Brake conversion – am I on the right track?

[wde_bdy]

Being an accountant I thought I would pick the brains of people who do this stuff in the real world to see if I have made any really obvious screwups in my thinking.

Background
My new wheels don’t fit over the factory KP61 Starlet brakes as the caliper sits past the face of the hub and the back of my wheels is very flat. Since I am fitting a 7K and KP rotors aren’t available anyway (or at least very hard to find) I thought it was a good opportunity to do an upgrade. The criteria I had were –
- Must fit my wheels (14x7 neg 17 offset Spitfires)
- Cost effective
- Un-modded consumables (rotors/pads) if possible
- Vented rotors
- Easily available parts
- Must mount to the rear of the Starlet hub
- Simple caliper bracket
- Not too heavy

These criteria put a few restrictions on what I could do, the wheels are the most limiting factor as there can only be minimal overhang of the caliper past the hub face and the 14” size limits the diameter. I looked at a lot different conversions on the net, most were no good as they mounted to the front of the hub. Most callipers also wouldn’t clear my wheels without setting the caliper well back which meant the rotor had to fit over the factory caliper mounts. Basically I had to find some low profile calipers or run a separate rotor hat and Wilwood or similar discs. The only real issue I have with this is I do some pretty high mileage so decided I didn’t really want race style parts.

So a session at the wreckers with a tape measure saw me pick up some calipers and discs from the wreckers, I think they are from a Ford Laser/Mazda Astina (based on the disc dimensions, only had engine and front suspension but definitely Mazda/Ford something). Discs were no good with out modifying (centre bore too small) but the single piston sliding caliper had a very low profile front face. Easy to find decent pads for as they a pretty common size. As a bonus the calipers are not much heavier than the factory ones.
Ford/Mazda Caliper Picture - Click Me

So with some serious measuring and an Excel based copy of the DBA catalogue I dug out some potential rotor options. Nothing was a bolt up fit, mainly due to the small PCD that the factory Starlet rotor bolts on with as well as having the thread in the rotors. Basically came down to a rotor from an E30 BMW which is 260x22mm, 100mm PCD and a 66mm centrebore. The total height of the rotor is 35mm which gives just enough room to get a caliper bracket on the front side of the strut (otherwise you need to machine the back of the caliper mounts flat), it will require the mount to be threaded though as there will not be enough rotor clearance to fit a bolt in. The caliper end will also need to be threaded to bolt the caliper up.
KP Rotor Picture - Click Me
BMW Rotor Picture - Click Me

So the key things I need to know is around the caliper bracket and fitting the rotor to the hub. For the bracket I am looking about 8 to 10mm thick, will this be thick enough to get enough thread into? When I measured up the factory mount that the caliper came off it had a thickness of about 8mm so I presume keeping the same thickness should be safe. The other question is would you just tap a thread in the flat plate or I have seem them done with threaded inserts that are welded to the plate.

For securing the rotor my first thought as a cheap bastard was just machine down the factory rotor, run longer bolts and use it to sandwich the rotor. Deciding not to be that dodgy I have planned on getting a ring made that centres the rotor on the back of the hub (hub 64mm vs rotor 66mm) and is threaded. BMW rotor would be redrilled to fit the PCD of the starlet hub and then sandwiched by the centering ring, seems safer than bolts and nuts as you don’t have the risk of a nut working its way loose.

Any feedback appreciated, have a used rotor on the way to test how good my measuring is and will dummy it up from there.

Callum

[Boost_4_Life]

I changed to wilwoods all round on my starlet, used to run primera p10 discs and calipers on the rear, ae86 discs and calipers on the front. Still got them laying in the shed if you want the whole damn lot... But otherwise yea youre on the right track. I would think 8mm is fine, thats all I've got, and just threaded I think. Dont discount wilwood stuff completely, its still very suitable for road use... In fact the low maintenance dynalite calipers are awesome.

[wde_bdy]

What diff were the rears fitted to? Presume for the front you were running AE86 struts as well or did you adapt them to the Starlet strut?
I actually did buy some Wilwood calipers as the price was too good to pass up, unfortunately they were going to be impossible to fit (Superlites, way too wide to clear my wheels). Have considered the Dynalites and may still go that way but just wasn't too keen on a 2 piece rotor setup if I could avoid it.

Callum

[Boost_4_Life]

standard starlet struts for both setups, i cant remember how the ae86 one was mounted, i think the disc bolted up fairly easily and it just had a bracket for the calipers. The rear was a liteace one at that stage.
With my setup now the discs are mazda astina or something, just bolt pattern redrilled to match up to the starlet hubs on the front. Rear is slightly easier but I'm now running an rx7 diff.

[Adoom]

I've got MA71(I think) 10.5" vented rear discs on the front of my Starlet. I chose them because they fit the dimensions I wanted. They fit over the hub/flange.
Some years after doing the conversion, I found that the discs are not very common. Unless someone restocks, I will have to import my next set.
So don't use them.
I used Holdon Camira alloy calipers. Again, because they fit the dimensions of the wheel and the disc and the bracket was simple. They were also cheap.
But, aftermarket performance pads do not exist for these calipers. I had to get some cheap pads relined with "good stuff" for about $300.

It stops well enough, but it could probably be better.

If I were to do it again I would use Wilwood calipers, there are loads of pad options and the pads are cheap compared to pads for other calipers.

You can learn from my mistakes.

[wde_bdy]

This is why I have the Mazda/Ford calipers, very common pad size with a few aftermarket options. The rotors are also really common, quick browse on Trade me gets you a pair for $100 brand new. A rotor over setup would have been much much easier but unfortunately I can't afford to push the track out any further than it is already.

Callum

[wde_bdy]

So as a quick test measure had a couple of holes drilled and tapped in the BMW rotor that showed up yesterday, this is trial fitment step ONLY (not really enough meat in the disc for this).



http://img809.imageshack.us/img809/5712/bmwbrakes04.jpg
http://img836.imageshack.us/img836/3397/bmwbrakes05.jpg
http://img838.imageshack.us/img838/961/bmwbrakes06.jpg
http://img708.imageshack.us/img708/2663/bmwbrakes07.jpg
http://img228.imageshack.us/img228/848/bmwbrakes08.jpg
http://img580.imageshack.us/img580/7456/bmwbrakes09.jpg
http://img204.imageshack.us/img204/2069/bmwbrakes10.jpg
http://img805.imageshack.us/img805/2087/bmwbrakes11.jpg
Looking promising, as it is a sliding caliper I test fitted it with a set of new pads so the front face of the caliper is as far out as it will ever get (moves in as pads wear). It is close but the caliper just clears the wheel face, I may be able to get myself a few mm more with a clean up of the bac k of the wheel or even the front edge fo the caliper if I really need to. Has a casting mark that sits out on the caliper that to my untrained eye does nothing but will get a second opinion on that.
Now to dummy up a caliper mount, will need to be shaped a bit but doesn't look too tricky at this stage. Not totallly convinced I can get the bracket thick enough to thread especially at the strut end but could could use a counter sunk allen head bolt instead and then weld threaded inserts in at the caliper end. That wold work for a 5mm plate flat bracket, or start with thicker material threaded at the caliper end and machind down to 6 or 7mm at the strut end.

Callum

[wde_bdy]

So I made me a caliper bracket, but it broke when I tried to to screw the bolt into it.





Next time I will make it out of something stronger
Bracket was dummied up in 10mm wood, with a little sanding to get it to fit at the strut end. Probably have about 7-8mm there, not really enough to be threaded but should be enough to recess a countersunk allen head bolt though. Caliper end will be 10-12mm thick, thinking threaded inserts welded in might be the best approach as to my non expert engineer mind machining a 12mm thick plate down to 7mm at the strut might introduce weak points that a flat plate wouldn't have.
Thinking of extending the bracket to meet up with two of the 3 brake backing plate bolt holes just as extra support. Open to any feedback anyone has.

Callum

[RomanV]

I done something similarish, but with different struts.

A big help was going to Toyodiy.com and finding the part numbers for the front wheel bearings, then finding what other cars have the same wheel bearing part numbers BUT different part numbers for the hubs.

As that would mean, the hub fits your strut but is different in some way.

Found some van hubs that had a different backspacing for where the disc bolts on, which made things heaps easier to fit.

May not work in this scenario, but just an idea that might help if you get stuck with that current recipe.

[wde_bdy]

The biggest restriction for my setup is the wheels. Need to find a caliper low profile enough to clear the back of the wheels while still leaving enough space for mounting the caliper to the front of the strut so I keep the machining to a minimum. Don't want to start shaving off the rear of the caliper mounts if I can avoid it.

Callum

[RomanV]

Yep, for sure.

One other thing to check, Make sure you fit the steering arm and LCA on and see if it clears, you can end up banging into that if your disc is a lot closer to the strut than before. Mine now has about 3-4mm clearance from disc to LCA.