1150 GSA Front brakes

[GhostCav]

Howdo,
Bike just failed it's MOT on the front brakes. The brake gauge was showing a difference between 100% & 50% as the wheel was braked. There was pulsing in the brake lever. Does this sound like a warped disc? I've never had one that bad before if it is. Or maybe new seals/pistons & replace the fairly worn pads? I know it's hard to tell without seeing/feeling the bike but just asking before I splash out on loads of bits..
Ta

BTW, Just to add. Bike is an 03 Non ABS version..

 

[rob's new bike]

Hiya,
If the brakes and pads look ok try getting some brake cleaner on the bobbins...my firestorm had a similar problem which turned out to be stuck bobbins. Plenty of cleaner and a bolt through the bobbin to work it a bit sorted them out
Regards
Rob


Sent from my iPhone 4 using Tapatalk

 

[GhostCav]

Will give the bobbins a good check, never thought of that to be fair. Should the disc move slightly or not?

 

[illustratedman]

Brakes

It's a known issue, they wear the holes oval. Take the discs of and have a look.

 

[warmshed]

Will give the bobbins a good check, never thought of that to be fair. Should the disc move slightly or not?

Yes they should have about 40thou" movement if you press them hard and compress the wavy washer.

 

[GhostCav]

It's a known issue, they wear the holes oval. Take the discs of and have a look.

When you say oval, like this?? or oval the other way (i.e. Horizontal as per that pic?)

Have stripped off the discs anyway & checked the bobbins. Thought I had got lucky as when I went to clean them one had two washers on it. However that had fell off another one in the tub I was using to hold them in..

However with checking two of my bobbins did reveal some wear. Top one dented down & other one the lip is higher one side to the other.. Would that be enough to make pulsing brakes??

Also I take it these discs are directional, which way from this pic should they rotate... Ok so I'm a tit & didnt take note when I took them off..

 

[JohnnyBoxer]

I'm interested in the collective wisdom of this

 

[GhostCav]

So would I be, Still need some help here fella's...

Sadly due to tax on car (& bike if I get MOT), paying for holiday & insurance renewal on car & bike this month the funds are a little tight right now. Otherwise I would just buy discs,pads,bobbins & seals & pistons & do the lot.

 

[(RIP) Kaister]

sounds to me like oil on the disc surface, not bobbins anyway

I'd put it back together correctly, douse the bobbins and discs and pads with can of brake cleaner, tap the discs side to side gently with a soft faced hammer to free them up all over - pressure wash all the crap off them.

then make sure they are free.

take the calipers off and make sure the pistons are all free and if the pads have any material on them, all should be ok.

 

[(RIP) DitchWater]

So would I be, Still need some help here fella's...
Otherwise I would just buy discs,pads,bobbins & seals & pistons & do the lot.

Firstly, your discs do look worn but are probably within the service limit: You could measure their thickness where the pads run and they should be either 4.5mm or 4.0mm minimum thickness (I've seen both of those limits on discs I have). To ensure their flatness, simply lay them on a flat surface and spread your hand across the disc and push down gently. If you feel any rocking movement then there is warping and you'll have to judge whether they are affecting the wheels' rotation.

Your brake calipers are also probably okay and may just need a service: Make sure your pistons are fairly clean and without corrosion. You might be able to see pitting on the pistons' surface and this is when you should consider replacing them. If not clean them and make sure they move relatively freely.

Now, your bobbins do appear to have flat spots worn onto the working edge and this could be causing some of the problems you have described. Mine were like that as well and I gave them a polish with some emery cloth and rotated them through 90 degrees in the hope they might present a different face. I'm not expecting any great performance from this adjustment but I'm content that I did something.

Obviously you need to replace your spring washers and I'd replace that bent bobbin while your making your order. Personally, I'd replace them all and be done with it and then you'll be in with the best chance of getting the result you desire.

By the way, I only have the bobbins, spring washers and bolts. I've never seen those other parts mentioned here.

 

[GhostCav]

Thanks for the replies.
Discs look worse in pic to be fair, only light marks on them & well within service limits. Have ordered two new bobbins & a full set of spring washers & a new set of pads. Should arrive tomorrow so I will wang them on after cleaning all the other bits up & see what happens. Fingers crossed, running out of days off here..

 

[Aidjay]

Your brake calipers are also probably okay and may just need a service: Make sure your pistons are fairly clean and without corrosion. You might be able to see pitting on the pistons' surface and this is when you should consider replacing them. If not clean them and make sure they move relatively freely.

I've very recently done a check on my front disc and can concur with everything DitchWater says except for the part about the pistons. Mine are made from a plastic compound, but I'm not saying this is the same for all 1150GSA's. But cleaning the pistons is a good idea. Water and a brush is good, if you want to spare the expense of brake cleaner. Just don't use lubricating sprays.

If your old pads are not worn, there's no point in binning them. It's unlikely to be the cause of the problem.

 

[GhostCav]

I stripped the brake calipers down before MOT, cleaned & all seals fine. Pistons slide in & out very smoothly. As for the pads, they were going to need replacing soon anyway so no worries. Now thinking I should of ordered some slide pins as well as mine were a little corroded so cleaned them up as best as possible.

 

[MattW]

... except for the part about the pistons. Mine are made from a plastic compound ...

Really?
Are you sure they're not made from ptfe coated metal?

 

[Aidjay]

Really?
Are you sure they're not made from ptfe coated metal?

Maybe. The fact that I managed to cleverly push a hole through one of them once convinced me they were made of plastic. I thought they were solid, so used a sharp impliment to push them back. Its the kind of mistake you make once. Once.

I have some spares at home, I'll have to verify for my own curiousity.

 

[illustratedman]

When you say oval, like this?? or oval the other way (i.e. Horizontal as per that pic?)

Pic looks ok, a little worn. I'd replace all the bobbins/washers and see if that cures it. Also check the obvious that the discs arent warped.

 

[GhostCav]

Bah... Bobbins & washers replaced & slide pins as mine had some corrosion. Felt good for a while but went bad again on way to MOT centre. Fella ran the bike on the rollers (But not as a retest) & it still is going from 100% to 50% braking with the lever in the same place. Doesnt seem to happen in sequence to the rotation of the disc though. Would of replaced the pads as well but MW sent the wrong ones. Will try tomorrow & failing that I guess new discs even though I can't detect any warp using my primitive screwdriver taped to foek leg method. Whats left to try after that?? Master cylinder?? I am bleeding the brakes at the calipers only, am I missing another bleed point (Non ABS bike)?

 

[fatnfast]

Funny enough I have just been reading an artical in Practical classics (cars) and they have a section all about brakes this month. One of their suggestions for uneven braking is down to a collapsed or collapsing brake line on the troublesome side. Are you still running with rubber lines?

 

[GhostCav]

Errr, it's a GSA. It's got braided hasn't it, looks like braided anyway. I may well be wrong.

 

[fatnfast]

Sorry, just a suggestion, my 02 gs has rubber pipes, but its not an adv.