Repairs, Uncategorized
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Jaguar XKE E-type Restoration: Brake Master and Slave Cylinders Part 3

Ok – now that I knew the brake master cylinder was trashed I decided to try my luck with the slave cylinder and the attached vacuum servo and see if that unit was rebuildable.  To open this unit up and inspect the seals, rings and cylinder you have to first split the large sheet metal shell of the vacuum servo. Inside that is a a large rubber diaphragm which uses vacuum from the engine intake manifold to provide power assist to the brakes. The two pieces of the shell are held together by a set of pressed in indents  one one side and ledges on the other and have to be twisted apart.

E-type vacuum servo shell separated and rubber diaphragm and support

Now twisting the vacuum servo apart requires securing the cylinder in a very large vice, attaching a bar to the exposed mounting bolts on the outside of the shell and exerting considerable counter-clockwise torque to get the two halves of the shell to slide. Once the indents are clear of the tabs the units come apart. Once the unit was open I could see a lot of brake fluid inside and on the rubber diaphragm. That told me right away that the slave cylinder was leaking fluid into the vacuum servo. That also meant that the fluid would have traveled through the vacuum hoses and was probably in places like the vacuum tank. I will tackle that issue later.  The slave cylinder was certainly leaking – but was it rebuildable? To find out I had to further disassemble the unit.

Bolts securing vacuum servo to slave cylinder on Jaguar E-type.

The next step in disassembly is to take the assembly off the vice, remove the rubber diaphragm and then push on the hard plastic diaphragm support to remove pressue on the spring and shake out the metal split-key that holds the support and shaft. Once that is done you can remove the support and get at the three bolts that secure the vacuum assembly to the slave cylinder. They have locking tabs that have to be bent down to remove the bolts. You can now remove the push-rod and piston assembly and clean and inspect the slave cylinder.

Disassembled Jaguar E-type XKE vacuum servo and slave cylinder

The moment of truth had arrived. Time to see if the slave cylinder was usable or if it was like the brake master cylinder – in need of replacement or resleeving….

Upon inspection, sad to say, the slave cylinder was also corroded and deeply pitted. This makes getting a fluid-tight seal impossible and means the unit must be resleeved or replaced. So much for saving money and using a simple bebuild kit….

Corroded and pitted Jaguar e-type slave cylinder. Resleeve or replace.

Once I knew that both the master and slaver cylinders were corroded and pitted I looked into the cost of rebuilt and resleeved units and brand new units. This was a no brainer. I found that I could purchase brand new units cheaper than I could purchase rebuilt and resleeved units. For the brakes on a car like a Jaguar XKE it makes sense to go with the new – and presumably reliable units. So I ordered the new brake master cylinder and servo-slave unit up.

10 Comments

  1. I’m really enjoying reading your blog. I’ve just started the search for a 2+2 E-Type, after selling my 911. I also have a ’74 914, which will now be pressed into more regular service until I find an E-Type. Your experience with master/slave brake units reminds me a lot of a similar escapade I had with those units on an MGB GT I restored – I wished I’d just bought new units right at the outset!

    Great stuff!

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  2. Gary Devenney says

    I was noticing in the picture that the corrosion and pitting of your slave cylinder is on the taper of the sleeve (very top). I thought that the only critical part would be the bore itself. The rubber seals are on the other other side of the pitting and corrosion. Am I missing something?

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    • gmmacdonald says

      Hi Gary – Take a careful look at the first picture (I think you can click and blow it up). You can indeed see rust outside the seal area – but below that you can see a huge kind of divot and then rusty scratches and then below that you can see corrosion pitting (just barely visible as low down the shaft as you can see). There were the big problem areas on the master. So, the cylinder got replaced rather than simply having new seals installed with a rebuild kit.

      On the second cylinder – the servo slave cylinder in this post – it had scratching down the shaft – but I am afraid the shot I took looks only black inside in this view. I do recall that some of the pits were in the sealed area also – but it was a while ago and I cannot recall exactly on that one. I suppose my feeling would be that if the exterior of the seals was badly corroded I would be super careful to make sure the cylinder inside the seals is super clean and smooth. As these are critical components my thought is that no amount of care is too much.

      Good luck!

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  3. Ryan says

    Gents. Thank you for the blog and the dialogue. I recently picked up a 73 E-type series III. Found in Nebraska while attending my girlfriend’s grandfather’s second wedding. shipped to CA. Arrived with break fluid leaks and break pedal travelled to the floor. I’ve been trouble shooting with a jaguar mechanic who works on E-types with some reluctance – one mile from my residence. We are stuck on one issue in particular. There is a significant amount of break fluid leakage – and appears that the fluid is being pushed up through the top of the bottom reservoir. The top reservoir will show fluid loss or fluctuation although the bottom reservoir stays relatively full (despite the leakage). And although the fluid is in our belief coming from the top of the bottom reservoir- it is dripping from where the hose meets the reservoir tank (otherwise the bottom, probably as subject to gravity). We replaced what I understand to be the two working mechanisms referenced in your blog (break master and potentially slave cylinder plus new hoses/lines….blead the breaks). Any thoughts or suggestions that may come to mind based on your rebuild experience would be welcome. Forgive my lack of expertise-have only spent one weekend to date under the bonnet. My mechanic as well is looking for/open to advice. Despite the initial set back-the E-type is incredible. Tks-Ryan

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    • gmmacdonald says

      Hi Ryan – sorry for the late reply. I have been traveling for work. Hey. congratulations on the E-type! Enjoy! Now to the brakes… there are cases where bad seals in the master cylinder can force fluid between reservoirs. In your case it seems different – are you 100% sure the fluid is being forced upward and through the top of the reservoir? Can you completely rule out a crack in the reservoir or a problem in line coming out? Judging by all you done in terms of component replacement and bleeding I am a little stumped and ask you to make 100% sure the reservoir does not have a hidden hairline crack etc.

      In any case – the fact that pedal sinks to the floor suggests that there is either no fluid/lots of air in the lines/ completely blown master cylinder gaskets. I am not sure about the geometry you describe for the reservoirs – on the V12 there should be two brake reservoirs on different sides of the engine. If you have a clutch (4 speed tranny car) there will be a clutch reservoir next to the reservoir for the master cylinder also. In any case – take a look at the hose coming from the ‘leaking cylinder’ trace it back to the either the master cylinder (small unit that does not have a big metal vacuum chamber) – or if it the other reservoir it will trace back to the vacuum servo unit (large unit) – it will be that cylinder that is shot. You can rebuild both of these if the bores are not shot (see the blog section on rebuilding the cylinders). You can also chose to replace them altogether (not a bad option – and that is what you did…). Wow – you replaced both the master and servo cylinder and the brake lines, led the brakes and the problem persists. I do know that a friend of mine purchased a ‘rebuilt’ master for a series II car and had a similar problem to yours with the rebuilt unit. I also had to return one new master cylinder unit as it was defective out of the box. You may be unlucky with the new unit you bought and it is ‘pre-blown’. If you are sure your lines are 100% correct in how they are hooked up – and there is no blockage in the high pressure line coming out of the offending cylinder (since you were able to bleed the brakes I am assuming you had pressure coming out at the calipers and the lines are ok…. I am at a loss. I go back to either a bad reservoir or a bad cylinder or both.

      Any one else have the solution? If you are in southern California I can recommend some specialists to have the car towed to. In any case – don’t despair the car will be a blast when this is sorted.

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  4. jose franco says

    Hello i have got and etype 1972 v12
    and i have a poblem every time i used the car after 30 miles my rear bracke loks,
    any one got any idea?regards joe

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    • gmmacdonald says

      Hi Joe –

      It is almost certainly one of three things – one cheap and easy and the the other two more time consuming and expensive. First, it is possible that the flexible rear brake hose has collapsed – when you apply the brakes it is enough pressure to send through the fluid, but the return flow does not fully clear the pressure on the calipers. There is one flexible hose that connects the braking system to the metal piping in the rear subframe that feeds the calipers. You can change this without dropping the rear cage and differential etc. However…. it is possible that the reaction valve at the front of the master cylinder or the shuttle in the vacuum servo unit that actually powers the brakes has gone bad. You will need to remove and test/replace. These are both on the engine side of the bulkhead – so access is ok. Trouble is they are expensive components and if you simply replace them and it does not fix the problem you may not be too happy (on the other hand you have some new components…). You can do some bench tests once they are off. I have heard that a brake line flush and change of fluid sometimes can help with this problem. If replace the rear hose you will want to do this anyway. Finally, you may have frozen pistons in the rear calipers. As you use the brakes and they heat up they may alter enough to stick locked against the pad. If it is the pistons you will have to drop the rear suspension cage to work on this – a big job in general. In any case, all of these fixes will require you to bleed the brakes etc – and getting to the rear caliper bleed nipples is a bear (I pull one of the shocks on each side to make it easier.

      If you are not comfortable with brake work I might leave this one to a pro.

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      • jose franco says

        Wow, thanks so much for this useful info, I thpught it was the server unit, because I drove it last time for 30km without touching the brakes and it still locks , I then have to leave it for 1hr and it clears it’s self automatically.

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      • jose franco says

        Wow, thanks so much for this useful info, I thpught it was the servo unit, because I drove it last time for 30km without touching the brakes and it still locks , I then have to leave it for 1hr and it clears it’s self automatically.

        Like

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