Steering relief valve?

[sh4kes]

A couple of weeks ago I noticed my steering wheel wasnt returning to the same position after being on full lock. Not really think about it and not having any time to look at it, I kept driving it. Then, going through a roundabout one afternoon I lost all steering (spun the steering wheel, no movement at the wheels).

I got her trucked home and pulled out the steering box - sure enough, it was a sheared shaft inside the box. (It sheared right above the gear teeth on the shaft.) So I ordered a new Adwest box, and fitted it a couple of days ago. As part of the process I was bleeding air out of the system and turning lock-to-lock. However, on full lock the PAS system seems to really bog down (the sound of the steering pump suddenly gets very audible until I take it off full lock).

So now I'm wondering if the whole problem was caused by a failed relief valve in the power steering pump? (i.e. too much pressure meant the shaft sheared.) Anyone else have this problem, or have any ideas? And if people do think it might be the relief valve, any help on how to check it out?

[Blknight.aus]

if the relief valve goes you blow the seals out of the box, blow the hoses apart or blow the seal out of the pump. Ove pressure doesnt snap the sector shaft.

The sector shaft normally fails from impact loading, stress fractures through a wear point and bad assemlbly.

[Jode]

It's normal for the pump to sweat when on full lock - you'll hear the engine labour and the pump complain, as the PAS pump has to work harder (pressure increases). IIRC the driver's manual says that full lock shouldn't be held for more than 30 seconds.

[Sitec]

IMO full lock shouldn't be held for more than 1 or 2 seconds.... Get the steering to full lock, then back just enough to stop the pump labouring.. Lost count of how many times I see someone puling in or out of a car park whilst hanging of the wheel (with that look of horror) in the hopes that it'll turn sharper... belt squeezing, pump labouring.. Surprised to hear you sheared a shaft tho!

[sh4kes]

Cool, thanks guys. Would rather not have to buy a new steering box again haha ;p

Yeah i had a bit of a look around the net sitec and I could only find one or two cases where people have documented it. It looks like it was half sheared at some point (straight shear lines), then me going to hard lock (for much less than 30 seconds mind) has sheared the shaft rotaionally through the other half. Im suprised too though given the size of the shaft!

[Bush65]

I agree with what Dave said.

I very much doubt it failed from over pressure.

If it was a failure due to overload, such as a heavy impact, the sector shaft will twist and bend, but rarely shear. The failure plane will be very rough/jagged.

From your last post it was a classic fatigue failure over many loading cycles.

If the failure was across the diametrical section, the fatigue was mostly cycles of side load from the drag link. If it was at 45 degrees, then the fatigue was mostly cycles of torsional load.

Suspension lift reduces the fatigue life of sector shafts, by changing the angle of the drag link, therefore increasing the magnitude of the side loads.

It is a fairly common failure of sector shafts in Landcruisers and Patrols when they have big suspension lifts.

[sh4kes]

https://www.aulro.com/afvb/images/imported/2013/08/27.jpg (http://www.iforce.co.nz/View.aspx?i=mjbanbaf.pd2.jpg)
https://www.aulro.com/afvb/images/imported/2013/08/28.jpg (http://www.iforce.co.nz/View.aspx?i=1osvhvot.ujc.jpg)
https://www.aulro.com/afvb/images/imported/2013/08/29.jpg (http://www.iforce.co.nz/View.aspx?i=jjvh0kvj.mup.jpg)

No suspension lift - it looks like the first half shear is at an angle, so might have been from an impact under the previous owner, then ive sheared the half shaft at full lock. Interesting. Thanks for your input lads.