What colour to paint my AP brake calipers & brake upgrade projects

[Rob Bell]

A little more digging provides the equivalent AP part number for the MG 4-pots - it is a CP7601-17SORD, and the rebuild parts for it are available from AP distributors if you use the CP7601 caliper part number. In general, the CP7600 series calipers are matched to 295mm rotors, so I am hoping I can retain the 280mm rotors on Project Shed. But if I need to swap over to 295mmx24mm rotors, that would not be a big deal.

Currently in process of obtaining a quote from BG Developments Failing that, I'll find another way to do the job

[Rob Bell]

The slow-burn AP brake project is making progress. I sent the manky calipers shown in the photos in the previous posts to BG Developments after a thorough clean and along with a spare front hub.

The idea behind the project is to convert these abused calipers to radial mount and then come up with a mounting system that would permit their use with practically any wheel.

I was sent some prototype 3D printed parts on Friday and I played with these on a TF front subframe that I will be refurbishing. The parts permit the caliper to the spaced to suit either the 280mm rotor that I currently have on Project Shed, or the 295mm rotor that is the more natural compliment to this caliper (and actually is the same diameter rotor used on the MGF Cup cars).

Here's what the parts look like fitted up, along with a new radial mount AP caliper that I shall return to BGD when the prototype work is complete:

Note also the 3D printed spacer on the hub - this is to mimic the material thickness of the rotor bell/ top hat that will be used when it the project work is finally finished and ensures that the wheel fits as it should so as to correctly assess clearances with the different styles of wheel.

Fitting up a freshly refurbished and straightened ULW - a 16" wheel that was designed from the outset to be used with the AP caliper, there is no surprises there that the rotor fits perfectly (and looks resplendent!):

Equally encouraging was the masses of clearance this wheel design offers - at least 10mm to the spokes:

Things then get complicated. Project Shed currently has a set of 16" Abingdon (aka MGF Cup) wheels - so I offered up a spare rim to the hub:

Looks okay from a distance, but it fouls the inner edge of the wheel spokes, particularly where the spokes curve inward towards the centre of the wheel where they meet the mounting boss:

This wheel would still need at least 5-7mm of spacing to get the the 295mm rotor to fit with sufficient clearance for the caliper - although ironically, the wheel *almost* clears the caliper if the caliper is spaced out to match a 304mm rotor!

Based on this, I didn't have high hopes of clearing the 15" wheel:

Good news, bad news. Good news is that the caliper actually fits within the 15" 5-spoke VVC rim, even with the caliper spaced out to suit a 295mm diameter rotor! The bad news is that the caliper severely fouls the inner face of the spokes. As in "this wheel will need more than a 10mm spacer" fouling of the caliper... May be 15mm.

Conclusion
The caliper in the 295 and 280mm rotor positions clear the ULW wheel comfortably - perhaps no great surprise as the wheel was designed to clear the AP racing brakes from the outset - albeit with a different rotor offset and with a 304mm rotor diameter. As I'll be likely swapping Project Shed over to these wheels (because they are usefully lighter per corner than the current wheels and therefore further reduce un-sprung weight), I could just go with this prototype solution right now and run with it! However, this would be a fail on the "make the brakes clear many different wheel designs" ethos of the project.

16" Abingdon/ MGF Cup wheels foul the caliper in the 295mm position - and that interference would only increase if the rotor diameter were reduced to 280mm. However, modifications to the caliper mounting bracket would be fairly minimal, with a change of caliper offset inwards of about 5-7mm. Even 280mm could be accommodated if needed, albeit with a deeper rotor bell housing.

15" VVC style alloys could accommodate the AP racing 295mm set up, but this would require an even deeper rotor bell and caliper offset. However, this would be potentially do-able I think...

Plan
Not quite sure which way to go. Here are my thoughts so far:

1. I don't want to go with the full-sized 304mm rotors because of (1) weight and (2) the limitations it places on wheel options.
2. Ideally, I would go for 280mm rotors because of weight, but this would necessitate a much deeper bell (or top hat) for the rotor for all wheel styles bar the ULW tested.
3. 295mm rotors are the ideal size for the MG AP rotors, so for purity and increased front leverage, this would be a good option - but even if using a 295mm rotor, I would still need a different offset rotor bell/ top hat. However, any option other than the ULW-mandating current set up would necessitate this anyway!
4. If I ever wanted to drop to a 15" wheel diameter (cheaper track day tyres for this rim diameter with arguably better availability in suitable sizes), then 295mm with the AP caliper appears to offer the best chance of working with the 15" VVC wheel style.
5. If going to 295mm front rotors, I think I would need to consider the knock on impact of altering the balance of the car's braking and the need to upgrade the rear brake arrangement in parallel (perhaps also to 295mm? perhaps also change the rear caliper? - all these are adding £££s to the original project budget, not to mention the associated "project creep" that this would provoke).
6. How likely am I to go down the 15" rim route given that the ULW 16" is actually (paradoxically) so much lighter than the 15" wheel design?

I need to know what the cost implication will be for the deeper rotor bell/ top hat - and perhaps based on that, make a decision.

What are your thoughts? Anyone else considering fitting AP racing brakes but under a 15" wheel or one of the many 16" wheel styles that are non-compatible with the standard AP brakes? Remember that what I am working on is a long way away from being a simple bolt on option with the standard AP racing calipers and would necessitate conversion to radial mount calipers - an option I doubt that many would be prepared to make?

[Rob Bell]

Currently giving some thought to having 304mm rotors all round, but my current thought is that 295 might be the sweet spot... Need to think about rear caliper options though: Lotus Elise rear perhaps?

[Leefy]

Whatever colour you choose check out “Cerakote” products.
It’s pricey, but you won’t ever be needing to repaint calipers ever again.

[Rob Bell]

I actually used MG burgundy red engine enamel - little too early to say how good or otherwise it is, but some did come off when bleeding the brakes - but then brake fluid is a pretty good paint stripper...

[Rob Bell]

But an excellent heads up, thanks Leefy

[mgb281]

Currently giving some thought to having 304mm rotors all round, but my current thought is that 295 might be the sweet spot... Need to think about rear caliper options though: Lotus Elise rear perhaps?

Rob
How about these calipers: https://www.ebay.co.uk/itm/134186636319 ... SwJTFi5oZc
38mm piston and uses a 278mm brake disc as standard. Charles Durning in the USA sells the adapter brackets to fit these on MGB's Just weld another tab to take the clevis pin. This caliper was used on various Renault cars as well ie Safrane, Meganne, Vel Satis and Espace.It takes a banjo fitting so might fit with little effort. The Ebay reference is only for the most detailed and clear photos. The Almera caliper is virtually identical but has a 34mm piston.

[mgb281]

Having returned from work and gone up to the garage loft I have got out the Nissan Primera calipers destined for my MGB. They could be adapted to fit but probably isn’t worth the effort although the pads offer a circa 15% increase in area.
Have you looked at the R56 mini 294mm brake discs? They are exactly the same height as the AP 204mm discs (only 22mm thick though) 100mm PCD and a 64.25 centre bore. It may offer a solution.

[Rob Bell]

Great food for thought - thanks for this!

Ideally, I would love to have access to a list of calipers available with all the technical specifications. I am sure that such a document exists - I just don't have access to it!

[mgb281]

Rob
I have a pair of Mini 294mm brake discs, 4 bolt hole 100mm pcd, so only a limited mod needed. The good news might be that the disc height is 44mm which is 5.5mm greater than a standard 304 disc and lighter, if this was feasible you might not need spacers for cup wheels.