600 Master Cyl & 850 caliper questions

[boxy02]

The stock discs are only 10.8mm (some brands are 10.5mm) thick when new, so if you've removed 1.5mm of material then I can't see how they are still 10.42 thick.

7mm thick machined discs, I would think you'd have issues with rotors warping... you obviously have never had them hot enough (yet) to warp them

SteveC

My rotors are still in stock form (material not removed yet) so, they are still 10.42mm thick. After I remove 1.5mm total of material, they will be just under 9mm.

 

[fiatfactory]

You know that the 9mm minimum thickness is after use, ready to throw away once under 9mm... generally if you were to skim them to renew the surface you'd be machining to a minimum of 9.5mm and allowing 0.5mm for future wear....

SteveC

 

[boxy02]

Yes, I am aware. Thanks.
If, however, it does present a problem, I do have the option of widening my calipers by 1/8” using 6061 aluminum strap. I performed a test run of machining the recesses for the seal between the halves, but my 3-flute end mill didn’t provide a smooth enough cut on the base of the recess. I think I can do better, might find a 2-flute. I have another set of splash shields to re-center/mount the calipers to. That’s an option to keep the rotor in spec.

 

[fiatfactory]

Yes, I am aware. Thanks.
If, however, it does present a problem, I do have the option of widening my calipers by 1/8” using 6061 aluminum strap. I performed a test run of machining the recesses for the seal between the halves, but my 3-flute end mill didn’t provide a smooth enough cut on the base of the recess. I think I can do better, might find a 2-flute. I have another set of splash shields to re-center/mount the calipers to. That’s an option to keep the rotor in spec.

That sounds like a far preferable solution from an engineering perspective...

All discs are not alike either, as mentioned some are 10.8mm, others thinner , (factory OE specifies 10.5 and 10.8 as new dimensions, pre/post a certain production date) mostly depends which manufacturer your discs come from.

Surface finish on discs is pretty important too, to get the pads to bed properly. If you were to have the discs machined on any regular brake lathe, the cut on each side would be a bit like a vinyl record groove, one continuous spiral from inner to outer. Better quality discs feature a Blanchard ground finish (that swirly pattern you might see when you get a flywheel refaced) which provides a vastly superior surface for the pads to bed against.

Brembo make a nice 10.8 x 227.5 disc that's Blanchard ground.

Rather than welding the equivalent of two over length nuts to screw the radial mount caliper bolts into, I'd be inclined to machine something a little more sturdy....caliper deflection is a bad thing.

SteveC

 

[boxy02]

That sounds like a far preferable solution from an engineering perspective...

All discs are not alike either, as mentioned some are 10.8mm, others thinner , (factory OE specifies 10.5 and 10.8 as new dimensions, pre/post a certain production date) mostly depends which manufacturer your discs come from.

Surface finish on discs is pretty important too, to get the pads to bed properly. If you were to have the discs machined on any regular brake lathe, the cut on each side would be a bit like a vinyl record groove, one continuous spiral from inner to outer. Better quality discs feature a Blanchard ground finish (that swirly pattern you might see when you get a flywheel refaced) which provides a vastly superior surface for the pads to bed against.

Brembo make a nice 10.8 x 227.5 disc that's Blanchard ground.

Rather than welding the equivalent of two over length nuts to screw the radial mount caliper bolts into, I'd be inclined to machine something a little more sturdy....caliper deflection is a bad thing.

SteveC

Thanks for the perspective and great information.

Re: caliper deflection, would triangulating the coupling nuts suffice? Or adding additional material to the plate? The nuts are welded on two planes now (the splash guard plate and the 90 deg lip), but the thickness of the guard is maybe not that robust as to combat deflection.
Mike

 

[fiatfactory]

Thanks for the perspective and great information.

Re: caliper deflection, would triangulating the coupling nuts suffice? Or adding additional material to the plate? The nuts are welded on two planes now (the splash guard plate and the 90 deg lip), but the thickness of the guard is maybe not that robust as to combat deflection.
Mike

The part that most concerns me from your pictures is the point where the caliper and the overlength nuts meet....

One is the area of the nut face, for a start won't be absolutely flat and square, nuts/threaded hex shaft/whatever you use wont be perfectly flat on it's end face unless you machine it so.

The next is the surface area it provides is much smaller than the corresponding mating face on the caliper, personally I would be aiming for a surface area on the mount that is at least as large as the area on the caliper, or preferably larger.

The interface is where the caliper radial fastener will be under the most stress, and you've increased the loading considerably (IMO beyond the fasteners likely failure point) by having the mounting face a) not absolutely flat and square, and b) too small an area

SteveC

 

[boxy02]

The part that most concerns me from your pictures is the point where the caliper and the overlength nuts meet....

One is the area of the nut face, for a start won't be absolutely flat and square, nuts/threaded hex shaft/whatever you use wont be perfectly flat on it's end face unless you machine it so.

The next is the surface area it provides is much smaller than the corresponding mating face on the caliper, personally I would be aiming for a surface area on the mount that is at least as large as the area on the caliper, or preferably larger.

The interface is where the caliper radial fastener will be under the most stress, and you've increased the loading considerably (IMO beyond the fasteners likely failure point) by having the mounting face a) not absolutely flat and square, and b) too small an area
View attachment 72098


SteveC

I spoke to my machinist friend, he said he could easily machine a piece (like the one in the photo) to suit my needs. I think this would solve the weak junction between the caliper and the coupling nut. Using a steel, shouldered, drilled & tapped (M10x1.5 thread) piece that fits into the recessed base of the caliper would be a lot better. I can widen my calipers and re-center & weld them on my other set of splash guards in two planes. Thanks for the engineering perspective, Steve.

Mike

 

[fiatfactory]

OK, I had no idea the caliper had a recess there, the fact that it does makes my point about surface area and flatness of the mounting even more relevant... and your solution is a definite step in the right direction.

As for the advice, you're welcome, nice to see you're taking it onboard. I have no problem with the concept of the bike calipers in this application, they appear light / sturdy / compact and suitable for the task at hand, but I don't want to hear about a failure / issue I might have helped to avoid due to something that seems quite obvious (to me) and not piping up ... it's a duty of care thing.

SteveC

 

[boxy02]

Finally got the front sorted and assembled. Kingpins fit and work perfectly! Welded the new improved shouldered caliper mounts to my splash guards and they fit nicely now with no possibility of caliper mount flex/deflection. Caliper-half spacers were installed and allow use of full-thickness rotors. New upper knuckle bushings and upper A-arm bushings were installed and almost ready to assemble front end back on the car.
I rebuilt the calipers as well, nice and clean/fresh for use!