Citroen XM Forum

After looking at previous posts I see you have tried toothed belts Dean so my comments are not that helpful!! Regards,Matthew T.

My V6-24 has a toothed belt. Perhaps that's not a reliable statement as it squeaks due to being loose.

The solid belt did seem to be much better and long lived than the toothed belts, in fact, it may have been another tow home had i been using a toothed belt so i will be using my other solid belt when the root of the cause is cured, just got to wait on my new pressure gauge and then i can have a good look and see what is going on.

D

For normal drive purposes and loads V-toothed and V-solid belts are interchangeable.
The advantage of the toothed belt is that it can be more easily wrapped around small diameters (small pulleys - eg alternator), and operate without so much heating due to flexing. Toothed belts are usually less likely to squeak, because less surface area is moving over the polished pulley.

I'm guessing that your current set-up Dean is severely overloading the belt, to the point of rapid destruction.

As you said much earlier, the pump unloaded sends fluid back to the reservoir without problem, so it cannot be tightness or slop in the pump preventing it rev freely. Must therefore be excessive hydraulic load, either by too high a regulator pressure setting, or failure of the regulator to allow excess pressure bleed off back to the reservoir (eg a jammed pressure relief mechanism, or blocked return path).

Brakes and steering working more-or-less ok 'downstream' suggest regulator is set to a pressure which will operate these things ok . . . although I have no idea how much excess pressure the downstream system might take. Possible the regulator is supplying an acceptable figure, but bleed-off back to the reservoir isn't happening adequately, so pressure (pump load) builds up.

The system is not designed to have the pump pumping against a solid obstruction. The pump is capable of moving a lot of fluid into the steering - when it demands it - and a much smaller amount of fluid into the suspension and brakes. When the steering is not calling for its large fluid flow, that flow has to be able to go somewhere (back to the reservoir) - it cannot just be blocked off or obstructed. That's my understanding of it, anyway.

At the risk of sounding silly.... could it be a bearing inside the HP pump? Maybe once it's warm the bearing is heating up, expanding and seizing, causing the pulley to not run and the belt to slip? Again, apologies if this has been mentioned already.

If I was Dean I would certainly be trying another pump, although I agree that the system pressure and any obstructions to the movement of fluid may also need to be checked! With regards, Matthew T.

When I got home last time with no belt I stopped and turned the pump, it turned freely by hand but was difficult to turn at speed, when turned at speed there was a hissing sound that appeared to be coming from the flexi pipe section between the regulator and flow valve, this was difficult to pin down though as turning the pump at speed and sticking my head down the side of the engine at the same time wasn't really possible, it does not do this unless it is hot and been driven a good few miles.
The noise was coming from that area though, I do have a video of the noise I took to ponder over later I could post up later.

Hoping my new gauge turns up today and I can test the regulator output to see if anything is going on there, also want to blow through the flex pipe.

D

Bit hard to make out, especially since the sound seems to go funny when uploading to youtube but you can hear the restricted fluid flow type noise.
https://youtu.be/ZVHCUvADLp4" onclick="window.open(this.href);return false;

D

Dean, I keep forgetting you have an FDV in circuit (after the 5-piston pump).
Could that be blocking?

Just had a look at Peter Russek XM manual, which gives info about this set-up.
Says that 5-piston pump is capable of more-or-less unlimited pressure output . . . so an obstruction downstream of it would make it extremely hard to turn.

PM'd you a Russek link (you probably have it already).

Citroen added flow restrictors in some of the hydraulic pipes and fittings.
These varied by engine type and by model as evolution took place.
The external appearance and fit can be identical while the parts are incompatible.
Examples are flow restrictors moving from pipes to blocks and use of double wall pipes.
There is no marking or list of these variations.
This can make pipe and component swapping difficult.
I found the early model restrictor move in the Tech Notes.
The other restrictors have only come to light when cutting in for replacement pipe.

John