Replacement stainless steel rear disc.

[Stevex]

I'm in the process of replacing all 3 discs on my LM2 with stainless items.
I've bought and fitted the rear disc; it is sourced from HMB-Guzzi in Germany and is is mounted onto an aluminium alloy carrier.
The first thing I noticed was that it was advertised with the disc to carrier allen screws being countersunk, but mine are button head allen screws.




I assumed the countersunk screws would be used to centre the disc and hold it central against braking forces.
I removed the button head screws to see what the disc to carrier fit was like. The screws are not shouldered and are fully threaded with no shank.
The fit of the screws through the disc is not close tolerance and before the screws are tightened, the disc can move around the carrier to a small extent.
The only way to centralize the disc onto the carrier it to ensure the disc edges adjacent to the mounting screws are flush with the carrier edges.




I have fitted the disc to the carrier, torqued the allen screws up using Loctite and fitted the assembly to the back wheel.
It feels solid enough but I haven't come across this disc to carrier mount before, it's either been shouldered bolts, floating disc buttons or a single assembly disc/carrier bolted to the wheel as per the standard LM2 rear set up.
My worry is that braking forces will overcome the friction forces between the carrier and disc and the disc will move off centre.
The disc is stamped with ABE and TUV.




I've talked to HMB with my concerns and they replied:

its the new version of the disc. Reason is: The countersunk version was not completely sunk, as the disc did not have suffivient thickness to sink a 6mm screw
Tightness of the bolts is more than sufficient. Compared to the front disc of a LM-3, we have 12 Bolts instead of 9 (also not self centered, not close tolerated 6mm) despite the fact that braking forces are lower in the rear.
Also, movement, if there was any, would be limited by tolerance of screw stem and the hole.

Should I have cause for concern (I've not seen the LM3 set up)?

[pressureangle]

You should as much as possible shoulder the bolts in the holes against the edge that the application of brake will move to. Center up, shoulder up, torque up. In reality the rear rotor doesn't have very much force before the tire locks up anyway, I wouldn't worry about it as I would on the front-which of course I worry about a lot.

[lucky phil]

 It won't be an issue with front or rear disks. Would be nice to have a mounting bolt with a nice little shoulder 1mm less than the thickness of the disk carrier for mounting but it won't matter.
It's the clamping force and associated friction the mount bolts provide between the carrier and the wheel that does the real work of preventing disk rotation, not the shear resistance of the bolts.
Ciao

[mtiberio]

you could bring the bolts up finger tight, and then grab the rotor and rotate it clockwise against the slop. that is what the pads will try and do to a rotating wheel as it slows it. Then get a dial indicator, and set it up to ride the outer circumference of the rotot (the ~5mm wide face). Using a lead blow hammer, make it concentric. Then finish torqueing. recheck the runout. It is a nice piece, and frankly a little run out (radially) is of no consequence.

[Fangit]

Stevex, I'm keen to hear how this disc has worked out for you after getting a few miles on it. I'm considering the same.

I would also be interested in what SS discs you fitted on the front wheel and your opinion of the quality, fit and any noticeable improvement in performance.

Thanks,

Joe

[nc43bsa]

It is a nice piece, and frankly a little run out (radially) is of no consequence.

True.

It's much more important to have nil axial runout than radial.

[Stevex]

Stevex, I'm keen to hear how this disc has worked out for you after getting a few miles on it. I'm considering the same.

I would also be interested in what SS discs you fitted on the front wheel and your opinion of the quality, fit and any noticeable improvement in performance.

Thanks,

Joe

Joe,

I've put about 100 miles on the bike since it went back on the road and am bedding the discs in slowly. Actually, the newly lightened flywheel
now provides an abundance of engine braking, which helps.
The rear disc has not moved, and after further searching, as Phil says above, it's the clamping forces that prevent the disc from trying to rotate.
I haven't really used the discs in anything approaching 'anger' at the moment; I'll give them a while longer to bed nicely, then give them some welly
and see how they perform.
Early indications are that they will be an improvement on the original set up when coupled with the carbon ceramic pads which appear to be well sintered.
Quality is first class and they are TÜV approved.
I bought them from HMB-Guzzi:

Front - http://www.hmb-guzzi.de/shop/Bremse/Bremsscheiben/Bremsscheibe-vorn-300-mm--LM1-3-Edelstahl.html
Rear - http://www.hmb-guzzi.de/shop/Bremse/Bremsscheiben/Bremsscheibe-hinten-242-mm--Edelstahl-gelocht--LM-1--LM-2--LM-3-etc-.html

[Fangit]

Thanks Steve. I have a 1984 1000SP. That same rear disc will fit I believe.

The front discs are different to the Lemans discs. I am looking at this kit from HMB:

http://www.hmb-guzzi.de/shop/Brakes/Brake-Discs/Front-Brake-Disc-Kit--300-mm-floating--T3--SP--Cali-2etc-.html

If anyone has these fitted would appreciate any feedback.

Cheers,

Joe

[mtiberio]

Thanks Steve. I have a 1984 1000SP. That same rear disc will fit I believe.

yet oddly they say this:

If a drilled rear disc is requested, also for:

750-S, 750-S3, 850-T, 850 T3, T4, 1000-SP, V 1000-G5, Convert, Cali-2

And some versions of  850 T5, Cali-3, Mille GT, SP-2. Please ask us

[Fangit]

yet oddly they say this:

If a drilled rear disc is requested, also for:

750-S, 750-S3, 850-T, 850 T3, T4, 1000-SP, V 1000-G5, Convert, Cali-2

And some versions of  850 T5, Cali-3, Mille GT, SP-2. Please ask us

I can confirm the Lemans 1/2/3 rear disc will fit on a 1000SP. I fitted a new drilled cast iron one on my SP today.

I still want to get those stainless front discs from HMB though.


 

[mtiberio]

I'm well aware that the can be moved from Lemans I to Convert/SP, etc. If you get right down to it, the Lemans I had 6 cutouts in the cast iron to slip the caliper hanger into and help get the caliper off the rotor. Making the rotor lighter (plus drilling). The touring bikes had only two cutouts (like your picture above, not a Lemans I spec rotor even with the drilling, sorry) meaning more cast iron, heavier.

[Stevex]

Joe, as a matter of interest, are your cans straight through or are they baffled?
What do they sound like?

[Fangit]

I'm well aware that the can be moved from Lemans I to Convert/SP, etc. If you get right down to it, the Lemans I had 6 cutouts in the cast iron to slip the caliper hanger into and help get the caliper off the rotor. Making the rotor lighter (plus drilling). The touring bikes had only two cutouts (like your picture above, not a Lemans I spec rotor even with the drilling, sorry) meaning more cast iron, heavier.

Ah, OK. Did any of the touring models have drilled discs? Or are these just drilled versions of the touring model discs?

[Fangit]

Joe, as a matter of interest, are your cans straight through or are they baffled?
What do they sound like?

Steve, they are straight through with stainless packing, so yes it's quite loud. They are from Cone Engineering in California. They just supply the mufflers bare and any other pipe bends and hangers you need and then you need to weld them up. They also do quieter versions.

Sound can be heard here:

https://www.youtube.com/watch?v=G0be3VCznaQ

Headphones give the most realistic sound.

[mtiberio]

Ah, OK. Did any of the touring models have drilled discs? Or are these just drilled versions of the touring model discs?

None of the touring bikes had drilled AFAIK. Yours is an interesting design I have never seen. The corner from the plane of the swept surface to the cylinder that goes inboard, looks sharp, not like the stamped and drawn "ashtray" of the stockers.

[Fangit]

None of the touring bikes had drilled AFAIK. Yours is an interesting design I have never seen. The corner from the plane of the swept surface to the cylinder that goes inboard, looks sharp, not like the stamped and drawn "ashtray" of the stockers.

Mine looks exactly like this item I just found from Gutsibits (scroll down):

http://gutsibits.com/pr/TheShop/index.php?f=e&Shnew=1&Model=8&ModelName=Le+Mans+1000&Cat=BRA&CatName=Brakes&Sort=PriceDesc

Probably the same supplier.

[mtiberio]

Mine looks exactly like this item I just found from Gutsibits (scroll down):

http://gutsibits.com/pr/TheShop/index.php?f=e&Shnew=1&Model=8&ModelName=Le+Mans+1000&Cat=BRA&CatName=Brakes&Sort=PriceDesc

Probably the same supplier.

someone is repopping them... glad for that. I was getting paranoid about rear rotors a couple of years ago, and I found a couple of the 6 cutout rear rotors with no drilling. I sent them out for drilling, and one hangs on the garage wall, and the other is in service...

[mtiberio]

here is a picture I took of my rear rotor/wheel spacer to show my buddy what the "top hat/sombrero" space should look like installed. He had his mechanic reverse the spacer, which causes it to dish, and weld itself to the axle. That is another story. In this picture, you can see two of the adjacent 6 cutouts of which I speak which are common to Lemans and other "light" rear rotors...