294mm front brake disc upgrade (down grade?)

[mgb281]

When I bought the TF both front and rear discs and calipers were in a sorry state, I decided to ditch the 4 pot AP calipers and go for the popular 280mm conversion. Having sold the AP’s I thought there might be other options so I have been working on this for a couple of months now. The brake discs are from a Mini R53 as are the calipers. The first pair of calipers that I bought were seized solid, fortunately the seller refunded me and I bought a second pair for £21. I had already bought a pair of discs which were at the back of someone’s garage. This enabled me to prove that the concept would work. The calipers were stripped and new pistons and seals were fitted. The discs use off the shelf spigot rings to centre them on the hub, today I have cut the mounting brackets and bolted them together for the first time. I need to get some spacers to replace the stack of washers between the bracket and calipers. The weight of the discs and calipers is virtually identical to the AP setup.
You might well ask why I have gone to so much effort, there are multiple reasons firstly having sold the AP’s for a £100 and having spent a total of about £115 on what you see in the photos it was far cheaper than rebuilding the AP’s plus new discs and pads. Another factor is these calipers take a larger brake pad than either the AP’s or the standard calipers. I have machined my hubs to take MX5 wheels so wheel to caliper clearance is not an issue but the Mini discs are 44mm tall rather than the VW ones used on 280mm conversions so there’s more clearance if using MG wheels. With increased braking effort on the front I have a 276mm conversion coming along for the rear.
I have used a brake balance calculator and these are the results.
Standard 240mm front and rear 61.5% front 38.5 rear
AP 304 front /standard rear 64.4% front 35.5 rear
AP 304 front 276mm rear 60% front 40% rear
Mini 294 front 276mm rear 62.5% front 37.5% rear
Edit
I can see now that I have used the wrong handed caliper in the photos, bleed nipple should be at the top, the brake discs are shiny not black IDNKW

[EllsoJo]

Looks interesting, and I follow your logic regarding costs et. Also Mini R53 is becoming an "emerging classic", so future availability of discs & pads should be no problem.
2 Questions though:
1. do those discs fit onto the 3.75" PCD of the standard F/TF Hub?, or are you using MX5 hubs and wheels?
( you said: " I have machined my hubs to take MX5 wheels so wheel to caliper clearance is not an issue "

2. Would this assembly fit under standard MGTF 15" wheels?

Regards and good luck with the ongoing build, hope your wife (and you?) are pleased with the end result.

[mgb281]

The attached photos show the redrilled hubs, they are now a 100mm pcd to take MX5 wheels. Due to the increased offset of the MX5 wheels a 13mm spacer is required, the hubs were machined to MX5 centre bore. Conveniently Demon Tweeks sell the perfect spacer. The 276 mm rear disc is a MX5 one, it’s a perfect fit on the hubs and the adapter bracket doesn’t need countersunk bolts.
I chose the Mini brake discs because they are readily available and are a decent compromise size. The fact that they sit 5mm further In was a happy coincidence, from what I have read you need 7mm for AP calipers. The mini calipers may or may not clear 15” wheels, perhaps when the car is on the road someone might like to try. I used the calipers from the mini because they were used on 280mm discs by the factory, it’s not the same as stretching from 240 to 280mm discs. It would not be possible to use these calipers on mini 280mm discs due to the caliper mounts fouling the hub.
One factor to bare in mind is that 48mm calipers exert more clamping pressure than the AP’s , in fact 16% more so bigger rear discs are needed and maybe a more aggressive pad as well.
The MX5 wheel shown is my wife’s favourite, in the photo no brake disc, caliper or spacer is fitted, the copper grease is just for rust prevention.

[EllsoJo]

Thanks for the additional information. This mod is not for me though:
I want to retain the existing MGF wheels as IMO they look good and are in good nick. If I do upgrade the front brakes, I will use the MGFMania 280mm conversion. This will allow me to keep my TF looking standard, and would allow any future owner to return it to totally standard very easily.

Whilst not wanting to be a "wet blanket", have you checked if your insurer is O.K. about your brake modification (+ the more minor issue of non-standard wheels)? My other thought is that tyres which are perfectly O.K. for an MX5 with near 50-50% weight distributing might be unsuitable for an MGTF. Something to do with sidewall stiffness I suspect.

[mgb281]

I have already checked regarding insurance so that’s no problem, from memory it’s about £12 a year more. The tyres are the Falken’s which are recommended for the TF and in the correct sizes. Going back to standard TF wheels is no problem, you just knock out the wheel studs and replace them in the original holes. The only thing extra is a spigot ring to take the standard wheels. If I was doing this again then I wouldn’t machine the front hub as I have done for the brake disc but would have left it standard.
There are several reasons why I have gone this route but in no particular order;
Large disc diameter
Larger brake pad area compared with the standard caliper
The Mini brake pad and caliper is dimensioned to work with a 276mm disc so only an increase of 18mm whereas the standard MG caliper and pads are dimensioned to work with a 240mm disc so with a 280mm disc (40mm increase) the pads may overhang the disc.
The combination that I have chosen both front and rear mean that anyone with a pillar drill and angle grinder can fabricate the brackets, I used en3b steel for its dimensional accuracy.
The brake discs are easy to modify at home, IIRC the front discs will fit straight onto an unmodified hub with the mounting holes being elongated slightly, the rears would need the centre bore enlarging and the bolt holes elongating.
I am not saying that this is the best mod and certainly not suggesting that all should copy, just letting people know what I have done.
Interestingly the rear calipers were designed to work with 260mm brake discs. A benefit of the MX5 wheels is that they weigh considerably less than the TF ones, ie the five spokes that I have shown fitted weigh about 2.7kgs each less than an 11 spoke TF wheel.

[talkingcars]

Nice to see people are still experimenting - well done.

[mgb281]

Nice to see people are still experimenting - well done.

Thank you for the kind comment. The only benefit with my 276mm rear brake conversion is that I can walk into any motor factor and walk out with a brake disc that slips on with no mods required, so I am not tied to any supplier who only stocks their choice of discs.
The front conversion potentially has considerable benefits, the Mini calipers give a bigger pad area and the pads sit properly on the disc whereas with the 280mm conversion they don't.
I was inspired by Rob Bell in his thread "what colour to paint my calipers" where he talks of 295mm brake discs with AP calipers. A search on Ebay for 295mm brake discs was not fruitful but the following search for 294mm discs produced the mini ones with a 100mm 4 hole pcd. These require minimal modification to fit onto standard hubs and none to fit onto my modified ones.
Initially I thought I had made a big mistake, I had forgotten that the disc heights of 240mm discs are 5mm lower than for the304mm discs. It turned out to make no difference due to the mini calipers having their mounting 38mm further apart, it was at that point that I realised that you could probably fit these larger discs under 15” wheels. Having found the discs finding the calipers was straightforward, they even retain the standard brake hoses. Another benefit of the Mini caliper is that having the wider spaced mounts you are able to use hexagon headed bolts with no clearance problem.
For anyone trying something similar EBay is a great comparison source in that you can search for particular sizes easily. Both QH and Febi Bilstein give all the disc and pad dimensions so again it simplifies a search even if you don’t buy their products. Once on the road I will report back on their performance