Rear brake piston won't unwind - ideas?

[BonzoGuinness]

As per title really, I'm half way through fitting new rear pads - right side went perfectly, now stuck on the left side.

Basically can't get the piston to unwind far enough, so that the caliper will swing back down over the new (thicker) pads. Feels like I've been turning the key for AGES.

Thoughts before I get angry with the beastie?

Thanks in advance...

Edited by BonzoGuinness on Thursday 16th July 17:01

[DennisTheMenace]

try aiding the piston back while turning the grub screw .

[franv8]

It's possible the return 'gear' as I'll call it has stripped its teeth. Often you can pull it out by cocking the allen key to one side and removing it, have a look at the end. They're made of toffee, but you can get a bit of extra life out of it by hacksawing the stripped end off to leath healthy teeth.

Sadly they are one of the weak points on these cars, as it was on the MX6 I had too.

[BonzoGuinness]

Result! Checked the little return gear - it kept falling out anyways - all teeth intact. So it might be the spline shaft that's mullered.

"Aided" the piston with my puny thumbs, no no avail. Borrowed a friendly neighbour and some sturdy G-clamps, clamped around the back of the caliper and the piston 'head', popped right in with minimal effort.

Adjusting it to seat the pads will be a pain, but it's a good excuse for a brake upgrade come pay day methinks...


Thanks guys

[Stickers]

Useful tip:

I know that this will sound a tad like 'locking the door after the horse has bolted' but, it's always a good idea to force the pistons back as far as humanly possible BEFORE caliper removal......remembering to keep an eye on reservior levels to avoid overspill.

The disc itself can be used as leverage when wedgeing a screwdriver/lever between the disc & the old pads, leaving the new pads with plenty of slack on refitting the caliper.

[MX-5 Lazza]

Stickers said:

===Useful tip:===

I know that this will sound a tad like 'locking the door after the horse has bolted' but, it's always a good idea to force the pistons back as far as humanly possible BEFORE caliper removal......remembering to keep an eye on reservior levels to avoid overspill.

The disc itself can be used as leverage when wedgeing a screwdriver/lever between the disc & the old pads, leaving the new pads with plenty of slack on refitting the caliper.

BG was talking about rear brakes. You retract the calliper using a grub-screw, not by pushing it back in like you do with the front brakes

[Stickers]

MX-5 Lazza said:

Stickers said:

===Useful tip:===

I know that this will sound a tad like 'locking the door after the horse has bolted' but, it's always a good idea to force the pistons back as far as humanly possible BEFORE caliper removal......remembering to keep an eye on reservior levels to avoid overspill.

The disc itself can be used as leverage when wedgeing a screwdriver/lever between the disc & the old pads, leaving the new pads with plenty of slack on refitting the caliper.

BG was talking about rear brakes. You retract the calliper using a grub-screw, not by pushing it back in like you do with the front brakes

Did my rear's Easter & simply backed them off wothout all the issues posted so far!

[skinny]

MX-5 Lazza said:

Stickers said:

===Useful tip:===

I know that this will sound a tad like 'locking the door after the horse has bolted' but, it's always a good idea to force the pistons back as far as humanly possible BEFORE caliper removal......remembering to keep an eye on reservior levels to avoid overspill.

The disc itself can be used as leverage when wedgeing a screwdriver/lever between the disc & the old pads, leaving the new pads with plenty of slack on refitting the caliper.

BG was talking about rear brakes. You retract the calliper using a grub-screw, not by pushing it back in like you do with the front brakes

unless they are a bit sticky in which case you do need to give them a bit of 'help' after you've unwound the adjuster

[bluetone]

^^^^ Wot he said (in my experience). I can see your future Bonzo and it involves a replacement/re-con rear caliper! May as well do both is my advice, the other side will likely be on it's last legs as well...

[BonzoGuinness]

I don't disagree, the recon calipers have been budgeted for in next months MX-5 shopping list!

After fitting the new pads, the piston still wouldn't go back far enough to adjust properly, resulting in binding brakes and risk of a toasted disc should I be stupid enough to persist in driving it.

The good news is, I've removed the caliper from the car today, cleaned the entire thing with methylated spirit and filed down the narrow ring of corrosion just below the piston lip. Replaced the seals/rubbers, put it all back together, and it now slides in and out of the bore using the adjuster with no problems at all. Bled the system and all was well after a short, and then a slightly longer/more enthusiastic test drive. Groovy!

[bluetone]

Good work fella! There may yet still be life in the old caliper Keep an eye/finger on and compare disc temperatures after a run to see if it's still binding at all. Hopefully sorted

[GravelBen]

franv8 said:

It's possible the return 'gear' as I'll call it has stripped its teeth. Often you can pull it out by cocking the allen key to one side and removing it, have a look at the end. They're made of toffee, but you can get a bit of extra life out of it by hacksawing the stripped end off to leath healthy teeth.

Good advice - mine has just seized a piston, tried moving it in and out with grub screw to free it up and stripped thread on the end. Will try chopping the end off to see if I can get things functional, cheaper than replacing the caliper!

Edited by GravelBen on Saturday 15th August 04:14

[nfo]

Join the club, I had exactly the same problem!! Still haven't stripped apart the old caliper, but I suspect something very similar to your problem as there was definitely corrosion under the piston seal. I also used a g-clamp (there seemed to be no alternative - the adjuster simply had no effect), had an 'exciting' mixture of sticking handbrake, lever travel getting longer each time and one rather hot rear disc. Not good.

There was a guy on eBay doing a deal on new (pattern - nothing special) rear calipers, £108 posted for a pair, so I did that. Took a bit of faff to get all the air out and a decent pedal back.

[vrooom]

Did you undo the reservior cap off in engine bay? (dont forgot to wrap the towel round it)

[franv8]

[quote=GravelBen
Good advice - mine has just seized a piston, tried moving it in and out with grub screw to free it up and stripped thread on the end. Will try chopping the end off to see if I can get things functional, cheaper than replacing the caliper!

Edited by GravelBen on Saturday 15th August 04:14

[/quote]

Glad to be of servie! Hope it works for you!

[GravelBen]

No such luck unfortunately, tried but its well and truly seized - so now I decide between a refurb caliper for it or spending twice as much and upgrading to the bigger 1.8 brakes all-round

[BonzoGuinness]

GravelBen said:

No such luck unfortunately, tried but its well and truly seized - so now I decide between a refurb caliper for it or spending twice as much and upgrading to the bigger 1.8 brakes all-round

Could try rotating the piston itself - protect the rim with some cloth and grab it tight with mole grips/pliers, and rotate the entire thing. Should have the same effect as turning the grub screw, though you might end up with a scratched piston (which you can replace for about 15 quid).

All this talk of brakes remindeth me, I still need to send my calipers in and get the exchange money - need something to tide me over til' pay day

[GravelBen]

Would turning it actually solve the problem or just cause it to seize again in a different position? I got it moving in and out on Saturday, then found handbrake wasn't holding the car this morning, no longer cooking the brake but piston is now seized in rather than out.

[BonzoGuinness]

Turning it should actually allow you to wind the piston in and out of the caliper, completely. With the grub screw you're turning a spindle/shaft inside the piston, with the pliers and brute force method you're turning the piston around the spindle - but with the added risk of gouging into the piston with whatever muck/rust/etc is in there.

[nfo]

Digging this up again as it seems to be the most recent 'MX-5 rear brakes = PITA' thread...

Annoyingly one of my new calipers failed this week - not just a small leak but properly peeing fluid when the pedal was pressed. Thankfully the guy on eBay I bought them from was very good and got a replacement sent out the next day. When I took the adjuster cover bolt off, the fluid came pouring out so I assume it was the seal to the adjuster that went.

Anyway, I'm back to the 'fun' job of trying to get a decent feeling brake pedal (having today replaced the leaking caliper) - any particular hints or tips? Brakes work fine, but have an annoying 'dead zone' at the top of the travel. I think I'm now 'under-adjusted' on the handbrake, there seems to be a very fine line between red-hot, smoking discs and a long lever/pedal travel. How tight do people set the adjuster?

I was also wondering if there's any complication with having ABS and bleeding the brakes - there's certainly more plumbing to get air trapped in, but I've not yet found any specific references. A friend suggested there might be, but that was based on experiences with a BMW E30. Not sure how much ABS systems have changed, but I know there were weird old ones with accumulators. I digress.

I'm hoping that a proper traditional '2-man' bleed (as opposed to pressure bleeding with the eezibleed) combined with yet more handbrake adjustment (pretty fed up of doing it now...) will improve it but any tips would be great.

Cheers.