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MG MGB Technical - Brake rotors and pads

I have a brake problem and I am ordering new pads. On rotors, I will probably replace them but

Does anybody have any ideas about the differences between slotted rotors and normal OEM rotors?? If I do the work to replace rotors, I wonder if the expense of the slotted rotors are worth it.

Also, I never liked the brake screatch. I have dampening pads on the back of the brake pads, it is still noisy. Any recommendations on the type of pads to use???


1965 MGB currently dead stock brakes
Frank Baker

I researched the issue of rotors when I rebuilt my 67 GT. For the GT, with a stock engine and no plans to race or do a lot of driving where constant breaking is required, the stock rotors are more than adequate.

As for pads, I used whatever my local parts house had. No screatching so far.
Bruce Cunha

Frank, I have started using Autozone's brake pads for my MGB's. They offer organic and also semi metallic pads. The organic ones are cheaper, but they heat up the rotors more quickly with minimal braking and they don't squeek, they have a hideous grunting type of grind to them. Like running a semi damp finger over a piece of clean glass. Hated them. Took them back and got the semi metallic. Their pricing is actually a few dollars cheaper than Moss' retail. About $38 plus tax and have a three month warranty on them. Sold thru Beck Arnley under the AXXIS part number 088-0282M. (Just bought a set yesterday for another B). They work just fine with spirited driving in the Smoky Mountains on stock rotors with no fade.
Mwhitt

Use standard rotors and fit V8 pads. Smear a little copper grease on the backing plates where the pads touch the pistons to minimise squeal.
Iain MacKintosh

I like having very good brakes, as they can make the difference between a hit and a near-miss with someone not paying attention to your little car.

The stock rotors are fine, but I would use the braided stainless lines available from Moss, and EBC "Greenstuf" pads. You can get them from Moss, The Tire Rack, and even Pep Boys. Put the anti-squeal strips under the pads. I just went to a racing school last weekend, and the brakes were fantastic. Good hard stops with no squeal or fade, and a very solid pedal.



Paul K

I too, had squealing problems with the standard, stock pads sold by Moss. Also, living in the rain capitol of the country and with wire wheels, the rotors would get quite wet when driving on rain wet freeways. The result would be a time delay for the front brakes to grab while the pads pushed all the water off of the rotors. This gave an unacceptable delay before the car started to slow (in a quick stop situation the delay felt to be somewhere between 1 to 2 hours as I watched the car in front of me approaching at great rate of speed). I opted for the slotted rotors and the EB green stuff pads and was able to get them quite reasonably from the MGOC. The slotted rotors have reduced the time delay for the brakes to take hold on wet roads to an almost imperceptible time and the Green Stuff pads have completely eliminated the squeal, at the cost of a slightly higher pedal effort. The higher pedal effort is slight and once we got used to it, it hasn't bothered us at all.

The theory behind the slotted rotors is that the slots get rid of any water on the rotor quicker than on non slotted rotors. For those using the brakes hard enough to generate gas build up from the pad material, the slots also dissipate this faster so there is less brake fade with hard braking.

An interesting note, and I don't have the article to quote from, I recently read that "warped rotors" are not actually warped. Instead, during hard braking, microscopically small bits of the pad adhere to the rotor and build up to cause the familiar pulsating of the brakes that has always been attributed to "warped rotors". The cure stated in the article was to have the rotors ground sufficiently to remove the build up and change pad material. I can't say how accurate this article is (or even where I read it), but it does raise an interesting point and one I am going to check out on our pickup truck since it has a "warped rotor" on it. Cheers - Dave
David DuBois

I bought Hawk pads from Pegasus Racing. They are a great performance pad and CHEAP! No squealing, but I also use a spray-on brake squeal reducer on the backs of the pads.

Jeff Schlemmer

David,

I assume this is the article

http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml

Paul
Paul

Sometimes (maybe even most times), the warped rotors are caused by the tire rotation man & his heavy hand on the air wrench. Happens on occasion to the wife's car. I do my own rotation & torquing the 'B.
Carl Floyd

Carl

This is a issue although the problem does vary between set ups.

Ford did a study on brake judder warranty and went through all possible reasons that there might be variability in the shape of the disc after running.

Disc profiles of vehicles under warranty that had problems were measured. They had 'flats' on them coincident with the location of the wheel studs.

Using a turned down wheel disc runout was measured with wheel studs torqued to extremities of tolerance. When you have two adjacent studs at bottom limit and three at top or vice versa there is varing conformity to the wheel mount face and run out changes. It doesn't by much, but enough that if you do a lot of motorway miles the constant brushing of the disc on the pitched out parts of the disc gets worn. Under braking torque the spot on the discs that is low cannot generate the uniform braking torque to remain shudder free.

Paul
Paul

Frank-
Directionally grooved slotted rotors offer the advantage of being less prone to becoming clogged with brake pad material and are far more efficient to use centrifugal force to duct water off of the surface, making them the superior choice for street use. They are also far less prone to glazing the brake material. The 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.
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 race track their performance is actually inferior to that of materials intended for street use. Rather than use racing brake material, install a set of MGB GT V8 brake pads in the calipers. They will fit without modification and, due to their larger surface area dissipating heat more easily, are more fade-resistant. Avoid the use of 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.
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 for only 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 stock materials to make them worth the additional expense. The second choice is the Semi-Organic/Semi-Metallic type. Being more heat resistant than organic compounds, they also have a superior coefficient of friction of .48 mu, a fifty percent improvement over that of stock 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 which has an equivalent coefficient of friction but yet an even greater resistance to heat: the Carbon Kevlar type (F 1,050). These are available from TSI Automotive (Pads- Part # CKPMGA/B, Shoes- Part # CKSMGA/B). They have a website at http://www.tsimportedautomotive.com . Be advised that whatever material that 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 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 or by changing the slave cylinders to ones with a smaller size piston. The latter change may require modifying the rear brake backplate in order to fit the different size slave cylinders. Another solution is the fitting of tires with more grip, although this can be said to be treating the symptom rather than the cause.
Steve S.

I am using pads from a TR8 Bendix D81 as suggested by someone on this BBS. They offer @23% more braking surface area and fit right in. A clunk did develop when I applied the brakes and this off season I am replacing the brake pad retaining clips. Hopefully that will stop the clunk.

FWIW
Bruce Mills

Hi All, here is my (inexperienced) tuppence worth....
Have had frankly awful brakes on BGT since buying about 6 months back. not a problem since its been off road for most of that time. However, recently stripped and rebuilt the brakes (standard issue) due to leaking rear wheel cylinder (on advice from these pages, changed both sides, new shoes etc, then moved to the front, stripped. cleaned, new pads). Now, the result, and remember this is all standard gear, nothing special or uprated, is that my car has superb braking, indeed, its hard to imagine how it could be improved. great balance between front and rear, no shudder, squeal or other hassle. My point being that its probably better to have well serviced and cared for standard brakes to begin with, then if required, upgrades can be made - a solid platform to leap from in effect. but as i say, i am unsure what advantage if any i could get from upgrades, as currently i can out peform (at least brake wise)both of my modern cars. that said, i appreciate if you have something under the hood that is more than the standard MGB engine, yes, perhaps it would be a good idea to have uprated anchors. I just feel that original gear is pretty good on these cars, and often, myself included, its easy for us to go down the line of replace and upgrade, when standard, if set up correctly, seems to be great. or am i just to mechanically simple/tight with my cash - you decide. Keep on giving out the advice folks, i am lost without you all.
FWIW
mick
mick

Paul in Surry - That may well have been the article that I read.

For the record, it was on Steve S. information that I made the switch that I outlined in my earlier post - thanks Steve
David DuBois

As an engineer I must admit that I find this a load of guff. Yes, discs can become glazed and so on but to actually form some sort of skin as a result of particles transferred from the pads is hard to believe. Discs can become warped for all sorts of reasons, they can be warped from new by sheer bad manufacture which I have experienced or from poor material. Cast iron is not a stable material and does 'move' for about the first five years of its life if I remember. Moreover, misuse by continuous hard braking and overheating does no good either. These are single discs and are usually very reliable, its when we come to ventilated discs on modern cars that the real fun starts. A good pair of discs can be checked for truth by an engine reconditioner who will also grind the discs for you and provide an as new condition.
Iain MacKintosh

I'll second Paul K.'s reccommendation for Greenstuff pads and braided lines. Made the stock brakes much firmer. I'm also running slotted discs as a change from drilled rotors. The drilled rotors tended to have tiny cracks between the drilled holes after a while.

A nice xtra from the greenstuff pads is that they make less brake dust, much less. If you have wire wheels like I have, just because of that its worth it.

Note: Both sets of new rotors I have rec'd in the last five or so years tended to be slightly "warped" from the factory. Because of the installation process and the shimming required, it may be worth the time to have them checked before installing.
Luigi

Iain

Blue points are a localised conversion of cast iron into cementite an extremely hard substance. This transformation takes place at very high temperature and is non-reversible: as the blue points will be less subject to wear than the rest of the surface, the phenamenon will spread with each braking action. Transformation of the cast iron affects it to such a depth that a reworking of the surface would not resolve the problem.

Look for examples re cementite
http://home.tiscali.nl/annevelink/deterioration/Brembo_deterioration.html

Paul
Paul

I have standard discs, greenstuff pads and braided lines, no servo. With a little copper grease on the back of the pads, no squeal either. The best thing I ever did was fit stainless pistons. I'm very happy with stopping distance and pedal pressures. In heavy rain with the wire wheels you do seem to get a lot of water on the discs, I have never found this to be stopping ditance problem, but have found it challenging when one side dries out and grips before the other.
Stan Best

I must admit, In the past I would have had the same opinion as Ian. But, I think this pad deposits on the discs thing explains my problem! Over the past 2 years I have "warped" the original set of discs twice and a replacement set once. I had the originals turned and they worked good for about a month before I gradually began to feel the "warp" get worse and worse. I bought a new set and the problem was fixed again until a month or 2 later, the problem started reappearing. I did this one more time with the same result.

Recently I took one of the "warped" sets back to the shop, but this time asked the machinist to check which one was warping. He found that both were fine and he simply surfaced them for me. I put them on last night and the brakes are great again!

Now I'm wondering if the pads I have in the calipers are of poor quality. I checked my log book a few minutes ago and found that I purchased the pads about 5 weeks before the discs warped for the first time. I purchased the pads from Moss in August of 2004; they are the standard ones. I've never had a problem with stock pads before, but tomorrow I'm ordering a better set. I'll put them in and see if the "warping" comes back.
J Brown

I installed EBC Green Stuff pads on my GT, replacing what I believe were stock pads. There is far less brake dust with the new pads but more foot pressure is required for the same stopping power. I plan to go back to stock pads next time to regain the better stopping ability.

For the record I did not change the rears to Green Stuff and it does seem the car has a slight tendancy to drift the rear more than the front in the rare occasion I need to brake hard in a turn.
Steve Simmons

Hawk Ferro Carbon brake pads are available from Performance Center.com for under $50.

The pads have very little dust, are quiet, and take much less pedal pressure.

Because of the extra grip on the front I changed the rear brake cylinders on my '67 GT to the largest size, with stock rear brake shoe linings. (The early GTs had smaller rear brake cylinders than the later GTs) There is no sign of rear locking or overbraking. Probably could use an even larger slave cylinder with the high friction pads in front.

The upgraded disc pads are a big improvement and a necessity with the early non-boosted brake system.

Barry
Barry Parkinson

"Probably could use an even larger slave cylinder with the high friction pads in front."

Are you sure about that? Doesn't matter what the co-efficient of friction is between pad and disc or tyre and road, a given amount of retardation will result in the same amount of weight transfer from front to rear, and hence the same likelyhood of locking the rears. Increasing the friction between pad and disc may cause the wheels to lock with a lighter pedal pressure, but the weight transfer will be the same as before. However if you increase the friction between tyre and road then you will get greater retardation and weight transfer, and hence a greater likelyhood of the rears locking, therefore may need *smaller* wheel cylinders. The factory V8 GTs always used the (smaller) roadster cylinders, although 4-cylinder GTs did change to a larger one in late 67 or 68. Personally I've found the remote brake servo, which was optional on an otherwise unchanged single-circuit braking system, reduces pedal pressures very little. Not so the integral servo on twin-circuit systems.
Paul Hunt 2

Paul
Your comments are well taken, but the practical effect of a high friction pad in front and old style low friction rear brake shoes, is to reduce the rear braking power in the rear in comparison to the front. The issue is balance of breaking power. Pragmatically the increase in friction is the equivalent to more more brake pressure at the front and less at the rear.

This could be compensated by either hi friction shoes in the rear, or larger wheel cylinders in the rear to apply more lbs per sq in to increase the friction to balance with the high friction front brakes.

The big problem with this whole system is the geometric progression of friction with a self energizing leading brake shoe in the rear, contrasted with the linear relationship of pressure and friction with the disk brake system in front.

The rear brakes have to be calibrated for less than optimum pressure for normal breaking, because they are more prone to lockup under extreme breaking.

The '60's Alfa Romeo had two leading brake shoes in the front brakes. Rolling forward it took modest pedal effort to stop the car. Rolling backward the self energizing feature "deenergized" the brakes and you had apply high pedal pressure to stop the car.

This self energizing feature of the leading brake shoe - to some extent - may be increased or decreased by internal geometry. The closer to the center the shoe pivot point the more self energized application pressure.

In the real world - which is what counts - I've found that with the hi friction pads in front and stock shoes in the rear with the large wheel cylinders, that I have no problem with an unstable tail end in hard braking and cornering or for that matter in wet conditions.

Barry

Barry Parkinson

Paul

Weight transfer is also dependant upon CG etc. When increasing front brake torque, because tyre grip is key, the effect is to reduce rear brake torque due to change in f/R balance. Increasing rear brake torque may therefore be necessary to balance front upgrade, as long as early rear wheel lock is avoided.

Although tyre grip is key with more brake torque you can generate maximum braking force with less pedal pressure, less pedal travel, and therefore less time. It's this reaction time and the faster ramp up of the torque applied at the tyre (as well as aviding fade) that can create shorter stopping distances. When you're traveling at 60 mph, you travel 88 feet per second. If your brakes reach peak torque .1 seconds faster, then you just reached limit braking 8.8 feet sooner.

Paul
Paul

Paul Surrey - just don't see that for the reasons I give in my previous post, i.e. maximum retardation is governed by the grip between the tyre and the road, not the pad and the disk. If you *do* increase that then you increase the weight transfer, which means a lighter rear end, and a greater chance of locking.

Also the faster you apply maximum braking effort the more likely you are to lock the *fronts*, as the weight transfer needs time to happen and apply more friction at the tyre/road surface contact. Progressive braking will give you more retardation than banging them on, a locked wheel has much less friction with the road surface than one just short of locking as the locked wheel is floating along on a layer of molten rubber.
Paul Hunt 2

Paul
Even crummy pads and shoes can lock up the wheels if you push hard enough. The faster you stop the more weight transfer to the front and the less traction is available to the rear.

The isssue is balance - so that ideally both ends lose traction simultaneously in an emergency stop.

With less pedal pressure with hi friction pads the front brakes are going to be carrying a disproportionate share of the braking load. If equivalent hi friction shoes are available, the original factory balance between front and rear would still be appropriate.

If instead you use sticky pads in front and stock shoes in the rear, you have, in effect, transferred more braking bias to the front brakes. It isn't all bad, as that increases understeer on heavy braking, which is inherently stable in contrast to oversteer.

However, for maximum braking and cornering a proper balance of breaking power is desired. As a practical matter, in extreme braking a great amount of weight is shifted to the forward wheels and the rear brakes are a minor factor in stopping the car. Engineers in designing the system, intentionally underpower the rear brakes to create a more stable system.

Probably the best solution is to use hi friction shoes along with hi friction pads. Apparently though some of the new friction materials only exhibit the high cf with the higher pressure of disc pads, and are not as effective with the lower pressure applied to brake shoes. This, of course, varys with the propietary materials used.

Barry
Barry Parkinson

Sticky pads only reduce the amount of pedal pressure needed to lock the wheels, they don't alter weight transfer for a given amount of G retardation! Do you get the same amount of weight transfer driving on ice as compared to dry tarmac? Of course not, and whether you have sticky pads or not makes no difference.
Paul Hunt 2

Paul
Your point is well taken. The underlying assumption is that you won't push as hard on the brake pedal with sticky pads. The result of less brake fluid pressure with sticky front brakes and slippery old style rear shoes is that the front is doing more of the stopping than it would otherwise do.

Braking too biased towards the front will produce understeer braking through a corner.

To balance the system with sticky front brake pads you either need equivalent sticky shoes in the rear, dual separatly calibrated master cylinders (one rear- one front) or larger brake slave cylinders for the rear.

If you shove your foot all the way to the floor and lock all 4 wheels the issue I agree is moot.

Barry


Barry Parkinson

This thread was discussed between 04/02/2006 and 14/02/2006

MG MGB Technical index

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