ALFAGTV6.COM

[Zamani]

JimK,

I think Mats meant a receipt.

BTW, Jose, why don't you just use the Supra rotors and FD RX-7 calipers (also 4-pots)? They look nice (the calipers). Minimal fabrication.

The only problem is you can't say you have a Brembo 4-pot caliper to all your friends.

[Jose_76]

I already have the red GTA Brembos and at the rear I'm going to fit a pair of 281x26mm vented discs from a 164 24v

[Jim K]

Somehow, I think your planned 281mm discs at the rear are too large. Speaking from my own experience mostly in a short heavy-braking track and a 1400kg car, I have no complaints yet from the rear 75 std brakes with DS 2500 pads. In the front I have 310x32mm and Red Brembo 4-pots with DS2500. I haven't touched the factory bias valve (although having bought a Speedway knob-type one). When we have track days, I may do anywhere from 20-30 hard laps in a row.Same thing in the long fast track and the brakes haven't failed me yet (Motul Racing fluid). I use both 15 and 16"wheels for this setup.
Maybe your 281mm rears are overkill? 305 front and 281 rear doesn't sound like a correct proportion. I even bought a pair of SZ rear vented Brembos, but I just don't have a compelling reason to put them on yet!I will eventually, but not because I expect lap times to improve!
Jim K.

[Jose_76]

Jim, proportions are just the point. That's just what I've taken care at while thinking of the right rear discs.

Standard brake discs on the GTV6 are Front 269mm and Rear 250mm. That makes a 1,076 to 1 ratio between axles.

Fitting front 305mm discs and rear 281mm, you have a 1,085 to 1 ratio, so you have proportionally more braking power at the front than stock.

And that would be just keeping the standard calipers!! With the 4 pot calipers you have even more braking power at the front than stock.

[Jim K]

I suspect that there's a lot more to consider than just the ratio of diameters. Swept area, clamping pressures (piston sizes) and a higher weight transfer due to racing speeds, all come into play. There are people selling 330mm front kits for gtv's who don't offer rear brake mods (why? They can't just be negligent)
Maybe think some more about it?
Jim K.

[tectoteam]

Jim, proportions are just the point. That's just what I've taken care at while thinking of the right rear discs.

Standard brake discs on the GTV6 are Front 269mm and Rear 250mm. That makes a 1,076 to 1 ratio between axles.

Fitting front 305mm discs and rear 281mm, you have a 1,085 to 1 ratio, so you have proportionally more braking power at the front than stock.

And that would be just keeping the standard calipers!! With the 4 pot calipers you have even more braking power at the front than stock.

joze.....
take care for the rear.....
too bigger disk will never comes hot and squizze a lot, the after.
they are near from the floor.
they are heavier.
big mods for rear calipers and mounting points.

in france there the gtv6 had run and win a lot from the past trough the eigthes against BMWs...
the balance for a 270hp car
front 284*28 4 pot(2* the brembo oem) + air ducting.
rear vented rear in 255*24 in 4 pot....
so this translate to lots of braking.... in hard issues.

so you can let the 250 mm disk for sport or track days.... however if you encourted some heating problems, after tries air ducting, go to SZ/RZ (or any 250-255) vented (20-24mm) rear disc and caliper spacers...


BUT.......!!!!!!!!! dont forgot something.......if you let the gtv6 rear brake pressure limiter, you never !! never had to power up rear brake.
the rear limiter is .......very limiter.....! it will never cause a rear brake heating failure..(with good pads..)

if you fit a adjustable rear limiter....consider that the minimum limit is far(bigger) from the oem limiter. and this will give you good rear clamping, then at this moment if you fit....280mm or more.... this will become undrivable, oversteering on braking comings.

over all......the brake pads.....is from far a very important thing.

[Mats]

My -77 GTV: Std 75 TS stuff, drilled rotors, adjustable bias valve for the rear, good set of pads and good fluid. Booster removed and no handbrake.

Never had a single issue with them, haven't had the car for very long though. Not very powerful car and 900Kg, sticky track tires.

Jim, usually a serious track car is lowered a lot and maybe this cancels out (to a certain degree) the increased weight transfer due to stickier tires?
I did mean a reciept.

[Jose_76]

Ok, guys, I really appreciate your comments.
I've never done something like this before, so I just went for some hipothesis before practice. The logic I applied was simple:

The 156 GTA has those brakes at the front, right? and 275mm discs at the rear, but the weight distribution makes its rear end lighter than the GTV's one in any condition, so if Alfa Romeo engineers put those brakes in, they work fine. On the other hand, there is not many difference between 275mm and 281mm so I was thinking about leaving the discs as they are or machine them to 275mm. Also, the rear swept area on the 156 calipers is bigger than in the GTV6, so unless the proportioning valves and brake master cylinders are very different from each other, that should works.

This is just what I've been thinking about, I already haven't tested any other braking system on transaxle Alfas but standard.

I think I should say too that I'm fitting in my car front oilovers with 100Kg/550lbs springs and rear 60kg/335lbs springs. Also 30mm front sway antiroll bar and street tires. I was planning to try all this with OEM brake pads, at least at the beginning.

Did anybody try such big discs at the rear? Bad experiences?

I reallly don't want to lock in every hard braking manouvre and enter sideways!!

[LENZ]

Because of the shape of the gta brembo's it's not possible to use adapters. Unlike other universal brembo's the ears are positioned further away from the pistons on a gta caliper.
I'm using the gta 305mm set up in front and moved my front brakes to the rear at the wheels.
I had a picture to illustrate but the maximum filesize for alle attachemenets is reached??????

[Zamani]

Why big rears? When you brake, the rear goes light, lock the rear wheels, flat spot some expensive race rubbers.

I think Barry has big rears (rear disc I mean, what were you all thinking??), and he said he would have gone for smaller ones.

BTW LENZ, can you get me used 155 V6 cams? I don't know why Alfa made shorter cams for the 155. Probably had too much veno before he hit the CAD program.

[Jose_76]

What Barry posted (at least what I saw) is that he regreted the front 164 calipers for the rear, but didn't mention anything about the size of the discs.

My reason to fit bigger brakes at the rear was just trying to keep the standard proportions of the braking systems. You can't fit the same brakes front and rear, but in my opinion, you can't either forget about the rear ones and improve just the front ones.

I see a lot of people fitting bigger calipers with racing pads at the rear, but don't want to fit bigger discs instead. I don't understand why. Shouldn't both options work aproxiamtely the same way?

[Barry]

MMmmm,Ive skipped this topic for a while.....
Jose,for the rear brakes I believe ive probably found the ideal STREET setup.

Bmw e34 rear discs(307mm dia.)
Solid disc.
Alfa 155 q4 rear calipers WITH the handbrake assy. and cables.
Std.155 rear pads.


No bias problems,no lock up ,You have a handbrake thats better than the original and the brake torque is 18 % more than the std.setup.(measured on our local roadworthy brake machine-hate it-seems its going to rip the rear axle out.....)

I will change my Giulietta soon.

[Barry]

Ive got pic`s,but some crap of being whatever............will try...........

[Barry]

Ok,checked out allowed file size and attachments and...........browser not found..Oh,well.

Can anyone tell me what the new rules are as to posting pics??

[Jose_76]

Barry, thanks for the pics. That looks stunning!
What front brakes did you fit to match? It looks that there's a lot of people that disagree with my proposition. What about you?

JJ, what do you think?