Sticky drum brake puzzle ...

[Abarth982]

My front offside brake has always been a bit sticky so I've finally got around to having a look and must admit it puzzles me so I'm wondering if anyone else has had something similar ...

The drum, shoes, auto adjust mechanism etc etc are all pretty clean (spotless now actually) and look to be in good working order.

When I put the drum on and rotate the wheel it's fine.  However, when I put the two bolts in that hold the drum to the hub and do them up tight(ish) the wheel stops rotating.  If I ease off the two bolts it rotates again.  I thought maybe the drum is catching the shoes on the edge so I temporarily put a spacer in so the drum sits a bit proud and it made no difference.  It seems that the tightening of the drum to the hub is causing the sticking.  Of course, this is exacerbated when you put the wheel on and tighten it up.

I wondered if there's too little end float on the wheel bearing and tightening the drum to the hub is 'pulling' it ever so slightly but nevertheless enough to stop its rotation.

Any thoughts?

 

[ChrisRLewis]

Have you tried swapping the brake drums over? This will eliminate a problem with the drum, maybe oval or worn?

[Abarth982]

Just spent the afternoon taking the brakes/hub completely apart, cleaning (to be honest it wasn't really that dirty anyway) and re-assembling.  No difference 😠 So yes, I'm now wondering if the drum has gone slightly oval ... Will swap nearside to offside when I muster some more enthusiasm and will report back.

[Abarth982]

Well, after much disassembling, assembling, disassembling etc etc I finally got to the bottom of this ...

One of the two pistons in the wheel cylinder had seized, this wasn't readily apparent on inspection as the brakes still worked via the one good cylinder but does account for the 'stickiness'.

Anyway, I clamped the hose and put a new wheel cylinder on and bled it through for what seemed an age.  There's a lot more movement in the pedal now (maybe to be expected?) but I'm not convinced I've got all the air out.

Are there any 'tricks' to bleeding on the 126 or is it just perseverance and copious amount of new fluid?

[andyzeetec]

That's great news, I know a mechanic that worked for Fiat back in the day. He said gravity bleeds the best way, (which is what I've done), but might have to pump the pedal once to get it going. The other way to get it flowing is open the bleed nipple up, then squeeze both pistons in with your fingers, then shut the bleed nipple, let the pistons come out and repeat if necessary. Also, when bleeding brakes on an older car, what you don't want to do is push the brake pedal down too far, because the seals in the master cylinder are only used to travelling a certain distance and if you push them too far they can turn inside out and then you cant bleed it at all.

[Macmonkey]

I was in a similar position to you in that I too had a binding front brake but that was caused by a dodgy hose. I ended up changing all my brake shoes, cylinders and hoses as they were past their best. When I bled my brakes I too felt as though there was a lot more pedal travel. Like you said some of this will be down to the brakes no longer sticking/binding so the pedal’s bound to feel different but also the brakes were a sod to bleed! What I found useful was when I was happy I had got all the air bled out of the lines (I eventually found gravity bleeding worked the best), I took the cap off the fluid reservoir, gently depressed the brake pedal a bit and keeping it depressed tapped the master cylinder to dislodge any air trapped in it. I found that if I left it and came back to it the next day it had given chance for the air in the system to work it’s way up into the fluid reservoir. There was still a bit of travel in the pedal but I have now covered a couple of hundred miles and the travel is getting less as the shoes bed in. Also I have done the old trick of driving quickly in reverse and slamming on the anchors which took away a bit of travel too.

[Abarth982]

Thanks both, gravity bleeding tomorrow it is then (too knackered today from getting up and down umpteen times!)