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Discussion Starter #1
Hello All,
I've got a problem with my both front brakes dragging. I'm a bit stumped so would appreciate any advice to help with the diagnosis.

I've cleaned the caliper guide pins and lubricated with silicone grease in the hope that it would be a quick/cheap fix. It seems the pressure is not being released. With the front end jacked up, engine off, when I give the brake pedal a good few pumps then try and turn the wheels they remain locked/very very hard to turn. When I pull the caliper to retract the piston it seems to release enough pressure to be able to turn the wheel. When driving, the front wheels get hot (so hot you can smell them so I'm not driving until fixed).

The rear brakes seem to release fine.

This has happened in the last day and I've not done any work on the brakes recently. As the problem is with both front brakes would this indicate a master cylinder fault? Or it is possible that I've got a problem with both brakes hoses or both calipers.

Thanks for taking the time to read this and any pointers would be appreciated.

Thanks.
 

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The only thing I can think of is the flex lines (internal collapse) or flex line brackets that surround the flex lines are rusting and expanding on the inner side and choking the flex line.

It is fairly easy for your foot to force the brake fluid past an obstruction, but it is a lot harder for the fluid to get back past the obstruction.

I don't think it is your master cylinder as all your brakes would be locked up, it is was.
 

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I believe the most common cause of dragging front brakes is binding caliper slides.
 

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Here is the quick and easy test, pump up the brakes (locked), then open the line at the master, if the wheels unlock, the issue is in the master...

The front and rear work off different chambers in the master...

... Philip
 

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With regard to Naut's suggestion...or just crack the bleeder at the caliper instead. :)

Also checking the Master for full linkage release (thus allowing the line pressure to port back to the reservoir) would be an item to check.
 

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Max: I made the suggestion at the master, because we know the pressure is moving to the wheels, not sure if it is releasing back at the master.. Makes a difference if some where is acting as a one way valve..


.... Philip
 

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I think that we are both looking for the same pressure release, just at different ends of the same line. :)
At the caliper you will also be sampling / releasing pressure AFTER a suspect hose constriction.

I just thought it was easier than possibly picking the wrong Master connected tubing line, as well.
 

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Discussion Starter #8
Many thanks Sperold, Fordem, Philip & Max for the replies overnight here - very much appreciated and they cheered me right up this morning.

I've been out this morning and cracking the bleed nipples on the calipers didn't unlock the wheels but there was a flow of fluid so, I think that indicates the issue is local to the calipers/slides?

So what I've done so far today is cleaned up the slide pins with steel-wool, pushed the caliper pistons back, greased the slides, re-assembled and bled the brakes. Now when I build up pressure in the lines, the wheels can be turned by hand.

I will go for a spin later and let you know how it goes (fingers crossed). Thanks again.
Mike.
 

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If bleeding off line pressure at the caliper releases the pad to rotor grip, then I suspect a Master Cylinder issue. ;)
 

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If bleeding off line pressure at the caliper releases the pad to rotor grip, then I suspect a Master Cylinder issue. ;)
This can also be caused by a collapsed line - which is why aqua is suggesting to release the pressure at the master - that is a more definitive test.
 

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caused by a collapsed line
A rare occurrence / cause, particularly simultaneous affecting BOTH calipers.

My $'s are on the Master. ;) We'll see!

And checking for a hose restriction is easy peasy. A conventional "bleed" procedure at the caliper will indicate whether adequate fluid flow is present.

9 time out of 10, stuck caliper pistons (from pushing the piston back into a filthy bore with the installation of new / thick pads) or faulty Master's are the cause here. We seem to have ruled out the calipers in this scenario.
 

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Discussion Starter #12
Hi, well I've been for a spin and it's still getting pretty hot at the wheels. I'm not getting the wheels locking as I was before this mornings efforts - when I build up the pressure it's possible to rotate the wheels without too much effort. But I guess when driving the slight rubbing is causing heat to build up causing more friction and goes from there!

Just to clarify - before I started working on it this morning, when I released the pressure at the calipers the wheels remained locked - so would that indicate a problem with the calipers? When I opened the bleed nipple there was a slight flow of fluid but I wouldn't say it was under any pressure. If this is correct then I'd better some calipers ordered.

Cheers.
 

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when I released the pressure at the calipers the wheels remained locked - so would that indicate a problem with the calipers?
Yup. You got it! Pistons stuck in bores. ;)
 

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Discussion Starter #14
Cheers Max,
A comment on your previous post reminded me - when I got the car, first thing I did was check the brakes - the pads were nearly down to the metal and so the pistons were just about fully extended. Pads were replaced but now as they are wearing perhaps the pistons are hitting an area corrosion.

My next call is to order the calipers. Will let you know how it goes. Thanks again!
 

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Pads were replaced but now as they are wearing perhaps the pistons are hitting an area corrosion.
Bingo! :)
 

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Cheers Max,
Pads were replaced but now as they are wearing perhaps the pistons are hitting an area corrosion.
I'd say this is unlikely - it's fairly common to have the piston sealing surface plated with either nickel or chrome - every caliper I've ever stripped that had the dust boots intact has had the piston sealing surface in impeccable condition and many of the ones with torn dust boots just needed a thorough cleaning - no corrosion whatsoever.

I've never bought new (or rebuilt) calipers, I've rebuilt more than a few and the only ones that needed new pistons were a set I picked up from a scrappy to do a "big brake" conversion - those were so bad it took me a week to free up the slide pins.
 

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Discussion Starter #18
They had Tokico calipers at the store rather than the Sumitomo ones I need so I get the night off. Picking up the correct calipers tomorrow.

Thanks Fordem - I kind of hope it is the calipers now as I just want to get back on the road (and not replace any more components).
 

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Discussion Starter #19
I picked up and fitted the new calipers today. Just been for a drive and everything good so far. Hopefully this has fixed the problem and it's not that the fresh seals in the new calipers are masking the original problem. If there are any updates I'll post them.

Thanks to all for your help and advice.
 

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Sounds SWEET! :)
 
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