PNM engineering rear brake calipers

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Re: PNM engineering rear brake calipers

Postby muley » Thu 11.06.2015, 14:59

Geoff,

Sorry I didn't take a picture of the cable re-routing. By the time I'd figured it out I was too brassed off to bother. To do this I had to re-install an old cable because Robin Bob's was too stiff to bend smoothly enough.

This was to fix the too acute angle of the cable from the bracket to the lever. Curiously the nearside wasn't too bad.

(Maz-r has the car now - if you asked him very nicely he might take a pic for you)


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Re: PNM engineering rear brake calipers

Postby router » Thu 11.06.2015, 22:55

Geoff,

Did you pass this info back to PNM as it may save others the headache
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Re: PNM engineering rear brake calipers

Postby maz_r » Fri 12.06.2015, 08:18

muley wrote:Maz-r has the car now - if you asked him very nicely he might take a pic for you


Or you could come to the West Mids meet and have a look yourself...

Let me know if that is too far away and I'll see what I can do.
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Re: PNM engineering rear brake calipers

Postby John_W » Fri 12.06.2015, 08:22

router wrote:Geoff,

Did you pass this info back to PNM as it may save others the headache

I think Geoff's problem is more to do with the non-standard rear hubs he has fitted, rather than with the PNM rear brakes.

Geoff,
What rear disc set-up are you trying to make the PNM brakes compatible with? Is it Bobrobber Brown's or another version (hopefully it's not PNM's own offering, in which case Router is right)?

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Re: PNM engineering rear brake calipers

Postby muley » Fri 12.06.2015, 08:40

router wrote:Geoff,

Did you pass this info back to PNM as it may save others the headache


I passed the info back on both issues.

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Re: PNM engineering rear brake calipers

Postby GeoffSmith » Fri 12.06.2015, 11:10

Confirmation that mine are the original pre-production BB hub kit which I believe were unchanged (why would they be, they worked fine) and more worryingly appear to have been used by Jeemy so there must be quite a few out there. To be fair, I was aware of BB/PNM incompatibility issue when I bought the PNM kit a few years ago and they advised skimming the disc like Jim did but I only remembered when I went to fit them. As I hadn't cut the old brakes off I researched discs to see if i could find an off the shelf solution but the thinner Astra discs don't work as-is. What I am currently looking at is a solution that will work without having to skim discs. If I ever need to replace the rears again, I'd prefer to be able to fit them out the box. I will feedback to PNM as it may be something they could offer.

Anyway, I've found an extra set of four 1.3mm wheel spacers (thanks for those Bob Brown, how much do I owe you.... send me your address and I'll send you payment) and am getting them turned down to fit inside the hubs. They should be ready on Monday so I can try out a couple of offsets.

I have now removed the old offside calliper and offered up the new one, so I can see the potential handbrake cable issues that Jim identified, although I do have OEMs which appear to be a lot more flexible than BB's. I can't get to see your setup on Thursday unless I get the handbrake sorted Martin, so any photographs would be useful and gratefully received.
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Re: PNM engineering rear brake calipers

Postby elanman610 » Sun 14.06.2015, 09:21

I will pass on the information outlined here to Pete at PNM although I know he had been made aware that the different hubs caused issues. To be fair, he can only design a kit which fits on the standard cars to which he was servicing and MOT'ing and can't design stuff for a minority of cars that have been changed from OEM unless he actually sees one with this set-up (and he has never seen one to date despite looking after a large number of M100's). He wasn't even aware of this modification until someone told him. He can find a solution to pretty much any problem put in front of him but he can only do that if he can see it.

The kit was initially designed purely for PNM customers who were having trouble with the handbrake at every MOT. The word got out and well over 100 kits have now been sold. The vast majority have no problems with fitting and the feedback seems to be that the handbrake is superb and the footbrake is improved too (although the kit ISN'T designed as a performance upgrade kit, hence why there isn't larger discs needed in the kit). It was purely made to give a modern and reliable foot and handbrake for MOT time. It's not easy finding a solution to issues with cars and a great deal of time has been invested into coming up with the kit and making it work. Sometimes, minor compromises have to be made but from what I can gather parts for the original rear calipers are almost impossible to get now and not exactly cheap. If it was easy, I guess PNM's competitors would have designed something but I haven't seen anything else.
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Re: PNM engineering rear brake calipers

Postby GeoffSmith » Sun 14.06.2015, 10:22

John, I've got no problem with a bit of fettling and as soon as I have quantified the problem (and come up with a solution that I am happy with), I will be reporting back to you and Pete. There are no issues at all with the PNM kit - just that minor tolerances between the this and the hub upgrade (which are inevitable whenever OEM designs are being copied) have conspired against each other.
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Re: PNM engineering rear brake calipers

Postby cliff » Tue 16.06.2015, 21:26

Geoff, late to this thread, I have a set of Robbin BB's hubs with Mintex MDC266 disks. The only issue I had fitting the PNM kit was that the caliper bolts were a little too long.

P2110046.jpg


A spacer washer cured this.

P2110049.jpg


Handbrake cables were re-routed and p-clipped into place.

P2110055.jpg


This was in February 2013 and I sent a detailed mail to PNM about this. Still very happy with them and the car has sailed through the last 2 MoT's
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Re: PNM engineering rear brake calipers

Postby GeoffSmith » Tue 16.06.2015, 22:11

I've got my spacers back and given them a quick trial fit and the disc is now running with a gap of ~2mm either side so it looks good.

Thanks for the info Clive. I had wondered whether mine were an issue as they were the first pre-production set but Jim had a similar issue. I could do with the drawings from Jamie to see if I can measure any discrepancy.
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Re: PNM engineering rear brake calipers

Postby GeoffSmith » Mon 22.06.2015, 22:59

RECAP - with Bob Brown's hub kit:

The standard (front) Astra disc inboard side of the disc will not allow the calliper bracket to be tightened:

Img_1449x640.jpg


Four spacers were turned down from external spacers to fit inside the discs:

Img_1456x640.jpg


Img_1459x640.jpg


A single 1.6mm spacer leaves the inboard side of both the standard 12.5mm disc and the 10mm disc touching the calliper bracket.

Img_1451x640.jpg


Two 1.6mm spacers puts the outboard side of the standard 12.5mm disc touching the calliper bracket but the 10mm disc is pretty central:

Img_1462x640.jpg



The brakes work a treat and look pretty damned good.

Img_1479x640.jpg


Thanks Pete and John. :smt023
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Re: PNM engineering rear brake calipers

Postby rip » Tue 23.06.2015, 09:21

I would be interested in some spacers so I can swap out my OEM hubs if & when the MOT fails the discs for being pitted..
Geoff, you mention that you would send this info on the PNM. Do you expect they could make the spacers & sell them separately?
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Re: PNM engineering rear brake calipers

Postby GeoffSmith » Tue 23.06.2015, 20:13

I'd hoped that Jeemy would have replied with the engineering drawings, so I could see whether there is an inherent problem or whether it was just the first pre-production ones turned by Bob's fair hands. But I haven't heard from Jeemy.

Anyway, I've got the old discs and (external) spacers, so I'll try and draw up the plans and get a trial one cut in FR4 (pcb material) then the drawing can be passed over to PNM or whoever is interested. They are eminently suitable for laser cutting if enough people were interested.
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Re: PNM engineering rear brake calipers

Postby Fredjohn » Mon 03.08.2015, 22:37

I have just acquired a used set of PNM rear callipers which I am fitting to my car which also has the Jeemy hub conversion.

Initial observations confirm findings above: the Mintex disc fouls the inner side of the caliper, but can be rotated, and there is a 2.5mm clearance on the other side.

If a spacer is fitted between the disc and the hub the 2.5mm clearance would be split either side of the disc (eg 1.25mm spacer = 1.25mm clearance both sides.) If you have the disc skimmed, the zero clearance would become however much was skimmed off and the 2.5mm would remain unchanged. In theory it would be possible to skim 1 to 1.5mm off the calliper mounting lug, which would move the calliper inwards so distributing the 2.5mm clearance onto both sides of the disc. However this may weaken the lug so probably not an option.

I have had the discs skimmed by 1.5mm, so hopefully giving 1.5mm and 2.5mm clearances on each side. I am assembling it tomorrow, so will let you know the outcome. Lotusbits skimmed both discs for me, did a great job but did effectively put up the price of the (cheap) Mintex discs!
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Re: PNM engineering rear brake calipers

Postby Jon » Thu 10.09.2015, 11:26

I'm certainly interested in more details on the spacers - where did they come from and how much effort is involved in the turning?
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Re: PNM engineering rear brake calipers

Postby Jon » Thu 01.10.2015, 09:40

Hi Geoff,

Just wondered if you'd had any chance to make progress on the spacers?

I had my new hubs/disc combo fitted yesterday and it seems the passenger side rear calliper handbrake doesn't even tighten to the disc (probably never did), so I'm even keener to look at the PNM kit...
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Re: PNM engineering rear brake calipers

Postby Jeemy » Thu 01.10.2015, 23:03

OK.

Ready to start working on this with relation to the next run of hubs. I've also been asked once in the past whether it was possible to make the hubs 15mm deeper to save use of spacers. The answer was in the affirmative, but only in batches. It strikes me there may be offset issues with aftermarket wheels, especially as originals get less prevalent. Whether the two can be fixed with one stroke is unlikely.

Shall we continue discussion in this thread or start a new one?
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Re: PNM engineering rear brake calipers

Postby Jon » Thu 01.10.2015, 23:09

Jeemy wrote:whether it was possible to make the hubs 15mm deeper to save use of spacers


Surely you mean 1.5mm?

Just as an aside I spoke to John at PMN today and he said they were aware of the compatibility issue and were investigating options (though obviously this is no guarantee they can/will do anything) - Pete who is looking after it is away until next week, so may be able to get more info then....
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Re: PNM engineering rear brake calipers

Postby Jeemy » Thu 01.10.2015, 23:18

No, I was asked if I could make hubs 15mm deeper. For a guy who was using 15mm spacers and wanted to change it. Maybe it was 10mm, I can't remember. It was nothing to do with PNM stuff. The point is the hubs can be made bigger no problem.
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Re: PNM engineering rear brake calipers

Postby Jon » Thu 01.10.2015, 23:26

Wow, that is a big difference.

Sounds like your next run could be made up of a bunch of one of a kind jobs :lol:
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