Hairline split in TVR PAS rack

[shpub]

The day after the LS1 powered Cerbera gets its MOT, I have just experienced the strangest of faults. The PAS rack is leaking fluid through a hairline crack in the main casting, parallel with the TVR stamping. There was a large "cracking sound", the steering got heavy and then the fluid started to leak. There are several small micro cracks on either side and the fluid just ouses through the ally. It looks like the ally has simply failed.

The setup is using a Renault Kangoo electric PAS pump - similar to that of the Saxo/Citroen 106 used as a replacement pump and in the later T cars - but I can't believe that the pump could develop sufficient pressure to crack the casing. I would have thought that too high a pressure would have simply blown the seals. The pump has a 40A fuse so again I would have thought that that would have gone had the pump gone into overdrive.

The only thing I can think of is that the casting had a flaw which weakened with age and eventually gave up - possibly with the pressure from the PAS pump. The pump has been performing fine over the last few months so this has not been an instant failure.

Has anyone experienced something similar before?
Anyone know what pressure the pump puts out?

I am going to measure the pressure before the repaired rack goes in and if necessary, limit the pressure but this is very wierd. I don't know if I was really unlucky or there is something else is at work.

[Le TVR]

Local Renault mechanic seems to think they should be good for 150 bar maxi.
Cant imagine that the seals would have held that.
What metal is the rack cast from then?

[shpub]

Thanks for the info.

If it is then that is higher than the engine driven pump which is around 75 bar.
The rack is cast from ally but I have to say it is not the best casting I have seen.
As I said, I would also have expected the seals to have gone first.

Current thinking is a controller for the pump to limit the pressure and also make it speed sensitive.

[GreenV8S]

Is the crack in a place that could have been mechanically stressed at some point? Perhaps it's a mechanical problem rather than hydraulic. It seems unlikely that hydraulic pressure would ever be high enough to burst the casing and if it did I'd expect it to go with a huge bang.

[shpub]

It is right at the top in the middle of the ram cylinder, about 5 mm up from the TVR etc embossed part number. Unless you know what you are looking for, you can't see it - it's that fine. The engine can't physically hit it and there doesn't appear to be any damage. The way the fluid is leaking is very much like a porous bit of casting but that does indicate that there has been a manufacturing flaw that has weakened it. You get porous engine blocks, how about porous steering racks?

There was a loud crack when it went but that doesn't help with the " was it too much pressure" or a "weakened/damaged bit of ally casting"? It could be a bit of both. The flaw made it weaker and the higher pressure finished it off.

As racks are scarce to get, I don't want to wreck a second rack if it is a pressure issue.