Hello,

My power brake unit is starting to go. The red "BRAKE" light has been going on and off intermittently; usually when I step on the brakes, but not always. Also the "Anti-Lock" amber light has been taking longer than usual to go off when I start the car.

This morning, I had no power brakes and FUSE 6 (30 amps) was blown. After I replaced the fuse, the power brakes returned, but I know it's just a matter of time before the fuse is blown again.

Would appreciate references for websites where I can order a rebuilt power brake unit?

 

Hi,

Do you have any leaks or any other symptoms? A fuse blowing sounds like a short/electrical problem rather than the booster. Also, what's the VIN and size of engine, there's a few variations to the system dependent on the engine and VIN#.

 

Hello Rob,

No visible leaks, brake fluid reservoir is to the full mark. Had vehicle checked by automotive electrician. he confirmed no shorts, suggested the problem is on the ABS power unit.

Years ago, when the vehicle was still under factory warranty, I had a similar problem. The dealer replaced the ABS Pressure Monitor Switch. But, since this part costs around $600, I'd like to be as confident as possible this is the problem. It may be that this time the switch is working properly and detecting low pressure in the system.

I've located a used unit on eBay and included the pic to give you an idea of what it looks like. This unit is used and has no warranty. I'd like to find out if there is a rebuilt unit available from an auto parts store that may come with some type of warranty.

Below is the vehicle information you requested.

Really appreciate your help.

VIN: SAJKY1743NC650173
Engine: 4 liter inline 6

 

Palmero,

Wish I could be more help to you. I had my system converted years ago because of the repetitive problems with the Jag ABS systems. Take a look at this post:

https://www.jaguarforums.com/forum/x...booster-85830/

This vehicle is in New Zealand and is RHD, but the principle is the same. This guy converted very recently, I think the post is from 12/03/12. You might consider contacting him via private msg and pose some questions.

His conversion is the same as mine, conventional booster and eliminate the dual system Jaguar developed. Here's another post from a few days back from a guy who sounds like had similar symptoms as you:

https://www.jaguarforums.com/forum/x...cm-code-83526/

The reason to give serious consideration to a conversion is because original parts will become more scarce the older these cars get. If you're going to spend $600, you might as well nip it in the bud and be done with it for good.

If you still have the SLS (self leveling shocks) on your vehicle, this is another system that is terribly expensive to maintain and it shares components with the ABS system. I also had the SLS converted to traditional shocks over ten years ago and have had zero issues with the conversion. Use conventional shocks now, and I'm very glad I got rid of the SLS, it costed me thousands to maintain....not kidding... I replaced the SLS struts twice before the conversion.

Again, sorry I can't give you more solid advice as to a direction to go. Search the archive and read up. Also, you may want to pose your questions on jag-lovers.com, in the XJ40 forum. Lots of seasoned members there and the site has been around for a number of years, I think 15 or close to 20 yrs.

Hopefully someone with directly related experience will speak up......

Good luck

 

Palmero:
Hold the phone! Could this be as simple as a failing brake accumulator sphere? It doesn't (at least to my pea-sized brain) explain the blown fuse, but that could also be a coincidence. The sphere on my '91 is failing and the symptoms are the intermittent brake light and occasional ABS light as well. It comes on when the brakes are depressed because the sphere is failing to keep the correct pressure. It obviously comes on at other times for the same reason. Here is the diagnosis procedure which, so as to escape plagiarism, comes directly from (the Great) Bryan N from the 'other' Jaguar website.

''Turn the ignition key 'ON' to position (I) to
operate the Teves pump. When the pump stops, turn the
ignition key 'OFF'.

How many full applications of the brake do you get before
you loose brake boost pressure (i.e. the pedal 'goes hard')?
It is sometimes easier to judge that if you operate the
brake pedal with the heel of your hand rather than the less
sensitive foot and leg!

You should get 25 to 30 (or more) applications of the brake
before you lose brake boost. If you get significantly less
than that, suspect the Teves accumulator sphere and replace
it with an AC Delco part number 25528382. ''

The good news is that Amazon has the part for $100!! The other good news is that if you try this first before replacing the whole unit, you can use the new sphere on the replacement unit. Personally, I'd go with a salvage part from one of the suppliers or perhaps the one from Ebay that you've found... if it's cheap.

Cheers!
Scott

 

Bingo.

Red brake light is a sensor issue on the pads. Yellow taking time to go off mean the ball is filling up, which means there is a leak.

Red and yellow at the same time, is ABS sensor issue or other.

Red with a slight delay before the yellow comes on, it's close but not at the exact time means a pad sensor issue and the brake accumulator losing pressure.

If you have a Haynes manual, it will show you how to test that accumulator. Or search within the XJ40 section....Brake Accumulator.

 

Rob,

I converted the self-leveling system long ago. When it first failed under warranty, the dealer suggested the conversion. I'm glad I agreed, since it was the second time that it had gone back to the dealer due to failure.

I'll consider the conversion you suggested.

Thank you very much for the tip.

 

Hi Scott,

I tried the test you suggested. I get exactly 15 pushes of the brake pedal before it goes limp.

If it is the accumulator going bad, it is possible that the constant running of the motor causes the 30 amp (fuse #6) to blow after a while. By the way, it does this occasionally. It's been running fine for the last several days with a new fuse.

I went ahead and purchased a used unit on eBay for about $122 that the seller guarantees. Once I get it, I'll replace the accumulator first. If this doesn't fix the issue, then I'll put the whole unit in with the accumulator it came with.

If the accumulator is the problem as you suggest, then I'll still have a whole power brake unit stashed away.

Thanks for the tip!!

PS. Does the accumulator sphere just unscrews from the unit? After disconnecting the battery and depressurizing. Never had to change it before.

 

P,
Well, it can never hurt to have the extra parts on hand. Lord knows I now have a box full of them! However, once you get the spare motor, it could also very easily have a worn out sphere. Just thinking...

If you only get 15 pumps, that seems to be too few and is probably the reason both for your brake light and quite possibly your fuse problem. I'm not a mechanic, remember; it just makes sense to me. But I do know that the sphere does just screw off AFTER the system is depressurized. I won't be doing mine now until the spring, but when I do I'll be sure to have plenty of extra rags handy because I've heard there can still be quite a bit of slop.

Scott

 

Palmero, we have the same issue that I successfully troubleshoot and resolved. The blown out 30 amp fuse was cause by too much current being drag by the abs pump. It is dragging the voltage too low that the abs and brakes lights will turn on. I looks like that this system is voltage sensitive.
I test the abs pump and it was confirmed that it is going south. I have this item replaced and now I am back on the road. No more blown out 30 amp fuse. Replacing the accumulator ball and the three relays did not completely resolve my issue. Some says that I had a open ground, ..but none has been confirmed. Eventually, ..you will loose abs and brakes as a whole.
Hope this helps ....

 

The problem was caused by a faulty hydraulic pump relay, a $50 part. Everything's back to normal after replacing it.

It pays to heed Occam's Razor...

Thought I'd post the resolution for anyone who's having similar problems.

Best regards.