High Spec Rears not bleeding

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High Spec Rears not bleeding

Postby surfboardfiller » Mon 13.09.2021, 19:08

I have a set of Bob Brown Hi-Spec rear calipers, probably one of the first sets he did. Its taken 10 years or so to get the car to the point of an MOT.
I'm trying to bleed the calipers but they won't bleed.
Can anyone who knows these calipers help?

Thanks
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Re: High Spec Rears not bleeding

Postby Steve A » Mon 13.09.2021, 19:49

If I remember correctly, there was an issue with the original seals leaking, which led to Bob paying them a visit, which in turn led to a seal redesign.
This could be totally unrelated to your problem or not relevant ,if it is relevant, how you would know which version of seals you have, I haven't a clue, a lot of water has gone under the bridge since then.
This might jog someone's memory though :poke:
Good luck
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Re: High Spec Rears not bleeding

Postby MPx » Mon 13.09.2021, 23:24

I believe the seal issue was a weakness whereby if you pulled the handbrake on while pushing the footbrake (ie normal!) too much force could be applied to the relevant seal and it would let go. I never use the handbrake other than to pass an MOT so I never suffered that issue.

I did suffer the bleed problems though. As I recall it was because the bleed nipple was too low in the caliper. The caliper had to be removed from its bracket so that it could rotated on the flexi pipe and the nipple raised to the top to be the highest point. It would then bleed to a firm pedal.

Others may have a different recollection....
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Re: High Spec Rears not bleeding

Postby Rambo » Tue 14.09.2021, 06:58

MPx wrote:I did suffer the bleed problems though. As I recall it was because the bleed nipple was too low in the caliper. The caliper had to be removed from its bracket so that it could rotated on the flexi pipe and the nipple raised to the top to be the highest point. It would then bleed to a firm pedal.

Others may have a different recollection....


I remember reading about peoples woes years ago and I believe your recollections are right Mike
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Re: High Spec Rears not bleeding

Postby lotusflasherman » Tue 14.09.2021, 20:41

Yes know them well.. bought a set from DVB .forum link
The rear calipers are Ultralite 2 and mine have the hydraulic handbrake that I know not to push brake pedal and use handbrake together but MOT Testers and garage guys still do it when told not to. Creates a hydraulic lock that I release with the bleed nipple ON TOP of the caliper. If it's not at the top some dork has assembled them wrongly and put the OS on NS and vice versa!

264x10 nsr.jpg


My first question is "Have you ever bled them or is this the first time?

The two parts of the caliper are separated by two alloy spacers and only one has a port (a.k.a. hole) that must be fitted where the 'O' ring seal is.
If not the outer pad will do no work and you'll never be able to bleed them.

Had to change my handbrake seals after somebody rolled them 'inside out' ... photo is the job in progress.

Ultralite 2.jpg


I just bunged the bits on a board to take the photo and the alloy spacers are in the wrong positions in the photo ..

The other thing I'm thinking about is the issue with the way the handbrake seals function ... not sure you'll be able to bleed them with the handbrake on .. make sure it's fully off.

Edit .. correction - the spacers are correct for the rear casting, it's the red outer casting that was flipped to give an internal view.
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Re: High Spec Rears not bleeding

Postby MPx » Tue 14.09.2021, 23:48

lotusflasherman wrote:.... that I release with the bleed nipple ON TOP of the caliper. If it's not at the top some dork has assembled them wrongly and put the OS on NS and vice versa!

Hmmm! I am that dork Phil, and indeed initially put the front disks on the wrong side Doh - but in this case have photographic evidence that the calipers were the right way up. This is my fitting them thread.

I still remember taking them off again when bleeding to get an initial firm peddle - rotate nipple highest and tap lightly - it worked but could be coincidence, the bubbles may have come out eventually with them still in place, but hadn't with quite a lot of fluid passed through. Also I know bubbles sometimes get trapped in the proportioning valves...so maybe the OP is having trouble there??
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Re: High Spec Rears not bleeding

Postby lotusflasherman » Wed 15.09.2021, 12:57

MPx wrote:
lotusflasherman wrote:.... that I release with the bleed nipple ON TOP of the caliper. If it's not at the top some dork has assembled them wrongly and put the OS on NS and vice versa!

Hmmm! I am that dork Phil, and indeed initially put the front disks on the wrong side Doh - but in this case have photographic evidence that the calipers were the right way up. This is my fitting them thread.

I still remember taking them off again when bleeding to get an initial firm peddle - rotate nipple highest and tap lightly - it worked but could be coincidence, the bubbles may have come out eventually with them still in place, but hadn't with quite a lot of fluid passed through. Also I know bubbles sometimes get trapped in the proportioning valves...so maybe the OP is having trouble there??


Looked at your thread and bleed nipples are at the highest point of the hydraulic circuit so that's fine ... (everything above it is solid aluminium so irrelevant). No idea why you found taking them off helped to bleed them .. totally beyond me and no logic behind it!
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Re: High Spec Rears not bleeding

Postby surfboardfiller » Thu 16.09.2021, 14:19

Thank you for the replies. :D

I think they were bled 10 years ago but not used, I used the front calipers on another car for a while and have just re fitted them to this one.
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Re: High Spec Rears not bleeding

Postby chrisP » Wed 13.10.2021, 15:15

I would certainly make sure that the handbrake levers are in their fully off position (maybe take the cable off) The difference between on and off is just a fraction, after that point the handbrake mechanism has sealed the rear caliper and starts to ramp up the compression on the enclosed fluid.
As much as I like the look of the hispec calipers and their working under normal conditions - I don't trust their mechanism!!
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