Urs4/urs6 hp2 front struts and calipers????????

[audi100s4]

My s4 has been sitting for over 5 years and im finally doing bits have managed to run her up and other than a few teething problems its nearly there I'm looking to replace my ufo brakes on my urs4 though as they have officially seen better days am looking to upgrade and am looking for struts and hubs with calipers complete ideally or any other info of upgrading these please

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[audicoupeparts]

Ive a pair of HP2 calipers and carriers. will need a refurb though

[audi100s4]

Good stuff buddy I don't mind doing a refurb to them i would propboly regardless to be fair as doing the whole car bit by bit! Where about are you!?!? And what kinda money you looking for and have you any pics!.!?!?!

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[Hanuman]

it's about now that I start kicking myself for not finishing my brake projects, among so many things that have slipped in the last 4 years.

HP2 setup.
The big issue is obtaining the struts. The UF struts use 3 12mm bolts to attach that huge single point inside out calliper. HP2 use 14mm. I stated looking at a conversion that was easy to do having 2 cars with UFO brakes at the time. Converting the existing strut is either easy, or a bit complex, dependent on whether you want to cowboy it, or do it with a little finesse.

UFO
The hub face on UFO disk setups is a larger diameter, and a different height (offset from the strut face). Standard disks from an HP2 won't work. The larger diameter of the hub won't fit inside the hat of the disk, and the various disk options have differing hat heights that conveniently won't centre in the calliper, or come into direct contact with the hub.
Yes, there are videos of people converting their car with a large angle grinder, and the engine running, etc. I'll not comment further, right now. Save to say that HP2 callipers aren't a straight swap. You need the whole strut from 100/A6 (C4 based) cars, which I have on two of my cars. I like HP2, but it is a heavy setup, as well.

I've read about, but not in sufficient detail to know what they did, calliper conversions using Brembo callipers. This is the project that i was embarking on when life took several unexpected detours.
In the garage, I have several callipers from the behemoth Audi/VW Q-Touareg and a couple of others. I was looking at a Mercedes disk using Brembo callipers, and a custom mount that would use the 3 point mounting of the UFO strut, and require only minimal machining.

[audi100s4]

Originally Posted by Hanuman

it's about now that I start kicking myself for not finishing my brake projects, among so many things that have slipped in the last 4 years.



HP2 setup.

The big issue is obtaining the struts. The UF struts use 3 12mm bolts to attach that huge single point inside out calliper. HP2 use 14mm. I stated looking at a conversion that was easy to do having 2 cars with UFO brakes at the time. Converting the existing strut is either easy, or a bit complex, dependent on whether you want to cowboy it, or do it with a little finesse.



UFO

The hub face on UFO disk setups is a larger diameter, and a different height (offset from the strut face). Standard disks from an HP2 won't work. The larger diameter of the hub won't fit inside the hat of the disk, and the various disk options have differing hat heights that conveniently won't centre in the calliper, or come into direct contact with the hub.

Yes, there are videos of people converting their car with a large angle grinder, and the engine running, etc. I'll not comment further, right now. Save to say that HP2 callipers aren't a straight swap. You need the whole strut from 100/A6 (C4 based) cars, which I have on two of my cars. I like HP2, but it is a heavy setup, as well.



I've read about, but not in sufficient detail to know what they did, calliper conversions using Brembo callipers. This is the project that i was embarking on when life took several unexpected detours.

In the garage, I have several callipers from the behemoth Audi/VW Q-Touareg and a couple of others. I was looking at a Mercedes disk using Brembo callipers, and a custom mount that would use the 3 point mounting of the UFO strut, and require only minimal machining.

I've had the same issue many a time have I been able to get hold of this brake setup and life has got in the way and now life is kind of being alright again now I can't get hold of anything that I need my project has been sat sooooo long it took a while to even get the enthusiasm to get started again on it to be fair theres a few different versions of putting brackets and calipers and disks on to ufo but I don't like the idea of having BMW this or merc that on my motor as everything else is original hence why I'm looking at trying to get hp2 complete struts /calipers so I can just do a big swap out :/

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[Hanuman]

HP2 Callipers are fairly straight forward, although it does appear that there may be two slightly different versions, for different disc sizes. It's the struts that are the big issue. Eastern Europe/baltic states are where I've seen these most often.

[spink]

https://www.s2forum.com/forum/techni...ton-ufo-to-hp2

[audi100s4]

Originally Posted by spink

https://www.s2forum.com/forum/techni...ton-ufo-to-hp2

Very good info cheers bud but want to bin the ufo off completely i think

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[audi100s4]

Originally Posted by Hanuman

HP2 Callipers are fairly straight forward, although it does appear that there may be two slightly different versions, for different disc sizes. It's the struts that are the big issue. Eastern Europe/baltic states are where I've seen these most often.

Yeh I've found this aswell i also found a few sets on german ebay a while back but shipping killed it made a front set of hp2 calipers and struts well over a grand once shipping was put on top and I didn't particularly want to spend a grand on standard brakes lol


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[Hanuman]

I'm adding to this, but hopefully I'll be adding to my own thread properly some time soon.

HP2 calipers
There appears to be 2, maybe 3 or even 4 distinct types.

All steel cylinder body, frame and bracket
Aluminum alloy cylinder body, steel frame and bracket.

then there's the variant that uses spring clips to retain the pads, and the other type that use a clip into the piston recess for the inboard pads, and a torn head retaining screw for the outboard pads.

Then, the most obvious difference is 314mm discs, which were used on ur-S6 and A8, (ur-S4 as well?) and the 323mm disc used on the S6plus and S8s.

I bought 2 brand new calipers with a possible part number of BCT120, but I did have the option of going with a slightly different part number. The ONLY discernible difference that I could see from the photos was that the hub mounting holes were drilled slightly more out, radially speaking. I didn't have the option at the time to measure them, but it did seem obvious ni the photos. I think I went with the 314mm version, clipped and screw retained.

The discs have the same pad face and contact area, but there is a difference in the inner discs dimensions which move the friction area outwards. We're only talking a radius change of 4.5mm.

Original UFO discs were 310mm x 25mm, and obvious gripped by the inside out single pot caliper. It's a love hate thing.
I like the idea as it solved a technical difficulty, albeit short lived. Big disc in a small space. 15" wheels, 310mm disc.
urS4/S6 has a 314mm x 30mm disc, HP2 calipers, which are heavy. The other version HP2 using a 323mm x 30mm disc.

And then the fun begins, because all is not as it might appear.

The struts are different, some obvious, and some subtle differences.
The hubs very different.

Originally Posted by Hanuman

These are not insurmountable, but might easily be missed if your approach to converting with mixed components also involves using an angle grinder and the gearbox as an adhoc lathe...

The mounting hole centres are not the same.

The UFO caliper mounts on 3 points, using M12x1.5 bolts. HP2 mounts with 2 M14x1.5. The hole centres are 145ish mm. So, both struts would use the bottom hole. The UFO strut has a superfluous top hole. But the lower of those two holes is not the same distance radially from the hub centre, as the bottom one. As far as I can tell, the lower hole is 94mm, while the upper hole is 100mm. All measured in a cold wet garage, so accuracy is not assured.

If HP2 caliper were to be sleeved for a M12 bolt, and then mounted to the strut, as far as I can tell, the upper mounting would have the caliper sitting slightly out of true.

As for the hub itself, it’s slight thicker, giving a small offset on the disk mounting face. The hub is slightly offset also, giving a cumulative difference of about 3.5 mm.
The OD of the hub is 143mm, compared to the standard 131mm. So the UFO hub does not fit inside the hat of a standard S6 314mm disc.

All is not lost though, with regards the discs, as A4-B8/B9 cars have a 142mm OB hub. And there is a 318mmx30mm A4-B9/Q5/A5 disk. I have two on order to trial my prototyping.

Hat height of the A4 discs is 57mm, and the S6 disc is 60mm. Quick maths suggest that this will give a disc centre error of about 5mm, which is huge in terms of caliper positioning.

One useful fix is that the rear hubs on the V8/urS6/S6plus cars do fit the fronts. In the C4 chassis, the same hub is used front and rear.
So if worst comes to worst, I’ll just swap the hubs, as I have some spares. They are also available at a price on fleabay.

But this does not resolve the immediate issue of the caliper positioning.
As my brake conversion is likely going down the Radial mounted Brembo, all I need to do is fabricate suitable mounting brackets. But I would like to come up with a fix for the HP2 caliper.

That’s all I’ve got for now. And I know it’s a long winded reply in a parts wanted thread, but I’ll fix that in coming days.