Hello, just picked up a 1993 XJS 4.0 with inboard brakes. The rear brakes are sticking so I am going to replace the hose first. Two questions: 1) I see only one hose, is that correct? 2) I also only see one bleed fitting and its on the driver side caliper. Looks like the path of brake fluid comes in to the passenger side caliper out the crossover to the other side of that caliper, then out of the passenger caliper over to the driver side caliper, through the crossover and the last remaining port is the bleed fitting. Hoping this is OK and someone hasn’t modified the brake hard pipe.
That is why working on the inboard brake system is such a pain.
Finding and bleeding the bleeder screws is a chore at best.
Also, after locating them, getting a wrench to them is a PITA.
Even using a lift doesn’t make it easy, but it does make it possible.
Keep looking for them and you will eventually find them.
Hi Travis, this is a picture of the rear on my '88 car, showing the correct brake lines. You can see the bleeder, covered with a rubber cap, close to the exhaust on the RHS of the photo. Similar bleeder on the other caliper.
Thanks. My brake line comes from the passenger side and goes to the passenger caliper. It does not have a tee with separate lines to each caliper like the picture. It is not set up like the picture and all four of the ports on the top of the passenger caliper have tubing coming out. On the driver caliper three ports have tubing and one has the bleeder.
Ah. I’m guessing that it has an ABS setup, then. Sorry.
Any difference in piping would not be related to ABS since the ABS is only 3 channel.
I need to ask as I can’t connect the dots no matter how hard I try. What replacement of flexi hose has to with seized calipers?
There shall be only one flex hose going to rear subframe (T-piece, then to each caliper)
There shall be bleeding nipple on each caliper.
Have fun, just make sure you’ll have someone close - to mentally suport / during rear brake strip down…
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Technically the rear brakes should be fed from parallel pipes, but in series will still work.
ABS pipework.
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I think the O/p suspects the flexi may have collapsed internally, stopping the flow of fluid.
Assuming there is a genuine one still fitted - no chances/unless kinked visually. Seized brakes are notorius here, won’t release/spring back.
Internal hose split will affect performance/force applied (easy to diagnose/differentiate).
There is plenty of fun related to disassembly of IRS’s inboard brake calipers. Brings back memories, bloody knuckles, tears and rage…
That is correct. I have seen this in two other cars I’ve owned where replacing the flex hose has resolved the problem. The hose looks fine but has deteriorated internally.
Not the same symptoms. You can distinguish between both problems easily.
Stock flex hoses in XJS are truly finest quality, these shall be changed every 5 years. Surviving 40+ under 'JagLover’s ownership, with corrosion on metal elements only. This shall be replaced anyway, so no need to debate…
So my hose did not come in today. I spent lots of time on the forum and found that a faulty Pressure Delay Valve could cause the rear brakes to lock. This thread was helpful:
I found the pressure delay valve under the hood and eased off on the downstream side fitting, the one that connects to the line to the brakes. As a drop of fluid came out of the threads the car suddenly rolled back. I found that I could put it in neutral and roll the car easily. I tightened the fitting, started the car and pressured the brakes. When I slightly loosened the upstream fitting and relieved pressure the rear brakes stayed locked and the car would not roll. I ultimately removed the pressure delay valve and connected the two brake lines together. Several trips around the block and no issues with the rear brakes. I will keep testing and take apart the pressure control valve. But wanted to include this update in case others have this problem too. XjsBanger seems to be right about the hose.
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These are usually going bad only on very neglected systems… Haven’t seen one going bad, ever. The chances of finding working one/second hand are over 90%… your donor brands are covering Ferrari, Aston Martin, Saab and Volvo. Suggesting full system flush before other bits will fail… You’ve got ATE mk3 by the way. I have never seen this pressure stepdown (simple reducer 25bar) disassembled but by the look of it - it is doable (if possible - keep us updated, with photos), guessing there is an aluminium washer in between the hex housings. This is somehow very good news (no tears under rear craddle). Just don’t try to brake while taking turns, as per now - you have full capability of your pressure accumulator on the rear calipers…
An excellent find and result.
I have taken the liberty of adding your thread to the Teves III brake system thread, as it provides useful information for others.
You may wish to peruse that thread as all the information you need for the Teves III system is there.
You will need to cut through some “guff”, but the main issues with Teves III are lack of fluid changes causing corrosion and stuck components, such as ABS and pressure reducing valves, and flat accumulator.
I’ll create a cut down version of the thread as a Teves III How To thread, once a few fixes have been performed.
Many people have binned perfectly good Teves III systems due to peer pressure from some posters that couldn’t understand how it functions.
The pressure reducing valve will have a pintle and seat controlled by a spring. The pintle should seal once pressure rises too much, yours appears jammed in the closed position, or just gummed up.
The O ring is just to seal the hole from dirt admittance.
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Thank you Dieselman! I have not broken the pressure reducing valve down yet but plan to soon.
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