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MG MGB Technical - Improved braking
|Would anyone be able to shed more light on this subject. |
Im trying to research improving the braking capacity. With things like economy, availabilty and ease of upgrade ie bolt on alternatives as a pose to the stock front disc brakes on the MGB.
I have a stock set up at the moment. Everything is brand new and in perfect working condition. what can I do to this to improve braking? A Servo? would that suffice?
Any links to threads articles and your own methods greatly appreciated.
|What are you trying to achieve? Are you looking for ease of braking or better stopping distance? If the former, then a servo (I assume you have a non-servo model) would help, yes. If the latter, then better tyres.|
Generally, owners find the ability to lock the wheels of a B quite easy and many would not entertain a servo. Once the wheels are locked, then the stopping is purely down to the tyres.
If you want to lock your wheels quicker, then there are several options - you can bolt on four pot calipers from a Rover SD1, Princess or Wilwood and/or larger discs from the Peugeot 505, but all this requires some home engineering - if you want to make sure the job is done properly, consider this excellent bolt on kit. I wish I had used this instead of messing around re-drilling Peugeot discs and sleeving Rover calipers. I think Mike Howlett has this kit and may come in later confirming:
But do bear in mind, increasing the efficiency will only be realised with top quality tyres. You cannot have good braking on poor tyres.
Back to ease of braking,. you can try a servo, but as I said earlier, there are many who say that a well serviced non servo system is every bit as good. Other options are changing the master cylinder for a more efficient one, but this will be a headache on your car.
|I use Hi Spec four pot alloy calipers with big pads working on grooved and dimpled discs. Cars is fitted with a servo, though this only keeps pedal pressures slightly lower and does not add to efficiency. Rears are standard. Tyres 185/65/15. This setup works fine for me and shows excellent figures on the MOT brake test.|
Thanks for the input and the links.
Well looking at it like that, ease of braking isnt an issue, so a servo is wasted on it I guess.
I do have a problem free imaculate system at present although in the midst of a long 2yr engine upgrade I do feel the need for adressing the braking capacity, at least -evaluating it.
I know cross drilled discs will dissipate heat quicker and minimise fade. I have sneaked a look at Hoyles stuff, very nice kit and ill definately bear it in mind with the next project when this ones finished.
Brake pad wise, are there any out there that really are as good as they say? Ive read varied opinions on Green pads. Perhaps theres a proper brand that just does what it says on the can..so to speak.
Something ive pondered is this; If the front locks up "quicker" what effect will this have on the rear?
A servo only reduces effort at the brake pedal.
In recent years, much has been made of the use of cross-drilled disc brake rotors. These items were developed primarily for racing use. Some people think that they are intended to facilitate cooling, but rust quickly builds up in the holes, acting as insulation. Other people think that the holes are present for water to be displaced into by the brake pads. However, they were originally intended to allow the venting of gases that formed at high temperatures between the brake pads and the disc brake rotors. However, modern brake pads have a reduced tendency toward out-gassing, so today the primary purpose of the holes is to reduce unsprung weight in the suspension system. This introduces a problem: as the mass of the disc brake rotor decreases, so does its ability to contain heat. In addition, since drilling creates stress lines that radiate outwards from the holes, they have a tendency to develop a cracking problem, especially if a dull drill bit is used to create them. In addition, the more holes drilled into the disc brake rotor, the weaker it becomes. To make the reduction in unsprung weight worthwhile, well over a hundred holes have to be drilled ($$), which results in lots of stress lines. All of these holes should be chamfered slightly to equal depths after surface grinding, reamed smooth, then the surface lightly reground to a non-directional finish in order to remove any lipping (more $$), subsequently the disc brake rotor has to be stress-relieved in a furnace in order to reduce the likelihood of cracks forming along stress lines (more $$). These are the reasons why such racing disc brake rotors are so expensive. The majority of aftermarket disc brake rotors that have far fewer holes drilled in them remain sufficiently strong after drilling so that the furnace-dependent stress-relieving process is not as necessary and can be eliminated (thus saving $$$), and are surface-ground only once, this being afterward drilling in order to reduce the need for chamfering (thus saving more $), but in practical terms the total reduction of unsprung weight is insignificant. The brutal truth is that the fewer holes in such disc brake rotors are in effect nothing but a cosmetic sales gimmick aimed at the “monkey see, monkey do” market niche. The cross-drilled disc brake rotors used by track racers have so many holes in them that few would buy them for street use because their higher cost would make them too expensive. While their reduced unsprung weight makes them a useful modification for the racetrack, the tendency of the holes to become coated with rust and clogged with brake material make it questionable as to whether or not they are a worthwhile investment for a car that is intended for use on the street. Track racers can take the time after a race to use a radial brush in order to remove these materials from all of those holes, but how often would you perform such maintenance on your street machine?
Directionally grooved slotted disc brake rotors offer the advantage of being less prone to becoming clogged with brake pad material and are far more efficient in that they use centrifugal force in order to duct water off of their surfaces, making for faster and better brake response under wet driving conditions, thus making them the superior choice for street use. They are also far less prone to glazing the brake material. The downside is faster brake pad wear. The disc brake rotors manufactured by Tarox and Red Dot are of exceptionally good quality, so much so that warpage even at the highest temperatures is a quite rare experience. These are available from the MG Owners Club in the UK. They have a website at http://www.mgownersclub.co.uk . They also sell slotted brake drums as well.
While the Original Equipment disc front brake system of the MGB can be upgraded to a higher level of performance, there are always those drivers who will either need or demand something better. In the UK, many drivers are aware that either four-piston Rover SD1 calipers or the calipers from an Austin Princess will bolt directly onto the MGB stub axle; both calipers have the same distance between their mounting holes, but thin-wall sleeves or special stepped bolts are required for their metric holes. In addition, custom-made brake hoses (flexible pipes) are also required with an imperial fitting on one end and a metric fitting at the other in order to connect the Metric caliper to the existing Imperial MGB hydraulic system. The dust shield will have to be cut slightly in order to clear the larger brake caliper. The brake calipers bolt up with no other modification. The combined area of the four Princess caliper pistons is the same as the two MGB pistons, and therefore pedal travel is unaffected. The SD1 brake caliper has slightly larger pistons which need more fluid displacement in order to move the same distance, so there will be an increased pedal travel if used with the original master cylinder, although in practice this additional pedal travel would probably go unnoticed. The late Rubber Bumper MGB master cylinder with the integral servo has a larger bore and thus is a better match for SD1 calipers. However, it is necessary to change the whole pedal box assembly in order to fit this to a Chrome Bumper MGB.
Although there are several aftermarket disc front brake systems that can be adapted to the MGB, such as the Wilwood system, such adaptations usually employ racing components that are not entirely suitable for use on a street car, and normally require modification in order to fit. However, the disc front brake system of the MGB GTV8 presents an easy bolt-on solution. MG had originally intended to introduce this system on all models of the MGB, but the proposal died when production of the MGB GTV8 was terminated.
The disc brake rotor (BMC Part # BTB 1319) of the GTV8 is the same diameter (10 3/4” / 273 mm) as that of the MGB, but is thicker in order to allow it to absorb more heat without warping, and the bridge of the inner caliper (BMC Part # 37H 8099, left side; 37H 8100, right side) is extended out further in order to accommodate the extra thickness of the disc brake rotor. In addition, the backplate (BMC Part # BTB 1320, right side; BTB 1321, left side) has a deeper lip in order to protect the seal track of the hub bearing, and the brake pads (BMC Part # GBP 240) and brake pad retaining clips (BMC Part # 17H 7990V), are also different from those employed in the design of the standard MGB. Other than those items, the system is otherwise identical to the standard MGB system. That is, the same pistons (BMC Part # ), the same seals (BMC Part # 8G 8641), the same fluid channel seal (BMC Part # 17H 7679), the same bridge bolts (BMC Part # 27H 4353), the same hub mounting bolts (BMC Part # ATB 4074), the same tab washer (BMC Part # BTC 114), the same bleed screw (BMC Part # 3H 2428), and the same plug (BMC Part # 17H 7917). This commonality of the majority of hardware makes for a relatively simple upgrade conversion.
Note: The RV8 vented disc is smaller at 10 5/8 inch (270mm) diameter and the Rover SD1 vented or solid discs are considerably smaller at 10 1/8 (258 mm); fortunately neither will fit the MGB hub as the offset is incompatible.
Today’s brake pads and shoes are available in a wide variety of materials. Materials intended for racing applications are unsuitable for street use as they perform well only when hot. At the temperatures incurred outside of a racetrack their performance is actually inferior to that of friction materials that are intended for street use. Rather than use racing brake material, install a set of MGB GT V8 brake pads into the calipers. They will fit without modification and, due to their larger surface area that dissipates heat more easily, are more fade-resistant. Be aware that these brake pads are “handed” not in terms of right and left, but of inner and outer.
Avoid the use of brake pads made of the Original Equipment organic compounds as they are the least heat resistant, have the poorest coefficient of friction of .32mu, and produce more brake dust than any other type of material. The scientific definition for coefficient of friction is the ratio of perpendicular force required to move or stop one surface. This is expressed as Mu = F/W Where: Mu = coefficient of friction, F = force required to move one surface over the other, and W = perpendicular force. The industry give brake pads a numeric tag that describes their friction coefficient (Mu) wherein 0 is classified as the worst and 1.0 is the best.
Be aware that the transfer layer of material deposited on the disc brake rotor is what determines the stability and effectiveness of the brake pad's coefficient of friction. Brake pad material is constantly moving between these two surfaces during brake engagement. Every brake pad leaves a transfer layer. This is one reason why a new brake pad will not work optimally against a disc brake rotor that had previously run a different type of brake pad. Consequently, if you change to a different type of brake friction material, you should have the disc brake rotor either resurfaced or, ideally, replace it with a new one.
There are essentially three options for high performance brake friction material. The first and perhaps the most commonly available material marketed for a high performance street application are the Carbon Metallic compounds such as those marketed by Hawk. These seem to come in two categories: those suitable only for racing and those suitable only for street use. Those suitable for street use have a coefficient of friction of .36mu, which is too small an increase in performance (11%) over that of Original Equipment materials to make them worth the additional expense. In addition, they produce a black brake dust that is difficult to remove. The second choice is the Semi-Organic / Semi-Metallic type. These produce less brake dust than Carbon Metallic materials. While being more heat resistant than organic compounds, they also have a superior coefficient of friction of .48 mu, a fifty percent improvement over the .32 mu of the Original Equipment material, and a thirty-three percent improvement over Carbon Metallic materials. These are available from Carbotech Engineering. They have a website at http://www.carbotecheng.com . While these may be popular, there is another material that has an equivalent coefficient of friction, but yet an even greater resistance to heat: the Carbon Kevlar type. Most performance pads need warming before becoming effective. Kevlar pads do not. They work 20% to 25% better from cold and will not begin to outgas until it reaches a temperature of 1,0500 Fahrenheit (5650 Celsius), thus making brake fade a factor than can be dispensed with. These are available from TSI Automotive (Brake Pads- Part # CKPMGA/B, Shoes- Part # CKSMGA/B). They have a website at http://www.tsimportedautomotive.com . Be advised that whatever material you choose for the front brakes should also be used on the rear brakes as well so that the coefficients of friction will be equal, otherwise one pair will prematurely lock up their wheels under heavy braking.
It is possible that, under the heavy braking loads generated by stronger brakes, the rear brakes may lock up prematurely, creating tail drift. This can be tuned out of the braking system by installing a proportioning valve into the rear braking system of the Roadster model or by changing the brake slave cylinders of the GT model to those of the Roadster model with their smaller-diameter pistons. The latter change will require exchanging the rear brake backplates of the Roadster model for the ones of the GT model in order to fit the different size brake slave cylinders. Another, though partial, solution is the fitting of tires with more grip, although this can be said to be treating the symptom rather than the cause.
|Wow, I can't compete with Stephen's essay - superb. All I will say is that for a car of its size and weight, the MGBs disc brakes are huge and should be more than adequate for all road use. Compared to an over-servoed modern car, they may feel a bit dead and lifeless, but you soon get used to putting in a bit more effort. While a servo may help, the standard one fitted to the MGB is not that efficient and may disappoint. It is also something else to go wrong.|
My V8 has the Hoyle brake set up with Peugeot ventilated discs at the front and 4-pot calipers. The rear has standard Ford Sierra discs and calipers. I am using the late master cylinder with in-line mechanical servo. First thing is, you have to use 15 inch wheels with these 4-pot calipers. Second thing is, my brakes don't really feel a lot different from a well maintained standard MGB. I suspect that in extremis mine would suffer from less fade, but on the road, the difference is small.
|Wow, thanks for the answers! :P|
Its not like ill be hammering round public roads so GTV8 pads will be the way forward for me it seems. Even track days should see them okay. If I need more pinch then Ill try the GTV8 disc upgrade first. I like the thought of keeping it inhouse with the hardware.
A question- rear drums, are the v8 liners better than, the same as or not an option for std GT. What im pondering is slightly more cunch up front should in my way of thinking be equalled at the rear for an even braking?
Mike thanks, your car sounds awesome! Hoyles kit, how has it met your expectations with ease of set up and performance? Curiosity, with that set up you perhaps have sharpened the std RV8 a tad?
|You will be doing the right thing by keeping it all in house with the hardware. I deviated away from it in every respect, and cannot admit to having anything over someone with a well maintained standard V8.|
Two things - as said earlier, you do not necessarily need more crunch on the rear brakes - in fact could be a bad thing. You do not want rear wheels, especially, locking up. They are there to stabilise the whole braking operation. Once they lock up, then all sorts of problems - one of the benefits of having discs on the rear.
When you are set up, spend a bit to experiment with different pads and you will find one that suits you. But be careful with some of the 'ceramic' variety. My main request of brake pad material is minimum black dust. I find Red Stuff meets this, but they bring in a whole set of other problems.
|Don't forget that the limiting factor is (or should be) the tyre contact patch on the road. If you can lock the front wheels on a dry surface with steadily applied pedal pressure (rather than banging them on) then there is nothing wrong with your brakes. You can put the biggest discs and calipers in the world on your car, and it's not going to affect that. In fact reducing pedal effort on the front brakes reduces *overall* braking performance, as the lower pedal pressure means the rear brakes aren't doing as much as they did before. For competition different discs and pads can reduce fade, but that is a different matter. And tyre choice probably has the biggest effect on overall braking performance, new stickies will be vastly better than 10-year-old cheapos.|
|Thanks once again, great input guys!|
Really interesting with opinions and experiences.
Thanks for the clear and sound explanation Hal.
I have brand new tyres with around 200 miles on them, not remoulds- Dunlop I think which sit on 72 spoke rims. Spokes have a bad rep and allround alloy is not beaten, I just cant help liking them and they will do for a simple cruise. I have considered other options in different enviroments- 15" and street slicks, we will see exactly where that lands. Really I need to stop talking and start driving, then ill know.
I can say that although mine will look stockish GT, it will surprise a few people, hopefully in a pleasant way.
Paul is it true that you have the best local Indian? :P
|Jamie, thanks for your comments about my car. I like it! It is in fact a 1969 GT that I converted to have a 3.9 litre fuel injected V8 from a Range Rover. It also has the Rover 5-speed transmission, full Hoyle suspension and brakes, power steering, cruise control....etc, etc. My car looks fairly standard from the outside, apart from alloy wheels and a bump in the bonnet. Here's a photo.|
|JS - not me personally :o) Although we did have a very good one last night at Shimla Pinks which we can walk to. I suppose it depends what you are reading or who you ask, there are a lot to choose from in the West Midlands, for some reason ...|
|Mike, really nice car, I like the bump in the bonnet. The alloys are nice too. Auto cruise is a nice motorway feature which probably saves petrol..until you put your foot down- bliss :)|
Paul, I love curry- wish I had more than 2 to choose from up here!
|Mine are without servo and completly stock except for green stuff front pads. I'm very happy with this set up. I've used it on tracks and it works fine for a few laps, although it does smell a bit warm when you get back into the paddock.The green stuff do generate a sticky black dust which is a pian with wire wheels, but other than that no problems at all.|
This thread was discussed between 20/11/2012 and 25/11/2012
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