400-406 Dynamo’s (Generators)



Warning – When working on your dynamo or indeed at any time whilst the engine is running, keep your hands well away from the fan blades!

YouTube Videos
Dynamos are often referred to as a generators. If the dynamo has been off the car for a considerable time, or your car has been standing for a considerable time, your Dynamo may require polarizing. Here are two YouTube videos on the subject.

YouTube Video 1

YouTube Video 2

Is My Generator Charging?

If you have a voltmeter, here are some easy tests to make – Measure the voltage across the battery, it should be about 12.6 volts with the engine off. As the engine speeds up, the voltage should increase to somewhere around 14 volts. If it does, the generator is working and charging the battery. If the voltmeter does not go up with the engine running, first check to see that the generator brushes are not worn excessively. If you can, apply a little pressure to the brushes while the engine is running and see if the gen light goes out or the voltmeter reading increases. If it does, the brushes may be worn to the point that they don’t exert enough pressure on the commutator.

Generator Testing

If the brushes check OK, do this test: Disconnect the generator from the regulator (probably easiest to simply take the wires off the generator). Connect a jumper from DF on the generator to the generator frame. Now run the engine and measure the voltage from ground to D+ on the generator. NOTE: Some generators have different types of terminals; verify which is DF and which is D+. As you increase the engine speed, the voltage should jump up to +35 volts or so (@3000 RPM). If it passes this test, the generator is good. (Don’t run this test longer than necessary as it will overheat the generator.)

If it fails that test, the generator may need to be polarized. Leave the jumper wire connected from DF to ground. Remove the fan belt. Connect a wire from the battery + terminal to D+ on the generator. The generator shaft should start to spin. Don’t run this way for more than a few seconds to avoid overheating. The generator will now be properly polarized. If the generator did not spin during this motoring test, the generator is likely defective. Put the belt back on and re-test for generator voltage with DF grounded. If the output voltage is still low, the generator is defective.

About Polarizing

Why do generators need to be “polarized”. Auto generators need some magnetism to get started. This “residual” magnetism remains in the Field pole pieces even after the engine has stopped. The next time the generator starts up, the residual magnetism creates a small voltage in the Armature windings. Not enough to charge the battery, but enough to allow the Field windings to draw current. As the Field current increases, the pole pieces create even more magnetism. That makes even more voltage in the Armature, and the cycle continues until the generator is capable of producing maximum output.
What happens though to a generator which has been stored a long time or is freshly built? The residual magnetism may have decreased to the point where it can no longer get the generator started producing voltage. In the case of a new generator or one which has been mis-treated, the residual may even be of the wrong direction (North and South poles reversed). Polarization is a simple process used to restore the Field pole residual magnetism and ensure the magnetic direction is correct.

Do regulators need to be polarized?
No, regulators are not polarity-sensitive. But my regulator came with instructions to polarize it… These instructions actually polarize the generator, not the regulator. The regulator mfr simply wants to ensure that your generator will work properly so you don’t blame the regulator.

Generator Diagnostics & Troubleshooting

Generators must spin clockwise to make voltage. They won’t make voltage if they are spun counter-clockwise. Generators always make some voltage when they are spinning. The red Generator light in the dash is an important part of the charging system. The system will not charge if the light is bad or not hooked up. The ignition powers the light, the Generator grounds it when not charging. This makes the light stay on. Here’s how the connections on the voltage regulator go and what they mean: (NOTE: this may depend on your type of regulator)

B = Power out of the regulator to the car and battery
F = Generator Field Winding
WL = Warning Light
D = Generator (actually D is for Dynamo) output
E = Ground to the body (actually E is for Earth)

So, make sure the wide spade connectors are on the “B” terminals. Make sure that there is continuity in the F and D wires. In other words, unplug the D wire from the back of the Generator and unplug it from the voltage regulator. Now take an Ohm meter and touch the leads to each end of the wire, you should get a small amount of resistance which shows the wire isn’t broken. Now do the same test on the F wire.

If those are both okay, hook them back up to the Generator. Now leave them off the regulator. Bridge them with a short piece of wire and using a voltage meter, put the pos. lead of the meter into one of the ends that you’ve bridged. Touch the black test lead on the meter to the battery ground. With the engine running at about 1,000rpm+ you should get 18 volts. (This is called “full fielding the generator”)

If you get 18 volts, the Generator is fine and you have a bad regulator if you get less than 18 volts, you have a bad Generator….for whatever reason. They are extremely easy to repair. New brushes and springs are dirt cheap and take abot 15 minutes to replace. Polish the commutator with fine sand paper while your’re in there and finally, I cannot stress enough the need for clean, tight, and large, engine and body grounds. If you want to check them touch the leads of your Ohm meter to the engine block and to a screw going into the body in the engine compartment somewhere. You should get nearly zero Ohms. Any other reading shows bad grounds. Do the same test between the battery ground POST and a screw going into the body on the inner fender. Do the same test between the “E” terminal on the Voltage Regulator and the body in the engine compartment.

2 Litre Cooling Systems

AC Thermostats

  • Replacement Spindles – available from bearing stockists. (Ransome, Hoffman, Pollard) RHP Part No. FPS15 or the equivalent from another manufacturer. SOURCE = C. Millward Tel: 0121 – 745 – 2087. Note: the spindle has been case hardened and you will need to use a Carbide Drill to drill the cross hole to allow the insertion of the cross pin. It might be beneficial to grind a small start flat with a dremmel or the like, to remove the case hardening (usually a maximum of .025″ deep) to assist the drill start.
  • Replacement Seals – reproduction seals are available from C. Millward Tel: 0121 – 745 – 2087.
  • Replace impellers – are available from C. Millward Tel: 0121 – 745 – 2087.
  • Replacement Thermostat Hosuing – castings may be available soon-  Contact C. Millward Tel: 0121 – 745 – 2087.
  • For those who feel unable to tackle this kind of work, contact C. Millward (BODA Member) OR E.P. Services (Water Pump Reconditioners), Tel: 01902 – 452914. Unit 1 Central Trading Estate, Cable Street, Wolverhampton WV2 2RJ.

The Ferodo Specification was 5/8″ TW – 7/16″ Thick – 32 degrees angle – 39 1/18″ IC – 41 7/8″OC

The Ferodo V155 was the original fan belt recommendation, but was not necessarily the only belt to fit. It seems to have been used on:- AC Ace, Acela and Greyhounds with Bristol engines from 1957 to 1964, and Bristol types 400, 401, 402, 403, 404, 405 and 406.

There may have been other makes of fan belts that also fitted reasonably well. For those searching for a belt, the V155 was also fitted to the following and the relevant clubs may be able to help with an alternative belt.

  • Aston Martin – DB3-S 1955
  • Austin – 14 Taxi 1946, Eight 8 h.p. 1939 – 1947, Big Seven 1937 – 1939, Commercial 6 cwt 8 h.p. K2VV s ton 1952 – 1954
  • Daimler – Ld10 10 h.p. 1939
  • Frazer Nash- 326 & 6 Cylinder 16 h.p., 2 Litre
  • Gardner- Engines LK
  • Jensen – Commercial – Jentug, 5 ton, 1947, Jentug Mark 1 1948 – 51
  • Morris – 6 from 5413 1950 – 1954
  • Skoda – 1101 1937 – 1948, 1102 1949 – 1951
  • Vauxhall – 6, 24.97 h.p. 1937 – 1940
  • Wolseley – Fifty-Four from engine 4447 1950 – 1953, Six-Eighty from engine 3554 1950 – 1955

400-406 Braking systems

406 Brake Data



However, this does not resolve the mystery that all 406′s are believed to have had disc brakes not drum brakes.

Master Cylinder Repair Kit Wheel Cylinders Repair Kits Brake Hose Brake Shoes
88840 KL 71410 Front 30635
Rear 83604
Front KL71490
Rear KL71529
Front KL57424
Rear KL57426
Front LB134
Rear LB135M20


The 88840 Master Cylinder was also used on a number of other vehicles, namely:

  • Austin Commercial LD1, LD01 (1 Ton), LD2, LD02 (1.5 Ton) up to chassis 16120
  • B.M.C. Commercial 1 Ton FC LDM20 1962 – 1967 & 260LD 1968- B.M.C. Prime Movers FD.2 Loader 2WL Loader
  • British Jeffrey Diamond – Wakefield Road Grader 603 1966 on
  • Conveyancer E20-20 / 6-20 (Some) / E20-20 1955 Mk XXV / E2-24, G4-24
  • E3-20, D4-24 / E4-15, G4-15 / E4-20, G5-16 / E22 RC Truck 1965 on / MkII, MkIv, MkVI
  • Coventry Climax IGY / Electrical IndustrialTractor Model-TE 1965 on
  • Universal Major Trucks Models MSD, MSDA, MSP, MSPA, MCD, MCDS, MCP, MCPA, MED, MEDA, MEP, MEPA,
  • Universal Major Electric Fork Lift Truck MSE, MCE, & MEE 1963- / Research Truck RT.812 / TLJ / UTF
    Universal Petrol & DieselFork Lift Truck IGPT, IGPTA Series II, IGDT, IGDTA Series II / IGEUS
  • Universal Major Electric Fork Lift IGET / Series I & II, IGETA Series II / Bulkloader (Mechanical Shovel)
  • Halifax Tool Company 26Hr Battery Electric Tractor1967 on
  • Lister Tractor 50cwt 4’7.5″ W.B.
  • Morris Commercial LLD1, LD01 (1 ton), LD2, LD02 (1.5 Ton) up to chassis 16120, LD4 LDOA Petrol RHD & LHD)
  • Morrison Electricars E type25 cwt. BE, E25 cwt. / BEV (Morrison BM60 & BM60 MkII 1928-
  • Trojan 15cwt, Van 1950 on / Electrojan Battery Electric 20cwt Van 1952 on / Trojan-Carrimore Articulated 1952 on
  • Trojan-Tasker Articulated 1954 on
  • Yale & Towne K51-60 Fork Lift Truck Model Yale Tractor Shovel (Throttle Control).

400-403 Wheel Cylinders


As of Sept. 2010, the following are the cheapest prices that could be found

and there were significant difference in the prices quoted and all include VAT at 17.5%

  • Rear Wheel 25453 £84 from PowerTrack Ltd.
  • Rear Wheel 34348 (The believed replacement for 25453) £74.03 from David Manners
  • Rear Wheel 34348 – possible replacement for 25453, £108.98 from Guy Broad
  • Front Wheel 25452 £45.00 from David Manners
  • Front wheel 25452 – If not in stock with David Manners, £88.71 from Guy Broad
  • Note these are also available from US Jaguar Parts suppliers
  • Rear Wheel 34348 (The believed replacement for 25453) £74.03 from David Manners
  • Rear Wheel 34348 – possible replacement for 25453, £84.00 from Guy Broad
  • Rear Wheel 34348 £75.50 Recon. Exchage Classic Brakes
  • These are also available from US Jaguar Parts suppliers

405-406 Wheel Cylinders


Again, the latest prices as of September 2010 were as follows:

  • Front wheel 30635 £59.00 from David Manners
  • Front wheel 30635 – Jaguar XK 120 late available from Guy Broad
  • 30635 £68.50 Recon. Exchange Classic Brakes
  • These are also available from US Jaguar Parts suppliers

We have yet to compare the 1 1/8″ 401 rear 25453 and the 1 1/8″ 405 rear 83604 to see if the only difference is the handbrake lever?

Brake Master Cylinders


The XK120 early/single brake system Master cylinder looks the same as the Bristol Master Cylinder. An unknown person has apparently tried one but legend has it that it didn’t fit. However, it is not known which Jaguar Master Cylinder was tried. Nevertheless they still look identical and this is still worth exploring. It may be that just the bodies are the same as it uses the same KL71410 repair kit – has anyone physically compared the two?

Brake Shoes


Brake Pads for the 406

Brake pads for the 406 are often listed on EBay. However, as an alternative, EBC state they are the Manufacturers of the World’s largest Range of Brakes. For more information see EBC Brakes Direct or Tel:0845 225 5011.

406 Servo

Servo Data (from a Lockheed list)

  • There seems to be some cross information in the Lockheed catalogue, as elsewhere the unit listed below is shown as for the 407 and below (4257- 551) as the correct unit for a 406.
  • “Major Repair Kit” – includes the items that should be replaced whenever the unit requires servicing regardless of cause.
  • “Piston Packing Kit” – includes parts which must be used, in addition the parts included in the major repair kit, if the leather Piston Packing needs to be replaced.
  • “Air Control Valve Kit” – consists of a sub-assembly of the end cover, valve and air pipe to be fitted as a complete unit each time a valve requires replacement.
Servo Unit Repair Kit
V4257-567 Major Repair Kit SSB.72573
Piston Packing Kit KL 72523
Air Control Valve Kit 72525



(See also 407 LOCKHEED SERVO 4257-567)

The Jaguar XK 150 Servo 4257-552 is much the same as the Bristol one but we have yet to work out the exact difference and whether or not it actually makes any difference in use?

4257-552 units are available from David Manners. for £480 including vat (Jan 2011).
406 Servo Kits & Parts are also available from J & L Spares Export Ltd.

The remote brake servo kit enables the fitting of a remote brake servo to cars which do not have one, and enables the easy replacement of non-functional or obsolete servos. Boost ratio 1.9:1 Measures approx 224mm length by 189mm diameter. The beauty of a remote servo is that fitting requires no interference, modification, or change to the existing brake master cylinder. As well as being a suitable fitting for all single circuit cars lacking a servo (and kit cars), it is also a direct replacement for remote Girling Powerstop servos fitted to Austin, Bedford, Ford, Hillman, Land Rover, Lotus, MG, Morgan, Morris, Singer, Talbot, Triumph to name a few, covered by the Girling part numbers 64949023, 64949077, 64949178, 64949354, 64949330, 64949000. Supplied as a kit complete with brackets, hose, connections, instructions etc. Please note that if fitting to a modern car with twin circuit brakes, then you will need twin servos.

Fitting instructions for a remove servo


Remote servos are available from Ratsport, among other sources.

2 litre wheel and axle bearings

There is no “where used or used on” section in the attached catalogue, but a lengthy search through the catalogue is under way to find out what other vehicles the bearings where used on. This will take some time to finalise.  In the meantime if you want a specific information on bearing please contact on of our technical coordinators.

Just one supplier (so far) has been found for bearings, Simply Bearings. However, 401 front & rear bearings are sometimes listed for sale on EBay.