Rear brakes stuck on.

[benji106]

Whilst on the motorway :shock:
My normal journey to work involves travelling down the M4 for 1 junction. This morning I left the house, bike was fine on the way to J11, felt normal.
I was making progress down the Motorway and just before my exit the bike started to feel sluggish, not picking up as it should, but revving freely with the clutch in, hmm odd.

anyway get off at my exit J10 and coming up to the lights the bike is slowing down way quicker than it should be off the throttle, touch the rear brakes and they are locked on solid! turn round and there is brake fluid ****ing out of the back and smoke coming from the rear caliper/disk. The fluid was coming out under the seat so I assume it was coming from the resevoir as a result of the fluid boiling over?

Well Im in the middle lane of the Mway exit slip road so cant hang about there, lights go green so I give the rear brake a good kick and pull away, when I get to the next set of lights on the roundabout the brake lever is free. Im 30 seconds away from work at this point so decide top carry on as the brakes have freed up. I got to the office car park and the rear disk is covered in brake pad residue and dust. The rear brake is now free, but not much left in the way of pads.

So, Cause? I guess I must have touched the rear brakes and one of the pistons got stuck?

I will need to strip and clean the rear caliper, new pads, bleed and replace brake fluid.

Is my diagnosis correct? or could there be something else at fault?

Background: Y reg SV, 19000 miles. Been in my possesion a couple of months, not touched the brakes myself but has been serviced annualy.

[timwilky]

I would bet a dust seal has adhered to the piston and been pulled through, stopping the piston from backing off.

Fun part will be if the previous owner has not maintained the caliper and the retaining pins are seized in place. It is a poor design, well documented and a search will prove useful for rebuilding. Try to avoid splitting the caliper.

[benji106]

Thanks, will do a search, how likely do you suppose it is that the disks are fubared from the heat?

[benji106]

I dont bloody believe it....
Just went and had another look at the bike in the car park and found the cause...
I had the seat off at the weekend to put the battery on charge, I dropped on of the little allen key bolts that hold the infill panels, couldnt find it anywhere and assumed that it had been sacrificed to the garage gods, anyway looks like it had dropped into the rear brake linkage and been caught between the linkage and the hanger, jamming the rear brake on when I applied it DOH.

[husky03]

could have been a very sore lesson but if its only gonna cost you brake fluid you've got off lightly-always find that dropped bit

[benji106]

Looks like fluid, pads, and the hose has ruptured as well so will be upgrading to braided lines. Sometimes the garage does swallow up bolts/screws/sockets and I was in a rush this morning, but will certainly be doing a more through check to make sure it hasnt found a new home somewhere on the bike in future.

[Al_Sweetman]

Youch! As an aside, I thought that the insulator pad between the pads and the pistons was meant to stop brake fluid boil?

A.

[benji106]

About to order the following from Wemoto, unless anyone thinks I have missed something, or would recommend a different supplier:

1 x Suzuki SV 650 SK1/SK2/SX/SY Dot 4 Hydraulic Fluid 500 ml @ 4.50
1 x Suzuki SV 650 SK1/SK2/SX/SY HEL Rear Hydraulic Hose
@ 24.95
1 x Suzuki SV 650 SK1/SK2/SX/SY Pads Rear EBC Standard (GG Type)
@ 16.66
1 x Suzuki SV 650 SK1/SK2/SX/SY Rebuild Kit Full Seals Caliper - Rear
@ 17.63

[Al_Sweetman]

Does the rebuild kit include a new bleed nipple?

[benji106]

A bleed nipple cover, but not a bleed nipple going by the photo. only £3 so added onto order. anything else?

[Al_Sweetman]

That's all I could think of. Bleed nipple not essential by the way, but I always think it's best to do as much as possible especially if you're playing around down there anyway. Won't hurt

Cheers

Al.

[benji106]

Yeah not replaced them when done brakes in the past but for £3 might as well.

[keith_d]

Youch! As an aside, I thought that the insulator pad between the pads and the pistons was meant to stop brake fluid boil?

A.

When a brake pad rubs on the disk there are only two places for the heat to go, the disk or the pads.

With old asbestos pads (showing my age here) the thermal conductivity was so low that almost all the heat ended up in the disk. With modern sintered pads a lot of the heat ends up in the brake assembly, and a thin steel shim behind the pad doesn't make a significant difference.

Fortunately, modern brake fluids have very high boiling points, so it's very unusual to boil them on the road, even on long descents. But if a brake is stuck partially on you might still get well above 200C. New fluid should boil around 250C, but if it's old and wet 200C can be enough.

Just my thoughts,

Keith.

[Spoon]

Just FYI there are two bleed nipples on a curvy rear caliper

[benji106]

That will be why there are 2 covers in the rebuild kit then... oh well ordered now.