There are only Two Brake Pipes coming out of the Brake Booster which appear to be the same diameter

In the event that is the Case, then why is one of those fittings much bigger than the other if the diameter of the Brake Pipes are the same size, at least that's what they seem to be according to my Micrometer

 

OB
The cylinder has two chambers, one for the front and one the rear brakes. The fittings have different thread diameters to stop people connecting the wrong part of the cylinder to the brakes at the wrong end of the car!

 

Hi Greg

Cheers!

This is interesting, so the way I'm understanding that is that both Brake Pipes are the same diameter and only the fitting is different but since I haven't made any Brake Pipes up yet, which end is for the Front Brakes and which end is for the Rear Brakes?

Do you know if that Bigger fitting is a common size or if not where I can get one

 

,Hi OB,

More importantly why have you got a pre-ABS Brake master cylinder?! Or is it one from a late ABS car that uses a brake servo?

Paul

 

Hi Paul

I just knew you were going to ask me that!

Long Story Short, 'Cherry Blossom' my V12 XJS has been running fine up until I took her for an MOT where I think the Tester may have pushed the Brake Pedal much too hard

As on the way home the ABS Light came on and the Brake Pump was too hot to touch, so I Bled everything not forgetting to do the low pressure side but it wasn't long before the problem returned

She's got a Brand New Valve Block on the Master Cylinder Actuator and also a New Black Ball Accumulator, apart from that I couldn't think of anything else it could be, except I've had it up to here with ABS

So the Plan is to go Retro and Fit a Brake Booster and then see how She feels to drive after that

The ABS on my Grey XJS is working perfectly fine but even so the Pedal tends to lack feel, so it will be interesting to make a comparison to see which I like best, as it wouldn't be a big job to convert it back

And obviously I will be getting my Insurance Companies approval

Though from my own personal point of view, I've never been a fan of ABS

 

What you don't like random dead pedal while driving?? The thrill of never knowing if the system has a full charge until you need it? Personally I enjoy living dangerously. Not to mention the ABS pedal shuttering on bumpy or gravel road its like flying an airplane as its crashing.

 

It's amazing what stays with you from your younger days. The first cars and trucks I learnt to drive often had brake issues, and you always drove in case they did not work when you applied pressure to the pedal.

I still drive like this - foot off the accelerator way before the lights or stationary vehicles. I tried to teach this to my kids when it was there turn, but since they have always had dependable brakes, it was unsuccessful. Now when the kids drive and I am passenger - I still hit that imaginary brake pedal, way before they slow down

 

OB
The brake lines are the same diameter. All fittings are available. Totally agree about ABS. I have driven XJSs with both systems, and I find non ABS far better, proper feel, dependable, easy to fix and diagnose. Also there is so much more feel that getting into a four wheels locked and sliding situation has never occurred in 21 years of driving the car.

 

Hi VancouverXJ6

When the ABS that was fitted to my Car was Brand New, then I'm sure it worked wonderfully well but 29 years later not so much! as even though I have replaced the Valve Block with a New one and also fitted a New Accumulator

The Brakes have let me down too many times, nearly spinning me off the road on a couple of occasions but even on my Grey XJS where the ABS is working fine, there isn't any 'Brake Feel' and you only need a very gentle touch of the Pedal to Stop you

One of the Problems being that many of today's MOT Stations have a TV Screen, to instruct the Tester what to do and one of those instructions is 'Brake Hard' and if a Tester were to put his full weight on the pedal, then maybe that's the reason why the brakes are not working now

My Merc has a Brake Booster System and I always feel safer driving that Car than I do my XJS with ABS

 

Hi Greg

Cheers!

I'll pop down to my local accessory Shop and see if they've got one but which outlet is for the Front Brakes and which one is for the Rear Brakes?

 

Hi Bez74

I drive exactly the same as yourself and have been for as long as I remember

 

OB
Frontmost goes to the front brakes, rearmost to the rears! Also, in a correction to my email to you, BOTH go to a connector just below the m/c on the inner wing, so connecting up is pretty straightforward, particularly if the scrap car still has the two brakelines from the m/c to the connectors. Even if they are shot, it gives something for the brakeline maker upper to copy.

 

Hi Greg

Cheers!

Just got to give the Brake Booster a bit of spit and polish, before I connect it up!

 

Hi OB,

I sort of guessed that was probably the project!

I've always bench-bled master cylinders with a reservoir attached before fitting to the car and connecting the pipes. Just to make sure that you've got functioning seals and air removed from the chamber. Be careful, that fluid really spurts out when you press the actuating piston!

Also, I assume that you've sourced a servo / booster from the same scrap car? If so, perhaps it would be a good idea to change the vacuum pipe etc for new items to try and mitigate any problems with the servo functioning. A servo-ed system without the servo / booster working is very hard work and a disconcerting feeling when you're trying to stop!

Awaiting the next update.....

Good luck

Paul

 

Hi Paul

I never thought of 'Bench Bleeding' that sounds a great idea, of the kind that I've come to expect from yourself and who knows it may come to that, if my Insurance Company don't seem to be loving the 'Retro' idea, quite as much as myself

As Bench Bleeding is the only thing that I haven't tried!

It not so much that I hate ABS as the ABS on my Grey XJS has never been a problem and long may that continue but when it suddenly Stops working instead of Stopping the Car, the feeling that you get from that is not exactly great

Do you think its possible that if the MOT Tester really pushed hard on the Pedal, it may have messed up something in the Master Cylinder or maybe I am just imagineering?

The only thing I do know, was that everything was working well, up until after She had that MOT Test

As for the bits and pieces for my 'Retro Project' apart from a New Vacuum Pipe, is there anything else you can think of that I may need?

 

OB, i do not think that pressing the pedal, however hard, could break the system if it was 100%. I suspect that something else has given up. I do not know the system at all, but, for example, if it has a master cylinder, maybe that has gone bad, etc etc.

As for the bits you need to do the normal servo'd brakes, as well as the m/c, bits of brake pipe to plumb, and servo unit:

• Wing supplementary vac tank
• Steel pipe from that to the manifold and servo take off, and hard-walled rubber linking hoses
• Manifold take off fitting and non return valve

I think that is it.

 

Hi Greg

Is the supplementary Vac Tank absolutely essential, as I didn't come across one when I taking the Brake Booster off the Scrap Car and my Merc doesn't have one either, also where is the 'Non Return Valve' as I've got no idea what that looks like or where to find it

 

The non-return valve is in the large diameter flexible between the manifold take-off and the hard line it joins to on the bulkhead.

The vac tank is in the front wheelarch under the headlight nacelle, and the special steel line (black in photo) comes from it along the bottom chassis rail, with a short T off to the servo (in the photo with a bit of paper on the end to keep out dust etc) and after a short flexible joiner (clearly visible in the photo) it goes on round the bulkhead to join the manifold flexible takeoff tube. In the photo it is the black tube, the manifold flexible is the one hanging down at the top of the photo, and non-return valve is dimly visible on it if you look carefully. Without the non-return the servo WILL NOT WORK, as at wider throttle openings the vac will disappear. All these bits are on the scrapper, or on some other one, so why not do it all as per factory?
I would fit it all. You can then state that the brakes are exactly as factory pre-ABS. Do you need it, who knows...

 

Hi Greg

Cheers!

Good advice as usual and today we went out to get some more parts off the 'Scrap Car' but couldn't get to the Vacuum Tank at the moment, as the Car is up against a wall, although its still on the wish list

What we've rounded up so far is:

(1) Brake Servo with Master Cylinder

(3) Special Low Profile OEM Reservoir

(4) Vacuum Manifold with the extra outlet for the Vacuum Brake Booster, which the Car that this is intended for hasn't got

(5) The Non Return Valve

Have we got enough parts there to take the Car for a drive round 'Orange Blossom Towers' and if it works then add the Vacuum Tank later, just as soon as they can get a fork lift to move it away from the wall

 

I would say so! What is this about the reservoir? AFAIK, I think the only one that will fit is in the OEM position - is this what you meant? Just in case not, below some snaps. The actual factory one leaks like a sieve, so I used an aftermarket dual-exit one, complete with a low level warning light switch, from Car Builder Solutions. Miles better!
The OEM position is on a bracket bolted into the servo top two fixing bolts that extends inboard where the actual reservoir is sited, under the cross brace. Get off the scrapper this bracket, the reservoir and, most important, the feed lines from the reservoir to the M/C. Even if they are shot they are a good guide to making new ones. remember you must use brake fluid proof flexibles, ordinary petrol lines will not do.
Greg