Welcome to our resource for MG Car Information.
MG MGB Technical - Disc Brakes??
|I am researching rear disc brakes for my 1980 B. I have 14" LE rims. I read about disc setup from Honda and Saab that will work. Is there any kits out there that have everything I need including a emergency brake setup?|
I know there is an ongoing discussion about whether they're needed, I believe they would be, especially since I put the V8 in. I do drive hard sometimes and I believe they would be a benefit in certain situations.
|If you don't mind spending lots of money, the Hoyle IRS works really, really well and comes with rear discs. I have it on my '69 GTV8. http://www.hoyle-engineering.co.uk/html/suspension.html|
|Hoyle's kit requires 15" wheels.|
Try that site:
|Jean Guy Catford|
|Bill Guzman's web site has a brake kit as well. Mike|
|I can't see the point. Rear brakes are deliberately restricted in effectiveness compared to the fronts to stop them locking up and the car spinning under heavy braking, even to the point of most roadsters having smaller diameter slave pistons than GTs, as the heavier weight of the GT resists locking more. But even that only applies to 4-cylinder GTs, V8s have the smaller diameter as they have harder springs.|
I don't know of any kits that include the all-important mechanical parking brake, which is necessary to make the car streeet-legal. No, a hydraulic parking brake won't be legal. I converted my car to use the disc rear brake system of the MGA Twincam, but the calipers were a bear to find!
|You are right that the Hoyle kit needs 15" wheels. I have 6" x 15" Minilite replica wheels on mine. Because Hoyle uses stock European Ford rear brakes, there is already a working handbrake mechanism.|
|Paul is absolutely correct - rear discs are a waste of time on an MGB whether it has a V8 or not. Do it for bragging rights if that's what turns your crank, but don't try to justify it on safety or performance grounds - that won't stand up.|
|To be honest Ricmgb, The more one thinks on it the more involved and complicated the project would become, that of disc brakes on the rear. And it has been said, most of the breaking comes from the front. You might find rear 'lock-ups' would occur all too easily then a proportioning valve would be essential. I found that a well serviced and properly working drum at th rear seems perfectly adequate. Look at the old Camaros ( I had one!) I thought how primitive, drums at the back. I never had any problems with bringing the car to rest, even with 5.7 litres of engine. What I did find was vagueness of the braking system, and terrible fade. All this easily solved with different pads and discs if necessary. So a V8 MG? no problem, concentrate of the front brakes, and good pad material. Don't forget you will have a 'light ' car. Mike|
I have no desire to start an arguement, but I must disagree that disc rear brakes on an MGB are not justified other than for "bragging rights". Driving hard in the mountains of West Virginia I found that rear brake fade occasionally became a problem. I then had a set of rear brake shoes relined with Carbon Kevlar material. These go up to 1,050 degrees F before they will outgas, so fade wasn't a problem. However, I noticed that the drums got so hot that I could actually smell them! The VHT paint was peeling off of them, and the neck of the rear axle housing was also hot to the touch. I suspected that the engineers never intended that the brake drums should undergo such severe abuse. It was only then that I decided to convert the car to MGA Twincam disc rear brakes. No problems since. However, I will concede that unless you are prone to torturing the brakes by driving very hard on steep, twisting, winding mountain roads with lots of hairpin turns, or some other similar exceptional conditions, the additional unsprung weight (plus the expense and the agony of doing the conversion) isn't worth it!
|Do you remember the line in 'The Fastest Indian', when the scrutineers were looking at Bert Munros' motorcycle on the salt flats of Bonneville, and they exclaimed there are no brakes!, Anthony Hopkins says in his best New Zealand accent,' Well, Arr doount intend starpin do I! ? ( you have to sound out all the letters to get the accent right! ) Mike|
|Regarding whether rear discs are worth the effort or not, as one who has rear discs I would say don't bother unless you intend some extreme motoring like Steve described. I bought the Hoyle kit because I wanted the IRS (which is very, very good) and the disc brakes came with it.|
I now have Hoyle brakes front and rear, so the fronts are ventilated discs with 4-pot calipers and the rears are Ford discs from European Sierra and Granada models. I can honestly say that the brakes are no better than standard MGB brakes in good condition.
Maybe that's the EBC Greenstuff pads that John Hoyle supplies - I read on various web sites that Greenstuff aren't that good, and that maybe Redstuff would be better. Certainly my brakes don't have much initial bite, especially when compared to my modern VW. Or I could try Mintex 1144 or Pagid or Ferodo - its all so confusing.
and a wink to those who recognize me, Lazarus has risen.
I see ricmgb's point very well, I too fantasized about rear wheel disc brakes (and a TypeA overdrive, or Quaifes' own, and a lot of other stuff...)
May I point out that, even in 1962-63 to 1965, the B's rear drums were greeted by many ad a step back from the MGA TC'a rear discs, when the competition either had or had announced rear disc brakes:
- Fiat 124 Sport, DOHC+RWD, discs all around,
- Alfa Romeo Duetto, DOHC+RWD, discs all around,
- Lancia Fulvia, DOHC+FWD, discs all around,
- Porsche 911/912, OHV+RWD, discs all around,
- Alpine Renault A110, OHV+RWD, discs all around.
Even the boxy Simca 1000 R2/R3 and the Renault Gordinis (both OHV) had rear discs!
So, if the issue is the rear wheels locking, the first measure would be to fit small discs and small calipers, as from a BMC Mini/Metro.
The best thing would be to find a reference table with the "technical performance" of the standard drums, uprated drums and a number of standard disc brakes as the ones I quoted, and ensure the "pinch" of the disc brakes does not exceed that of the uprated drums by more than 30% (logarithm 5)
Uprated drums are far too expensive INHO
Your argument that drum brakes were outdated 50 years ago doesn't really hold water, as they are/were still being fitted in the 21st century.
|Mike- I have Greenstuff pads. On a Track day at Brands the other day, I noted that once they really warmed up they were very good. Much better than under normal road use! I suspect Redstuff would be great for track/racing but horrible for (normal)road use.|
As a tester I often find mechanical handbrakes operating rear drums work "better" that those operating on rear discs. How does yours compare?
On the general point, I can lock up with the standard set up, so can't see the point of upgrades for "normal" use. Can't see a V8 making any difference unless you regularly brake from 100+ IMHO.
|Drum brakes are old technology, no better than cast iron blocks, OHV distribution, points&condenser ignition or carburettors.|
Not to mention live axles...
They are inherently heavier than disc brakes of equivalent power, heat up more quickly and disperse that heat more slowly.
And in very rainy days, or after fording swamped roads... they hold much too much water ;)
Last, it takes a little training and 15 minutes off your lunch break to change pads; how long to change shoes?
So, wanting to improve overall efficiency, just as one will go for a solid state fuel pump... slotted front discs... radial tyres on a '63 roadster... FM radio... braided brake and clutch hoses... silicone radiator hoses and ingnition leads... electronic ignition... halogen front lights...
...I see the point in asking about rear disc brakes.
IMHO, Rover Minis and Metros should make good donor vehicles.
|Michael, thanks for your comments re Greenstuff. Looking at EBC web site, I think Yellowstuff could be a better bet for road use. I can't lock my wheels on a dry road with Greenstuff, although they are obviously good enough for the MOT test. I have the later dual circuit master cylinder with in-line servo.|
Don't get me wrong, the brakes work OK and don't give me any cause for concern in normal driving. But they lack "bite" on first application compared with my modern VW - but then that is so over-servoed that it is all too easy to stand it on its nose.
As for the handbrake, it is only just good enough. It needs a strong pull to hold the car on a steep incline. John Hoyle doesn't alter the length of the lever on the bottom of the handbrake lever. I think it could do with being a bit longer to allow a stronger pull. My local tester always comments that it isn't very powerful but is good enough for the regs.
|Just because something is no longer fitted to modern cars is no good reason to fit it to a classic. If you want a modern car then buy a modern car. What Metro had rear discs? My late 90s Haynes manual for the 100 series Metros shows drum.|
|Mike Interesting! FWIW I have single circuit non servoed brakes, so the handbrake has to be 25% to pass and regularly gets 30%. On a dual circuit it only needs to be 16%. I think the biggest difference was that I recently changed the brake fluid but perhaps it just felt better. I did no specific tests before and after.|
|Mini's metro's all had drums at the rear at least. |
As did first gen ford focus and a whole sh*tload of modern cars.
If you do not want old technology get an MGF and leave the B to the ones who care for it
The main 2 points every one is missing are:
What is braking?
Braking is turning kinetic energy in to heat.
The amount of kinetic energy depends on the speed traveled and the mass of the car.
What dictates the max braking force?
More power will not have any effect on kinetic energy if you stay within the speed limit.
So no need to upgrade then.
If you do want to upgrade then start with the most limiting factor.
If yours are over 5 years of age.
If they are a to hard compound.
If they have the wrong profile for the use.
If they are over or under inflated.
They are useless!!!!
If you have the best fresh tyres and a completely perfect braking system (fluid no older than 2 years) you will not need any brake upgrades for street use.
When do you need bigger brakes?
To resist fade under repeated heavy braking (racing or rallying)
When do you need rear disks?
When weight is an issue
When your drums need adjusting during long events
|Onno your observations are all true. I am considering Hill climbs, so, one needs to accelerate well and decelerate well. So in this case maybe a brake upgrade? Or rather the right brake lining material, up to correct temperature. But yes, this is confirming the fact that brakes systems, and linings are a compromise that the manufacturers are forced to make. Mike|
|For hillclimb/sprint/race use, it is worth considering a brake bias valve - assuming that the regulations allow. If not, think about fitting smaller rear wheel cylinders.|
|Of course Onno is right, and the reason I can't lock my wheels could well be to do with the grip I have from my 195/60 x 15 tyres. After all, a locked wheel shows that you have defeated the tyre's ability to grip. I do have a lot of grip because even with 200-ish bhp and equivalent amounts of torque, it is quite hard to spin a wheel on tarmac. The car just squats and rockets away.|
As I said previously, I bought the Hoyle kit for the suspension. The brakes came with it.
|I am not going to be invlved in a contest on who's more knowledgeable.|
I read a request and provided my opinion.
I quoted "disc brakes" from Minis & Metros because they were fitted to the front wheels on a car with 12" rims - hence the obvious issue of caliper clearance was solved.
There is no need to be sarcastic.
Braking force is dictated by tyre grip, true, but if shoe/drum or pad/disc friction is not sufficient, the tyre will only transfer what is available.
A nice weekend to you all.
|Ha! Didn't even notice your car was non-servo, Michael. Shows either how light the servo assistance is, or maybe I'm insensitive.|
You don't *want* the rears to lock or you will spin. That's why roadsters had the slave cylinder reduced in diameter early on, but the GTs kept the larger one. If you can't lock the fronts under steadily increased pressure (i.e. not banging them on which locks them easier) on dry tarmac with 'standard' wheels and tyres then something is wrong that needs fixing, not upgrading.
Not being sarcastic.
I just like the B for the old tech and am amazed how good it works every time!
And a lot of the tech is still being used today (some what evolved)
The mini/metro calipers are a bad option because there is no emergency brake on it so will never make it through MOT.
And if you want to go through all the trouble of makeing disks at the rear you might as well do it right the first time and use an alloy caliper and save a ton of weight
|Richard - Have you seen this?|
|On EBC pads, I am trying a set of Yellowstuff on my modern sports car which is in the 350 BHP range in the near future as the crappy stock pads they supply have insufficient initial 'bite. I'll try and remember to post results when I get around to it.|
I own 7 cars that have 4 wheel discs (including 2 MGAs) and I still say that rear drums are perfectly adequate for any reasonable use. In fact I purposely elected to keep rear drums when I built my Jamaican from scratch as I wanted a good hand brake.
Steve, it is true that you can torture the rears even on the street with extreme driving but it is still only a matter of proper lining material - the SCCA guys manage just fine at far higher stopping speeds than you will ever attain on the street, with drums. And as far as the smeel of overheated paint, why worry about it? You'll get the smell of overheated front pads too. Ignore it, or repaint with better materials if it causes the paint to blister.
The reason I use 4 wheel discs on my MGA race car isn't braking power, but rather predictability of friction characteristics over a whole race - drums normally will change more when they get really hot and the braking balance can shift. With the Twin Cam brakes I have never managed to fade the Carbon Kevlar pads I use evenm with repeated stops from 130 MPH.
I repeat my statement that anyone driving on the street doesn't need rear discs and that if they do fit them, they usually rationalize it as a better performing set up. But you've heard it here from 2 or 3 people that have personal experience that it really isn't.
|I worked on a program for a "modern" minivan for a major OEM and we found out that rear drums were superior to rear discs. The FWD platform and weight distribution had something to do with it, but mostly because well over 80% of the braking force goes through the fronts. |
I can't recall why exactly the rear disc set up was inferior, but test showed it didn't work as well.
If you're convinced you "need" rear discs, then be prepared to spend a good deal of time and money to dial them in, especially if you want something to work as well as the originals.
You said "The reason I use 4 wheel discs on my MGA race car isn't braking power, but rather predictability of friction characteristics..... drums normally will change more when they get really hot and the braking balance can shift." This is the best justification for rear disc brakes. By the way, because I, too, used Carbon kevlar linings on the brake shoes, fade wasn't the problem. I wasn't so much concerned about the peeling paint on the brake drums as I was about heat over-stressing the drums themselves. Tractor trailers use drum brakes, and a Federally-mandated part of every driver's pretrip inspection is a close examination of the brake drums. They sometimes crack, always as a result of overheating!
|There's been quite a few problems on cars with disc brakes rolling away down a hill when things cooled down and slackened the handbrake. Some American stuff at least has disc footbrake and drum handbrake in the same assembly, leading The Garage to quote for wheel bearings and all sorts when it was the shoes that were worn and rubbing and the mechanic didn't know it had them.|
|Also, some modern cars with all-round discs have a drum inside the rear disc, with shoes for the handbrake.|
|Hello Stephen, one of my previous jobs was a test technician for one of the 2 biggest brake lining and pads manufacturers in the UK. We regularly attained 350- 375 deg c on truck drum brakes and we never had any drums crack, and my colleagues in the car brakes department also never had any problem to the best of my knowledge. |
|Implementation of a working hand brake that actually does something is a big issue.|
I read (and inwardly laughed) when I read a post from an owner that had proudly 'upgraded' to rear discs - and then parked on a hill and had his car roll down and savage some other car (don't recal what it was, but think it was much more expensive than the MGB was).
I still have some brake shoes for MGA front kicking around my garage that were used for competition - look like some sort of congealed steel wool, and would wear out a drum in a season, but would never fade. The guys with old Corvettes used to resort to some sort of ceramic shoe material that would go through 2 sets of drums a year, but they would stop.
But that's for the front. The rears, at most, carry 40% of the braking burden on a car and unless they are placed unaturally where they get zero cooling (e.g. XKE), are rarely a problem. In fact I have run races with no rear brakes at all when I had a rear wheel cylinder failure on a rear drum car, and no time to fix it before start time. A bleed screw into the rear brake T fitting left me with no rear brakes, and a lap time only a little bit down on normal.
I repeat that IMO, no MG owner NEEDS rear discs, but a lot seem to WANT them. As is their right, of course.
That's all well and good, but not necessarily relevant as the drum brake system of the MGB was designed a half-century ago when the standards were lower.
I'm curious about the tests you were performing. If you weren't heating the brake drums to the point of failure, what was the purpose of the test? To determine the temperature at which outgassing occurs?
|It's not uncommon for discs to crack when pushed hard.|
This was on my Sprite.
|In '55, Mercedes used drum brakes on the front and rear of their race cars with no ill effects. Granted, they used 5 types of brake material on each shoe and used aluminum brake drums with steel inserts. I know a gentleman who owns one. He purchased it from the factory right after the horrendous crash at Le Mans. He drives the car hard to this day and says that the brakes are better than those on any modern car. RAY|
|"... not necessarily relevant as the drum brake system of the MGB was designed a half-century ago when the standards were lower."|
I don't see how that is relevant. MGB brakes stopped the car then and still do when maintained properly. Physics haven't changed either, and too much braking effort at the rear will still lock the rears before the fronts when most people will lose control. Only extreme use and/or massively wide and sticky tyres NEEDS uprated brakes.
It is a real discussion about that subject, but I have mixed feelings and I am unable to have a clear opinion. I have owned 2 B-GT and despite extra's B-GT weight, I could easily live with that Precambrian braking system. But the idea of all discs brakes is attractive.
I agree that adding a disc-disc proportioning valve is mandatory to avoid rear locking as Paul mentioned. It is less $30 on e-bay. For parking brakes issues it is easy to find calipers with parking brake device, like Scorpio(Ford Granada) and may be some other cars without the fuzz of dealing with dual shoes+pads system like Volvo 240 or recent Jag. XJ6.
|Jean Guy Catford|
|I don't know why some people think that the "B's" braking system is from the dark ages, it's not, there is not a lot of difference to the braking system on my Citroen Berlingo. The Lockheed calipers are good if they are kept in proper working order, they were designed when price didn't come into the equation. Take a look at racing calipers and tell me the difference. The rear brakes work fine, you get a high brake factor from the leading and trailing shoe set up, and because of this set up you get a handbrake that works, you also have manual adjustment which works.|
Most of the time these days car manufacturers fit discs all round because the marketing department think it will make the car sell better.
|On current cars having discs all round: Wasn't their also a problem getting ABS to work with drums? I thought the response time with the large components involved with shoes meant discs were essential.|
|Drum brake maintenance is much more time intensive and costly especially on the rear due to the handbrake cables. This is especially true on automatic adjusting drums brakes, where it is almost impossible to disengage the adjuster to retract the shoes. (Some of the Ford Taurus models require a special tool as the adjuster hole is blocked by suspension components.) The alternative is breaking the drum. Of course that's not a problem with the MG's and most European drum brake designs of the period.|
Friction characteristics are also better with discs. However, with a properly set up MGB in street driving that is rarely a problem. ABS has helped the modern cars with rear drums avoid skids.
I had a 67 Mustang with drum brakes all around. Even with new hardware, new linings, and new trued drums - making a hard stop without swerving was almost impossible. If they were wet or hot then it was even worse. Of course the design had a lot of self actuation which multiplied any friction differential. Overall an awful setup typical of American cars of the era.
Bottom line to me, four wheel discs are superior if you have the right handbrake set up. For an MGB upgrading to rear discs probably won't give you much performance improvement for your expenditure.
This is a very interesting thread with lots of good input.
65 MBG Roadster
|You are probably right Mike, but then I don't rate ABS that much anyway,not many drivers will ever press hard enough to get the ABS working anyway and I have seen some actually release the brake because they are worried that something is wrong with the car. It has it's uses, but in very bad conditions, like icy roads etc it's not going to be of help to the driver who thinks " I can drive like a kn*b" and the ABS will save my bacon. |
|Although interesting, I suggest our discussion of the pros and cons of the two brake types is irrelevant for all but extreme driving conditions. The point that escapes, concerns the efficiency of our elderly systems. My local garage tell me that they have only once in recent years tested a car where the brakes were working as designed. Special pads may help but there is no substitute for good maintenance and regular hose and oil replacement.|
Your B needs to stop as well as the moderns in the fast lane ... it used to, doesn't it still ?
Happy Christmas wherever you are.
|The Scarebird kit mentioned previously uses Totota calipers (on the kit I fitted) which include the handbrake, so not problem. I have them on my B, easy to install and work as advertised.|
|My 20cents worth is|
The main advantage of rear discs on a "B" is the availability of different compound pads that can be fitted to match the performance of whatever you have on the other end
The problem with drum brakes for sporty driving is finding a lining material that corresponds to what is happening at the front
R31 Nissan Skylines have rear discs, the rotors are the same bolt pattern as a B and the calliper has the handbrake built in.
One of the blokes here has them on his V8-- with vented rotors and modified Volvo calipers on the front. The thing just stops and stops and stops on our local circuit which is notorious for brake troubles
Having said this, a LS Diff is probably one of the best things to fit to a B to stop it waving around under heavy brake applications
This thread was discussed between 11/12/2011 and 17/01/2012
MG MGB Technical index
This thread is from the archive. The Live MG MGB Technical BBS is active now.