Can not bleed rear brakes

P.S. After thinking about this a lot, I am wondering if the ABS unit or the ABS computer are at fault here. The pedal is not spongy as if the brakes were not bled properly. I have no external leaks. Not at the wheels or down the inside of the firewall. I would think that, even if the brakes were applied for minutes at a time (say at a stoplight and even if the accumulator were bad) the pump would catch up and shut off. It does not. It runs as if one of the rear bleeders was open. As an aside, all the bleeders are on top. So that suggests that there is an internal leak. That the fluid is recirculating somehow. I also do not believe the brakes are releasing properly either. After applying, then releasing the brakes the wheels are difficult to turn as if the pistons in the calipers were not retracting properly. Rears difficult to tell as you are having to overcome the resistance of the differential but fronts don’t seem right. Not in comparison to what I am used to. I have not read anywhere (either here or other forums) where the computer is a problem. The ABS unit itself seems to be a problem when it sets up for an extended period of time. Again any thoughts/help is much appreciated.

dldstrock

Nobody has any ideas/help? I really could use some help please.

dldstrock

Buy a set of speed bleeders?

That could put your mind to rest as to whether there is air still in the system.

Have you got brake accu on the abs unit ormounted separately on the other side??? Your accumulator sphere should be fine. Have a look in here to check if the entire accumulator assembly works fine: https://www.xjsbanger.co.uk/jaguar-xjs-brake-accumulator-diagnostics

Forget about ABS for now. It is possible that one of the ABS solenoids failed open but the chances are residual (as long as you haven’t introduced rubbish/swarf into the brake system). The accumulator pump kicks in due to air in the system.

On my car the accumulator screws into the side of the pump itself. I am not going to get a chance to work on the care until next week. Monday or Tuesday. I will perform the tests you suggested and bleed it some more and report back.

Thank you for the reply,
dldstrock

I want to give everyone some further information about our brake accumulators. About this system I am still learning. About accumulators I am familiar with. I am a retired aviation quality control inspector. I have worked on small Cessna aircraft to the heavies with Continental Airlines and I retired from Bell Helicopters. As you know aircraft use all kinds if accumulators.

So this is what I have found out about our accumulators after days of internet investigation. Before beginning I must include the usual disclaimer. This is information I suspect is true and some I know is true. I will tell you which is which. Use it for what you think its worth and be responsible for your own actions. I give absolutely no guaranties.

First there are the ones you can buy from Classic Jaguar. Then the ones from eastcoastreatta. Obviously Jaguar has them under their part number and eastcoastreatta has them under the AC Delco part no. I have read the they both buy the Hydac unit, rebadge them, mark them up and sell them. Both for 650$ ish. Is this true? I don’t know. Can you buy the Hydac (p/n 305-5720) unit from Hydac? Is this the part no? I don’t know. I have several e-mails in to this company in the past month with no replies.

Second you can buy the Bosch unit which xjxbanger has verfied works, or a Wabco unit (p/n STC2784). The Wabco unit was installed on Range Rovers of the same era. It is somewhat larger in size so you get some extra capacity. Both of these units can be purchased from Amazon for slightly less than 200$. I purchased the Wabco unit. I can verify that the thread pitch is the same and the thread depth is the same. The operating pressure is slightly less 200bar, but that is only 5% less than the Jaguar one. Obviously our system is going to pressurize the accumulator to 210 bar. But you should be within the safety margin of the Wabco unit. Use at your own risk! I have read of several people that state they have used these with success. I have yet to get my system bled out properly but it should work.

Thirdly. Can these units precharge be renewed? Yes they can. There is a gentleman in PA that has been renewing the precharge for years. His web address is http://www.audibombs.com. He charges 75$ plus a 13$ shipping charge. I plan on sending him one of my dead ones to have as a spare. Now if the bladder/membrane (whatever you want to call it) is bad, the unit is dead. If all it needs is a precharge he can do that. He services all the respective accumulators not just Audi.

Again this is information only. The use of it is your own responsibility. Own it. It is a sad thing I have to say this, but in our litigious society… Any replies given in a respectful, considerate manner I will reply to. Any others I will ignore.

dldstrock

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I had to replace the accumulator in my '94 a week ago and went with the Bosch unit (p/n 0265202070), ordered through Amazon from RM European Auto Parts for $95, shipping included. So far so good. I had previously replaced the accumulator 16 years ago (2005) with an AC Delco unit.

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I did all of this research about 2 months ago. I saw the Bosch accumulator on line and looked at some pictures of it and wondered if it would work. I though could find no one who had tried it. I could find people that had tried the Wabco. So purchased it and truth be told probably would have even if I had known the Bosch would work. I like the idea of the reserve capacity. I am fighting getting the brakes to work as designed. Because the car sat up for 6 or so years, everything brake related was corroded. Disks rusted; only one of the calipers worked. So, as I had thought the system was bled properly, good pedal etc., I was wondering if something else was wrong. ABS part of the system for example. xjsbanger seems to think that I need to continue to bleed the system, that there is air remaining in the system. So I am going to follow his diagnostic advise and then bleed some more. Hopefully I can get it to work properly.

dldstrock

Those speed bleeders I mentioned earlier are pretty foolproof, just sayin’

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I saw that in one of your posts. I have used Bryan_N bleeding procedure with somewhat of a twist. As I live alone, wife died and kids live in another state, I mostly have to do things on my own. For the rears I wedge a long screw driver between the front seat and the brake pedal. Then reach in through the door and turn on the key. Engine off, key on. Then I open one of the rear bleeders for 60 seconds or so. Then close it and either let the pump build pressure and shut off on its own or turn the key off. Let pump rest and repeat. For the front, I purchased a pressure pot years ago to bleed the brakes on a 740il I owned. Into BMW’s then. Still like them. Anyway it seems European car builders must buy their brake parts from the same vendor as I have yet to find a European car it will not work on. So key off I pump the pot to somewhere between 10 and 12 psi and bleed the front brakes. It has always worked before. If you all know of some reason why this will not work on our Jaguars please let me know.

dldstrock

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I have had some health issues and have had to suspend working on my XJ12. I am now about 75% and have resumed working on my car. I am still having brake issues. I followed XjsBangers tutorial and I believe the braking system components are good. I think. I really do not understand why I cannot seem to get the system bled out and in a way do not completely understand the system. In the braking systems I am familiar with the master cylinder has a return port in it so when you release the brakes the fluid returns to the reservoir. When the brakes are applied the master cylinder blocks this port so brakes can be applied. If the Jaguar works in the same way, why when the brakes are applied for an extended period (like at long stoplight) does the pump run and why does it need to. If the return port (if the car works this way) is blocked when the brakes are applied it should be a (in essence) hydro-locked system. The fluid has no where to go so the brakes are applied for as long as you foot is on the pedal. When you release the brakes on the Jaguar and the pump runs to recharge the accumulator then shuts off, the fluid must be locked somehow, I would think. Please excuse my ignorance I am just trying to understand the system. With understanding perhaps I can get the system to work properly. At the present time as soon as I push the brake pedal the pump runs. I have bled and bled and bled at least a gallon of fluid and the brakes are still not correct. At wits end, don’t know what to do next. If there is more air in the system how does anybody get it bled out?

Do you have the part number for the speed bleeders? I have had some health issues and am now just getting back to working on my car.

dldstrock

Speed bleeders are widely available, Amazon has them but lots of other sellers do too. If you google “speed bleeders” you’ll get lots of hits.

here’s the maker’s site:
http://www.speedbleeder.com/

dldstrock, this is what I bought after consulting them on the phone. They didn’t have my car on their list so I had to call them.
Last time I bled the brakes (Jan. 2022) I turned the ignition in the 2nd position.

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Thanks. I googled speed bleeders and no one seemed to know or have the correct thread pitch. I have a friend coming over this afternoon to help me bleed the brakes again. I fail to understand how it could be so hard to get the air bled out of this system. Other than trying the speed bleeders I do not know what to do next. I read earlier in this post that some one replaced this system with the vacuum boost system out of an XJ6. I this a viable modification? Is it a straight bolt in replacement or is fabrication necessary? Not unfamiliar with fabrication. I have been doing it is some form or fashion all my life. You cannot work on cars without some fabrication necessary at some point. If I cannot get the system bled out in the near future I am going to look at alternatives. Don’t know what, but really want to drive/use the car and it is not safe the way it is.

If you look back ONE post to Joe’s picture, the label has the part number you need (SB8124L -SS) and that the thread is M8 x 1.25 - plus the phone number to call to order them.

Larry, the number after the 812 is 5 not 4 as you wrote. But if I were dldstrock, I’d give 'em a call just in case.

Thanks Joe, getting sloppy in my old age LOL

Hang in there Larry!
I checked speed bleeder’s website and they still don’t have any Jaguar on their list. And I ordered my screws from them in Jan. 2012.

A few yrs back I replaced a “regular” bleeder with one that fit from a Mercedes …(although it was a bit long, it was the same thread)