Disc Brake Conversion

[Geoff Kingston]

Has anyone done a disc brake conversion on a 401 or 403 without using parts from a 406 and which has worked properly. If so were the parts sourced new as a conversion kit or were they off another make also were any modifications needed to the rear brakes for example change of wheel cylinder size.
Any ideas, pointers or tales of failures/problems to avoid would be a great help, alternatively is simply fitting a servo a better bet, the last 401 I drove had a servo fitted and the brakes were very good, much better I thought than one I had years ago with a servo fitted .
Geoff.

[Geoff Dowdle]

Geoff,



Although I have not done this conversion myself I believe a rear disc
from a Mercedes 300TD can be fitted to the front hub of a 400 - 403 with
very little modification (possibly just enlarging the stud holes). It is
approx 11inch diameter x 1/2 in thick with correct offset & PCD .



A caliper carrier must then be made to suit . Note the 403 uses a sway bar
and the caliper can hit the vertical sway bar link on full lock . Also
select a caliper that is not to bulky as you need clearance on the wheel . I
used a Girling #17 caliper from a Humber Hawk post 1960, they use a larger
pad than the 406 Dunlop calipers. There are probably many calipers available
that would fit but most modern calipers are designed to fit thick ventilated
discs and are not suitable to use with the MB 300TD disc.

Bristol used 7/8in diameter rear wheel cylinders when converting 400 - 405
to Dunlop front discs .If you don't reduce the diameter you could get severe
rear brake lock up on panic stops.
OR
You could retain the original rear wheel cylinders and fit a adjustable
brake proportioning valve in the line to the rear brakes to get the correct
brake balance between front & rear.

I suggest you get some advice from a brake specialist who prepares
race/rally cars.

The 406 brakes front & rear on my 400 with Girling #17 front calipers
certainly makes the car stop as well as most modern cars.
Good luck ,its a worthwhile update .

Geoff D

[kfitzgerald]

My former Arnolt Bristol was fitted with TR2 disc brakes in 1957 by Ed
Rahal. The servo was the normal Bristol brake servo. I updated to a
dual circuit with a bias adjuster. It would out brake a Jaguar XK 120
or a Morgan +4 with Disc brakes. All of the fittings were off the shelf
Triumph and Bristol pieces except the bias adjuster. A 403 is a heavier
car but for average road use I would think the Triumph brakes would
work. Kevin

[Geoff Dowdle]

Geoff,



one other point I forgot to mention , most front discs (like TR3 , Bristol
406 -411 are designed to bolt to the inside of the hub with separate bolts&
the disc has very little offset . The MB 300TD fit on the outside of the
hub ,in place of the drum and are attached using the original wheel studs &
wheels . They have sufficent offset & internal diameter to fit over the hub
,as they are originally designed to accomodate a handbrake assembly with
small shoes .
Regards

Geoff D

[Geoff Kingston]

Geoff/Kevin
Thank you both for your advice, I have got quite a few brake catalogs from the late 50's early 60's so I will have to look up the part numbers and cross references and see what specialists have in stock. The Mercedes option is an interesting alternative as sourcing the 300td parts should not present a problem, I am just sorry now that I scrapped a couple of 380SE's a few years ago as they might have also yielded some useful parts.I shall. have a word with a brake specialist who I know has uprated the brakes on at least one 411 and does a lot of conversions and upgrades on later sports/racing cars.
I am also going to have a word with Brian at BCL just in case there is anything on the horizon. We have an engine swap to do first and as all the brake cylinders need an overhaul or replacing I thought now would be a good time to think about disc brakes.
Thank you both again for your advice, I have a complete front cross member with hubs etc on it so at least I can have a play on the bench to see what fits best without dismantling the car.
Hopefully there will be some progress to report in the new year.

Geoff.

[Kenneth Andrén]

Interesting information Geoff!