11 replies to this topic

[Strak]

Hi all,

 

I'm quite a novice when it comes to things mechanical, so my mini is really a learning project for me. It's a '79 mini, and I'm having some problems getting the brakes sorted - it's a front/rear split system.

 

When I got it the brakes barely worked (you had to jam your foot all the way down on the pedal to get any braking at all). I've replaced calipers and shoes in the drums, changed all brake lines for copper excluding the 2 pieces that run from the 3 way t-junction thing (not sure what it's actually called) at the back to each rear wheel, and also one of the pipes that runs from the pressure regulating valve to the master cylinder. Front drums have also been completely replaced with a disc brake conversion kit.

 

A couple of weekends ago I tried to bleed the brakes, but still got loads of pedal travel and the brakes only worked with the pedal pushed right down. Today I replaced the master cylinder and tried bleeding the brakes again - I was using a one man bleed kit and had lots of trouble, which I assume was due to my incompetence. In the end I bought an Eazibleed kit (that works by using pressure from a spare tyre). I couldn't get it going properly at first, but then read that bleeding can be funny (in a non comedy way) if the brake adjusters aren't done up enough, so I tightened them until the rear wheels locked and tried again... it seemed to work a treat and I got clean, bubble free fluid from all 4 bleed nipples (bled in order according to Haynes manual). I then did my test... pushed the brake pedal and there was resistance. I think I even cracked a smile at this point thinking it was finally sorted. That soon faded when I went to bolt the front brake calipers on (I had them unbolted while I was sorting out something else with the wheel hubs, but they were bled with the bleed nipples at the top).

 

The problem is that the calipers are jammed as if the brakes are on, so the pads are clamped together on both front calipers. I read something about opening the bleed nipple (I guess to release some pressure) to free up the calipers, but although some fluid came out of the nipple it wasn't loads and didn't seem to make a difference. Could I have put too much pressure in the system with the Eaziibleed kit or something like that? It just seems like the brake pedal is pressed but it's not!

 

I thought I actually made some progress today only to find I'd gone from no brakes to permanent brakes. Any ideas would be much appreciated!

 

Cheers,

Strak

[Dan]

  You did this without a disc between the pads I take it, so the pads are touching one another?  They will take some real effort to force back but they will go eventually.  In use the pistons don't normally slide back and forward through the seals, they use the flex in the seal as the spring to pull them back off so as they move in and out they only move by the amount of flex in the seal.  They slide through the seal as they wear down but never normally have to slide back in again and there is nothing to make them do it other than you forcing them manually.  If you have to force them right back in from fully closed to the fully open position you are going to have to push them a long way.  It will be very easy to gouge or otherwise damage the pads doing this so be careful.  Ideally you will use a winding back tool.  A large amount of fluid is going to return to the master so be ready for that and don't let it spill everywhere.  Collect some from out of the reservoir a few times as you go.  Usually once you get them moving it gets a lot easier, they will just be reluctant to start.

Edited by Dan, 17 May 2013 - 10:53 PM.

[Strak]

  You did this without a disc between the pads I take it, so the pads are touching one another?  They will take some real effort to force back but they will go eventually.  In use the pistons don't normally slide back and forward through the seals, they use the flex in the seal as the spring to pull them back off so as they move in and out they only move by the amount of flex in the seal.  They slide through the seal as they wear down but never normally have to slide back in again and there is nothing to make them do it other than you forcing them manually.  If you have to force them right back in from fully closed to the fully open position you are going to have to push them a long way.  It will be very easy to gouge or otherwise damage the pads doing this so be careful.  Ideally you will use a winding back tool.  A large amount of fluid is going to return to the master so be ready for that and don't let it spill everywhere.  Collect some from out of the reservoir a few times as you go.  Usually once you get them moving it gets a lot easier, they will just be reluctant to start.

 

Yep, no disc between the pads - is that what caused the problem? Or would it just be easier to fix if the disc was there as the pads would be further back? I might be able to get the pads out so I don't damage them and to create a gap. I've never used a windback tool before, but the ones I've seen don't look like they would work with my caliper. The caliper looks like this:

 

 

but the windback tools I found on Google seem to be only for single piston ones like this.

 

 

Am I looking at the wrong thing?

 

Cheers

[Dan]

  Yes if you had done it with the calliper assembled onto the hub and the disc fitted, there wouldn't be anything to fix at all!

 

  Never mind it's not a real problem, it's just all the returning fluid that will be an issue.

 

  There are all sorts of wind back tools for different calliper types.  You'd want one with two flat paddles that spread out, but it might be something you don't really need to get if you can start them moving.

[Dan]

  Cheap-ish windey one:

 

http://www.motamec.c...uide-67309.html

 

  Cheap-ish windey one:

 

http://www.motamec.c...tool-ak711.html

 

  Expensive windey one:

 

http://www.motamec.c...ke-pistons.html

 

  Squeezy one:

 

http://www.ebay.com/...=item35c333cde1

[jime17]

To get them started you could try a wide bladed tool like a chisel of right width to just fit flat between the lugs on the pads. Then move the handle sideways to a ease the pads apart enough to take them out. Doing this however is easier with calliper bolted to hub. I've seen a silicon cartridge gun used to slide pistons back before but you have to be careful to ensure they slide back in straight.

[Carlos W]

Don't beat yourself up over this, its not the end of the world! Are the caliper pistons nice and shiny or is there evidence of corrosion/dirt on them? If there's a kind of ring of brake dust you could clean that off with some brake cleaner whilst the pistons are out a long way!

Make sure the pistons stay square in the seals and don't twist!

Good luck, and well done for getting them bled!

[letsoffroad]

Hello, if you have a large pair of water pump pliers, set them to an appropriate size and then use them to squeeze the pads apart using the caliper body and the metal backplate of the pad. You only need a small amount of movement to be able to remove the pads from the caliper.

 

Once the pads are out, you can then bolt the caliper to the car which will make it easier to push the pistons back in fully.

 

As for the excess of fluid, attach a pipe to the caliper bleed screw and open the bleed screw while pushing back the piston. This way the fluid will go out the bleed screw rather than back to the master cylinder (which will overflow). When the first piston is fully returned, put the brake pad in to stop it moving out again when you do the other side. If your calipers have 4 pistons, you will need to find something smaller to block each piston as you do them - preferably something that won't compress!!

 

have fun! would rather be doing brakes than suspension cones this morning!!

[Strak]

Thanks all, heading up to the car to try this in a while so I'll let you know how I get on. To stop the overflow I'm going to screw the cap from the eazibleed kit back onto the master cylinder. It has a tube coming it of it so I can collect the overflow from that.

Fingers crossed, cheers for the help.

[Dan]

  There is nothing wrong with draining the excess through the bleed screw as said, it would be safer as brake fluid is both highly toxic and corrosive to paint.  You really don't want to get it everywhere.  Oh and it's very flammable too.  As with bleeding though only open the nipple while you are applying pressure, in this case by pushing the pistons.  Otherwise it may draw some air back in.  It's a bit fiddly to do and you will feel like you don't have enough hands but that's all.

[Strak]

Managed to find a g clamp in the garage which fitted really well, tightened it, pistons went back in nicely. Cleaned everything up, put the calipers back on the hub. I now have a pretty solid brake pedal and working brakes!

Thanks all, this was a great help to me.

Strak

[Carlos W]

Well done mate!