The Question
I have an MG RV8, an ex Japanese market car that has done a very low mileage since it was made in 1995 so is in superb condition. Having said that I don’t feel that the brakes are as good as they should be, and I was wondering what modifications you would suggest to improve the brakes?
The Answer
Unfortunately when you raise this question, I do not know what level of expectation you have, or what you are comparing the cars braking against.
The spec of the RV8 brakes is at the pinnacle of any MGB, C or V8 car with 25.4mm thick vented front discs and four piston calipers with much larger surface area pads, and then wider brake shoes at the rear, although an inch smaller in diameter. As the front brakes do around 70 to 75% of the cars braking and the cars weigh on average around 1200kgs isn't a large mass to stop when compared to an MGB at a similar weight. The expectation for these brakes is for a very sharp and responsive braking system that has great reserve.
MGB GTV8 brake pad left which are already slightly bigger than 4 cylinder MGB pads, compared to much wider MG RV8 pads, right.
Against that background I would certainly not in the first instance be looking to upgrade the brakes but to ensure that they are delivering the best they can be in standard form. My expectation is that the low mileage the car has done could mean that the original brake pads are probably still fitted, and the lack of use has seen slow inexorable deterioration of these over the cars 27 year life that would degrade braking performance.
Additionally experience with many thousands of MG RV8s and MGBs fitted with the same spec of front brakes shows that often braking performance when uprated pads have been fitted is actually reduced, sometimes noticeably, as the brakes simply do not generate enough heat to warrant pads designed to run at hotter temps, so this is another possible reason for your poor braking performance, if the pads have been changed.
My first suggestion would be to replace the front brake pads with standard spec replacements as the original pad material is the most likely aspect to have degraded, but it is also very important to clean both sides of the friction surfaces of the discs using abrasive pad/cloth of around a 360 to 400 grit to fully clean off any glaze or surface contaminants so that you end up with a very clear scratch pattern over both sides of the discs friction surface, almost like the honing you see on freshly honed engine cylinder bores. Not doing this risks contaminating the new pads friction materials and degrading their ability to correctly bed in and perform.
As the RV8 has such a strong spec front brake set up with considerable heat soak and dissipation capabilities it is worth noting the experience that comes with standard solid disc MGB brakes when using the usual types of uprated pad material such as EBC Green Stuff, Mintex 1144 or Ferodo DS. This is often not that good when the car is solely used in road conditions and often generates glazed discs because normal road driving doesn’t work the pads hard enough and won’t generate enough heat, irrespective of the guidance indicating that such pads work from cold. Let me be clear here that they do work from cold, but continuous use in a soft normal road environment will over a relatively short period of time see the pads and discs glaze over which reduces braking performance and is often accompanied by brake squeal.
If the thinner 8.8mm MGB solid disc and smaller contact surface area pads is unable to generate enough localised heat in road conditions to prevent frequent pad glazing, then the RV8 brakes with discs three times the thickness with much greater mass for heat soak and ventilation with a much larger surface area for heat dissipation will run at even lower temps. Add to this a bigger pad surface area spreading heat generation will certainly not help raising temps to ideal working levels as our experience proves. This is why the focus is to use a standard quality brake pad for a pure road use car and especially one not driven hard and in fairness most are used for touring.
The comparison between a new standard MGB at 8.8mm thick disc (bottom) and a ventilated MG RV8 disc at 25.4mm (Top) is stark. Note the RV8 disc as those have no bell.
In addition, little use of the car can also allow caliper pistons to stick, so when changing pads, the eight caliper pistons need to be checked for ease of movement, and note that MGOC Spares stock rebuild kits for the RV8 calipers and new replacements that are also available in alloy that provides a significant reduction in unsprung weight. It’s also worth noting that the caliper springs and pins that were unavailable are also available from MGOC Spares.
GRK90182 - 4-Pot Caliper Repair Kit for MG RV8
Whilst the rear brakes add only a small element to overall braking, checking that they also work as well as they can and checking that the rear wheel cylinders are not leaking, a problem that has raised its head on little used cars, is also advised.
RV8 with weepy rear brake wheel cylinder (circled).
See our full range of RV8 braking components here. For further information contact our helpful sales advisors by phone on +44 (0)1954 230 928 or email at sales@mgocspares.co.uk.
Please Note: The information provided in this blog is intended as a general guide only. While we aim to ensure accuracy, classic vehicles can vary, and procedures may differ depending on model and condition. Always consult your vehicle’s official workshop manual before carrying out any work. If in doubt, seek the services of a qualified professional.
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