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Discussion Starter #1
I have got issues with both rear calipers on my 156 V6 (year 2000).
Started looking for some replacements yesterday but then remembered that I have two spare calipers off my GTV V6.

Does anyone know if these will fit on my 156?

Thanks
 

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Maybe, will likely depend on the year of your GTV and the hangers. IIRC the both use the same type of handbrake mechanic, so take a wheel off and try them. It's not like you have to disconnect the hydraulics to do this so it's a 15min job...
 

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The calipers will most probably be able to mount over, they are very similar in all aspects, except the radius... The discs will need to come with... The GTV used a 240mm rear disc, the 2000 156 used a 251mm rear disc and then later (2002+) used 276mm
 

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Discussion Starter #5
The calipers will most probably be able to mount over, they are very similar in all aspects, except the radius... The discs will need to come with... The GTV used a 240mm rear disc, the 2000 156 used a 251mm rear disc and then later (2002+) used 276mm
I see. .. does that mean the GTV rears are not as good as the 156 ones?
 

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It's not quite as simple as that. Braking systems are designed as a whole and not as individual components.

In completing the design they will consider:-

Weight of the car.
Weight distribution (front/rear)
Weight transfer under braking (suspension design will affect this.)
Car performance.

Yes the 156 rear discs have the potential to give better braking that the GTV ones but the GTV may not need such good rear brakes as 156.

However initial bite is also affected by master cylinder diameter as a % of braking cylinder diameter and pad contact area. So unless you know the different size of the brake and master cylinders of both cars and the pad area it isn't really possible to know which will perform best.

Also, in knowing how the brakes between both cars would feel if swapped over you also have to consider the servo diameter and any vacuum (pressure) regulation inside that servo.

rear brakes aren't really for stopping you but are for keeping the car in a straight line under braking. The risk in having rear brakes that aren't in harmony with the front is that there will be either:-

a) too much force at the rear causing them to lock and the rear end to start a spin.
b) too little and the rear won't help under braking and may again initiate a spin under braking.

Now having suggested "a" and "b" can happen your ABS/VDC should prevent that but in doing so it will have to regulate and reduce brake pressure to appropriate wheels and may increase, in emergency situations, your braking distance.

In real life none of this might happen so it is up to you to give it a try.

So - in theory there is no difference between theory and reality. In reality there is!
 

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I see. .. does that mean the GTV rears are not as good as the 156 ones?
Debatable on the definition of "better"... longer lever (larger diameter disc) with the same clamping force equals more stopping force. But most of the stopping force in a car is done on the front wheels anyway... The construction of the calipers are all the same - the wind-back tool is needed since ever... The handbrake actuator is the same since ever and even though the pads look different - they are +/- interchangeable if you are brave enough.

I race with race grade endless ME20 compound brakes up front and el-cheapo Messi pads at the rear... If I take the ABS fuse out (that also does Electronic Brake Distribution) - the car does hand-brake turns when I brake hard.

All that said - I still would not put the smaller discs in. I'd rather refurbish my current calipers or get new ones
 

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Discussion Starter #8
Thanks gents. . . Lots of info to digest there.
I'll work out what I'm going to do next week.
I may see if I can swap the calipers and then get the original ones refurbished and then revert back!
 

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The calipers will most probably be able to mount over, they are very similar in all aspects, except the radius... The discs will need to come with... The GTV used a 240mm rear disc, the 2000 156 used a 251mm rear disc and then later (2002+) used 276mm
My guess is they'll probably fit if you use the 156 caliper hangers. And I'm 99% sure they wouldn't work with a 2002> 276mm disc but that's not relevant to this conversation...
 

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It's not quite as simple as that. Braking systems are designed as a whole and not as individual components.

In completing the design they will consider:-

Weight of the car.
Weight distribution (front/rear)
Weight transfer under braking (suspension design will affect this.)
Car performance.

Yes the 156 rear discs have the potential to give better braking that the GTV ones but the GTV may not need such good rear brakes as 156.

However initial bite is also affected by master cylinder diameter as a % of braking cylinder diameter and pad contact area. So unless you know the different size of the brake and master cylinders of both cars and the pad area it isn't really possible to know which will perform best.

Also, in knowing how the brakes between both cars would feel if swapped over you also have to consider the servo diameter and any vacuum (pressure) regulation inside that servo.

rear brakes aren't really for stopping you but are for keeping the car in a straight line under braking. The risk in having rear brakes that aren't in harmony with the front is that there will be either:-

a) too much force at the rear causing them to lock and the rear end to start a spin.
b) too little and the rear won't help under braking and may again initiate a spin under braking.

Now having suggested "a" and "b" can happen your ABS/VDC should prevent that but in doing so it will have to regulate and reduce brake pressure to appropriate wheels and may increase, in emergency situations, your braking distance.

In real life none of this might happen so it is up to you to give it a try.

So - in theory there is no difference between theory and reality. In reality there is!
Or, short answer, if they fit, check the piston diameter is the same. If it's different, you may encounter problems with brake bias.
 

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My guess is they'll probably fit if you use the 156 caliper hangers. And I'm 99% sure they wouldn't work with a 2002> 276mm disc but that's not relevant to this conversation...
;) same problem / solution - If you get the caliper for the 276mm disc - it should fit the same mount points on the stub-shaft (upright) - the caliper determines the size off disc, not the stub-shaft (upright)
 

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;) same problem / solution - If you get the caliper for the 276mm disc - it should fit the same mount points on the stub-shaft (upright) - the caliper determines the size off disc, not the stub-shaft (upright)
I'm talking about the caliper hangers, not the uprights... ;)
 

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Chris155: Yes spot on but it's still nice to know the theory and even if the caliper piston is the same size the master cylinder may not be.

To be honest, in the real world, even if they are different I bet they are close enough that you wouldn't notice.

If you want to tear your hair out try reading all the threads and possibilities for improving 4 cylinder Alfetta GTV brakes where a lot of the problem is caused by the rear inboard discs overheating. Even more to consider if you want to stay 4 stud hubs and wheels!
 

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Chris155: Yes spot on but it's still nice to know the theory and even if the caliper piston is the same size the master cylinder may not be.

To be honest, in the real world, even if they are different I bet they are close enough that you wouldn't notice.

If you want to tear your hair out try reading all the threads and possibilities for improving 4 cylinder Alfetta GTV brakes where a lot of the problem is caused by the rear inboard discs overheating. Even more to consider if you want to stay 4 stud hubs and wheels!
Yeah, I had a 3.0 75 for a while so I know what you mean about the rear brakes (and getting the sodding things to blead!).
 

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Yeah, I had a 3.0 75 for a while so I know what you mean about the rear brakes (and getting the sodding things to blead!).
Yes, just going through getting my 2.0 Alfetta GTV back on the road after 9 years and all brakes seized almost solid so strip, clean and renew seals in every caliper; thankfully it's now worth more than scrap value so worth it. At least with a 3.0 you have vented discs up front as a starting point.
 
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