Braking Bad pt2

In the previous post back in June, I had a crack at improving the MGB's braking performance, replacing the leaky 54 year old master cylinder with a brand new one.  The result was a definite gain but nowhere near expectations which one takes for granted with the later servo-assisted versions.  In the intervening months since that post, it's been like an itch that I couldn't scratch - are my expectations of an old system too unrealistic?

I don't know whether engineers are OCD by definition but I couldn't settle for the status quo and decided to squeeze a bit more out of the braking system by replacing the flexible hydraulic hoses which were probably original items. It took the best part of a day to replace them and bleed the system, all to marginal benefit.  Fortunately, the replacements were relatively inexpensive and sooner or later, they would need to have been done anyway.

It was inevitable that admitting defeat wasn't going to be an option, even if it did cause a certain amount of eye-rolling and sighing from my Chief Financial Officer who as always; has plenty of other "honey-do" jobs queued up for my attention.  

This time, the task was to replace the front disc rotors and pads.  Whilst it was by no means proven, a cursory previous inspection of the rotors showed them to be both grooved and rusty in places. Like the master cylinder, time had taken its toll; although the pads had plenty of life in them.  Any incremental gains from replacing the whole assembly would still be worthwhile.  

There are multiple excellent videos on YouTube on how to do the job and easier to follow than the manuals.  First job was to whip off the front wheels and check the existing rotor thickness and runout.  Thickness was just within tolerance, as was runout.  

Using a dial gauge with magnetic base

Here's where it got interesting.  Pulling the pads before removing the rotors, they were pretty rough, particularly towards the hub. Part of the pads had been running over a rusty and pock-marked/grooved area.  As there was plenty of meat on the pads, it lead me to wonder whether the previous owner had replaced the pads not long before selling to me for whatever reason.  The reasons for the uneven wear apart from the poor rotor surface would be purely speculative but looking at the wear pattern, something odd has previously occurred.  The photos below show the worst set of pads and rotor.  The other set show similar, but lesser characteristics.  I also noticed that the cutouts in the caliper pistons weren't positioned as per the manual.  However, from owner discussions I've read on MG forums, there's a considerable divergence of opinion with respect to whether this matters or not.  Just to complicate things further, there are no cutouts at all on the left hand caliper!

Unusual wear and/or damage

Different wear patterns towards the hub

Close-up of an old rotor

The only assumption which can safely be made is that the full area of the pads were not being effectively used for braking and contributed to the indifferent braking performance.

Removal of the hub and rotor assembly was straightforward, simply removing a split pin and castellated nut which held the assembly onto the stub axle. The bearings were well-greased and in excellent condition so they weren't touched.

 

Stub axle and brake caliper

Hub separated from rotor

A brand new set of rotors were then bolted to the hubs and refitted in reverse sequence.  They were a joy to behold with their finely ground surfaces.  Just out of curiosity, runout was checked at 0.03mm, compared with the maximum permissible of 0.15mm - great result!!!

Almost an art installation - a brand new Powertune rotor

New assembly looking a sight better than the old one

Copious amounts of brake cleaner was applied to remove preserving oils, then the calipers were refitted.  Borg and Beck pads were used and it's nice to see pristine items.

Replacement Borg and Beck pads

The first short(ish) run on the road has demonstrated an improved and pretty satisfactory stopping power which should improve further as the pads bed in.  Brake pedal travel has also improved compared with the pre-upgrade but it's still a tad more spongy than I expected.  A double-pump on the pedal tightens it up which suggests that there might be a small amount of air remaining in the system.  It's been bled twice after fitting the new hoses, once using the 2 person method and again using the Gunson Ezibleed single person system.  There was no evidence of residual air but a third attempt may be in order when everything has been bedded in.  A good example of Kaizen - small continuous improvements.  There may also be a case for checking the rear drum brakes as an MG specialist serviced these over a year ago when he was re-shimming the differential.  Chances of an error are probably low but not zero, even with a team that specialises in MG's.

Some concluding thoughts.  As a retired professional engineer, tinkering has been a lot of fun over the last few decades, principally with motorcycles.  Reaching 79 years in less than a month's time has taken the gloss off any tinkering which is conducted near ground level, despite being reasonably fit.  We live in a rural area so getting someone nearby to professionally do the work a bit further down the track could be problematic.  A good incentive for living life to the max whilst we can!

Rural mailboxes on our road