabby the pads may be contaminated with grease or some such. As far as the fronts wearing more than the rears, that's normal for most cars since about 60-70% of your braking energy goes to the front.
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Old 09-19-2007, 08:55 PM
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348 brakes are pretty well balanced. If you have excessive wear on front pads you may want to check you rotors. I would be very careful about trying to adjust brake biased especially for street driving.. Too much rear brake and you will be going the other way pretty quick. Even for track the 348 brakes are pretty welled proportioned.

Having said that, I don't believe they are adjustable.
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Old 09-20-2007, 12:15 AM
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348's and 355 brake bias is adjustable via the factory brake bias valve.

But it makes a big difference in whether you have ABS active or have it disconnected.

348/355 should not be run without ABS unless you modify the factory bias valve and remove the delay valve. If you race without ABS on these cars, you'll soon find out there is way too much rear bias, which is there by design for the proper functioning of the excellent Bosch/Teves ABS system.

That being said, the 355 Challenge is entirely different. With ABS turned off on 355CH's you will lock up your front brakes first.


348's and 355's can use different brake bias valves to adjust front/rear brake bias and line proportionality based on input (from your brake pedal) pressure.

Ferrari 456 GT - BRAKING REGULATOR
Part No. 155808

...is the same as:
Ferrari 355 Challenge (1999) - BRAKING ADJUSTER (AS AN ALTERNATIVE FOR P.NO. 157908)
Part No. 155808


and
Ferrari 355 (2.7 Motronic) - BRAKING REGULATOR
Part No. 157908

...is the same as:
Ferrari 355 (5.2 Motronic) - BRAKING REGULATOR
Part No. 157908

...is also the same as:
Ferrari 456 GT - BRAKING REGULATOR
Part No. 157908



348's have a "VALVE CORRECTOR"
Part No. 136313 in place of the 355's "braking regulator"

Go figure.
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Last edited by No Doubt; 09-20-2007 at 12:44 AM.
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Old 09-20-2007, 02:52 AM
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Pls do not adjust the brakes unless you know exactly what you are doing.

You might end up with a Gocart with brakes only at the rear, which means you will spin in every corner where you brake.

//B//


Quote:
Originally Posted by Dr.T348 View Post
348 brakes are pretty well balanced. If you have excessive wear on front pads you may want to check you rotors. I would be very careful about trying to adjust brake biased especially for street driving.. Too much rear brake and you will be going the other way pretty quick. Even for track the 348 brakes are pretty welled proportioned.

Having said that, I don't believe they are adjustable.
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Old 09-20-2007, 09:18 AM
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Originally Posted by fxdwgs View Post
Pls do not adjust the brakes unless you know exactly what you are doing.

You might end up with a Gocart with brakes only at the rear, which means you will spin in every corner where you brake.

//B//
I'm in no way advocating changing the bias.

I have a 348 C car with the ABS disconnected (previous owner, not by me) and on the track I have to be very carefull with late braking or the rear end tries to come around. So I think there is more than enough rear brake bias (assuming mine has not been changed), and if you don't know what you are doing you will create a very unsafe driving condition. Unless you are really making a race car and have time to play with the adjustment during practice sessions (may need to be set differently for different tracks) don't change it! Even for an occaisional track car, don't change it just because you front pads were slightly faster than you rears. Get some track pads and change them for the track. You will notice more from that than playing with the bias.
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Old 09-20-2007, 04:07 PM
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Quote:
Originally Posted by No Doubt View Post
348's and 355 brake bias is adjustable via the factory brake bias valve.

But it makes a big difference in whether you have ABS active or have it disconnected.

348/355 should not be run without ABS unless you modify the factory bias valve and remove the delay valve. If you race without ABS on these cars, you'll soon find out there is way too much rear bias, which is there by design for the proper functioning of the excellent Bosch/Teves ABS system.

That being said, the 355 Challenge is entirely different. With ABS turned off on 355CH's you will lock up your front brakes first.


348's and 355's can use different brake bias valves to adjust front/rear brake bias and line proportionality based on input (from your brake pedal) pressure.

I have not found this to be true at all. The brake bias is not user adjustable. Even with ABS there is very good balance and good pedal feel. I have run without ABS on the track for no good reason. When I do that the bias is the same. I can lock all 4 with no ABS no problem and it seems very simultaneous front to rear. I'm a diy'er and a racer so if I thought i would have an advantage (at my race ability) playing with brake bias I would have done it. First, one should use matching pads that are part of a set unless you are trying to achieve specific goals or tune out specific problems. Race pads in the front and stock pads in the rear may actually be worse than stock pads on 4 corners. Second, you can tune some braking with chassis rake which of course will change some other charactoristics of the car. So when in doubt keep it factory since they have proven the handling. make sure that odd rake positions are not effecting braking through changes in weight transfer. Third, bad shocks, springs, bushings, damaged suspension can greatly change braking effects and so can alignment even the rear alignment. Fourth, depending on driving conditons, don't forget the effect heat (and its dissipation) can have on repeat braking perfmance. So when you are having issues make sure to look at the big picture before you focus in on specifics. Good Luck.
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Old 09-27-2007, 07:37 PM
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Thanks for all of the input guys!!

Since the original post, I have been to the track and it seems that the new pads that I installed have behaved well (no real premature front lock-up). I do believe that the previous owner disabled the ABS (which is fine with me) because I can easily lock up the front brakes, and on the wet skidpad can easily lock all 4. I agree that the bias is good stock , but I was looking to optimize for straight line braking if there is adjustability (I have decided not to monkey with it for now); and don't worry, I am fully aware of the pitfalls of improper trail braking!

I love this car on the track - so raw, responsive and capable (in the right hands), yet refined, beautiful and delicious to drive unleashed.

Heaven is Track Days with my 348ts.

Can I get an AMEN?!?
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Old 09-27-2007, 08:01 PM
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AMEN!!!!
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Old 09-27-2007, 08:42 PM
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Say HALLELUJAH brother! AMEN!
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  #11  
Old 09-27-2007, 11:14 PM
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Quote:
Originally Posted by Phil Altomare View Post
Thanks for all of the input guys!!

Since the original post, I have been to the track and it seems that the new pads that I installed have behaved well (no real premature front lock-up). I do believe that the previous owner disabled the ABS (which is fine with me) because I can easily lock up the front brakes, and on the wet skidpad can easily lock all 4. I agree that the bias is good stock , but I was looking to optimize for straight line braking if there is adjustability (I have decided not to monkey with it for now); and don't worry, I am fully aware of the pitfalls of improper trail braking!

I love this car on the track - so raw, responsive and capable (in the right hands), yet refined, beautiful and delicious to drive unleashed.

Heaven is Track Days with my 348ts.

Can I get an AMEN?!?
Well you should have a brake light on the dash if the ABS is disabled. If you like no ABS then gut thesystem and drop out 30lbs or so.
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