Larger brake master cylinder sizes?

TonyK said:
I had a few moments to look into this as I have all of the Fiat 500 Abarth brake components
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Tony, please tell me if I followed everything correctly:
1) The caliper brackets will bolt up if the mounting holes on the X knuckle are enlarged from 10 to 12 mm.
2) The rotors will fit the X spindles, but the outside diameter of them is roughly 10 to 13 mm too big, causing interference with the caliper - based on where the caliper mounts to the knuckle.
3) With everything mounted, the rotor is not sitting in the midline of the caliper/pads, by about 1mm.

If I got that right, here are some thoughts. Tell me if any of them might work based on what you see:
Could the caliper be moved outward (radially) away from the the rotor's axis (the approximate 10 to 13 mm), to allow for the extra diameter of the rotor?
Could a shim of some sort be used to better center the rotor with the pads; either between the rotor and hub, or the caliper bracket and knuckle? Or can it only be corrected by shaving some material off one of them?

There are other rotors with the same mounting dimensions (that will fit the X) in a selection of diameter sizes. Steve C posted about this in the past. So using other rotors would solve the diameter issue. But keeping everything from one donor vehicle simplifies things, so it would be nice to make the 500 parts work.
 
Dr.Jeff said:
Tony, please tell me if I followed everything correctly:
1) The caliper brackets will bolt up if the mounting holes on the X knuckle are enlarged from 10 to 12 mm.
2) The rotors will fit the X spindles, but the outside diameter of them is roughly 10 to 13 mm too big, causing interference with the caliper - based on where the caliper mounts to the knuckle.
3) With everything mounted, the rotor is not sitting in the midline of the caliper/pads, by about 1mm.

If I got that right, here are some thoughts. Tell me if any of them might work based on what you see:
Could the caliper be moved outward (radially) away from the the rotor's axis (the approximate 10 to 13 mm), to allow for the extra diameter of the rotor?
Could a shim of some sort be used to better center the rotor with the pads; either between the rotor and hub, or the caliper bracket and knuckle? Or can it only be corrected by shaving some material off one of them?

There are other rotors with the same mounting dimensions (that will fit the X) in a selection of diameter sizes. Steve C posted about this in the past. So using other rotors would solve the diameter issue. But keeping everything from one donor vehicle simplifies things, so it would be nice to make the 500 parts work.
Click to expand...

In reply.

1) The caliper brackets will bolt up if the mounting holes on the X knuckle are enlarged from 10 to 12 mm. YES
2) The rotors will fit the X spindles, but the outside diameter of them is roughly 10 to 13 mm too big, causing interference with the caliper - based on where the caliper mounts to the knuckle. YES
3) With everything mounted, the rotor is not sitting in the midline of the caliper/pads, by about 1mm. YES


Could the caliper be moved outward (radially) away from the the rotor's axis (the approximate 10 to 13 mm), to allow for the extra diameter of the rotor? Not without welding new tabs to move it outward that small amount.

Could a shim of some sort be used to better center the rotor with the pads; either between the rotor and hub, or the caliper bracket and knuckle? Or can it only be corrected by shaving some material off one of them? The Pad Holder needs to go inboard not outboard so milling of the pad holder would be the simplest solution.


Not sure about the other rotors for the Fiat 500 series of vehicles. I think the 500 Pop has smaller rotors that are vented as well, but am not sure about it.


TonyK.

Grimsby Ontario Canada.
 
Thanks Tony, very helpful.

I'll have to go back and see what we discovered previously about the various rotor diameters. Good point about the "normal" 500's; you have Abarth components that might be bigger rotors.
I also recall that the North American 500's (not sure if that includes Abarth editions) have several differences from the European ones. And brakes was one of those changes. I believe the NA brakes are made in Mexico. Not sure if they are any different in size though.

Granted these are bigger brakes than needed for the X1/9. But if they are a easy fit (which it appears they are), and they are readily available in wrecking yards or used online for decent prices (which they are), then it is a reasonable option to trying to find and afford the UT upgrade or aftermarket custom options.
 
Jeff, find out the rotor diameters for me and I can purchase a smaller diameter rotor from Car Quest. The knuckle in the picture is a spare that I would be willing to drill out to 12 MM and face the pad holder to centre it. I could then put the whole thing together and post pictures. Just remember adding a bigger front caliper will cause the fronts to lock up sooner. My thoughts were to use the Abarth fronts along with 2 Lockheed remote servo brake boosters located in the front trunk windshield washer tank. Then to install two Wilwood brake proportioning valves between the X1/9 master and the boosters. The X1/9 master would be the pilot that would be variable to the boosted brake circuit, the valves located under the dash for tuning of the power brake system. In theory it sounds like it would work, proof is in the putting.

Comments welcome.

TonyK.

Grimsby Ontario Canada.
 
I don't know about the US, but some 500s, like 1.2 L have 240mm rotors, solid 11mm thick and caliper with 54mm piston. 0.9 L have 257mm rotor, 12mm thick, 54mm caliper. 1.3 L diesel have 257mm vented 22mm thick, with 48mm piston caliper. Larger diameter rotor than 227mm X1/9 will giver better braking force. Maybe the caliper carriers have the same hole centres as the Abarth and X1/9. Most or all of these will probably need wheels larger than 13 inch to clear the caliper, partly due to the shallower top hat of the rotors. Edit, also 240mm vented rotor, 20mm thick, used on some 1.3 diesel.
 
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Dr.Jeff said:
Actually the pedal effort will not increase IF the calipers (slaves) are also increased in size by a proportional amount. Hydrodynamics: equally larger volume on both ends = same effort, same pedal throw. It's when you start changing one end more than the other that the dynamics change. This is why going to a larger MC is worth the effort if you upgrade the calipers' piston size.
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Jeff, I agree that the theory says the pedal effort will not change but I don't believe it really works that way in real life. Several things to consider:

1. Increased piston size on both ends leads to greater wall friction.
2. Pushing more fluid simply requires more effort. If the pistons were the size of 55 gallon drums, you could not expect the same effort to move the fluid as a 3/4" piston, and not just for the reason stated in #1. Size really does matter.
3. If the size of the ENTIRE system was upgraded, that's one thing. But what is not changing in this application is the size of the pipe connecting the cylinders, it will remain standard 3/16" piping. Pushing more fluid through the same size pipe will simply offer more resistance, which will be felt as pedal effort.

I am definitely expecting higher pedal effort due to all these things, and I will be looking into some type of pedal effort assistance.

Pete
 
Sorry about that. Possibly Mr. Decker can pull these posts and start a new thread for us.

TonyK.

Grimsby Ontario Canada.
 
TonyK said:
Sorry about that. Possibly Mr. Decker can pull these posts and start a new thread for us.
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No problem Tony, it's all good discussion, so no need for that. I just would also like to resolve the original question, if possible. It's sounding a lot like all Fiat brake MC's that bolt on are 3/4", since I haven't heard otherwise.

Pete
 
Pete Whitstone said:
I agree that the theory says the pedal effort will not change but I don't believe it really works that way in real life.
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Actually Pete, this happens one of those things where science is correct. There are mathematical formulas to calculate all of this. Some brake companies have created a 'calculator' so you can just plug in your sizes and get answers (I think Wilwood has one on their site?). And if you play with one of those calculators you will see the theory holds true. The size of the hose between the two cylinders will have just as much resistance regardless of the other components. With larger cylinders at BOTH ends you are still moving the same volume of fluid (you don't empty the MC when you push the pedal) so the MC moves the same distance as a equally sized slaves. Therefore no change in pedal effort. Check with a aftermarket brake specialist to get better info/explanation.
 
Ok after some prodding by Pete I looked further into this.

In looking at a variety of Fiat MCs I found that a version of the Multipla used a 1” MC but it is a single circuit unit. Which led me to the 900T which does have dual circuits. There is also an Iveco vehicle that uses it as well.

To be clear, it doesn’t mount in the same way as an X MC and I so far have not been able to verify the diameter of the pistons in the MC. Prices for this thing are all over the place.

You would also need to have a splitter for the front brake circuit versus the two outlets on an X MC.

It looks like this:

9DFB50E1-C9B1-4DED-9946-DA363622E6CF.jpeg

8455C7F5-410C-4A5E-8DB1-AFCB66C56489.jpeg

Versus an X MC:
EB58290D-FE50-4158-A288-92E7118DFBC5.jpeg

Hopefully this is a start. I will cast around for some more solutions.
 
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kmead said:
I looked further into this.
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Excellent Karl. :) The difference in mounting holes shouldn't be that difficult to overcome. The metal bracket for the pedal box (the 'box' I guess) could be modified. Please let us know what else you find. ;)
 
TonyK said:
My thoughts were to use the Abarth fronts along with 2 Lockheed remote servo brake boosters
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Actually my thoughts are to use 4 front 500 calipers/rotors - both front and rear. With equal size brakes at both ends you could easily balance braking with a simple proportioning valve. If a proper sized master cylinder can be included in the mix, then the pedal effort/travel won't be wrong and the 4 larger calipers would work. It would have IMPRESSIVE braking ability. Granted more than necessary, but refer back to my earlier comment about the availability, cost and simplicity of this option. Also refer to my earlier comment about a parking brake.
 
Pete, Tony and I (and anyone else interested) will continue the 'big brake' discussion on the other thread (linked in my last post). Please feel free to join us, just trying to keep from hijacking your thread here. But I am very interested in the master cylinder question and want to apply the results with the outcomes of the other (related) thread - larger calipers. That could make for a neet setup.
 
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