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Low brake pressure switch

Eddie_6505
Posts: 82
Joined: Thu Jan 21, 2016 9:38 pm

Low brake pressure switch

Postby Eddie_6505 » Mon Aug 01, 2016 10:15 pm

Hi guys.

So I've been getting the usual low brake pressure warning for a while now and have seen the odd drip of alien blood around the pressure switch. Was hoping to get away with just replacing the seals but the low brake pressure switch finally gave up the ghost resulting in a rather large green puddle. Luckily it was on a mates drive...

Has anyone changed one before? Couldn't find much on here about changing them. Is it a case of depressurising the system and unscrewing and screwing another one in? I've gone for an aftermarket one so I know I'll have to crimp a few wires etc. Am I likely to get a load of the green stuff on my drive? I've bought a few bottles so have enough to be able to top up easy enough.

Regards,
Eddie
1988 Daimler 3.6

Per
Posts: 85
Joined: Thu Jan 01, 2015 7:50 pm

Re: Low brake pressure switch

Postby Per » Mon Sep 26, 2016 5:58 pm

The large puddle indicates it has depressurised itself .....

However do press the brake pedal a few times with engine off until it goes hard. Then it is a case of simply unscrewing and screwing in the new one. I had to hold the body the valve screws into with a seriously big plumbers visegrips. Not much dripping fluid duting the changeover.
1989 3.6 Sovereign

naki_k
Super Moderator
Posts: 28617
Joined: Sun Feb 21, 2010 9:25 pm
Location: Kirton, nr Boston, Lincolnshire

Re: Low brake pressure switch

Postby naki_k » Mon Sep 26, 2016 6:08 pm

Pictures of course always required.
So which switch did you buy?
88 3.6 XJ6 PDH/CEM
90 Range Rover Vogue SE 3.9 V8 LPG
91 4.0 XJ6 Manual
92 4.0 XJR Manual
92 4.0 XJR
93 3.2s - 4.0 Manual conv
93 4.0 Sovereign
93 6.0 XJ81 DD6 x2
93 6.0 XJ81 XJ12
94 4.0 XJR
94 4.0 Daimler
96 4.0 X306 XJR
96 4.0 X300 D6
97 4.0 X300 Sport Manual
2000 LR Discovery ES TD5 A
Breaking 40/ 300

Eddie_6505
Posts: 82
Joined: Thu Jan 21, 2016 9:38 pm

Re: Low brake pressure switch

Postby Eddie_6505 » Thu Sep 29, 2016 6:57 pm

Yeah, bit of a saga this was...

So originally I went for an aftermarket switch from SNG Barratt. Took my old one off and it was clearly past it. When I took it off the back of full of fluid. You can't see it in the photo but it was literally full:
Image

Was on properly tight, no way I could undo it on the car so off came the whole thing. If you think it's fiddly getting it off, just wait until you try putting it back together... Had to take off the liner from the bottom of the spoiler to be able to get my arms/spanners in to undo it all and of course all the fastners were rusted.
Image

Whilst it was out I gave the holder a bit of a clean up and paint although I found they're still available new for less than £1 if anyone needs one

The best way I found to get it all back together was to hold the accumulator sphere with an axle stand to keep the whole thing in place freeing up your hands to be able to screw in the pipe at the top.
Here's the only picture I took before getting it all back together:
Image

Anyway, after wrestling it back together I fired her up and no brake pressure. Hmmmm. It then occured to me that I'd replaced the wrong switch :oops:

At this point I was pretty frustrated to say the least. Even worse was coming back the next day to find a huge puddle of the green stuff underneath. Grrrr. Anyway, I've been so busy at work and the car was stranded on a mates drive I decided to take it to a nearby garage who I know are 'classic car friendly'. Was an experience driving there with no brake pressure but no harm done. Anyway, they refused to work on it. Pretty sure they were scared by the complexity! :shock:

Although they did recommend a jag indy specialist who was literally a 2 minute drive away so I took the car around there. When I turned up the guy had amongst other things a track prepped xj40! Which apparently weighed 1350kg!! :shock: So I was pretty confident the guy knew his stuff. But yeah, long story short, he replaced both switches with genuine items for £300 including labour so pretty pleased with that given each switch is £250 + VAT at JCP. Brakes feel so much better now but not convinced 100% right. Got to love these old cars :lol:
1988 Daimler 3.6

naki_k
Super Moderator
Posts: 28617
Joined: Sun Feb 21, 2010 9:25 pm
Location: Kirton, nr Boston, Lincolnshire

Re: Low brake pressure switch

Postby naki_k » Fri Sep 30, 2016 11:28 pm

Good post Eddie. Most 3.6 by now will have had brake issues of one type or another, I suspect.
There are not that many on here, which may explain why there are not many posts on it.

I suspect your garage must have had some of the pressure switches in stock to do then that much less than the JCP price. Or maybe a local main dealer had them at an old stock price?

So did the part from Barratts not work? I thought you had simply changed the wrong switch?
88 3.6 XJ6 PDH/CEM
90 Range Rover Vogue SE 3.9 V8 LPG
91 4.0 XJ6 Manual
92 4.0 XJR Manual
92 4.0 XJR
93 3.2s - 4.0 Manual conv
93 4.0 Sovereign
93 6.0 XJ81 DD6 x2
93 6.0 XJ81 XJ12
94 4.0 XJR
94 4.0 Daimler
96 4.0 X306 XJR
96 4.0 X300 D6
97 4.0 X300 Sport Manual
2000 LR Discovery ES TD5 A
Breaking 40/ 300