Changing rear brake pads - stuck piston

[james.c]

Hi all,
As lots probably have, I'm trying to do a few simple bits to the car whilst we're in lockdown. Thought I'd try replacing my rear brake pads as I'd not done it before and I could see they were low. 

Standard Delphi rear pads on a late 2016 620S (if it makes much difference!):
https://caterhamparts.co.uk/calipers-pads-discs/668-brake-pads-rear-use-with-4-pot-front-brakes.html?search_query=rear+pads&results=317

There are some good videos and articles about on how to do this:

and
http://www.alcester-racing-sevens.com/rear_brake_pads.htm

....so I thought that even I might be able to get this done. I'd ordered a wind back tool so felt I had all the kit. 

The first problem that I've got is that the pistons seem to be a long way out. I guess because the rears were fairly worn out. In fact they are so far out that you can't get back plate of the wind back inside the caliper to allow it to brace in order to be able to apply more force to the twist. Hopefully you can see that from the photo below. BTW - you can't even (quite) get the wind back tool in place without the back plate and then slide that on from underneath. 

However, even with what feels like a lot of force using pliers or the wind back tool (in place but without the back plate) I can't get the piston to rotate / rewind at all. 

The hand brake is off and I've taken the master brake cylinder cap off. I've even tried with loosened brake bleed nipples to make sure that I'm not working against pressure. 

Am I doing something daft? I'm not sure what to try next (other than to give up and take it to a garage when all this blows over!). Is there any reason why I might need to be able to take the handbrake cable / hook off? If so what's the technique for that?

Perhaps it does just require considerable force to rotate the piston and without the backing plate on the wind back tool I have no chance of even shifting it a few mm.

Or perhaps my pistons need to rewind anti-clockwise and I need a different tool. I can't seem to shift it in either direction! Could someone confirm which way they go? From what I can tell people seem to have wind back tools that push in when turned clockwise (the more common way I guess).

Any thoughts?! I'm frustrated that I've failed in such a simple task! All part of the learning curve I guess. 
Thanks in advance for any help.
James 

[Jonathan Kay]

Standard Delphi rear pads on a late 2016 620S (if it makes much difference!)

Please can someone confirm that the callipers are the same on these as have been used for some decades on previous Sevens. (Otherwise a lot of the experience in the archives and of the advice that's about to appear might not be appropriate.)

Could someone confirm which way they go? From what I can tell people seem to have wind back tools that push in when turned clockwise (the more common way I guess).

Yes. On the previous ones it's clockwise to wind back in on both sides.

However, even with what feels like a lot of force using pliers or the wind back tool (in place but without the back plate) I can't get the piston to rotate / rewind at all. 

If you're running out of access space do have you an angle grinder doing-up tool or similar with pegs of the right size with the right spacing?

Jonathan

[SM25T]

Clockwise only !! Ask me how I know

[SM25T]

I don't use the plate .... you do need to push really hard as you turn it.

[ECR]

Try tapping the end of the tool with a hammer as you push inwards and turn (it might just shock the thread loose....)

[james.c]

Thanks all. I'll have another go. Sounds like it might just be a brute force  issue and maybe I'm being overly careful! I'll try the hammer tapping technique too and report back.  

I don't have an angle grinder but plan B is to get hold of a hacksaw to take the metal studs off the back of the back plate (if you look at the original photo you can see that the studs that fit a different sized piston are stopping me from finding enough space!).

Some of the videos / articles make it look relatively simple (i.e. not huge amounts of force). But perhaps they are just a little ceased up for some reason.
J

[SM25T]

My wind back tool has lugs each side of the drive disc ... one for Ford (for the 7) and one for something else. Your piston looks an inordinate way out of the caliper in that photo. Have you tried using the tool without the plate .... it is surprising how much force is needed to turn the piston to screw it back down the thread ... but, as I said above, I don't use the u-shape plate, having misplaced it. Just get the lugs in the slots of the piston, push hard and turn clockwise. Wear big gloves.

[ChrisC]

Hi James

Late 2016, will mean Caterham branded remade (not refurbished Ford) Sierra caliper.  

My experience with these calipers is mixed.  The first pair I had where fine, they came as a warranty replacement for a 2015 kit which has been supplied with refurbished Ford items.  I have seen photos of a friends car where he had a rear caliper fire within weeks of IVA / PBC, and my recent (this week) experience of leaks from brand new item for my current build. 

My leaking new caliper would normally be no problem, but apparently Caterham supply chain for them has run dry due to China lockdown, and I had a choice wait of a part with no ETA or looks for an alternative.   I decided to rebuild my new kit calipers with parts from BiggRed. 

Obviously I started with the leaking caliper, which dismantled very easy, only to find swarf in the caliper a scratched piston and what was described by BiggRed as a "slack seal".  The rebuild using BiggRed parts was successful, so I decided with what I found to rebuild the other side.   This time (and the point of my post) removing the piston was a pig, it took a lot of persuasion to get out, much like your piston is taking to get in. 

I had the luxury of working on the bench and yet it still took a good half an hour, your working under the arch, with the brake line connected.

All I can say is persevere, and keep the pressure on with the backplate of the wind back tool, so its the pressure from the tool that pushes the piston in as you wind back the adjuster nut (inside the caliper).    And yes clockwise is correct to wind the piston into the caliper. 

Can you not assemble the tool in the caliper so it fits, if not then the grinder sounds like a plan (I hate tool abuse).  

Chris.

[SM25T]

You said using a lot of force with pliers won't move it .... you wouldn't get enough torque with pliers in the slots ... and risk slipping off and ripping the dust seal or stabbing yourself ! Silly question ... have you still got one bolt in place and the caliper tilted upwards, so you are not just holding the caliper by hand ? If all else fails, disconnect the hydraulic line and remove the caliper and take it to a work bench if you have a big vice to hold it. You would obviously need to bleed the brakes after refitting.

[SM25T]

What is this gap here ? Assemble the drive disc on to the tool without the plate and engage it centrally on the piston. Then slide the plate in. If you can't get the plate in,  you should be able to start to turn it without.

[7 wonders of the world]

Engage the lugs in the piston,

Wind the collar on the tool to butt the plate against the caliper body

Turn clockwise - often needs a high initial force then it will go in smoothly,

Without the plate there is insufficient pressure applied to the piston and the lugs cam out of the piston.

[elie boone]

The other day i had to use an wrench on the hexagon part of the tool to get the piston going and i did bent the small bar on the tool so difficult it was to wind back the piston, so far it was the most difficult one i have ever done. The best one's are 30 years old OEM Ford calipers and 20 years old master brake cylinders. I guess it all comes down to quality control and that is one thing another is finding another manufactory for small batches if needed. 

[james.c]

The gap in the photo is created by two other metal studs on the other side of the disc (in different positions so you can flip it around and use the tool on a different sized piston). Plan B is to see if I can cut them off with a hacksaw (an "essential" delivery of a bench clamp is on its way from Amazon!). That should give me the space to get the plate in. At the moment, even if I position it correctly without the plate there isn't enough space to slide the plate up from underneath. 

[james.c]

Thanks - it does sound like I just need apply more force. But I can't set the tool up as you describe as there just isn't enough room inside the caliper as the piston is so far out (see earlier response). I either need to cut the lugs off the back of the disc or find one that is thinner that would fit on my wind back tool. I'll see how I get on with a hacksaw when my clamp turns up!

[SM25T]

Forgetting the plate for a moment, can you get it all engaged without the plate, and turn it with a big adjustable or a socket and ratchet handle ?

[Jonathan Kay]

I either need to cut the lugs off the back of the disc or find one that is thinner that would fit on my wind back tool.

Or use a peg spanner that isn't necessarily designed for this specific purpose. They're widely used in the bike world, so it might be worth looking there as well as in general purpose tool shops.

Or could any helpful Member lend one?

Jonathan

[SM25T]

He has the right tool that is designed for this purpose. I wouldn't risk injury or damage from a tool that isn't.

[Wrightpayne]

Having used a bicycle peg spanner I think they are a little dainty for the task. Good idea though!

I think Ian is right, just needs a bit more force while twisting at the same time. Once it gets going...

[7 wonders of the world]

Without the plate in place though you can simply end up turning the piston without sufficient force to push it back in

The plate can be slide in from the front too as its slotted.

 

[james.c]

Thanks all. Comments gave me enough confidence that this might be something I could solve with brute force! An adjustable spanner in the back on the wind back tool gave me more leverage. Still took a bit of force but after a few turns i could get it back far enough to slide the back plate in and finish the job.

[SM25T]

Good news. All continuing your 7 education. We are all learning, no matter how long we have had our cars.

[Guy Lowe]

Sorry only just seen this ( wife has got me decorating) and my solution may already have been tried.

As with #13 I had the same problem so cut off the unused lugs on the wind back tool to get more clearance , worked a treat. 

[james.c]

Thanks Guy. What tool did you use to cut those off? I blunted a few blades of a hacksaw and got one off. But ran out of blades to get the other one off. Clearly the wrong tool (and / or wrong blades!).

[Jonathan Kay]

Well done. Thanks for the update.

Comments gave me enough confidence that this might be something I could solve with brute force!

That effect deserves a name. Knowing that you're turning the right way and wearing those big gloves often seem to make things work when they they wouldn't before.

Jonathan

[garybee]

Angle grinder will have those lugs off in seconds. More specifically an angle grinder with a cutting disc.