Hot Wheel! Seized Brake Caliper

[Mysterae]

The latest thing to stand in my way of getting my Esprit back on the road (not including fuel prices!) is a seized rear near side brake caliper. 

It certainly bites, just doesn't let go resulting in a very hot disc, pads and wheel. Got my trusty thermal camera out (new toy ) to see how hot and compare it to the off side rear.

        

(First image is thermal only, second image is a fusion of thermal and actual camera).

The brake disc is 251C and the wheel is 104C, a bit too toasty. Compared to the other side:

Yeah, a lot cooler.

I renewed the caliper seals about 6 years or so but I can't remember if I removed the piston from the near side caliper at that time (no pictures), I certainly did for the off side:

Think I'll strip it down and have a look at the condition of the piston before deciding on sending it away.

An upgrade to the brakes is definitely needed.

[CarBuff]

A rubber brake line that swells on the inside, preventing the caliper from releasing, can overheat a wheel, too. 🙄

[Sparky]

If it's hard/impossible to turn by hand, my next check is to crack the bleed nipple just a tad.  If the issue is hydraulic, it should release; if not, it's likely mechanical.

[fjmuurling]

In addition to the Lotus manual.

Bendix Overhaul ex Matra club.pdf

[Mysterae]

7 hours ago, CarBuff said:

A rubber brake line that swells on the inside, preventing the caliper from releasing, can overheat a wheel, too. 🙄

Never thought of that, thanks. The overhaul info that @fjmuurling posted says that the hoses should be replaced every 10 years, who does that?! Makes a lot of sense, as the overhaul info says bits can break off internally and clog up the pipe or caliper.

7 hours ago, Sparky said:

If it's hard/impossible to turn by hand, my next check is to crack the bleed nipple just a tad.  If the issue is hydraulic, it should release; if not, it's likely mechanical.

Good tip @Sparky, thanks. I tried to turn the piston as per the service notes using a 1/4 ratchet in the slot but it wouldn't budge. 

1 hour ago, fjmuurling said:

In addition to the Lotus manual.

Bendix Overhaul ex Matra club.pdf 1.03 MB · 0 downloads

Many thanks for posting that info @fjmuurling, there's a lot more info in that than in the Lotus service notes! In summary:

- replace the flexible hoses if more than 10 years old - going to change all four as I'm sure they are the original ones.
- check the hand brake is not stiff or seized - done this and it's okay.
- separate the aluminium housing from the steel frame - interesting one this as I didn't do this when I removed the piston from the other caliper. It's marked as very important and looks to be a world of pain as the spring and pin will likely to be goosed a long time ago. Anyway, I'll try this using the wedge method mentioned in the document.
- interesting that it mentions to use compressed air to eject the piston if it's still too tight, which is what Lotus service notes say and what I did before.
- try putting the piston in the bore without the seal, it should spin freely and wind itself down as long as the bore is circular (but put the seal back in afterwards!).
- when putting the piston back in ensure it's the right way up so the groove for bleeding is upwards.

A few jobs for later then.

[RobinB5]

On 09/06/2022 at 22:49, Mysterae said:

It certainly bites, just doesn't let go resulting in a very hot disc, pads and wheel. Got my trusty thermal camera out (new toy ) to see how hot and compare it to the off side rear.

        

(First image is thermal only, second image is a fusion of thermal and actual camera).

The brake disc is 251C and the wheel is 104C, a bit too toasty. Compared to the other side:

 

 

Is it a FLIR?

[Mysterae]

@RobinB5 no it's not a FLIR, it's a HIKMICRO B20. 

I looked in to FLIR as I've used them in the past (as seen in my avatar) but they are so expensive for the same or lesser features. You have have to spend many thousands with FLIR to get anything similar to the HIKMICRO B20. For example the HIKMICRO's B20 IR sensor is 256 x 192 and has a refresh rate of 25Hz compared to most FLIR's antiquated 9Hz.

[Mysterae]

Finally got round to removing the caliper and inspecting the lines. 

Externally the brake lines look okay but you can never tell their condition inside.

Following @Bibs tip on releasing the bleed nipple there was no change and the piston was indeed stuck in the caliper. Removed the caliper and cleaned out the brake fluid and injected WD40 in to ease any corrosion and worked the handbrake mechanism and that eventually got some movement out of the piston. Wound it out as much as I could with a screwdriver then used compressed air to pop the piston out.

Pop! Always worried I'm going to catch my fingers. That would hurt.

It's not in bad condition, a few bits of corrosion but these cleaned up well. Followed the service notes and put it back together.

I've had this compressed air powered bleeder for years, it's awesome for one man brake bleeding.

Went out for a 10 mile test drive and although the brake is no longer seized, the wheel is still getting quite hot, a lot hotter than it's axle neighbour (I'll post some thermal images tomorrow). I know the exhaust manifold and turbo are on the side of the hotter wheel but I wouldn't think it would have that much affect. Wondering if the wheel bearing has been damaged from running so hot previously. 

[jonwat]

9 hours ago, Mysterae said:

Wondering if the wheel bearing has been damaged from running so hot previously. 

Jack her up & check for play, that will tell you. 

[Mysterae]

Thanks John, jacked it up and there is no play in the wheel at all, left to right, up and down. Incidentally I can turn the wheel by hand now (handbrake off ) but it's certainly not freewheeling, I can feel the pads biting on the disc but not enough for it to bind now.

The thermal images from last night's run show the brake disc being quite hot (around 121 - 147C) which although not ideal is 100C degrees less than before I refurbed the caliper. Ambient temperatures were warmer last night and the run longer than before so there is some improvement.

   

The source if the heat is definitely the brake pads on the disc:

The pads have taken a beating in this and are about approx 5mm more worn than the offside pads. 

[andydclements]

I'd suggest having a look at the sliding mechanism of the calliper, if that's not as free as it should be then the calliper can ease-off but you'd still have one pad in contact with the disc.

Also check disc for run-out as it may have been damaged by the excess heat (of the previous seize) and so you'd have excessive  disc -pad contact.

Finally, if nothing else has shown up, then revisit the calliper itself and check things like the internal surface (does it need a light hone), the piston surface (ditto, keeping in mind it's chrome plated so only very fine wet & dry) and the handbrake mechanism to ensure it is easing back as far as it should.

[Mysterae]

Thanks Andy. I've not put any lubrication on the sliding mechanism of the the caliper as it's not mentioned to do so in the service notes which I thought odd. It's cleaned up well and it was hard resisting the temptation to put a bit of copper grease on the 'sliders', perhaps some Ceratec would be better.

The disc(s) are practically brand new, probably less than 1k miles on them, still have some of the 'blue' as they are supplied on the edge. However, that's no guarantee they haven't been warped by the heat, so something to check. Need to find my dial gauge... 

I only cleaned the piston and bore of the caliper, lightly rubbing with a plastic tool so as not to mar the surfaces. Then assembled back together with a coating of brake fluid. The handbrake mech is lubed up and working well.

I'll strip it down again and check these areas once more. It's getting the time!

[andydclements]

Ceratech is a massive improvement over copper grease, but (and my Dad remembered it being new to the trade) was in itself a massive leap forward over normal grease. I'd say try it, it's not going to cause harm. A bit of 2000+ wet & dry would be fine on the piston and even a little bit more coarse on the inside of the bore.

[Mysterae]

I found some time today .

Removed the caliper and the piston from it, which came out a lot easier than before. Used some 2000 wet & dry folded and rubbed down on itself to make it a higher grit as it's all I had to hand. Some fine honing and the piston is looking good.

Did the same to the bore of the caliper which although an improvement I didn't want to take too much off so some marks remain which I don't think are detrimental. The internal seal is removed in the image below.

Checked the disc's trueness using my cheap-ass dial gauge I have about ~0.1mm out of true, that's not including areas of 'corrosion' where the brake pads affixed themselves to the disc when the car was parked up for ages. I'd say that okay.

The aforementioned corrosion on the disc from where the pads sat for (far) too long. The is below the surface of the disc.

All assembled, bled and tested with the brake pedal and hand brake. Ignore the cooked state of the brake pad, I'll get to that later!

Initially it's free as a bird but then it does snatch after applying the brake pedal, but a slight movement of the caliper and it's free again. Another test drive and...it's still damn too hot!

   

Compared to it's off-side neighbour:

TL;DR - The piston and caliper are definitely no longer seized, I think the problem is now the brake pads. They are worn to such a state that they are pulling the moving part of the caliper off true not allowing it to return properly and thus creates the friction and heat between the disc and the pads. I could swap the pads from the other side to prove it (and give the other side some gas mark 9 for 30 minutes treatment too) or just get some new pads.

Does anyone know what pads are equivalent so I can pick them up locally rather than paying the cost of the pads in delivery?

[Roy Lewington]

I think there is a slight biased edge on the sealing ring.  maybe it's in the wrong way round.  Just a thought.

[Mysterae]

On 26/06/2022 at 19:52, Roy Lewington said:

I think there is a slight biased edge on the sealing ring.  maybe it's in the wrong way round.  Just a thought.

I notice that when applying brake fluid to the bore, wasn't sure if it was the seal that was biased or the grove in the bore. If anyone knows the right way round that would be good to know!

Not done anything since, just waiting on some new brake pads.

[Mysterae]

I so fitted some new EBC brake pads to the rear brakes both sides and I could tell without driving it that the offending caliper was still catching and not releasing.

Took the caliper apart once again to inspect the internal seal to see if it was fitted correctly as suggested by @Roy Lewington. I'm pretty certain the groove in the caliper has a slight bias as well (unless I'm imagining it) as I'm sure I can feel a very slight difference depending on which orientation the seal is fitted to. It's difficult to explain so here's a wee image. 

The red line is the face of the seal and is exaggerated to make the point. The numbers are not in any units, they are there to illustrate the protrusion of the seal and how it differs between which way it's fitted. For example in a) it feels like it protrudes more at the top compared to when the seal is flipped as in b). The bottom of the seal in a) feels like it protrudes less that it does when flipped as in b). I swear I'm not imagining it! Which way is correct or does it even matter?!

The internal seal is important as not only does it stop brake fluid from leaking but it also provides some force to retract the piston ever so slightly. Here's a quote from a Bendix Brake Representative that I found on this post on a MG forum:

Quote

The piston seal does retract the piston usually from .003 to .005" to reduce drag. This is done by the leading edge of the seal groove being cut at a bevel of between 4 to 6 degrees. The only calipers that did not follow this build were stroking seal style of the 60's and early 70's. These had air issues that required more frequent bleeding and rotors had to be as true as possible. When it comes to runout...less is better. Any additional piston retraction needed is supplied by component deflection. Additional runout causes pedal pulsations, pad wear, noise, and low pedal issues.

TL;DR - I'm going to replace the internal seal of the caliper, I think it got cooked and is no longer providing enough force to retract the piston the fraction of a bawhair required.

[910Esprit]

Looking at the condition of the piston (very good) and the cylinder bore, I think your problem lies elsewhere.   If its not prohibitively expensive, I'd recommend exchanging the caliper assembly & flex hose.   

NB - I've personally not come across a directional internal seal on a caliper before.         

[Mysterae]

1 hour ago, 910Esprit said:

Looking at the condition of the piston (very good) and the cylinder bore, I think your problem lies elsewhere.   If its not prohibitively expensive, I'd recommend exchanging the caliper assembly & flex hose.   

NB - I've personally not come across a directional internal seal on a caliper before.         

I think what I noticed above may be a red herring; the groove in the bore is slightly angled (next time I have the piston out I'll shape it with some of the kid's plasticine as I can't get feeler gauges in there) and I think the seal is just worn having been sat in the cylinder so long and also heat cycled far higher than it ever should. I considered getting the caliper reconditioned but all they will do is what I have already done except from the hand brake mech which is operating fine.

I've driven the car today and although the caliper and disc still get hot it's no where as hot as before. I'm pretty confident a new seal will fix it although I think it's prudent to replace the lines while I'm there.

[DaKa]

It was few years back, but having wasted a lot of time (and money) trying to resolve rear caliper problems, I simply upgraded to new Brembo from PNM together and new disc and braided cable that came with the kit. Yes, it will set you back circa £900, but you'll likely get something back for the old ones. What price is worth safe braking?

[jonwat]

Or you can get a reconditioned one from SJSportscars for about £150 delivered 

Edited July 13, 2022 by jonwat

[Mysterae]

I am wanting to upgrade the brakes for sure, I don't have the budget at the moment to do it right now. I haven't seen an upgrade kit for the rears anywhere, or have it missed it?!

I called SJ's a week ago and they didn't have a N/S rear caliper for a direct swap and it was 6 to 7 week lead time for a refurb of my own caliper. PNM was the same but a shorter lead time. Thought I'd just do it myself but I should have replaced the seal the first time.