1983 Xj6 replacing brake fluid, tips for flushing lines and bleeding please. Jag vs. U.S. cars

83 xj old brake fluid I’m assuming.no leaks. Drove car after sitting for many years brakes were fine for a few hundred miles then lost rear brake pressure. Started with right rear bleeder valve, bled it properly with no help. Seems to be some moisture in line. I’m going to flush the brake lines. And replace fluid just wondering if procedure is the same on this Jaguar as other vehicles I worked on such as GM and Volkswagen. Any tips would be helpful thank you. P.s. where is the oil pressure sending unit located, haven’t crawled underneath to look yet assuming it’s under the throttle body.

Brake fluid: yes, standard procedure. I didn’t exactly flush but kept going until clear and needed a quart for all 4.

Sending unit is the can bolted into the block aft of the oil filter. Idiot light is smaller can at the oil filter housing. Below the throttle.

If car has been sitting for a long time, brake system should be flushed with denatured alcohol to ensure all moisture is removed.
Do one caliper at a time, vigorously pumping brake pedal to ensure any loose foreign matter is also flushed.

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Brake flush is fine and, as others mentioned, nothing unique about the task on your Jag.

I’ll just mention that sitting unused for many years is hard on brake systems. If you haven’t already, brace yourself for the possibility that more work may be needed. I can almost promise it.


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Thanks to all for the help.

Very short history on me…
I’m kinda the Florence Nightingale of clapped out P.O.S. Jags. Jag’s destined for the crusher. At the time of purchase, all were “no runners” of one sort of another, then I breath life back into them. After their breathing again, I discover I quickly discover not only are they “no runners” their “no stoppers” too.

Currently, I’ve got

  • one Series I XJ6 - it’s pink. Don’t judge me, It’s a Series I. It came with spares parts & all the bright work - re chromed :grin:
  • one Short Wheel Base Series II XJ6 - It’s white - This car and I have history. There’s a post about it on the board someplace.
  • two Series III XJ6, and
  • three XJ-S’s, a coupe, a convertible, and a cabriolet
  • one XJR-100 isn’t included in this list. I runs, it stops, it will pin your head to the seat. Not my favorite Jag.
    Does the quantity of Jag’s make me an expert? Not even close. Someone who’s got a problem is probably more appropriate.

OK, back to brakes - short version
Not to be Debbie downer, but if your pedal still isn’t firm, then may be (more than likely) (it’s been my experience) time to replace / rebuild the master cylinder. It’s pretty simple to replace. Bench bleed the master cylinder before you put on the car, it will save you a bunch of time.

For what ever it’s worth,

You might want to consider going back with DOT 5.1 (NOT DOT5).

DOT5.1 is compatible with DOT3 and 4, but is synthetic, has a higher wet and dry boiling point, and absorbs less moisture (which is how problems start in the first place). It still needs to be changed, but it’s a better fluid - thinner viscosity too.

~Paul K.

Get a Mity-Vac pressure bleeder - enables you to do it single handed with minimal wastage. Just have to order one with the correct reservoir cap . Highly recommended.

The only other point I have relates to not bottoming the master cylinder piston on bleeding. If you’re going to try with everything as is, bottoming the piston - into depths it does not go for bleeding can cut the seal up if there’s crud at the extremity of travel. No problem if refurbished. FWIW. Paul.

I have an 88 XJS (non abs) that had been sitting for a few years. Similar brake systems, i think, to your xj6 with rear inboard brakes?

My brakes were not great, and rear calipers were sticking. Fluid looked old. No cutting corners with brakes!

So I replaced the master cylinder (cheap and easy), both front rubber brake lines (easy) and single rear rubber brake line (harder). I also replaced rear pads (ugh!), and pushed those calipers all the way back with bleeder nipples open, a lot of crap came out. I then used my Motive pressure bleeder and ran 2 quarts of synthetic Dot 4 through it all.
A month later bled them again with two quarts.

Brakes work great, and fluid looks great!

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Hi, well I actually read all of your original post just now.
First off, I replaced all of my bleeders with speedy bleeders. These bleeders have a check valve inside so stuff comes out, but doesn’t get sucked back in, and you can do it by yourself - it’s like being married. The only downside if there is chunks in the system, the chunks will clog the bleeder. Nothin is free

Unlike GM products (which i have a few of 96 Impala SS & 70 Camaro RS/SS, 3/4 Ton Suburban, Sonoma Pick up) where the division is from right to left via a portioning valve. On a Jag, the division is front to rear. There are two chambers in the master cylinder the front half is for the front brakes and the rear half is for the rear brakes. Hence the two pipes coming off the master cylinder.

Again, unlike GM products, there is 1 brake line that feeds both rear brakes which splits off at a T fitting between the two brake calipers, mounted on the IRS sub-frame (aka cage). each rear brake caliper has two pistons, with a cross over pipe providing fluid to the other half of the caliper.

According to the Jag manual, the left caliper piston should be removed to drain old fluid. I do have a Jag manual that indicates how to replenish the brake fluid, I can send you a copy of these pages.

Anyway, start at the wheel farthest from the master cyl which is the left fill the tube with brake fluid, put a tube on the bleeder and stick the other end into a jar filled partially with brake fluid. then go to town.
then do the right rear, then the front farthest from the master cyl and lastly the front closest to the master cyl.

Speedy bleeders. I swear by them.


Hey thanks , haven’t done it yet probably would have if it wasn’t for the fact that the driver’s rear exhaust is pushing rate on the bleeder and I couldn’t get a wrench on it so I decided I’d wait till I got it on a hoist. Put 1500 miles on it since that post without doing anything so it’s not too bad. I can tell there’s chunks because sometimes it works like showroom brakes other times the front grab better.

If there’s lumps, there’s water, change it! It can fail suddenly.

If you have the car high enough to crawl under, take your jack with you and push the exhaust away. Make sure the loop is in the hanger in the top of the IRS!
As said before I did it in about an hour or two on my own with the onboard jack, four blocks of wood, a spanner, a jar and the hose from the fuel pressure regulator.