Brakes seem to be holding on too tightly

[steve lyle]

When I had those symptoms it was the result of rusty pistons. I rebuilt the calipers with new stainless pistons and it fixed the problem. The free rotation depends on speed of rotation, but it’s easy to get a full revolution, iirc.

The last time I had my car in the air, I gave one of the front tires a spin and counted the revolutions. I got just short of 10. I wouldn’t have guessed that many, but there you go.

[nmauduit]

You say "the pistons are certainly not seized, it's just that the piston does not pull back as far as it should". I don't think that is correct. The pressure in the system will be the same at all calipers and, assuming the pistons are not seized, the pads will not apply braking force to any of the discs until all pads are in contact with the discs. (The major advantage of disc brakes is that they don't pull to one side or the other because of this.)

The distance the pad has to travel is irrelevant. If you have one caliper binding as you say I suspect that piston IS binding, therefore the seals are not capable of pulling the piston back. When you brake it is taking more force to move that piston or it's bending the disc because the piston is not moving.

I suspect the piston is fully seized and it's bending the disc, so the car pulls under gently braking, disc not bending, but not under hard braking when the disc is bending.

Dave

it could also be that only one piston is stuck, so that under light braking the other piston of that side would make do, but under heavy braking the lack of clamping power would become evident...

[alaric]

Thanks again for all the help with this. There are some interesting proposals in the thread now, but I personally don't agree with them at the moment; but I have noted and considered them. Of course, when I get out there, if I find something conclusive I will come clean and admit my folly.

Regards

Sean.

[2cams70]

Thanks again for all the help with this. There are some interesting proposals in the thread now, but I personally don't agree with them at the moment; but I have noted and considered them. Of course, when I get out there, if I find something conclusive I will come clean and admit m

Note the more appropriate thing is to "come clean" first and give the full story first so others trying to help don't waste their time going down blind alleys!

[alaric]

I have described the symptoms as accurately as I can. my original question was only re how firmly the pads should be gripping the discs, and clearly I have a problem with the calliper. Since then it feels like I've been on the defence but I've been as diplomatic as I can with my responses. I haven't taken the calliper apart yet, but that's because I have very limited time to actually work on the car. So, it appears there's no way to keep you happy 2cams70.

So, what's the problem 2cams70? You don't seem like you enjoy posting on here. I do, it's usually quite fun and sometimes I help someone in return for the help that I get.

Don't hold back now. Let me know just how you feel eh!

Sean.

[2cams70]

You don't need to be diplomatic here just honest and don't waste other people's time. If you think what people have been suggesting is rubbish that's fine but at least give them the honor as to a reason why you think it's rubbish.

[Donels]

Come on guys we’re better than this!

[alaric]

I don't think I called the proposals rubbish, just don't agree. As I pointed out, I'll declare my folly once I've looked at the caliper. I refute your comments about my wasting people's time.Also, I think that it is very important to be careful what you post on a public forum, and diplomacy is preferable, so I try to be diplomatic. I don't always get it right though.

So, it appears I have a tight piston / pistons in my offside caliper, and that one may even be seized - although I was able to move both pistons back by hand to remove the pads when I first checked the caliper, so at the moment I'm thinking it's just tight or that the seals are not fitted correctly, or the piston is too large. I'll check the dimensions etc.

The symptoms are simply that if I apply the brakes quickly, but not necessarily hard, the car twists to the right, but does not continue to pull to the right. If I apply the brakes slowly, it's fine, and if I brake hard, it's fine i.e. stops in a straight line - at least it appears to - tbh I've only driven the car about 4 miles in the last few months, so this is with limited testing. With the car jacked up and wheel removed the hub on the offside is a lot tighter than on the nearside. If I remove the pads both sides rotate freely. So the caliper needs to come apart. I'll do both sides anyway though.

Steve thanks for your post re the number of revolutions - if the wheel is on that's similar to my nearside wheel, but the offside is less than one revolution - that's why it's getting warm I presume.

Thanks again for all the useful comments on this.

Regards.

Sean.

[alaric]

Hi again.

I have removed the pistons from the offside caliper. They pushed out together using the brake pedal, and I tapped them out the last little bit once the caliper was off. The pistons look quite clean and are, I think, stainless. There are scratches, so I'll be replacing them. The seals are in the correct way round, but feel quite hard to me. So, I think new pistons and seals are needed on both sides.

Haha of course I've just realised I should have pushed the pistons on the other side out with the brake pedal at the same time. Oh well...

Regards.

Sean.

[alaric]

Hi all.

I rebuilt the offside caliper with new pistons and seals from those lovely people at Kelvedon Lotus. It appears to have done the trick. I then rebuilt the other side, and of course that side now has the same issue - although not to as greater extent - as the offside originally had - i.e. it's not releasing the disc enough to allow it to rotate freely.

So, I'm ordering a pair of new calipers from Kelvedon. I'll fit them, and then know that it's not an issue with calipers.

The numbering on my calipers is a bit weird, with type 16PB on one half and type 16 on the other. So they'll be kept as spares.

Regards.

Sean.

[RichardHawkins]

Sean,

If it ant broke don’t fix it. Advice given to me as a young man, but then curiosity gets the better of me and I end up with a malfunction on something that had been working fine.

Hope this helps in the future,

Richard Hawkins

[RichardHawkins]

Sean,

If it ant broke don’t fix it. Advice given to me as a young man, but then curiosity gets the better of me and I end up with a malfunction on something that had been working fine.

Hope this helps in the future,

Richard Hawkins

[alaric]

Hi Richard. I know the old saying well. It's been said to me before .

Sean.