standard Imp pedal assembly: 1 brake master cylinder and 1 lutch
 Dawson's kit for Imp brake pedal assembly: mounting plate, yolks, tube, balance bar, bearing and lock nut
 Dawson's kit implemented: dual brake master cylinders, balance bar and re-aligned clutch
 Imp brakes
 Imp brakes - re-threaded pushrod can be seen with new yolk mounted and squared balance bar and lock nut for brake bias adjustment
 Imp brake pedal with tube welded in place half way from standard point to hinge to restore working pressure
 Imp brakes assembled. Clutch pivot modified to restore correct angle. a gusset between the 2 brake cylinders

The Imp Site

Braking System

Contents:
 
  
  van een kaart van Bert

The braking system needs regular servicing, checking for worn shoes, replacing brake fluid every few years; adjusting shoes and checking for fluid leaks.

If rear cylinders are not free to slide in backplate, the brakes will be mediocre. If the Imp doesn't see much action, all wheel cylinders are prone to seizing.

Uprating an Imp's engine and handling, according to CCC in 1976
Brakes

After lots of miles the locating pads will have worn out. When the shoes are replaced, remove the wear groves across the pads (<0.5mm - file or grind; >0.5mm - weld or replace). Then lubricate the pads very lightly with a copper-based grease.
On fitting new brake shoes, sand the brake drums lightly on the inner surface, to remove any glaze. (G. Harding, Impressions 95 Nov)

Undoing rusty bleed screws on brake cylinders
First take it off the car.
Cut the top off, put a drill down the rest to take out some of the metal in the shank then get the rest out with an 'easy out', (that is a tapered steel rod with a coarse left hand thread up it, you screw it in and when it tightens up in the hole it pulls the remaining thin-walled bit of bleeder thread out).
Then buy a new nipple, resurrecting the rusty one will always be a pain to work with in future.

You can install a dual master cylinder system in your Imp, with adjustable front-rear bias. You can get bias bar assemblies from most motorsport suppliers, Demon Tweeks being a good example. You would have to modify the pedal box to accomodate the extra cylinder. Part of the bulkhead will have to be cut back as three cylinders will not fit widthwise.

If anyone has trouble with the front brake assembly, worn-out cylinders etc: The complete brake system is completely compatible to the Ford Escort from 74-76.
There are two brake cylinder sizes around, 18.06 and 22.02 mm diameter. The smaller ones where used by Ford in the Escort Van, the larger ones in the normal saloon. I think Rootes used the smaller ones (which are a bit harder to get), but anyhow, you could at least swap all 4 ones, and then it's completely new!
They cost around 59 DM incl. VAT in germany.
The rear brake cyls have been used by Ford in the smaller Capri cars (1700 ccm) till '79, on the rear, too. Maybe there are some different sizes, too, I haven't figured out that point yet. But there are only two to be swapped on the rear side, so that's only half as expensive as on the front side :-)
They are all compatible Girling parts from the early seventies, so someone with an old Girling catalogue should be able to find out where they used the brake system, too.
-- Carsten Bussmann

renew all dubious brake pipes with rustproof brakelines (eg. Cunifer).

The standard master cylinder can be changed to the Sport one with no problems. The master cylinder is interchangeable on the connections, it is only the bore size of the cylinder that changes. Extra pedal pressure will be required, but you won't need a servo. Lost pedal motion will be less. If you can get the ¾" one: all the better - real good feel in the pedal.

The Sport brake master cylinder is a pretty well standard fittment in all Formulas of Single Seater racing.
Demon Tweeks carry them. They may also do a 0.75 version, which would presumably be even better for travel, but may be heavier. Check the fitting.

For most of the Imp's competition career the standard drum brakes were only modified by changing the brake friction material to Ferrodo VG95. The front to rear brake balance was usually made adjustable by adding a third (0.625 inch dia.) master cylinder and balance bar to the standard pedal box.

Suspension influences braking performance significantly; a matter of inter-axle load transfer and vertical dynamic tyre forces.

Brake Lining - VG95

From the start of the Imp in May 1963, there has been one change in brake linings. Ferodo MS2s got fitted to avoid sqeal.
Hard linings (VG95) and a Powerstop brake booster are a very good combination, according to Roger Nathan Racing Ltd. in December 1966.

Mintex brake pads

How to choose brake pads ? - there is no such things a the best brake pad, it's a matter of balance. Maximum stopping power without becoming unstable. Brake bias and valves help to get a balance.
A lot depends on the weight of the car. Use as soft a pad as you can run, while not running into fade due to overheating.
Also hard pads wear the discs more rapidly.

EBC front brake shoes (EBC code 5141) for the following cars: Hillman Imp 1963-76, Ford Esxort 0.9/1.1 1968-74.

Lockheed front brake shoes (LOCKHEED part number KB 1045) Interchangeable with: Ferodo F.294.G-Belaco RG.4294, Mintex MGR.9.
To fit the following: Commer Imp Van 5 cwt 1966-on; Ford Essort 1100 Jan 68; Hillman Imp I, II Californian 1963-76, Singer Chamois I, II sports 1964-70, Sunbeam Imp Stiletto Sports 1967-76.

Davrian say in their leaflet "Davrian Disc System", of August 1981:

With a rear-engined layout the rear brakes are required to contribute nearly 50% of the braking effort. The single leading shoe rear brakes, as fitted to Imp saloons, are almost ineffective when put under any form of repetitive usage. The small disc systems available, for the front, only lessen brake fade and contribute to stability.

Discs specially made for Davrian
are the largest diameter that can be fitted in the average 13" wheel. They fit straight over the Imp hubs like a conventional drum, needing no special studs or location devices. The discs can be cross drilled and machined in order to reduce weight slightly, but mainly so that the mass of the disc heats up closer to operating temperature on the first hard application. The cross drilling also allows excess heat to dissipate more easiIy. This is only recommended for Track and Hillclimb cars and should on no account be undertaken by customers.

Alloy Calipers
are approximately 1/3 the weight of steel calipers and dissipate heat more readily, but are not recommended for normal road use, as they do not have dust seals on the pistons, therefore they require far greater maintenance. Alloy calipers are also only available with DS II pads, which are quite unsuitable for Road use.

Steel Calipers
the production of Davrian's own disc has enabled us to use a steel disc, with a range of pad material available from most motor factors. Apart from these calipers being considerably less expensive, their maintenance is also straight-forward, due to the fact they have dust seals etc. Steel calipers are currently used on our rally cars, but for tarmac rallying some alteration to brake ducting may be found to be beneficial. Although the special disc we now provide gives far better clearance to wheels than previously, possibly some minor filling or grinding of the caliper castings may be necessary with certain types of cast alloy wheels. If in any doubt use a thin spacer.

Discs

Talbot Special Tuning did a disc conversion (expensive).
If you make up a back plate to hold the caliper, you can either fit Triumph Vitesse discs, hubs, etc., with Escort wheels, but that is a tight squeeze. Or you can turn doen the end of the stub axle so Viva discs and hubs will fit. However the idea of discs on the front of an Imp has never really caught on. It may not be of benefit, it only makes it easier to lock the front wheels.
The effort might be better directed towards fitting a servo.

Tim Duffee used to make a disc conversion for the Davrian.
Anybody intending to race their Imp will really need disc brakes as the drums will overheat and fade. With good tyres and suspension then the brake locking should not be a problem.

How to fit disc brakes to your Imp / by Peter Nunney. - Impressions 3 (1983), 8/9 (Sept./Oct.)
6 pages with 6 fig.

If you want to try discs, consider Sierra vented discs front and back.
Graham Cashmore's disc conversion is based on a Fiat X-19 disc that doesn't widen the track at all.

Early front disc brake conversions were carried out by machining Viva HB or HC hubs to accept Imp outer wheel bearings. Viva discs were available in both 8.4 and 10.2 inch sizes.
As the Imp is rear engined fitting discs on the front alone produced gross front wheel lock even with an adjustable balance bar and was of little or no advantage. In addition the Viva hubs made the front track wider causing problems with wheels fouling the lower front door hinges which are located in the wheel arch.
Only in the late 1970's did suitable 10.2 inch discs become available for converting the rear (originally made for some type of Alfa Romeo ?) and these could also be used on the front. With disc all round and slick tyres the stopping power of an Imp could only be matched by a full race Porsche 911 which had a similar weight distribution.

Literature on disc brakes

Disc brakes for the Imp - Part Two / Colin Valentine. - Impressions 2015, August. - p.31,33-38 (7 pages). - 7 photos, 1 table
- to be continued -

Servo

A servo won't make your brakes any better, it will just save your legs. A servo is only designed to give a lighter pedal. Imp brakes in standard form are very good. If you are having to press really hard, then it is likely that you are experiencing brake fade. A good improvement can come from fitting genuine Mintex brake linings. Some people don't even like the servo response on Sport/Stiletto models.
If you really want to fit a servo, then it can be fitted on the front R.H. wheelarch as on early Sports. Make sure you fit the correct type from an Imp Sport or a Stiletto (unless you know what you're doing). And use the corresponding Imp Sport/ Stiletto master cylinder: a .7" bore (standard: .325").
If a servo is fitted, then it is possible to fit harder shoes. This might (or might not) improve braking performance.

A Lockheed Powerstop Servo can be fitted in the front. It is compatible with the normal Girling unit of the Sport, which is no longer made.

Brake servo repair kit
from Norton Classic Servos (about £35 ?).
It seems like a fairly straightforward rebuild, being mainly the replacement of some rubber items.
Put the servo in a bucket when undoing the nuts etc, as there is usually a residual amount of fluid left inside.
There was an article on rebuilding servos in Practical Classics a while back and they seemed to think that these nuts and bolts were unobtainable. Use penetrating oil to try and get them shifted. (Wire-brush them first ?)

Norton Classic Servos also sells reconditioned servos that works and looks as good as new (about £100 ?). They can supply both early and late types and they take postorders.
0494 - 56 22 35

www.stoptech.com/technical
Stoptech is a brake manufacturer. Their technial information section has some valuable white papers.

Brake lights

Stiletto brake lights are supposed to work with the ignition switch off.

Brake fluid

Silicone brake fluid is marvelous. Being non-hygroscopic (as in: it doesn't absorb water) its boiling point will remain as it is; it won't corrode the steel brake pipes or the wheel cylinders. (advises G. Pearson) Ordinary brakefluid sucks up water dramatically. Water in the system will lower the boiling point of the fluid and it will create corrosion. If you do not know whether the brake fluid in your Imp has been replaced at the appropriate intervals then the condition of the brake pipes is uncertain. With ordinary fluid you have to change it every so often, while the silicone stuff is a fit-and-forget thing.
When switching to silicone fluid it is essential that all wheel/master cylinders etc. are either replaced or overhauled. (adds M. Jones)

Rootes Service Bulletin RSB 61-232: Braking System Fluids April 19, 1961

 



The Imp Site
   Imp technicalities
      Imp Tech Tips
         Imp Brakes (this file)
         4-page leaflet "Davrian Disc System", August 1981
         Coollist archive:
            Brake problem + possible solution
            Brake problem + possible solution
            Remote servos
            How much wider will my track be with the Vauxhall/Holden Viva/Torana discs

External webpages:

© Franka
Edition: 1 Nov. 2015
This came from parts.html (started: 1995, Dec. 2)
Separated: 16 June 2013