Front Driver’s Side Brake Caliper Locking Up Randomly

[George-S]

Hi all,

I'm really hoping someone has some advice for me ..
My coupe’s front driver's side brake caliper keeps randomly locking up, and I feel like I’ve tried everything to fix it.
The car sometimes drives fine, but occasionally, the caliper jams and won’t release until the brake cools down.

This happens even on short drives (e.g., a 5-minute trip).
It only affects the front driver's side—all other brakes work absolutely fine.
When it locks up, I can smell the pads burning, and if left too long, it completely seize.

What I’ve Done So Far:

Dismantled the caliper replaced seals, cleaned sliders, replaced brake pads & pins regressed everything multiple times.
Bled the entire system 5+ times—fluid is clear with no bubbles.


Brake Components Replaced:
Front Discs & pads
Both feed Copper oil lines & stainless braided brake hoses
After my refurbs didn’t work I purchased a new Caliper (newly refurbished one from Italy—same issue occurred)
Brake master cylinder (replaced about a year ago)


Questions ..

Brake Booster: This is the only part i have not replaced but I simply don’t know if this kind of behaviour can come from that ?

Master Cylinder Hard Line Placement: Is there a specific order in which the hard lines need to be connected to the master cylinder?

Here is a video of me spinning the wheel after the caliper locked up this morning https://photos.app.goo.gl/YRM2nzLo5CUmARBN7

At this point, I’m completely stumped. Any advice or suggestions would be greatly appreciated!

 

[SanRemo78]

Have you replaced the master cylinder? I had a similar issue on a Fiat 124 Spider. Slackening off the securing nuts between the master cylinder and servo would clear this indicating that the push rod length was incorrect - too long, needed shortening. If you've changed the length of the cross bulkhead pull shaft that may have had the same effect? It is odd that this would affect only one calliper though.

Guy

[George-S]

Hi Guy,


Yes replaced the master cylinder.
Defiantly wouldn't have thought to try this, I will loosen it off a bit see what happens.

Thanks for the idea.

Cheers George

[HFStuart]

Something odd about those sliders. Are they cracked?

[George-S]

Not to my knowledge...

They have been in and out a few times not noticed anything odd.
When its out the car it all sliders really nicely.

[peteracs]

Hi

You say it jams on even on short drives, but whennit cools down returns to normal. As Guy has suggested I seem to remember hearing this happening on a non Beta and it was the brake booster adjustment, but why only one side is a mystery.

If slackening off the booster rod does nothing, I would be tempted to get to the point where it is on, then crack the bleed nipple on that caliper starting with the one which only goes to the front ones and then do the same on the other caliper and see if that removes the sticking on caliper. You may find the other caliper does not actually work on the front only circuit, so two problems not one......

If that does not release the caliper then release the full circuit bleed nipples to confirm which circuit is staying on. Wonder if not the rod then is it the m/c somehow?

Hope you can make sense of my ramblings, as you say a very odd situation.

Peter

[SanRemo78]

Something odd about those sliders. Are they cracked?

I've seen two types of slider, one with a hole at each end for a retaining clip and the other with only one hole and the other end of the slider guillotined to create a bent tab to stop it sliding out. Could the wrong ones have been used and the wedge is jamming the calliper and stopping it moving? Unlikely.

[HFStuart]

That certainly explains why I thought the slider looked odd - usually the cotter pins are on the outside and there's a few mm of slide spare between the caliper and the cotter pin. I very much doubt this is the issue but it's worth swapping them round

[George-S]

Hi All,

Thanks for the replies.
I shall give slacking off the master cylinder a shot and also squiglyzigly has pm regarding the vacuum hose, I am currently using a none reinforced hose which could be potentially be collapsing under load.
Something I wasn't aware of so I shall swap that out to.

[peteracs]

Hi

Cannot see the vacuum hose being an issue, also mentioned re the sliders being handed. My car has a mix of the small spring retainers on both inner and outer off-the-peg caliper without any issues.

Peter

[Nigel]

Hi George,
The pads need to slide freely in the carrier with a slight gap, +- 0.3mm. I found an invisible layer
of rust on the carrier, removed with a file.
The anti-rattle pad springs are mounted only on the top of the pads, not visible
in your pics.
As Stuart said, the wedges must be inserted from the inside, clip outside.
I always very lightly lube the pad to carrier points, and the wedges with copaslip, but
there are specific brake greases that are safer.

Nigel

[George-S]

Hi Nigel,

I have anti rattle springs installed at the top of the pads like you mention, I used specific Caliper grease to assemble the sliders, and its all moves buttery smooth outside of the car.
Its rather tricky issue :/ I cant tell you how many times I have thought it was something simple like this cleaned and reassembled it all so many times.

Wondering if I can put some sort of camera on it so I can see whats happening.







 

[George-S]

Hi All,

Turns out their is an order for the brakes lines to be hooked up to the master cylinder.
Its not something I was aware of but seems like the place to start.

[SanRemo78]

There's no order that the brake lines should be connected, the picture posted is merely a diagrammatical layout for the system. Brake bleeding should be done starting with the longest line and working back to the shortest but if you have a good solid pedal that's not the issue.

Guy

[HFStuart]

There's no order that the brake lines should be connected, the picture posted is merely a diagrammatical layout for the system. Brake bleeding should be done starting with the longest line and working back to the shortest but if you have a good solid pedal that's not the issue.

Guy

But with the dual piston setup at the front if you had the hoses swapped round on one caliper that could mean different brake pressure going to the main piston on one side?

[SanRemo78]

But with the dual piston setup at the front if you had the hoses swapped round on one caliper that could mean different brake pressure going to the main piston on one side?

Not sure about this yet. If there were cross routed pipes it would mean you might get uneven pressure on the pads on application of the brakes and that would cause pulling to one side or the other but not jamming brakes unless there was residual pressure in the system stopping full pad retraction?

Got to be worth checking that the pipes from the front chamber of the master cylinder are routed to the outer chambers on the callipers though just for peace of mind.

Guy

[SanRemo78]

Here's a wild thought. Feel free to shoot me down in flames. The brake pads on the side that's locking have been confirmed as being free to move. How about the other side? Are they also moving as freely? If there was a tiny amount of residual pressure in the system it would affect the side that moves most easily, heat build up and fluid expands on that side?

Also, has the rear brake compensator been replaced recently? If that wasn't adjusted correctly could that be returning some pressure to the lines once released with the master cylinder at rest too? That's unlikely, I think, as any returning fluid should merely enter the master cylinder & reservoir.

Guy

[George-S]

I think the first possibility is unlikely, as I’ve gone through three different sets of brake pads from various manufacturers, and the issue remains unchanged.

To clarify, this isn’t a minor case of brake drag—it’s severe. It feels sometimes as if I’m slamming the brakes on, with enough force to noticeably slow the car down and even cause it to pull to one side.
I genuinely believe something is forcing the piston to not withdraw, Hence why I kept screwing around with piston seals etc.


The brake compensator is a good suggestion. I haven’t replaced it yet, but I assumed that if it were faulty, the rear brakes would also be affected rather than just the front right.

[George-S]

There's no order that the brake lines should be connected, the picture posted is merely a diagrammatical layout for the system. Brake bleeding should be done starting with the longest line and working back to the shortest but if you have a good solid pedal that's not the issue.

Guy

But with the dual piston setup at the front if you had the hoses swapped round on one caliper that could mean different brake pressure going to the main piston on one side?

Hi Guy

I think you’re on the right track here. If I’ve incorrectly routed the connections on the master cylinder, it could result in higher pressure on one side and lower pressure on the other, potentially causing the caliper to lock up.
This would also explain the randomness of the issue it might only lock up when the pressure imbalance becomes too large.

Regardless of if the Diagram is a "must" I am going to match it to at least start from their.

[SanRemo78]

The routing is a bit convoluted George, can I suggest that you start at the master cylinder and put a zip it around the pipe you're checking and slide it down the pipe until it reaches the calliper. That way you're 100% sure it's gone to the right chamber on the calliper. In reality you'll only need to check the routing from one chamber on the master cylinder. Should be a quick check.

Guy