Author Topic: Front disc run out (Read 8126 times)

Stevex · « **on:** November 05, 2014, 11:45:01 AM »

Since my LM2 rebuild has been back on the road I've noticed on occasions the front brake lever needs a double pull to become effective, although I've noticed no pulsing.
The brake system is de-linked and at a standstill or pushing the bike, the lever is solid.
The discs are well grooved and their thickness is 5.98mm. Can anyone please tell me what the max run out for these discs is; I've measured both with a dti and I'm getting 0.5 and 0.3mm from them. Guessing I might be investing in some stainless replacements over the winter.
I've seen some NOS discs but the asking price is about £450 a pair. HMB do some SS replacements with the original drill pattern for about Euro280 a pair.

http://www.hmb-guzzi.de/shop/product_info.php?info=p853_bremsscheibe-vorn-300-mm--lm1-3-edelstahl.html

rodekyll · « **Reply #1 on:** November 05, 2014, 01:14:24 PM »

Runout varies by rotor. The min is a number cast into the rotor itself. Look for the marking.

I'd agree that warpage could be the cause of the problem, although with a warped rotor you can usually feel some pulsing in the lever. It could also be the m/c leaking internally.

You can have warpage without runout and runout without warpage.

normzone · « **Reply #2 on:** November 05, 2014, 01:24:07 PM »

AND you lost me at this one...

" You can have warpage without runout and runout without warpage. "

I can understand runout without warpage:

- disc thickness variation can show runout
- mounting alignment issues could show as runout without there being any warp

But unless the disc was mounted so as to compensate for warp (highly unlikely) then how would you get warpage without runout?

rodekyll · « **Reply #3 on:** November 05, 2014, 01:39:00 PM »

Does this make it less muddy?

Warpage is a bent or wrinkled disk.

Runout is the amount the disk 'thins up' with use. It can be uniform or not.

nonuniform runout is not warpage. It can happen because of hardness or density differences In the rotor casting and oxidation as easily as by a bent/warped rotor.

Either is possible without the other.

:)

Wildguzzi.com · « **Reply #3 on:** November 05, 2014, 01:39:00 PM »

normzone · « **Reply #4 on:** November 05, 2014, 02:12:25 PM »

" Runout is the amount the disk 'thins up' with use. It can be uniform or not.

nonuniform runout is not warpage. It can happen because of hardness or density differences In the rotor casting and oxidation as easily as by a bent/warped rotor.

Either is possible without the other. "

Ah. I'm accustomed to just viewing " runout " as information obtained from the act of measurement, usually with small numbers being good and larger numbers being a bad thing. And I'd not considered localized domains or oxidization as causes of runout, but they probably are common in the model we're talking about.

I'd not thought about it, but I guess discs lead a hard life. Long periods of inaction followed by violent heating from localized friction. Sounds kind of sexy, come to think of it.

mtiberio · « **Reply #5 on:** November 05, 2014, 02:13:03 PM »

Quote from: rodekyll on November 05, 2014, 01:39:00 PM

...

Runout is the amount the disk 'thins up' with use....

since when?

mtiberio · « **Reply #6 on:** November 05, 2014, 02:15:43 PM »

OP, your problem is more likely a master sylinder that needs a rebuild kit (the internal leaking that roadkyll speaks of).

Triple Jim · « **Reply #7 on:** November 05, 2014, 02:22:55 PM »

The term "runout" as I'm used to using it around a machine shop is essentially wobble. There's also thickness variation, which is different. Thickness variation can be felt as pulsing at very small amounts, like 0.001".

Runout can normally be tolerated at values of a few thousandths of an inch. 0.5mm is about 0.020", and that's pretty high. I made some shims from brass shim stock for one my my Mille's rotors that was up around 0.012" runout and got it down to 0.005" or so, and it works fine.

Mike Tashjian · « **Reply #8 on:** November 05, 2014, 05:45:01 PM »

When servicing a rotor the stamped number on it usually is the minimum you can refinish the rotor to. Then there is the service limit which refers to the amount of material you have left after running the rotor, after you have turned it to the minimum number stamped into it. In other words there is a point when the rotor is deemed unsafe to use. Runout is not used to determine if the rotor has enough material to use it. Parallelism is the term used to see if there are thick or thin spots. Runout is used for the waviness. Checking the rotor entails dividing the surface into many pie slices with a marker and then checking for more than one problem. I am guessing that Rodekyll is on the right track with the MC leaking internally too. Mike

rodekyll · « **Reply #9 on:** November 05, 2014, 06:41:56 PM »

Quote from: Mike Tashjian on November 05, 2014, 05:45:01 PM

When servicing a rotor the stamped number on it usually is the minimum you can refinish the rotor to. Then there is the service limit which refers to the amount of material you have left after running the rotor, after you have turned it to the minimum number stamped into it. In other words there is a point when the rotor is deemed unsafe to use. Runout is not used to determine if the rotor has enough material to use it. Parallelism is the term used to see if there are thick or thin spots. Runout is used for the waviness. Checking the rotor entails dividing the surface into many pie slices with a marker and then checking for more than one problem. I am guessing that Rodekyll is on the right track with the MC leaking internally too. Mike

Thanks for clearing that up. :)

normzone · « **Reply #10 on:** November 05, 2014, 06:50:58 PM »

Interesting, I'd not thought about different behaviors between a warped disc and one that's worn to irregular thicknesses.

Would the varying behavior be a result of the caliper's ability (or not) to respond?

I'm out of my league here, but it seems like varying thickness would cause grabbing and pulse diving at the front end, whereas with warping the calipers might compensate for up to a given range.

Just guessing, but I'll have to play with my Bassa front linked disc sooner or later - at low speeds it pulse dives.

???

rodekyll · « **Reply #11 on:** November 05, 2014, 06:59:13 PM »

My experience has been several pumps to engage the brake with immediate fade as the pads and pistons get pushed back. Also, a stuttering, grabby, pulsing feel to the brakes. Front end will 'pogo' a little as the pads grab and are repelled.

Front wheel bearings can cause the same symptoms + possibly wandering steering/weave.

Chuck in Indiana · « **Reply #12 on:** November 05, 2014, 07:06:48 PM »

Runout is generally considered ok until it gets over .002" TIR. IIRC, that's the industry standard.

mtiberio · « **Reply #13 on:** November 05, 2014, 08:04:40 PM »

When I checked my cal1400, the max allowed runout was.008" according to the book.

Morizzi · « **Reply #14 on:** November 05, 2014, 09:15:14 PM »

If you still have the rigid Brembo cast discs with bolt on carrier the max runout stated by Guzzi is 0.2mm.

In addition to that minimum disc thickness is 5.8mm.

lucky phil · « **Reply #15 on:** November 06, 2014, 01:34:26 AM »

Have you checked the front wheel bearings? If they are worn it allows the wheel to move around and push the pads back into the calipers and give you a long lever. Wont be an issue at a stand still and you will be able to pump them up again at a stop and maintain a good lever but after a few corners it will have a long lever again.
Raise the front wheel off the ground with the calipers off the bike or the mount bolts loosened and grab the wheel and try twisting it back and forth. There should be no movement.
Ciao

Stevex · « **Reply #16 on:** November 06, 2014, 01:10:46 PM »

Some additional info that I didn't think relevant at the time is:
1) Every bearing on the bike (bar engine / gearbox) was replaced (and steering bearings correctly set up).
2) The PS15 MC I fitted was brand new.

Visually the discs look well grooved and the peaks of the grooves are close to the 5.8mm limit quoted above, so the troughs will definitely be past it.
Due to the grooving I took my measurements from the very edge of each disc at the small lip before the pad makes contact with the disc, so it's quite possible they are warped as well.
From what I've learnt above, I'm looking to replace the discs over winter; thanks to everyone for taking time to offer advice.

Stevex · « **Reply #17 on:** February 28, 2015, 10:16:00 AM »

New SS discs fitted; looking forward to seeing how these perform with carbon ceramic pads. (De-linked)

Chuck in Indiana · « **Reply #18 on:** February 28, 2015, 10:24:05 AM »

Pretty.. ;-T

mtiberio · « **Reply #19 on:** February 28, 2015, 04:35:34 PM »

With the costs of rotors so dear, I prefer nice soft organic pads vs sintered pads. I don't know how ceramic pads fall in this spectrum, but do you really want the rotors to wear out with one set of pads?

Stevex · « **Reply #20 on:** March 01, 2015, 04:28:28 AM »

When I received the carbon pads I noticed they were sintered so I'll keep an eye on wear rates.
Having said that I've run EBC HH sintered pads on Japanese original stainless discs and they held up OK.

molly · « **Reply #21 on:** March 01, 2015, 05:00:12 AM »

Did you check the disc runout after assembly with a dial test indicator?

I agree EBC HH pads will be fine with SS discs if anything they will give a more even wear rate.

Stevex · « **Reply #22 on:** March 01, 2015, 07:24:39 AM »

Quote from: molly on March 01, 2015, 05:00:12 AM

Did you check the disc runout after assembly with a dial test indicator?

I agree EBC HH pads will be fine with SS discs if anything they will give a more even wear rate.

Checked original discs after running the bike for a few hundred miles and finding the lever needed pumping every now and again to deliver decent stopping power. This was after de linking them, and yes, I used a dti.
The CC pads I fitted are Brembo and recommended by HMB for the stainless and original discs.
Discs are 5mm thick with a wear limit of 4.45mm.

Tobit · « **Reply #23 on:** March 01, 2015, 08:14:25 AM »

Late to the conversation but I've always considered runout of a flat rotating object to be a measurement related to the axis. A 300mm diameter rotor has a radius of 150mm. Runout is any deviation from the 150mm radius.

Warp is deviation measured perpendicular to the axis.

Correct?

Delta425 · « **Reply #24 on:** March 01, 2015, 01:47:28 PM »

This may help clear things up a bit: http://www.stoptech.com/technical-support/technical-white-papers/-warped-brake-disc-and-other-myths

Rough Edge racing · « **Reply #25 on:** March 01, 2015, 02:04:39 PM »

Quote from: Delta425 on March 01, 2015, 01:47:28 PM

This may help clear things up a bit: http://www.stoptech.com/technical-support/technical-white-papers/-warped-brake-disc-and-other-myths

Another explanation by brake experts, same thing only different....http://www.hendonpub.com/resources/article_archive/results/details?id=1787

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Author Topic: Front disc run out (Read 8126 times)

Wildguzzi.com

Morizzi

Rough Edge racing