Binding discs.

Post your 'Wheel, Brake & Tyre' FAQs, comments & questions regarding Ducati motorcycles here.
Post Reply
bobnorton
860 GT / GTS
Posts: 282
Joined: Wed Jan 16, 2008 2:18 am
Location: bromley kent

Binding discs.

Post by bobnorton »

My GTS's front discs both rub and sound horrid, everything looks clean and the pads push back freely,they have been out of use for 15 years. I also note that the discs are not central to the forks.There is a washer between the speedo drive and fork ,looks to be possibly too thin maybee a replacement for a lost one.Can anyone measure theirs for me? It seems likely that the seals have lost their reslience and ability to pull back the pads.The pistons are not corroded and are greased. Is scraping normal?
rwhc80
750 GT
Posts: 174
Joined: Sat May 16, 2009 7:19 am
Location: Melbourne Australia

Post by rwhc80 »

G'day Bob,
Are the discs running central in the calipers when sighted from the front of the bike ? maybe you could adjust the shims between the caliper and fork mounts to centre.

Cheers
Rick
I have desmo disease, I just hope they never find a cure !!!
bobnorton
860 GT / GTS
Posts: 282
Joined: Wed Jan 16, 2008 2:18 am
Location: bromley kent

Post by bobnorton »

Hi Rick, I thought I would sort out the axle first as it will affect everything, All fixings spacers axles are stainless and from experience you cant be sure they are dimensionaly correct so I need to get the discs central first to the forks then shim up the calipers if they need it. Do the pads normally scrape or does the wheel spin quiet? .this is my first disc braked bike in 50 years of riding!.
wdietz186
Cagiva Alazzura
Posts: 703
Joined: Sun Sep 10, 2006 5:40 pm

Post by wdietz186 »

Bob, If the calipers are original it is likely the seals have hardened a bit.The mastercylinder also may have accumulated some muck that can allow residual pressure to remain after the brakes are relased.All that being said,the pads do drag very slightly on the rotors even when everything is perfect so you will hear them and feel a tiny bit of drag when spinning the wheel.Keep in mind the way the seal retracts the piston is the seal untwisting itself after being distorted by pressure and drag on the piston so the movements are very small as the seal is only about 2.5mm in width. Wear on the rotor and pad,ridges etc. will cause some drag too if things have been disturbed and not in the exact position as before.On the axle there is usually a thin washer of around 1.5mm between the fork leg and speedo drive. Due to differences in manufacture it is sometimes not needed,You can check it by snugging the axle up and measuring to see if the wheel is centered in the forks.You can fudge it a little if needed to get the rotors closer to centered in the calipers too. Remember,Ducati in ancient Italian means SHIMS!
User avatar
Craig in France
Paso 750
Posts: 915
Joined: Tue Mar 23, 2004 3:58 pm
Location: Montpellier, France

Post by Craig in France »

Hi Bob,
bobnorton wrote:Do the pads normally scrape ...
No.
bobnorton wrote: ... or does the wheel spin quiet?
Yes.

Just to be clear :-D : There should be no contact between pads and discs with the brake lever released.

First off, make sure the discs are running down the centre of the caliper. Then, if you find the pads are still touching the disc, it's most likely 'cos the pistons in the calipers, and/or the piston in the m/c, aren't retracting fully.

In which case, you need to re-build the calipers (and/or m/c): i.e fit new seals. (And, if you discover you've got the old chrome plated steel pistons in the calipers, change them for the anodised aluminium ones which are a) lighter; b) don't corrode.)

The only other explanation I can think of is that the pads have swollen with age somehow. But I'm sure you wouldn't run with old pads anyway ... :shock:

HTH

Craig
User avatar
Craig in France
Paso 750
Posts: 915
Joined: Tue Mar 23, 2004 3:58 pm
Location: Montpellier, France

Re: Binding discs.

Post by Craig in France »

bobnorton wrote: <snip>There is a washer between the speedo drive and fork ,looks to be possibly too thin maybee a replacement for a lost one.Can anyone measure theirs for me?
Hi Bob,

Oops, sorry, mised this in my previous reply...

Ah yes, a little darling, this one. Yes, they DO wear and/or get pressed into the aluminium housing of the speedo drive. (Curiously, they were never listed as a separate item in the parts list, only in combination with the speedo drive.)

Unfortunately, I haven't got one loose that I can measure for you. But if in doubt, replace it with a stainless one, available, for example, from Steve here - who could also tell you how thick they are, I'm sure.

Ciao

Craig
User avatar
BevHevSteve
SITE OWNER
SITE OWNER
Posts: 2231
Joined: Wed Mar 10, 2004 8:53 pm
Location: Lafayette, California
Contact:

Post by BevHevSteve »

1.3mm thick and we made them out of stainless so all the guys that lost theirs, or, installed them in the wrong place, and dented the inside of their fork,.... These are hard so do not just immediately cup again, conforming to the messed up fork leg.
Image
Steve Allen (925)798-BEVL[2385] Ride'm, Don't Hide'm
Ducati/Euro Spares -> https://Store.BevelHeaven.com
Facebook > http://facebook.com/Bevel.Heaven
Twitter > http://www.Twitter.com/BevelHeaven
bobnorton
860 GT / GTS
Posts: 282
Joined: Wed Jan 16, 2008 2:18 am
Location: bromley kent

Post by bobnorton »

Thanks all, I found mine between the speedo drive and hub,had to be wrong!,the rotor only clears the forkleg by a few thou on this side so a new ss 1.3 may sort this out,plus a seal kit.As with my 250 I'm comming to the conclusion that everything needs to come appart to be checked.Wheel bearings appear new but don't turn smooth with a finger , c3 grade needed? .Someone spent a lot of time and money on this bike to no avail.Have to assume everything can be wrong, going to be another saga!!
User avatar
Craig in France
Paso 750
Posts: 915
Joined: Tue Mar 23, 2004 3:58 pm
Location: Montpellier, France

Post by Craig in France »

bobnorton wrote:<snip> Wheel bearings appear new but don't turn smooth with a finger , c3 grade needed?
Nope, regular is fine. The larger then normal internal clearance offered by a C3 bearing is applicable in situations where there is a high operating temperature or high vibration.

Neither of which applies to a motorcycle wheel.

Ciao

Craig

P.s I always assume the bearings and brakes are stuffed on any bike I buy ... :-D
bobnorton
860 GT / GTS
Posts: 282
Joined: Wed Jan 16, 2008 2:18 am
Location: bromley kent

Post by bobnorton »

I guess these new bearings have been indented by hamfisted dpo, does a standard axle have a shoulder? otherwise the tightening force seems a bit much for the speedo drive, an odd design?.Although theres absolutely no wear on the pistons the seals appear to have taken a "shape" so replacement is it.
bobnorton
860 GT / GTS
Posts: 282
Joined: Wed Jan 16, 2008 2:18 am
Location: bromley kent

Post by bobnorton »

Bought new parts ,fitted, rotors still offset to one side,could possibly be a "fashion" issue as PO turned the legs round to put the calipers behind the legs, and fitted a stainless spindle and spacers. I see that the slider bottoms are not both the same width at the spindle hole.I also note that the legs are pulled in when the spindle nut is tightened, not good for free action or wear.I need to compare with an orriginal spindle/axle.Just as well i now have 2 GTS's !!.
bobnorton
860 GT / GTS
Posts: 282
Joined: Wed Jan 16, 2008 2:18 am
Location: bromley kent

Post by bobnorton »

I've swopped the legs to put the calipers in front, speedo drive on the right ,all seems better however I note the 1.3 mm spacer now abutts the spindle shoulder and is about 1.5 mm away from the leg/slider,normal?.
Den
Mach 3
Posts: 89
Joined: Fri Apr 09, 2004 6:02 pm
Location: Florida, USA

Post by Den »

Sorry I'm joining this discussion so late. I am posting the text of two different emails I sent to two different riders at two different times a few years ago addressing this same concern. Good luck.


On bevel forks the spacer (or speedo drive/washer combo) that goes between the
hub and the slider on the side that is taking the axle nut will always determine the centering of
the wheel.

For it's rotation to be correct the speedo drive must always go on the right.
The spacer (or speedo/washer combo) that the axle step rests against can, within reason, be almost any thickness.

With the calipers in front of the sliders, the stock spacer determines the centering of the wheel.
With the calipers behind, the speedo/washer thickness will determine the centering.

My stock spacer measures 17mm.
My speedo drive measures 14.35mm.
My washer (non stock by design) is 2.45mm.
My speedo+washer combo adds up to 16.8mm

My calipers are behind the sliders. My speedo/washer combo determines
the centering of my front wheel.

In theory my front wheel is offset in the forks by 0.2mm.
That's about .008"

If you are running your calipers behind the sliders make sure your speedo/washer combo
measures as close to 17mm as possible.
Turning/shaving down the stock spacer on the other side so it matches your undersized
speedo/washer combo won't work.



==============================================

The bevel twins employ a stepped axle design.

So, the spacer (be it the plain spacer or the speedo-drive/washer combo)
that goes between the
hub and the slider on the side that is taking the AXLE NUT will always
determine the centering of
the wheel.

Ducati's design team determined that a 17mm spacer on the side of the axle
that is taking the AXLE NUT would be needed to assure the centering of the
wheel in the frame and with the rear wheel.

For it's rotation to be correct the speedo drive must always go on the
right.
The spacer (or speedo-drive/washer combo) that the axle step rests against
can, within reason, be almost any thickness.

If you are running your calipers in front of the sliders make sure your
plain spacer measures as close to 17mm as possible.
If you are running your calipers behind the sliders make sure your
speedo/washer combo measures as close to 17mm as possible.
Turning/shaving down the stock spacer on the other side so it matches a possible undersized speedo/washer combo won't work.
Post Reply

Return to “Wheel, Brake & Tyre Shop”