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Car Forum / Jaguar Cars / July 200588 XJ 6 Lost power brakes
The power boost has failed on my 88 XJ 6- self levelling suspension still works fine, and the fluid in the pump is ok- Any one know of some simple tests to determine the problem area? Thanks in advance. Most likely, if the fluid levels are fine but you are getting no boost -- the accumulator is gone. A simple test is to start the car and bring it all up to operating levels. Turn off the engine then pump the brakes. The pedal should not get hard for at least 15-20 pumps If it does, you will have to replace the black ball located on the right side of the car tucked up above the suspension. You can only see it from underneath. Webserve > The power boost has failed on my 88 XJ 6- self levelling suspension still > works fine, and the fluid in the pump is ok- Any one know of some simple > tests to determine the problem area? > Thanks in advance. Thanks, I tried your suggestion, and I have no power with motor off, so I am guessing the accumulator or maybe the booster. I think I will break one of the lines going into the booster to see if there is pressure. > Most likely, if the fluid levels are fine but you are getting no boost -- > the accumulator is gone. A simple test is to start the car and bring it [quoted text clipped - 9 lines] > > tests to determine the problem area? > > Thanks in advance. On the '88 XJ40, the accumulator IS the booster!! Unlike vacuum/air boosters with a separate servo, the XJ40 uses a liquid booster system. The pump on the front of the engine creates the pressure when the engine is started. It builds pressure in the system to between 1200 and 1500 PSI, When you step on the brakes, this pressures is released to assist in the braking process. The accumulator is simply a Nitrogen filled ball with a rubber diaphragm. Over the years of use, the HSMO (mineral oil) permeates the diaphragm and releases the Nitrogen and thus the pressure. If you are getting no power assist when the engine is off than this is most likely your problem. The system is designed so that in the event of engine failure whilst driving you will still have power assist with the engine off to aid in braking. I am surprised, however that you have no warnings as to low pressure on the dash. Webserve. > Thanks, > I tried your suggestion, and I have no power with motor off, so I am [quoted text clipped - 14 lines] > > > tests to determine the problem area? > > > Thanks in advance. There is a boost cylinder between the pedal and the master cylinder, which gets its pressure from the accumulator, so I need to determine if there is pressure coming from the accumulator to this cylinder. I do have the low pressure warning, but my digital dash also gives me a series of warnings about various other faults which are non-existant- I thnk that is an issue with the electronics. > On the '88 XJ40, the accumulator IS the booster!! Unlike vacuum/air > boosters with a separate servo, the XJ40 uses a liquid booster system. The [quoted text clipped - 39 lines] > > > > tests to determine the problem area? > > > > Thanks in advance. If you are not getting pressurized brakes with the motor off for 10-15 pumps of the pedal, it is the accumulator. This is the standard test for the accumulator. Amazingly, when I got my '88 5 years ago, I had 7 warnings at one time or another. Not ONE of them proved to be false. Some proved to be because of faulty solder joints but there was a cause for the warning. I now have 208,000+ miles on the clock and no warnings except for those that are supposed to appear at start-up or those that actually are warning of a problem. Webserve > There is a boost cylinder between the pedal and the master cylinder, which > gets its pressure from the accumulator, so I need to determine if there is [quoted text clipped - 51 lines] > > > > > tests to determine the problem area? > > > > > Thanks in advance. I have heard of the solder joint issue, that may be my problem, because all my lights are working, brake fluid up, washer full etc, but still get the warning light. By the way, my car has 287000 on the clock with the original engine/trans. It is really an amazing piece of work, because the car still runs tight and smooth. There is another good support group at www.motorscarsltd.com as well. I may try changing the accumulator if I can find one at a reasonable price- just hate to start replacing parts and find its the 900.00 pump that's out. > If you are not getting pressurized brakes with the motor off for 10-15 pumps > of the pedal, it is the accumulator. This is the standard test for the [quoted text clipped - 67 lines] > > > > > > tests to determine the problem area? > > > > > > Thanks in advance. I think if you ask Phil Prince at Motorcars Unlimited, he will say the same thing regarding the accumulator. It is an Extremely common problem with the '87, '88 and '89 XJ40 with the Girling braking system. Also go to www.jag-lovers.org and search the archives for "accumulator" You are best off searching the Moderns group since your symptoms were discussed for months, 4-5 years ago. Get an after market unit. They generally run $250-$300 depending. You want the JLM11659 NOT the JLM1904. The JLM1904 is for the 1990-1994 Teves system and won't work on your 3.6 litre. I bought mine from these guys http://www.prestige-spares.com.au/ back in 2001. I bought the JLM11659R because it was less AND it is rechargable. It also carries a slightly higher pressure so the pump cycles less. Current price is $192USD plus around $10USD shipping. I would think you can get the same deal or close here in the States. Another easy test, although not AS easy, is to pump the brakes til they get hard and then simply remove the accumulator. You will lose very little "Green Blood" Take a pencil and with the ERASER end of the pencil, slide it into the opening. If it goes much past the threaded collar and into the ball itself, you need a new accumulator. With 1200 PSI on the other side of the neoprene diaphram, the eraser should hit rubber nearly immediately after entering the chamber itself. In terms of the problem being with the booster -- it is possible -- but I doubt it. I have yet to hear of a booster being a problem with these cars, but I am sure someone - some where has had the problem. The accumulator, however IS a common problem. In terms of doing re-solder work. I have often wondered, after spending time on these cars, how the Brits keep aircraft in the air!! Usually, if you are having a bulb failure warning, it is the module that needs a re-solder. Anti-lock is usually the tall relay by the petrol inlet in the boot. Pads low usually means the wire has broken on one of the 4 sensor wires. The clock re-setting to 12 is re-solder. Usually anything involving a circuit board can be corrected with a re-solder. Well, I went ahead and bought a new accumulator from Motorcars and installed it- still no power brakes. I did the pencil test on the old unit and it was dead- pencil ( piece of wire) went in all the way- must have 2 problems going on I noticed that I was getting some vapor from the fluid reservoir, and pulled the little cap and depressed the check valve- there is fluid right up to the top- how do you open that cap to look in the reservoir? > I think if you ask Phil Prince at Motorcars Unlimited, he will say the same > thing regarding the accumulator. It is an Extremely common problem with the [quoted text clipped - 32 lines] > wires. The clock re-setting to 12 is re-solder. Usually anything involving > a circuit board can be corrected with a re-solder. I am sorry to hear that the accumulator replacement did not solve the problem. It was the easiest and most likely solution. First off, do not try to open the Green reservoir tank. It is designed in such a manner that there is an adapter made by Castrol that comes on the HSMO bottles that pushes in the check valve to fill the tank. Replacement of this tank will cost you hundred(s) of dollars. What you must do now is try to figure out which component of the system is not operating properly. If the Rear shocks are going up and down as they should, then that is an indicator that the pump is working and building pressure. My next thought, therefore is that if the pump is working and we know the accumulator works because it is new, then the pump must not be pressurizing the accumulator/power assist system. This would indicate that the charging switch is not operational. It is one of the two switches that were in your way when you changed the accumulator. What I have done, is I have posted the hydraulics section for the '87, '88, '89 XJ40 on the web. Go to http://www.jag420.com/jag%5Fxj40/ and download the pages and print them out. Click on the little picture and it will bring up the full size version for printing. These are from the Jaguar service manual CD. Page 66-02 is a drawing of how the system operates and what the components are. The rest of the pages are the manual section I hope this will help. Webserve > Well, I went ahead and bought a new accumulator from Motorcars and installed > it- still no power brakes. I did the pencil test on the old unit and it was [quoted text clipped - 3 lines] > the little cap and depressed the check valve- there is fluid right up to the > top- how do you open that cap to look in the reservoir? Thanks, After I ran the car on the freeway, it built some pressure, but it goes away in slower driving. I am thinking that I may be low on fluid, probably when the diaphragm failed on the old accumulator it pumped it full of fluid and the nitrogen went into the system ( maybe the vapors I see). I will see if the local dealer has a bottle of that miracle fluid and try to top off the system. > I am sorry to hear that the accumulator replacement did not solve the > problem. It was the easiest and most likely solution. [quoted text clipped - 35 lines] > the > > top- how do you open that cap to look in the reservoir? Got the 20.00 bottle of wesson oil and all seems to be working now, but still getting all the warning lights about low fluid,low pressure etc- that must be in the dashboard solder loints. > Thanks, > After I ran the car on the freeway, it built some pressure, but it goes away [quoted text clipped - 48 lines] > > the > > > top- how do you open that cap to look in the reservoir? Silly question time Earlier you said the Green reservoir was full -- now you say you put more oil in. I am confused. Usually BOTH the low pressure warning as well as the low fluid warning are indicators of not enough fluid in the reservoir. There is a clear cap on the top of the reservoir that a red indicator floats in. If this is red, then you need more fluid. Some time you can't see the indicator. The reservoir takes a LOT of fluid. Chances are you may have to replace the hose from the reservoir to the pump as it takes a lot of heat from the engine and this mineral oil has a propensity to bleed through the hose after all these years and you won't see a leak. Generally, at this point, I would recommend Barr's power steering stop leak -- just as a routine maintenance item. MAKE SURE you get the stuff made for HONDA power steering systems as they use the same Mineral Oil as the Jags and it won't hurt the system. Webserve > Got the 20.00 bottle of wesson oil and all seems to be working now, but > still getting all the warning lights about low fluid,low pressure etc- that [quoted text clipped - 63 lines] > > > the > > > > top- how do you open that cap to look in the reservoir? Thanks for the tip on the Honda stuff- I figured the Jag used some off the shelf type of oil with some food coloring added to up the price. Previously I had just pulled the little filler cap off and there was fluid , so I though it was full. > Silly question time > Earlier you said the Green reservoir was full -- now you say you put more [quoted text clipped - 95 lines] > > > > the > > > > > top- how do you open that cap to look in the reservoir? I have a funny feeling that if you add another liter or so, the warnings will go away. There is probably a leak some place so be prepared for the possibility of a small "Green Blood" puddle!!! Keep the Castrol bottle so you can use it over and over again with the reservoir adapter. Webserve > Thanks for the tip on the Honda stuff- I figured the Jag used some off the > shelf type of oil with some food coloring added to up the price. Previously [quoted text clipped - 113 lines] > > > > > the > > > > > > top- how do you open that cap to look in the reservoir? |
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