13 replies to this topic

[mini_1985]

hi i have metro turbo four pots and they are not up for the job. I need some big brake conversion like 280mm disc or any others that work well to fit under a 13 inch wheel thanks for reading dan.

[mini13]

the metty brakes should be fine, I think you need to look at the pads, you havent got nasty greenstuffs in there have you? a set of carbpon metalic pads in there shuld be fantastic if you can stand the mess!

also going for big discs / calipers can reduce the range of pads, if you go to somthing like 280mm you'll need to be running road pads otherwise you'll almost never get the heat into them, I have 266mm discs on mine with Mintex 1144's, they are good on a hot day, ok on a normal day, but can be trecherous on a cold day.

[mini13]

also dont forget the effect on other comonents, baljoints, tie bars subframe ect.... I'd recomend gussiting the subframe where the tiebar mounts and going to uprated tiebars, preferable Kad rosejointed ones,

also on mine I ditched that tiny bolt that connects the tie rod to the bottom arm and drilled it to take a 998 rod bolt and A+ head nut....

also I run metro hubs for the stronger ball joints....

If your looking at needing this level of braking, it may be an idea to look into converting to late rover metro Hubs, then see if you can get the MGF brakes under 13's... also you can then get rid of a lot of Scrub radius.

[Sam Walters]

Echoing the comments on the post above mine.

Another thought is they not be as bad as you think. If youve come from a modern car with a servo they may just feel woody for you.

[mini13]

yeah, good point on the servo, my missus could hardly stop my other car with S dics and no servo, I can make it stand on its nose though... stuck a servo on there and she damn near put me through the wind screen LOL

[jaydee]

hi i have metro turbo four pots and they are not up for the job. I need some big brake conversion like 280mm disc or any others that work well to fit under a 13 inch wheel thanks for reading dan.

Metro turbo brakes are not up to the job? Do you have a 250 bhp mini or do you need a brake overhaul?

[Midas Mk1]

Depends what your used to, my Dads A4 can stop miles better than my alloy 4pots ever can.

[tiger99]

I would be extremely worried about the tie rod bolt modification. The bolt is partly loaded in shear, while a rod bolt is designed to be loaded in tension, for a start. (It isn't strong enough to be able to torque it up tight enough to transfer all the load by friction.) Also, what about the amount of metal left around the hole, in both the lower arm lug and tie rod fork? Have you done any calculations to prove that it has sufficient static and fatigue strength? Can you prove that the result is actually stronger than the original? I strongly suspect that it is weaker.

The correct upgrade is to replace the existing nut and bolt with items of exactly the same dimensions, in grade 12.9 steel.

[Skortchio]

Which job aren't they up too?
The stock single pot brakes in 7.9 or 8.4" trim in half decent repair, are more than capable of stopping is lightweight little machine like a Mini from road legal speeds without much trouble at all.

The main problem comes when repeatedly braking hard or trailing the brakes, often seen when racing where the discs ineffective cooling and the large single piston retain heat and cause brake fade.

If you find your brakes aren't stopping you, as already said the first steps would be maintainance related. Make sure the pads and discs are in good order and not contaminated and that the calipers are functioning well, followed b making sure the system is properly bled.

[mini13]

I didnt run calcs on the joint as there is not enough info available on the bolts, but what I did do was to replicate the joints and faliure test them in a hydraulic rig, my set up failed at over twice what the std one did.

As for meat around the joint, that is a good call, I definatly wouldnt recomend doing this on std stuff, but on the uprated parts I used tere was more meat after the drilling than there was unmodified on standard parts, I did also make sure that the joint was a snug fit so interfaces properly when torqued up.

[tiger99]

Good. I am delighted to see that you have gone about it properly. I am rather used to seeing people on the forum who don't know what they are doing, and tend to react accordingly, because I dread to think what the authorities will do if the accident rate in classic cars starts to increase. There have been big clampdowns in Europe, apparently at the behest of Mercedes amongst others, so that you can no longer modify new cars, and in many countries a classic needs special permission and can't venture far from home. We do not want a spate of accidents triggering such legislation here. I was unaware that you had uprated arms etc, and know how little meat there is around the bolt hole as standard. I have had standard parts wear, and did not dare ream out the hole for the next size of bolt, as it was obviously marginal.

I don't like Mini tie rods at the best of times. One of Issigonis' few mistakes, carried over from the Morris Minor. My objection basically is the way the front end works, not truly pivoting in its mount, but moving at a strange angle which puts the bushes partly in compression, instead of the much preferable torsional shear. As an indirect result of that, some unsuspecting mug buys and fits a set of polybushes, only to find that the front end of his tie rod fails spectacularly due to fatigue, because when the polybush refused to compress, it had to bend. OK, the blame lies fairly and squarely on the polybush suppliers, but you get my drift. The rose jointed conversions do not have enough compliance to be comfortable for road use, probably wear quite quickly, and worse than that, put the pivot centre in the wrong place, so you get undesirable effects like castor change on bump. To do it right, the mount brackets would have to be replaced, and a more appropriate form of pivot introduced, something I am hoping to look at once I get Mini number 4 and a garage to work on it (the garage is the holding factor, I keep looking at half-decent Minis).

And yes, I will need to make arrangements to stress test my work. A decent hydraulic cylinder, hand pump and calibrated pressure gauge will do. But my field of expertise is instrumentation, so I would really like to measure the working stresses in a Mini, on the road, to see if they are anywhere near my estimates first. We can do things today with a laptop and some cheap hardware that Issigonis could only dream of.

[mini13]

I agree on the polly bushes, my prefered arms are the Kad ones as they have a machined bit for the rose joint to go into rather than the pressed steel arangement I've seen on others,

In my expirience rose joints last well on the road, as long as you get good quality ones and get a boot on them and a good lube, my current ones have been on there 4 years, and I'll probably change them this year

[mini_1985]

well the car is getting overhauled and im using a new servo and master from a vauxhall cavalier gsi. Well the old engine i have is more than 250hp and it is really working the brakes. I took on a track day with a remote servo and metro brakes with a turbocharged engine putting 310hp and 330 ft/ib and cooked them even with a good mintex pads and castrol race fluid I have seen a thread on here that has a group buy from hi spec using 280mm x 26mm. So may give hi spec a ring as i would really like to use them and give me super braking power with my new setup on the car.

[Cooperman]

Back onto front tie-bars, if I may, I've never had any issues with the tie-rod to lower arm bolts, even on international gravel rallies, but I have had issues with the 'ear' onto which the tie-bars mount at the front. In time they bend and/or fatigue. It's a good idea to 'triangulate' the 'ears' by welding a 4 mm steel web onto the ear to tie it to the sub-frame.
I've never done the calculation, but the impact shear loaqding on that bolt, which is 5/16" diameter, would need to be huge to cause a failure in shear. In fact it's in double-shear as it is a fork fitting. It's probably a 2 tonne load to shear the bolt, but the 'ear' probably wouldn't take anything like that before it failed.
On rally Minis I use the standard rubber bushes at the front of the tie-bar to keep the shock loads down a bit.

Edited by Cooperman, 13 August 2012 - 07:46 PM.