Braking Sorted

I wasn’t happy at all with yesterdays braking tests, even though they were OK for the MoT.  A long drive this morning on deserted roads to bed the brakes in resulted in only the smallest improvement.

The SIII master cylinder and servo were duly removed and replaced with a Discovery I servo and Defender master cylinder.  To do this, an 8mm adaptor plate was cut to match the square and stud holes of the SIII pedal box.  The centre had a large diameter hole cut for the nose of the servo, and two more holes were drilled for the servo’s retaining studs.  It was fitted with the servo’s original lozenge shaped aluminium spacer in place, which with the adaptor keeps the servo nose just clear of the pedal box uprights (the box is too narrow to take the servo nose).  All four corner holes were tapped for M6 bolts, which were then fitted to act as studs to secure the plate to the pedal box.

The clevis fork on the Discovery servo is just a little to wide to fit in the SIII pedal, so this was squeezed in the vice with an M6 nut inside to hold the sides parallel.  The clevis pin holes also needed drilling out just a little larger to fit the thicker SIII pin.  The servo was then attached to the adaptor plate.

The pedal box had alread been modified when it was out the other day to accept the new servo – two 15mm holes need to be drilled to accomodate the nuts on the servo securing studs.  The steering column’s lower clamp also needs to be rotated by 180 degrees to clear the the servo on fitting, which had also been done previously.  The wing top doesn’t need trimming, just a little folding of the lip alongside the servo area to about 45 degrees.  The servo doesn’t have a vacuum failure sensor like the SIII unit (perhaps because the pump on Tdi engines is so much more reliable than the SIII vacuum units), so to keep the brake failure warning light circuit active, the two wiring terminals had to be connected together with a short length of wire with spade terminals.

The Discovery and Defender master cylinders are similar but not identical.  The Discovery cylinder has four ports, two on each side, and has an irregular reservoir to allow for its inclined mounting.  The Defender cylinder has only three ports and a rectangular sectioned reservoir as it sits roughly level.  Unfortunately, while the hydraulic part seems comparable in each, the similar looking mounting flanges are also slightly different – the Discovery unit has slotted bolt holes but the Defender unit has circular holes which are too far apart to meet the servo’s studs, so these needed elongating.  I would have used the Discovery cylinder if I could have swapped the reservoirs over.  The last touch before fitting was to blank the unused port (the lower front port).

New pipes were made up to connect the master cylinder to the PWDA valve on the chassis.  The SIII lines cross over beneath the valve before heading for the respective axles, with the servo end of the SIII master operating the front brakes and the forward end operating the rear brakes.  Defender and 300Tdi Discovery brakes are piped such that the servo end of the master operates the rear brakes and the front end the front brakes.  There was no point in disturbing the old lines where they cross over, so the new upper lines were made to cross over aswell, so the lines cross twice and all works as it should.

The master cylinder sits on a slight cant to the left.  This is because I had believed the mounting studs were set at a 45 degree angle, but in fact they’re roughly 40 degrees from the horizontal.  This is something to bear in mind when drilling the adaptor plate if you copy this method.  It’s of little mechanical consequence, but it does slightly spoil the neatness of the completed job.

After bleeding and adjusting the brake light switch, I took it out on a short test drive.  The results are staggering – it now stops on a sixpence and with very little effort.  I’m finally content with the whole axle conversion.

The entire conversion has been done in a way that is simple (if a bit of hard graft) to return to SIII standard – axles, steering, brakes and all.  All of the original parts are being kept until I’m completely sure about the conversion, but so far, so good.  The last remaining item is the callibration of the speedo, which will wait until I’m sure about retaining the 3.54:1 diff ratio – if they prove too high, then I’ll retrofit the 4.71:1 ratio diffs and the speedo won’t need adjustment.


  1. Hi Nick.

    Thanks for your interesting article. Having just finished restoring a Series IIA LWB station wagon I also was disappointed with the performance of the Series III servo I’d fitted. And, although it’s passed it’s MOT – it stopped on the test amazingly quickly nearly throwing the tester against the window! – nonetheless the brake pedal nearly goes down to the floor. There appears no adjustment on this servo arrangement unlike the Series IIA/III set up. I do need to re-bleed the brakes as even pumping the pedal gives little improvement. Any solutions appreciated.

  2. Hi

    SIII 109 brakes are a little tricky to set up. They are notoriously difficult to bleed because of the PDWA valve on the chassis and the poorly designed front cylinders trapping air. Shoe adjustment is also critical. However, pumping the pedal should result in a firming up of the pedal and after two or three swift pumps,the pedal should not sink to the floor unless there is a great deal of air trapped.

    I did find a similar problem with my brakes when I replaced the servo years ago. There was excess play between the servo plunger and the master cylinder first piston. This is the only adjustable point on the pedal box assembly, even though the manuals expressly prohibit its adjustment, citing that it is accurately factory set. If you separate the master from the servo, you will see that the end of the plunger is an acorn nut with a locknut behind it. These need to be very carefully adjusted to take up the majority but not quite all of the gap when the master is refitted. You will need a vernier and plunger gauge to do it correctly. Make sure some slack remains so that the master cylinder pistons retract fully on pedal release or you’ll have worse problems.


  3. Hi nick

    I have a Land rover santana from 1979, almost 100% the same as a series III made in england.
    I disconected the brake pipes from the pdwa to rebuild the vehicle and now i do no remember which one goes to the front and which one goes to the back of the brake system.

    I notice that there is a diference between the brake pipe unions on the master cilinder, so it should not be the same

    Mine is a 88 diesel

  4. Good stuff here. By chance can you give up the wiring of the warning light for the brake? Connections are 1, 2, 3 and 4. Wires are B, W, WB and BW. any help would be appreciated.

  5. Hi Erik,

    I can’t get into mine to check at the moment, but it is just a standard relay. Check for a pair of terminals that have a closed circuit – they will be the coil that the black and the white plain wires go to. The other terminals will only be in contact when the white wire is energised, and it doesn’t matter which way around you connect the striped wires to these.

  6. Ashraf Latif says

    Ashraf from Maputo,

    I like Landrover so much that i bought one ex millitary defender 1990 model. am not able to see the chassis no. making it difficult for me to buy spares.Otherwis Landrover ,I am proud to say that ,
    it is the best car ever.

  7. Hi Ashraf,

    If you scrub back the paint on the outboard side of the right chassis rail above the jacking bracket (the welded part with the circular hole under the bumper), you should find the chassis number. MoD vehicles also had black and silver plaques riveted to the sides of the seat base, just inside the front doors, with their identity on them. You are looking for a long string starting with “Sall..”

    Failing that, most British MoD 90s were fitted in a set way, just the specialist equipment that would have been removed when they were sold off differing, so a Land Rover dealer should be able to provide the correct parts if you know the year of manufacture and engine type (probably 12j at that age, number will be stamped in the left side of the block behind the timing case and above the alternator.

    Good luck.

  8. Kevan Bunting says

    I have a 1978 Santana 109 and have been told there is no brake vacuum, is there an electric pump conversion for this model?
    I have converted the front brakes to discs and replaced the master and booster.
    Any help is greatly appreciated.

  9. Hi Kevan,

    To my knowledge, Santanas were mechanically identical to Land Rovers at that point, so a 109 of that age should have a vacuum servo.

    They didn’t use pumps, but used the engine’s induction system, a hose from near the carburettor on petrol models and from the butterfly valve before the inlet manifold on diesels. The diesel engine produced less suction than the petrol, so has a vacuum “reservoir”. The butterfly valve is notorious for problems, so the system can be unreliable. Installing an electric vacuum pump, or an alternator with integrated vacuum pump is a good upgrade. You’ll certainly need a reliable vacuum system and servo assistance for disc brakes.


  10. Kevan Bunting says

    Hi Nick
    Thanks for the response, mine is a diesel.
    Tell me more of the alternator with integrated vacuum pump upgrade.
    Also are you aware of an electrical conversion?
    Thank you

  11. You have a few options. You can refurbish the existing vacuum system, fit an electric pump, fit a mechanical pump, or fit a combined alternator and vacuum servo.

    Keeping it standard is easiest in terms of avoid fabrication and research, but is the most maintenance demanding. Set up is reputed to be fiddly, but I have never worked on the system.

    An electric pump would be easy to fit, mounted anywhere convenient and powered from the battery by a relay controlled by the ignition live circuits. The down side is that it may consume a significant amount of the puny output of the standard SIII alternator, so you might need to replace that with a higher amp capacity unit (simple swap).

    Fitting a mechanical pump avoids any electrical work, but you’d have to fabricate the bracket that holds the pump on the engine.

    The final option is the combined alternator and pump, one mounted on the back of the other and driven by the same pulley, avoiding changes to the fan belt geometry. These have been used on many modern cars, including some more modern Land Rovers, but I’m not sure which.

    You’d need to visit an auto-electrical shop to see what they have and the prices to determine the best option, but I’d opt for the electric pump and a 65a or higher alternator (from a 90/110 would suffice) or the combined unit if it will fit the existing alternator bracket.

    Sorry I can’t be more specific.

  12. Kevan Bunting says

    Hi Nick
    This info is most useful.
    Appreciate all the info, I will keep you posted which option I go with and hopefully it may be of help to others.


  13. Sorry I couldn’t be more specific, Kevan, but as the engines I installed had vacuum pumps fitted, it’s not a problem I have ever had to look into.

    Good luck, and please do get back with your solution.

  14. hi ive rebuilt my series 3 on a galv chassis ive put new brake pipes, cylinders, shoes, master cylinder bleed the brakes no end of times but cant get a pedel until 2 or 3 pumps any sugestions please

  15. Hi Phil,

    It could be brake shoe adjustment, as the two most common causes of problems with that adjustment are getting the shoes back to front on the single leading shoe systems (both axles on 88″, rear axle on 109), so the cam won’t engage on one of the shoe’s pegs and it fully retracts with the spring after each application, or certain notorious brands making their shoes with the wrong radius, so they don’t have continuous contact with the drum and flex with the hydraulic pressure.

    If you have dual circuit brakes, and particularly a 109, then it could well be air in the system as they are hard to bleed. The front cylinders on 109s are hard to get more than 50% of the air out, and the PDWA shuttle valve on the chassis’ right leg, below the foot well, tends to trap air.

    You could clear the PDWA valve by cracking the unions at the top of the unit and allowing gravity to work for you. Alternatively, slow and gentle exercise of the pedal or low pressure use of an Ezibleed should fill the unit and allow air out past the threads of the unions.

    109 front cylinders are the devil to bleed, because their bleed nipples are in the sides, not the top of the bores. The only way to get a full bleed is to remove the hubs and the brake back plate from the stub axles, lay the brake plate and assembly horizontal with the pipes uppermost and cylinders and shoes below, then bleed. It’s time consuming but gets great results. A shorter, less effect but usually adequate method is to remove the drums and shoes, clamp the pistons fully retracted with G clamps, and bleed in that condition, but it still leaves a small air gap that might not get fully cleared.

    Good luck – it’s a frustrating job setting up that system.

  16. Hi Nick
    Just doing this set up on my 88
    I have disco 1 axles and discs all around and am planning series 3 tower, disco servo and defender MC
    The question I have for you is re the adapter plate
    when mocking up to keep the servo in original position the servo studs would just slide past the outside of the “walls” of the tower
    Q1 – where did you drill the adapter plate for these studs?
    Q2 – from your description the 8 mm plate is to a) allow the pedal to travel fully back and hence disengage brakes and b) for clearance of the nose of the servo

    Any diagrams of the adapter plate?


  17. Hi Simon.

    I no longer have the drawings or photos. The plate was for two purposes – to act as an adaptor for the different stud patterns and also to allow for the greater length of the input rod on the Discovery servo. 8 mm worked perfectly for me.

    The holes are all based on the very centre of the plate, whih was sized to match the flanges of the pedal box. The central hole is a little larger than the neck of the servo, the four holes to bolt to the pedal box obviously match those on the pedal box itself. I set the two holes for the new servo studs on a 45 deree axis, but it transpires the servo studs are slightly off that line and I ended up with a small twist on the master alignment as a result. It’s nothing more than an aesthetic irritation, though. You would be beter off measuring that angle yourself to get the master straight. I did have to drill ckearance holes for the studs and nuts seciring the servo to the adaptor into the pedal box, but to may be able to use slim nuts and counyer bored holes in the plat so the nuts are immediately in front of the pedal box flanges, recessed into the plate. You would have to cut the servo studs to 8mm length to do this. If tou counyer bored by 6mm and used 6mm thick nuts, it’ll work.

    I hope that helps.


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