Talk Morgan Forums Morgan Sports Cars Morgan Plus Four, Supersport & Plus Six (CX & CXV Generation Vehicles) My23 brakes

Don’t the trads have drum brakes at the rear?

Yes - and all that's needed. ARP4 was the only road car exception.

Last week while checking the underside of the Plus Six for a pre MOT lookover. I can confirm the Plus Six does have 4 pot calipers on the front, they are of a overall physical size similar to the Caparo 4 pots fitted to the 3.7 Roadster, but the Plus Six caliper 4 pot has a different manufacturer marking.. The Plus Six rear caliper has a mechanical cable operated handbrake mechanism integral to the caliper, it appears to be single pot, but I did not see a slider or slider pins to allow it to equalize as pressure is applied to operate the brake, but at the time I was not looking specifically to see how the rear operated. Just a quick lookover to make sure everything was secure and not leaking etc.. The wheels are back on now, so I missed the opportunity to take a second look. I see looking at the website for 920E as previously posted that they were originally AP then became Caparo and now 920E their web site does not show examples of all their calipers as some images are missing.

My mid 80`s +8 Trad has two pot callipers, drums on the rear, no servo or ABS, has good firm pedal action to the extent that I can lock the wheels, which I know is not the best possible braking action. When multi-pot calipers became available for Mogs on the aftermarket, I imagined that they might just equate to locking the wheels with less pedal pressure, a subject Colin AKA spanner juggler engaged in some years back.. I have memory issues, though think Colin suggested that more pots in the callipers equated to more pedal "feel" in the braking process, though how that might work in panic braking... Hmm..?

I always assumed the extra pots were needed to apply even pressure over the longer pads used George, hence four, six and even eight pot.

By increasing pad area a lesser hydraulic brake pressure can achieve the same retardation so allowing increased feel. Careful choice of master to slave cylinder ratio together with increased feel would not increase likelihood of brakes locking, but would probably reduce brake fade given increased pad contact area.

Richard, from that which you typed above It seems we may agree, in that more pots and larger pads per calliper can relate to less pedal pressure to create a similar effect than a calliper with fiewer pots ..? That being the case it would seem that fitting multipot callipers to a pre ABS Morgan might as I suggested equate to quicker lock-up under panic braking..?

In fairness I did suggest above George that choice of master to slave ratio (read mechanical advantage) could be tailored to not increase likelihood of lock up in panic situation.

Richard, thanks for taking the time to respond, very much appreciated, your fair mindedness was never in doubt..

I wonder how many if any who retro fitted multi-pot callipers to their Morgans, or any other car, even contemplated fitting an alternative master cylinder...?

I on the other hand would have done, as the result of fitting a new master cylinder to a Mk1 Ford Escort, many years ago, when according to the part number the cylinder supplied was the correct part for the year of manufacture, but the brake pedal travel was discovered to be excessive after I fitted it...? With a bit of investigation I found that Ford had changed the bore of the master cylinder mid year and I had been supplied with the wrong part, which looked very similar.

If designing a multi-pot calliper for the aftermarket it may just be a consideration to ensure that the overall fluid displacement required is similar to that of the original larger cylinders, or perhaps just a tad more, thinking that a little bit more pedal travel might be acceptable... Other than that, selling multi-pot callipers to the home mechanic/enthusiast which also required the expense of upgrading to a matched master cylinder, could cause folk to think of reassessing the initial purchase decision, and risk reducing sales of the calliper..?

As ever just thinking in type.

I agree that by adopting larger total piston area of calipers compared to OE you will increase pedal travel. However this also means you are increasing mechanical advantage. In so doing you have the double whammy of increased likelihood of locking brakes from both the mechanical advantage and likely increased pad area if upgrading from say two to four pot. A reduction in caliper piston area would be better, or a more than compensating increase in master cylinder piston size.

As an example many years ago I improved the braking on my Guzzi Spada touring bike by fitting P09 Brembo calipers up front, an increase from 38 to 42mm pistons and attendant larger pads. I also increased master cylinder size from 15 to 17mm though to compensate and leave similar lever movement.

I do wonder if this may explain the dissapointment others have felt after fitting expensive caliper/disc upgrades to their Classics. If the new calipers have smaller pistons the pedal will feel very hard but requiring a heavier foot than previously. Possibly not what they were expecting!

Well I’d certainly be looking for wheels that hide those as much as possible

Obviously I’m jesting there, as the reason I originally wanted the coloured callipers was purely for aesthetics with the black wheels. On one of my spec options the idea was to link a flash of that colour with some stitching on the inside. Very un-Morgan, I’m afraid. What’s funny though is how people go for big brake kits with multi-piston callipers for aesthetic reasons, as opposed to upgrading for performance. Floating single piston callipers are not new on some performance cars, even a premium and heavy one known as the E92 M3 if my memory serves me right (the V8 one). Granted there aren’t many and certainly not in recent years that stand out.

I dare say Morgan chose this spec due to cost, although looking at it in the garage the piston is fairly large and there isn’t much room between the calliper and the alloy in the Plus Four design. Yet there is so much more to outright braking performance and resistance to fade than how many pistons are used, and the desire for many to simplify this in the world of tuning is misplaced. The lack of symmetry in clamping force, flexing and reduced distribution of pressure of course influence braking feel, but as you know there are many factors that will influence the overall braking performance and fade resistance. Pad compound/material and friction, heat management and dissipation/cooling, swept area, front/rear balance, fluid, tyres etc, even ignoring the influence of things like weight transfer and dive/damping. On paper yes the Plus Four callipers lack headline grabbing technical specs (in comparison to my other cars they are very under spec) and are hardly anything you’d want to show off as performance car brakes in flashy colours, but subjectively in normal road use I find mine effective and measured if not a standout feature. I also found them to be better than I expected on the driving academy at Bicester, maintaining good bite and performance lap after lap at ‘well’ beyond road speeds. Maybe I got lucky as they do seem better than that hire one I had 18 months ago, although I can’t be alone as I recall some reviews have been positive about braking too. That said I’ll definitely consider future upgrades if only for the fact I want to create a Plus Four that is even more performance orientated in time. Suspension first though; very un-Morgan again. I also recognise the best way to improve braking and performance generally will be to upgrade the driver first (me!) and I’d argue that will be the same for most on here.

Objectively who knows; I’ll assume that none of us have the data from controlled test environments to understand how they compare in repeated high speed stops vs the 4-pot/drum-equipped trads or other cars. Maybe I should try and borrow a vBox and Mira proving grounds.

As a slight aside my GR Yaris went in for a service last week and I was given a normal Yaris Hybrid as a courtesy car. The difference in braking setup was so stark, with the Hybrid having such sharp and over servoed brakes that I nearly went through the windscreen just navigating the forecourt. Horrid set up.

I hope those that have issues or find the braking not to their liking do get it resolved satisfactorily. Equally I hope we can all get out soon and enjoy our Morgan’s whatever flavour we have (said from a very icy part of the UK currently).

PS, Clemens you’re more than welcome on the link to the manual, I found it surprising just how much tech detail was in that. I recalled seeing the braking details when trying to read up as much as I could when waiting for build news during the recall.