Sorry about the corny alliteration/title reference to the popular TV series, but it does describe the stopping performance of our classic MGB GT. An understatement if ever there was one. This post may be of interest to MGB owners who find themselves in the same position as me - the desire to improve braking performance but not having any past experience of what's involved in replacing a worn master cylinder.
Manufactured 54 years ago, it came without power assist on brakes and steering. I've got used leaving a decent stopping distance and have bionic biceps from parking in town but Jennie point blank refuses to drive it - fine by both of us. I'd prefer to keep the car close to standard rather than fitting later power assist fittings but I was pretty sure that a new brake master cylinder would improve stopping distance. New seals in the original cylinder would most likely only have a moderate chance of success so I decided to go straight for a new unit as they don't cost the earth - about NZ$200 ($160 AUD $115 USD 86GBP) delivered ex-UK.
On the face of it, replacing a component is a straightforward exercise but it's the little things which can turn a job to custard. Reading manuals and searching for info on the Internet was time well spent. The physical location of the brake master cylinder which is paired in a housing with the clutch master cylinder is one potential difficulty in terms of easy access. It's recessed into the top corner of the engine bay where the bonnet meets the firewall as the photo below shows.
A good location for smashing one's head into the sharp bonnet edge and skinning knuckles
Most of the manuals and advice on MG owner websites centre on complete removal of the cylinders and mounting frame. Unfortunately, the multiple retaining bolts are all tucked up in hard to reach places under the dashboard amongst wiring and sundry components. I'd imagine that when the car is first assembled at the factory, the dashboard and wiring are fitted later. Owners who have already faced this problem recommend a 1/4" socket drive extension and universal joint fitted to a ratchet drive to reach the bolt heads so they were duly purchased.
For getting into awkward places
A quick trial run was held to see if all the bolt heads could be reached. This involved being hunched up like Quasimodo half in the driver footwell and half on the garage floor, looking upward under the dash. Not the most comfortable of positions, especially for a 78 year old. Cramp was narrowly avoided.
Working partially by feel under the dash
The quick trial run proved that it was doable, albeit with difficulty. It was also clear that replacing the bolts on reassembly could be a prick of a job, to use a well-known technical phrase. However, there was one Internet comment, unfortunately without much detail; that it was possible to remove the master cylinder without unbolting the mounting frame. This was achieved by removing the part of the cylinder ram which connects to the brake pedal in situ, which sounded like a sensible, time-saving approach. I'm naturally suspicious of misplaced optimism when there's no detail to back it up but the person making the post said that all that needed to be done was to pop a circlip out of its groove and lift the ram extension out of the way. Many respondents thought that this was near impossible in situ, or that the circlip would fly out into some dark corner of the garage or into the bowels of the engine bay, never to be seen again. However, it was a potential time-saver so I decided to give it a go as I could always default to the longer method if I stuffed up.
It so happens that I have a full set of proper circlip pliers which is a confidence-booster. Rags were packed round the engine bay to stop the circlip from disappearing forever if it was dropped. The circlip pliers worked perfectly in conjunction with a jeweller's screwdriver to ease the circlip out - job done in just a few minutes. Unbolting the cylinder after draining the reservoir with a syringe was straightforward, although undoing the hydraulic oil feed pipe at the back of the reservoir was one of those 1/4 turn at a time jobs because of restricted space.
New and old brake master cylinders
The old cylinder was lifted out and the oil feed banjo transferred to the new unit at exactly the same angle for reattaching the oil feed line. Some owners simply prefer to remove the mounting frame to address any corrosion from spilled hydraulic oil. Our paint is 2 pack which has greater resistance and no remedial work was required, another good reason for trying to cut corners. The mounting holes on the new cylinder were drilled and tapped to make any subsequent removal easier than the standard nut and bolt configuration. Reassembly was simply a reversal of the ram removal although a simple jury rig with a bit of timber was required to hold it in place whilst the circlip was clicked back into its groove. The rubber dust boot was then slipped over the ram and into place. New clevis pins and split pins were used and that completed reassembly to the stage where bleeding air from the system was the next step.
Ready for bleeding the system
Bleeding motorcycle brakes on your own is a piece of cake, simply bleeding the system into a plastic bottle whilst keeping the reservoir topped up. The same principle applies to cars but is easier with one person pumping the brake pedal whilst the other keeps an eye on what's happening at the brake end to avoid air entrainment or overflows of brake fluid. From personal experience, harmony is more easily achieved if a mate is helping rather than your lovely wife. Wives don't appreciate a raised voice, an abrupt tone or bad language if things aren't going smoothly. Mates understand, without the risk of repercussions! Said partially tongue in cheek, but I thought I'd minimise risk by buying a Gunson Eezibleed kit, which is perfect for a one person operation. This is it....
Without going into minute detail, it's a clever bit of kit and very simple to use. Basically, you pour brake fluid into the plastic supply container and connect it to the brake cylinder filler cap to form an airtight seal. At the brake end of the business, you have a catch bottle connected to the bleed nipple on the brake which is furthest from the cylinder. The supply container is then connected to a spare tyre with no more than 20 psi in it. Crack the bleed nipple open and the pressure from the tyre pushes the brake fluid and any entrained air through the system until all you get is clear brake fluid with no air bubbles. Close off the nipple and repeat the exercise for the remaining brakes in decreasing distance sequence. Smiles all round and everything is sweetness and light. Wish I'd bought one years ago.
Eezibleed hooked up to the brake cylinder reservoir. Black line connects to the spare tyre
The bottom line is that whilst the brakes don't match those in a modern car, the new master cylinder has made a worthwhile improvement over the old one. I've also learned more about keeping the car in good order which has got to be a good thing. Happy camper!
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