Hi Spec rears sticking

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Hi Spec rears sticking

Postby abmunro » Sun 02.10.2016, 00:33

Has anyone else had a problem with the Hi Spec rear brakes sticking on?

The drivers side brake keeps locking on, Its so bad I had to pull over and let it cool down just so I could get home.

The car started to shudder so I pulled over, Then they just locked on.

Any ideas?
91 Elan SE 24k miles, 270 BHP @ 1.25 barg. Roll hoops + fairings+ speed humps Elise lights. S2 alloys. Nitrons& Eibachs,AP's front & Hi Spec rear brakes
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Re: Hi Spec rears sticking

Postby Brit-Car-Nut » Sun 02.10.2016, 04:29

It would be a good test if you could pop the bleeder open and closed briefly when the brake is locked. I know this is near impossible on the side of the road.

If there is a high pressure vented, then a bad hose or bad proportioning valve might be the cause. Either of them might be constricted and the reverse pressure from the caliper can't overcome the restriction but the BMC is strong enough to pump fluid past toward the caliper.

Otherwise it could be mechanical internally with a piston sticking so something like that.
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Re: Hi Spec rears sticking

Postby lotusflasherman » Sun 02.10.2016, 11:41

abmunro wrote:Has anyone else had a problem with the Hi Spec rear brakes sticking on?

The drivers side brake keeps locking on, Its so bad I had to pull over and let it cool down just so I could get home.

The car started to shudder so I pulled over, Then they just locked on.

Any ideas?


Are these the sort with a hydraulic handbrake module?
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Re: Hi Spec rears sticking

Postby chrisP » Thu 06.10.2016, 12:44

In a word yes, I have exactly the same problem and have had the caliper apart several times. :banghead:

It is I believe down to the internal design. A test you can do is when you get the problem is to loosen the bottom banjo bolt off and if you can move the pistons back in the caliper the problem is elsewhere in the system if you cant - then the caliper has self sealed itself.
Basically as far as i can see the rubbers in the the handbrake piston blocks the inlet/outlet hole, the master cylinder can pump fluid past the seal but it then cannot escape. Have you got any pre-engagement of the handbrake at all? I am installing (in a vain hope) a spring to push the handbrake leaver on the caliper, back to a completely dis-engaged state. Incidentally I spoke to Alex at hispec and he knows the calipers, but did not say the was aware of problems (perhaps because there are so few out there in the wild.

Other possible cause is the inlet to the caliper piston is blocked - it is a 1mm diameter hole!!!! :shock:

It is a vicious circle as the brakes heat up and expand they lock even tighter

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Re: Hi Spec rears sticking

Postby lotusflasherman » Sat 15.10.2016, 10:34

chrisP wrote:In a word yes, I have exactly the same problem and have had the caliper apart several times. :banghead:

It is I believe down to the internal design. A test you can do is when you get the problem is to loosen the bottom banjo bolt off and if you can move the pistons back in the caliper the problem is elsewhere in the system if you cant - then the caliper has self sealed itself.
Basically as far as i can see the rubbers in the the handbrake piston blocks the inlet/outlet hole, the master cylinder can pump fluid past the seal but it then cannot escape. Have you got any pre-engagement of the handbrake at all? I am installing (in a vain hope) a spring to push the handbrake leaver on the caliper, back to a completely dis-engaged state. Incidentally I spoke to Alex at hispec and he knows the calipers, but did not say the was aware of problems (perhaps because there are so few out there in the wild.

Other possible cause is the inlet to the caliper piston is blocked - it is a 1mm diameter hole!!!! :shock:

It is a vicious circle as the brakes heat up and expand they lock even tighter

Chris


Set of HiSpec brakes I bought from DVB came with springs to return the levers operated by the cables (see photo). I can't see how it would work without it, or why the cable nipple should stay in the lever. Speaking to Alex, he mentioned that the handbrake should not be applied with any residual pressure in the caliper from the footbrake - which is a bit tricky when stopping on a steep hill. I do find putting on and taking off the handbrake is a two handed operation as well..
spring.jpg
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Re: Hi Spec rears sticking

Postby Steve A » Sat 15.10.2016, 15:46

viewtopic.php?f=41&t=23273&p=300120#p304424

I added spring to mine soon after fitting to stop them sticking, did the trick :smt023
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Re: Hi Spec rears sticking

Postby chrisP » Mon 17.10.2016, 15:48

Phil, there is a spring inside the caliper that pushes the piston back and this in turn pushes the lever back to its starting position.
I made some new longer levers to increase the force from the hand brake - so you could try that.

I believe the first iteration of the calipers had design fault where pressing on the brake pedal and applying the handbrake at the same time could nick one of the internal seals, Bobs later design apparently fixed this (Later types can be distinguished by having a black anodised rear half).

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Re: Hi Spec rears sticking

Postby lotusflasherman » Fri 18.11.2016, 15:42

abmunro wrote:Has anyone else had a problem with the Hi Spec rear brakes sticking on?

The drivers side brake keeps locking on, Its so bad I had to pull over and let it cool down just so I could get home.

The car started to shudder so I pulled over, Then they just locked on.

Any ideas?


Yes, I have now! Chris P said there shouldn't be a problem with the handbrake on the black anodised handbrake unit, which I've got, but I've still been trying to avoid putting the handbrake on with pressure from the pedal in the system. Seems likely I might not have done so yesterday and I now think there is a problem inherent in the hydraulic handbrake systems. Think I might just park in gear!

Set off this morning and a mile or so from home it didn't seem to be going very quick and when I lifted off slowed down very rapidly. Was on a twisty country road so carried on a short distance to a place to pull in and when I stopped OSR disc was red hot and flames coming off the pads. (Very F1 pitstop!) Threw my damp windscreen wiping cloth over the washer jets and gave it a good soaking and used it to snuff out the flames. I could see handbrake cable had slack but caliper lever still in 'On' position so jacked up car to remove wheel while disc was cooling down. Tried opening bleed valve & reclosing but handbrake still on, so released banjo bolt and quickly retightened and that did it - partly ... :?: Pads now had slack and rattled a bit but disc would only move a few degrees each way until I prised the pads away a bit more. Found a lump of pad was now bonded to the disc with a corresponding hole in pad so put wheel back on and drove home to sort it ... with a minor vibration... :lol:
burnt pad.jpg


Jack up, wheel off, pads out, disc off and blob of friction material removed with flapwheel on angle grinder and disc generally cleaned up and boss resprayed with 'heatproof' BBQ paint. (It burnt off so not that 'heatproof' !) Replaced disc and checked runout with dial gauge in case it had warped. I converted the caliper to use 264mm x 10mm discs so more likely to warp than OE but it hadn't. New pads just ordered from HiSpec will be here Monday. (My choice not to pay extra £20 for delivery tomorrow.)

Now need to clean glaze off OSR disc and swap pads around so 1 burnt, 1 not burnt, each side and do a test run for rear end balance. Should be OK for a couple of days until new pads arrive. Tea break over so back to work. Don't you just love owning a Lotus.. :lol:
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Re: Hi Spec rears sticking

Postby Steve A » Fri 18.11.2016, 17:19

So basically because you had your foot on the brake peddle whilst using the hand brake your brakes caught fire :shock:
Mine have been sticky but the spring did the trick, it's a bit of a worry you having all this hassle with yours :roll:
Have you got the longer actuating levers ?

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Re: Hi Spec rears sticking

Postby lotusflasherman » Fri 18.11.2016, 18:12

Steve A wrote:So basically because you had your foot on the brake peddle whilst using the hand brake your brakes caught fire :shock:
Mine have been sticky but the spring did the trick, it's a bit of a worry you having all this hassle with yours :roll:
Have you got the longer actuating levers ?

Image


Don't think so Steve. My lever measures about 47mm total length - that's pushing a digital caliper through the wheel spokes the best I can by torchlight. (Wish I'd seen your post when I had the car jacked up and wheel off.)
I'd say it looks more like the short one but I'll do a 'proper measure' tomorrow. I'm having to use 2 hands to apply and release the handbrake so longer levers would be better. Presume the cable is held further out by the bigger alloy block so it's not pulling at an angle.

Have you ever seen a drawing of the Ultralite caliper in cross section that shows the seals? I'm trying to work out how fluid can get trapped so it keeps the handbrake on. When I released it by undoing the banjo bolt I started wondering if it's anything to do with seals in the Brake Proportioning valves... and still wondering... :smt102
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Re: Hi Spec rears sticking

Postby Steve A » Fri 18.11.2016, 22:27

forum.lotuselancentral.com/viewtopic.php?f=41&t=17805&hilit=hi+spec+rears

Have a look at this thread Phil (when you get 5 mins :wink: )
It basically gives you the full history
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Re: Hi Spec rears sticking

Postby lotusflasherman » Sat 19.11.2016, 16:36

Steve A wrote:forum.lotuselancentral.com/viewtopic.php?f=41&t=17805&hilit=hi+spec+rears

Have a look at this thread Phil (when you get 5 mins :wink: )
It basically gives you the full history


Thanks Steve, that's not a thread, it's a rope! Read all 18 pages, plus links that work and link on longer levers was also useful.

Is indeed a bit of a saga, and interesting to note some people throwing their toys out of the pram and others trying to be helpful getting told to butt out if they haven't bought the setup, oh the rich tapestry of life.
Useful to learn Bob Brown conceived this conversion and I've now found his Group Buy threads for front and rears. He certainly put a great deal of time and effort in with very little thanks and a lot of criticism from some.
Why somebody leaves their car on axle stands for over a year when restoring OE setup takes so little time is completely beyond me. Perhaps they pay somebody to do the 'spannering', in which case, perhaps staying OE is wisest.
Think I now know why HiSpec is not liked on this forum, but so far I've had good service and assistance with my project.

Bought my complete HiSpec setup secondhand from DVB who posted lots of photos on ebay which I copied for future reference and this is part of one of theirs that shows the lever I've actually got. (Saves taking my wheels off)
handbrakemech DVB.jpg

This certainly look like the short version to me.. do you agree?

Believe I gleaned from the thread that BB got the levers manufactured so no point in talking to HiSpec. I've got a selection of alloy bars in my garage so will have to make something myself. Putting in the 90°twist should be interesting :lol:
Does give me a free hand on how long to make them ... What a vitriolic debate that was! One of the problems of involving others in prototyping. Best to sort one thoroughly before replica's are made.

BB's c.s. drawings don't make a lot of sense to me so still wondering about my stuck handbrake... can't rationalise why releasing the banjo released pressure when the bleed nipple apparently didn't - maybe I was misled by the pads having (unexpectedly) welded themselves to the disc so the bleed nipple didn't appear to do it, but had. The pistons appear to move freely so am discounting stuck pistons.

My drive has a slight slope so I park in gear since fitting HiSpecs rears (well shortly after, it's since I was woken at 3:15 by a guy who found my Elan had rolled off the drive, blocking the road through the village). Usually when I release the clutch next morning the car starts moving before the handbrake is released. A couple of times before my flaming seize up it stayed where it was even after the handbrake was released and I heard a 'bong' as pad(s) came unstuck from the disc as the clutch was released. Maybe stronger 'through off springs'?

I've had exactly the same with OE setup on my first Callapso Red SE though. I arrived at a pub after a 'good blast' with hot discs and parked on a slope facing the window to the bar with only handbrake on. After 1/2 hour my Elan tried to join us in the bar ! Also that used to 'bong' when driving off occasionally.

New pads should arrive Monday so I'll investigate the lever dimensions when I'm fitting them. (Old pads work OK but I don't trust the pads that caught fire to remain stuck firmly to the backplate in the longer term.)
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Re: Hi Spec rears sticking

Postby Steve A » Sat 19.11.2016, 17:05

Looking at the photo I would say you've definitely got the short levers.
I started with these but soon upgraded to the longer levers as I (and others) found that the hand brake was a nightmare to engage.
Having longer levers also gave the release spring more of a chance to do it's job.
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Re: Hi Spec rears sticking

Postby lotusflasherman » Sat 19.11.2016, 17:52

chrisP wrote:It is I believe down to the internal design. A test you can do is when you get the problem is to loosen the bottom banjo bolt off and if you can move the pistons back in the caliper the problem is elsewhere in the system if you cant - then the caliper has self sealed itself. Basically as far as i can see the rubbers in the the handbrake piston blocks the inlet/outlet hole, the master cylinder can pump fluid past the seal but it then cannot escape.
Chris


:bananasex: Good comment Chris. That helps me make sense of my experience.
rubbers in the the handbrake piston blocks the inlet/outlet hole - so releasing the bleed valve will do nothing as that piston is blocked off. Got to be the banjo bolt to release hydraulic lock.
the master cylinder can pump fluid past the seal but it then cannot escape - so don't press the brake pedal when handbrake is on, which I probably did. (Thought it was 'Don't put handbrake on with pedal pressed'.)
So to sum up HiSpec Ultralite rear calipers with hydraulic handbrake -
First version was 'Do not operate hand brake with pedal pressed' or internal seals may be damaged.
Revised version is "Do not press pedal with handbrake on" or hydraulic lock can jam pads on - and they can catch fire if you drive off

Note to self ... "DO NOT PRESS BRAKE PEDAL WHEN HANDBRAKE ON" and in case you ever do "CARRY 14mm RING SPANNER" to release banjo bolt.
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Re: Hi Spec rears sticking

Postby lotusflasherman » Sat 19.11.2016, 18:01

Steve A wrote:Looking at the photo I would say you've definitely got the short levers.
I started with these but soon upgraded to the longer levers as I (and others) found that the hand brake was a nightmare to engage.
Having longer levers also gave the release spring more of a chance to do it's job.


Thanks, 'Longer levers' is now on the Jobs To Do list.

ChrisP wrote "Phil, there is a spring inside the caliper that pushes the piston back and this in turn pushes the lever back to its starting position.
I made some new longer levers to increase the force from the hand brake - so you could try that."

Don't have any drawings do you Chris?
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Re: Hi Spec rears sticking

Postby Steve A » Sun 20.11.2016, 01:03

It's also important to move the cable position with the longer holder to keep it perfectly aligned with the lever

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Re: Hi Spec rears sticking

Postby lotusflasherman » Sun 20.11.2016, 02:45

Yup, understood that, hence my comment "Presume the cable is held further out by the bigger alloy block so it's not pulling at an angle." in my post at 18:12 on 18 Nov.

Think I can probably work out dimensions of the longer components by comparing scale in your photo against the smaller ones. Did BB keep the thickness the same or did it increase on the longer ones?

By the way, in the photo your spring looks thicker gauge than mine but bit shorter, in fact looks to have a gap which seems to indicate an internal spring on the piston.. do you ever hear it rattle?
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Re: Hi Spec rears sticking

Postby Steve A » Sun 20.11.2016, 11:27

lotusflasherman wrote:Yup, understood that, hence my comment "Presume the cable is held further out by the bigger alloy block so it's not pulling at an angle." in my post at 18:12 on 18 Nov.

Think I can probably work out dimensions of the longer components by comparing scale in your photo against the smaller ones. Did BB keep the thickness the same or did it increase on the longer ones?

By the way, in the photo your spring looks thicker gauge than mine but bit shorter, in fact looks to have a gap which seems to indicate an internal spring on the piston.. do you ever hear it rattle?


Sorry for stating the "bleeding obvious" :lol:

I think the cable holder was made from the same stock material just longer, if my garage wasn't so tight and the fact that it's persisting down I'd go and measure it up :roll:

My spring set up wasn't ideal but the spring I used was quiet stiff and gave adequate pressure when required ? not sure but I think I may of added a spacer.
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Re: Hi Spec rears sticking

Postby chrisP » Wed 28.10.2020, 12:34

So I had this problem arise again and having forgotten how to fix it had to release the pressure through the bleed nipple, drive home and strip the caliper down, it is working again. I spoke to Hispec for advise and was promised a call back, but their usual rubbish customer service has resumed and nothing........ :evil:

Anyway I have a couple of photos of the inside of the caliper if it is helpful for anyone.

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