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MG Midget and Sprite Technical - Rear Brake Upgrades

I thought some of you might be interested in this...

After (two) sessions at Croft, my rear drums were the weak link for track use. First trip to Croft set them on fire. Second trip with the smaller 1500 brake cylinders meant there was no fire (yay) but the drums went blue and I had no brakes.

After being slightly appalled by the price of a few bracket and carrier for a rear brake kit from the usual suspects I set about making my own.

There are some VERY good threads in this very BBS, and retrospective thanks go out to those who posted, and specifically to Paul W.

I've settled on the arrangement you can see in the picture. It's based around an MGF caliper for two reasons - one - it fits, and two - the handbrake is in the right plane unlike some VW group calipers. Ive used a Citroen disc.

At the moment this only fits under 14 inch wheels (because that's what I have)

There's also an additional link in there. It's in the same sort of place as a Frogeye radius arm. The locations are such that I've got less than 1mm length change between full bump and full droop. Sideways location is set by a Mumford Link, so there's a rose joint in one end to allow for roll, and soft rubber (spring hangar) bushes at the front. There's a crank in the rod to clear the axle under bump conditions. It's also totally bolt on, using the old lever arm damper mount at the front, and a bracket that sits between the spring and the axle at the back.

There is now NO axle tramp at all. Absolutely none. Instead of sitting down on the springs and battering the bump stop off the bodywork like it used to, there's very little squat and it shoots off like a scalded rat.

The whole lot has had about 150 road miles testing and a full day thrashing round Anglesey circuit. Neither of these has highlighted any issues whatsoever.

Total cost? About 80 quid.


Rob Armstrong

Hi Rob,

Missed this one until now. Interesting mods, really like it. Maybe what you needed was some ali drums! :-)

Interesting anti-tramp link too. I have been pondering fabricating something. Probably overkill with the power I am putting out, but I like to mess!

Cheers,
Malc.

Malcolm Le Chevalier

Hi Malc. Not sure that the alloy drums would have cut it on track. They would have helped I'm sure, but I managed to heat a set of standard steel drums until they went blue, and got through half a shoe thickness in 26 miles. A combination of heat and wear meant I couldn't get the brakes to adjust up at all later on in the day - I ran out of adjustment! I did the runs out on track in the afternoon with the handbrake on a couple of clicks or I needed a triple pump on the brakes in front of every corner.

However I think the main issue was relative overuse of the rear brakes for whatever reason, there are a lot of posts on here talking about brake balance and how upgrading one end doesn't necessarily result in a total upgrade. I run 260mm vented 4 pots on the front from JLH and they are un-fadeable.

Perhaps the rear brakes are always overheatable but on a standard car it's the fronts that give up first.

No fade with these big discs on the back. The front locks up first, just, which is ideal, and although they are a little heavy (I had to go up a master cylinder size) they are very nicely balanced with no compensation valve needed.
Rob Armstrong

Well done Rob! Especially about getting that radius arm geometry right, that's the key.
What size are the Citroen discs?
Paul Walbran

240mm ish. I think 237mm actually. I think if I'd had 13 inch wheels I probably could have squeezed it in. The biggest issue was finding something that I knew was going to fir over the halfshaft dome in the middle. These have a bore size of 71mm so fit fine.
Rob Armstrong

I had no problems with the standard rear drums on track on my car but I must admit I've not stripped them recently to have a look how much they've worn. This is the first year I've done track days and they don't get too much abuse on hillclimbs and sprints.

I've got standard brakes apart from Mintex pads and they are great, no fade and seem to hold up to a good few laps at Cadwell. My car is probably 100k lighter than standard which probably helps.

Must check those rear linings before next spring!
john payne

To be quite frank, I have no idea why I get through brakes like I do.

I've had fade on the original setup with green stuff pads on the road.

There's nothing obviously out of kilter with the setup I had, but for whatever reason it didn't work as well as I asked it to.

Yes it gets driven as fast as possible but it's not the only car that does.

Loads of racers race with drums on without them melting.

Very odd.

Rear discs have fixed it though.
Rob Armstrong

Rob,
(and please don't take the following the wrong way)
have you had any driving/track instruction?

One of the best improvements you can make to a vehicle is driver training (track or road).

I can't remember the wording now but there used to be an old (racing?) saying something about better drivers having smaller brakes, you're driving an old (design) car.

On the other hand - have you actually watched your videos :).
Nigel Atkins

Nigal

Remember David lieb...he was a big fan of driver education if you wanted to go faster...and he was proof it worked for him
1 Paper

Hi Nigel. Not taken the wrong way at all!

Short answer is Yes. Instruction received from friendly circuit types at all 3 tracks I've been to. It's normally worth the extra few quid as they are very good.

Tend to get plenty of praise for the midget's ability, which is nice. I don't tend to use the gears to slow down at all, it's all on the brakes, after a few hairy moments locking up the rear axle under exuberant downchanges. It gets lots of brake use as it normally spends most of the time on track 2 up - either willing passengers/victims or Jenni, who seems to enjoy it!

The other way to use the brakes less is to make it go round corners faster. Sadly my camera was broken at Anglesey where I used track tyres; the previous slidy videos are on road tyres. The other side of the cornering argument is now it's faster everywhere else too...
Rob Armstrong

Complete myth that better drivers don't need brakes. It is certainly true that in the days when brakes weren't up to it, better drivers adjusted braking habits accordingly, to the extent of not using them. But now we have real options for brakes.

If you have gruntier brakes, then you can leave braking later to drop to any given speed in a corner. It's a no brainer.

Rob your comment "The other way to use the brakes less is to make it go round corners faster" is true to an extent, but also a bit misleading. If you are already cornering on the limit, there's no room to go faster and use the brakes less. But if you are not cornering to the limit, that's where the improvement focus needs to be!
Paul Walbran

Hi Rob. Just out of interest, was the instructor at Anglesey, Malcolm Hamilton? He's an old pal of mine and an excellent racer. He used to race a phenomenal 7litre E type in the Intermarque series, against Gerry Marshall and Win Percy et Al. I just wondered.
Bernie Higginson

Wasn't him, though he sounds ace. A 7 litre jag? Marvellous. It was javelins instructor called JJ.

It's already driven as hard as it will go, so law of diminishing returns applies! Needs more power to go faster!

It now has very very grunty brakes. I can outbrake most things on the track, elises, in particular, which annoys them. There's a massive difference between how mine stops and a standard one. I had a passenger with a standard braked car who was a little surprised at the braking points!
Rob Armstrong

Hi Rob,
Did you make a bracket for the caliper? what did you make it out of??? - any dimensions??

Ta
Jon
Jon White

Bracket is made from 8mm steel with a spacer piece. I have the dimensions written somewhere on a bit of wood...
Rob Armstrong

Hi Paul,
I wasn't sure if the old saying (whatever it was?) would be suitable in the case of a Spridget (and certainly not modified) but the remark was more of a humorous one aimed at Rob. As you say, as with just about all things, it's about balance, not too little or too much.

Rob,
I'm sure you're aware your desire (need?) to keep improving the Midget for the track will dig very deep into diminishing returns in all areas so perhaps you might want consider something like going into a share on a more suitable track car, probably a different make and model (Caterfield style?) and keep the Midget (mostly?) for road use.

The couple of times I've taken passenger rides with track instructors, on roads not tracks, the thing that I noticed was how smooth and uneventfully the rides were despite the swiftness of the cars' progress.

When I was on a classic car track experience day with a mate I got told off by the instructor for going too slow - and my mate for going too fast.
Nigel Atkins

It's very smooth on track. And with the dampers and arb softened off its lovely and supple on the road.

Part of the fun is continously development of the car at minimal cost.

Nothing beats overtaking a lotus elise on a track in something that cost less to build than a set of posh dampers for the lotus.

I can deal with diminishing returns. To reset, add more power!

Next time we're down your way on a track I'll let you know so you can pop over and poke around.
Rob Armstrong

Rob any chance of a drawing for the top link?
O K

Hi Rob
I'm really surprised at your experience. I have JLH 4-pot disks on the front but standard drums on the rear and have never experience the kind of overheating and wear you have despite a number of flat out track days. Nice rear disk conversion however.
Chris Hasluck

Rob,

Likewise, I'm surprised at the extent of the rear braking issues.

On our Minor, which is heavier than a Midget, we have Metro 4-pot calipers with Metro ventilated disks at the front, and Mintex 1155 pads.

At the rear are standard 7" drums, with Mintex 'race' linings, 3/4" bore cylinders and an adjustable rear line pressure valve (modified Mini rear subframe one) to prevent rear lock-up under heavy braking.

To keep the pedal pressure reasonable, and not too far removed from a 'modern', it has a 2.3:1 boost ratio AP Lockheed servo.

On track days there is little that outbrakes us, and no fade or overheating 'ever'.

With regards to wear, the rear shoes seem to last about 15/20,000 miles, i.e. 3 or 4 sets in just under 60,000 miles, and front pads around 12/15,000 miles.

Richard
Richard Wale

Rob,
so sorry, I managed to miss the last line of your post until now, yes please do let me know when you're down my way, thank you.

If you behave yourself I'll let you see a photo of the 'good book' to really make your day.

If you want I'll also see my mate and borrow a large fire extinguisher so you can brake as much as you want on track.

Cheers.

Nigel Atkins

No worries Nigel! I carry a fire extinguisher anyway to put out various types of fire. I have a copy of the good book somewhere but please bring your photo so we can make sure they are the same. We can play originality bingo with my car.

I, like Richard and Chris, am also surprised. Everything (was) standard; I could get brake fade on the front on the road with standard brakes. When experiencing rear brake fire and overheating I had JLH big 260mm fronts, everything else standard. I went from fire to just really hot by changing to the smaller 1500 cylinders on the back and getting a set of proper Mintex shoes.

Now the only bit of the braking system that's left is the Kunifer pipes and the brake pedal.

I've got no servo, and no rear proportioning valve; never had an issue with the rears locking first.

Any hints on overheating the rears gratefully received! It's no longer a problem but it would be interesting to know thoughts.
Rob Armstrong

this was a brand new drum after 1 track day. It had gone so big on track I couldn't get it to adjust up.


Rob Armstrong

Rob,

While not ideal your drums are not actually getting that hot, they're cast iron in fact not steel but should still follow to normal tempering colours such as http://www.westyorkssteel.com/technical-information/steel-heat-treatment/tempering-temperatures/ so the inner edges may be getting over 300C but the rest not. Most times you wouldn't even notice as the surface would soon rust in use but on those nice clean fresh drums the discolouration is far more evident. Not sure why you would have lost the brakes though. I've done many track days at Castle Combe in my frogeye, standard drums rear and discs on the front, and apart from the odd slight leak of hot grease from the front hubs had not loss of braking.
David Billington

I used to get through Mintex M20 shoes at an alarming rate and burn the rubber covers on the (1500) wheels cylinders. I changed to the (even) smaller Cooper S cylinders and never had a problem again.
Dave O'Neill 2

I have been searching for up rated brake shoes. Mintex M20 was mentioned in this thread. I haven't found a source for these. 1275 Midget Any suggestions?
J Bubela

The shoes were originally lined with Mintex M20 material and now with the Mintex non-asbestos equivalent - they are relined by Questmead, the Mintex distributors in Rochdale.

The bigger JLH 260mm discs should use less line pressure than the smaller Metro 213mm discs, so less likelihood of rear lock-up, but the possible lower line pressure does not does not help to explain the exceptionally high rear brake temperatures on a Midget though?

Our local garage used to be puzzled at MOT time that the rear handbrake efficiency was much higher than the footbrake, but now has a note on file about the Mini line pressure limiter being fitted!

Richard

Richard Wale

I managed 35% handbrake efficiency with these rears
Rob Armstrong

Are these rear shoes midget specific or the slightly wider mini? I'm sure I read on here somewhere that mini rear shoes are an easy upgrade?

Thanks
Jon
Jon White

MOSS lists Midget and Mini as having identical rear brake shoes.

Rob
Rob aka MG Moneypit

I think Mini and Midget rear shoes are the same, but Mini fronts are wider.
Dave O'Neill 2

Dave. Which Mini fronts are the correct ones? There are some for use with very early Minis with single cylinders and later ones for twin cylinders. Which are the wide ones? I want to upgrade my Sprite's rear brakes.
Bernie Higginson

This thread was discussed between 29/11/2016 and 12/12/2016

MG Midget and Sprite Technical index

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