I just bought a 1988 XJS with 73,000 miles that the brake light is on constantly. When I was driving it the 120 miles home the brakes were working fine at first but after about 20 miles when I pushed the pedal down it went all the way to the floor. The car did stop. After a few more miles the brakes returned to normal then about 30 minutes later the problem came back. It did this on and off all the way home.
Does anyone know what could be causing this problem?
Could it just be in need of having the lines bleed? Is this something I can do myself. I am not a mechanic but I have worked on several cars in the past. Can someone recommend a good manual for this car because it didn’t come with any?
Thank You

 

Not going to try and diagnose your brake problem because I'm no great mechanic either. The factory manual (plus parts list) is available on CD from Jaguar Heritage and I think Coventry west and a few other places. Not terribly expensive either. The hard copy is available on the web from places like Faxon but is about 100 bucks.

Oh, and welcome to the site.

 

I had similar problems with my XJS, if you look at the brake fluid, there is a screen cover in the reservoir, pull that out and mine was filled with congealing fluid. Looked a lot like clear jelly. Also, my Brake light was on constantly too, never found the cause of that myself haha. Just be warned, if/when you have to change your rear brakes, they are one hell of a process. Especially when you compare them to changing brakes on any other car.

 

As far as a manual is concerened I would agree that the CD from Jaguar Heritage is a good investment, but I would also recommend downloading the excellent publication by Kirky Palm. If you google the author then the title 'Experience in a book' you will be directed to the appropriate download.

With specific reference to the brake light remaining on I would advise looking at the brake light switch. There were different types, depending on the year. One which I have experienced is found at the top of the brake pedal and the switch opens (light on) when the brake is depressed and closes (light off) when the brake pedal returns. This may need adjusting to ensure that the switch closes when the brake pedal returns. Try pulling the brake pedal fully back by hand and see if the lights go out.

If not it could result in a new brake switch.

 

Sounds like you should replace the master cylinder, all three flexibles, and change the fluid. The master cylinder seals do not last for ever, and good advice safety-wise is the change them every 5 to 7 years. Then while you are bleeding the brakes, you can also take a look at the pads and calipers to see if anything leaking there, too. Once this is done, if the brake light still comes on, check the float that activates/deactivates it in the reservoir top, it may not be floating!

Greg

 

HO! my jag did the exact same thing when i bought it. i made it about 20 miles through the WV mountains and the identical **** happened.

i ended up opening the reservior and swirling around the filter and it never happened again.

 

I agree with Greg....most likely a master cylinder.

What's the history of this car? If the brake system is original don't be surprised if one or more of the calipers is in need of overhaul.

Other than reaching the nipples on the rear calipers bleeding/flushing the brake system is the same as any other car. No special tricks.

To emphasize the obvious I'll say that repairing a erratic or stuck warning lamp and repairing the actual brake system are two very different things :-)

Cheers
DD

 

Heres something you might find interesting. in BBC Top Gear series 6, episode 2 "cheap coupe's that arent porches challenge", the same exact thing happened to James May's £1500 Jaguar XJS once he had reached Oxford. He susepcted the master cylinder as well.

 

A sticking piston, (or two) especially on the rear calipers that never get much attention, could be heating up the fluid to boiling, so causing the sinking pedal syndrome. The fluid vapourises so the pedal is pushing against vapour not fluid. When the system cools down it's back to normal, (for a while).

This happened to me once and I was too young and naive at the time to spot the problem, until I got more smoke out the back wheel arches than a steam locomotive, whilst on a holiday journey. The heat carbonised the caliper piston seals too. Cost a lot of money to fix !!

 

idk about the OP, but my fluid wasnt even hot. but again im certain that it was simply an issue with the reservoir filter.

 

Firstly before we can help in diagnosing the problem we need to know if the car has ABS or not being an 88 it could have this fitted.

There will be a black ball type object about the size of your fist on the passenger side firewall, and the car will make a wizzing sound from under the bonnet when you turn the key on.

 

definitely rebuild your master cylinder...theres nearly no reason to get a new one

 

Sounds like either a M/C or brake fade. The light can also be on from low fluid or a bad low fluid sensor. Easy enough to test, disconnect if the light goes out that is the source of the light. However if the brake pedal goes to the floor I would spend time sorting that out before driving it again. You can buy a rebuild kit and do it yourself. However many times the cylinder is pitted and needs to be bored and sleeved. Brake fluid attracts water so there is a very good chance the cylinder is corroded. If this is the case your calipers are in the same shape. Replace or have the M/C professionally redone with a stainless sleeve. Rebuild the calipers using new pistons and install new brake hoses. Since brakes are a major safety item I would not cut corners on good enough repairs.

 

The first time I had mine out it did something similar to this but without the brake light. Mine had been sitting for awhile and some rust built up on the rear caliper and caused it to stick on. Once I got it loose it never did it again.

 

Last night I took the reservoir screen out and cleaned it. I drove it for about 15 minutes in the city and the brakes seemed to work fine but the brake warning light was still on. Tonight I will remove the tires and check for any problems at the wheels.
If the light doesn't go out and the brakes still work should I still consider working on the master cylinder? Is this something I can do myself without major problems? I have ordered the service CD and I think I will wait until I get it before trying to take on this task. The car does not have ABS. I have not checked the sensor yet but will tonight.

Also, I have noticed a few other minor problems that need addressed.
1) Radio has "CODE" on the display and does not work. Where do I find the code?
2) The hood struts are bad. What is a good brand to buy? There are several out there.
3) The cover behind the seats that goes over the top when it is down is missing. Can they still be purchased and from where?
4) The cruise control doesn't work. Without the manual I may be setting it wrong. Does any one know the proper procedure to set the speed?

I want to thank everybody for their help. I have learned a lot about Jaguars in the last 2 days that I have owned this car.

 

its called a parade cover. a quick search might yield something.

 

I think you should absolutely definitely change the master cylinder and flexibles if they have not been changed in the last 5 years or longer. The light coming on is nothing to do with the pedal going to the floor, IMO. What happens is that as it gets warm under the hood, the rubber in the cylinder piston gets so soft that the fluid goes round the edges when you press the pedal. As it gets cooler, it seems to recover. But this is a BIG accident waiting to happen, I believe. Also change the flexibles. None of this is too expensive to do, and if the master cylinder walls are OK, new rubbers will do it, just make careful notes of EVERYTHING you take out and the order and orientation it came out in! Even a brand new master cylinder is not absolutely too expensive, considering the danger involved.

To set the CC, if you have the old fashioned original Jaguar column stalks, press in the small oblong button on the end of the LHS column stalk (direction indicators stalk), making sure the resume/off switch on the tunnel by the gearlever is not set to 'off'. If the CC does not work after doing this, it is a bit of a sod to chase down why. I suggest a separate thread for that!

Your car is about the time the stalks were changed for Ford units (much better made!) so they may be the more 'chunky' looking ones. But I believe the button is still on the end of the LHS stalk, but cannot be sure. Remember touching the brakes will deactivate the CC.

Greg

 

rebuilding the master cylinder can be done in literally 30 minutes depending on how fast you can bleed brakes. Took longer for me because i cleaned it off and repainted mine.

Hood struts?? Not a big deal, brand doesn't really matter.
mine were busted when i got my car so i got them on ebay the brand is "uro" which ive had alot of little things from like the struts, oil pressure sender, hoses and have had good luck with all of it.

the code is in the manual.

the cruise control may be bad, the bellows probably leak now.

 

greg he has an 88 it should be the button opposite the cigarette lighter on the center console.

 

Cruise control repair info

Cruise Control


Cheers
DD