Steering Pull following lay-up

[Addiston]

I've just got the car back on the road following lay up over the winter. Throughout the winter it was up on stands and hasn't been fiddled with.

Back on the road and MOT'd it's pulling to the left, but not consistently. Tyre pressures checked and re-checked, with as usual 26 front and 30 rear. No evidence of brake binding. My feeling is that it's the PAS rack or valve in the pump assembly? (The rack has always been prone to leaking a bit and needs topped up occasionally. It leave the occasional drip whilst parked up in the garage, but never any more.)

Thoughts, before I look at a rebuild and if so, who can you recommend. (I want my own rack back, not exchange, as the car's very low miles and hasn't been messed with).

Thanks

[andyborris]

Daft question...Are you sure it's pulling to the left, not just following the camber in the road? And because you haven't driven it for a while, it seems strange?

Might explain why it's not happening all the time.

[Alec]

Hello David,

have you had any tracking adjustments made, as if it is not done correctly and the rack is off centre when straight ahead it can cause the power side to activate and try and steer?

Alec

[Mike Stevens]

I would not have expected the PAS to do this. You can try removing the PAS pump belt and then see if it pulls. Be careful, the steering will be very heavy!

I would be more inclined to check brakes, wheel bearings and tyre pressures- which I think you've done. And as Andy says, could it be the camber of the road?

Also look at the strut top bearings and bottom ball joints. If one has become stiff, it might cause a pull.

I've had PAS on Triumphs since the early 80s. I think the only faults I've had were leaks and the fact that the steering gets very light when the rack gets older. I've not had a rack fault that made it pull.

Cheers,
Mike.

[Alec]

Hello Mike,

it's not specifically Triumph, but if the rack is not centralised with the wheels straight ahead, it can start to open the valve that allows oil to assist the steering, this could explain the inconsistency of the fault as road camber varies and it could be that some roads will cause the pull while others do not? There is some margin of error but tracking work over the years can allow the rack to be off centre, as very often tracking adjustment is only done on one side.
Just one of the possible causes that is worth checking.

Alec

[Jonathan Lewis]

According to the manual, steering assistance starts to be deployed at one half-degree of deflection of the torsion bar linking steering column and rack spool valve, with full assistance being attained at four degrees and direct mechanical drive at seven, so you wouldn't need that much in the way of off-centring to the rack to induce this.

Still a bit of a mystery, however, if nothing on the car has been adjusted since the car was last used, assuming the pull was not present then? Various other possible causes as already suggested, though I doubt that the relief valve in the pump will be one of them, as this only operates to return excess fluid under low demand conditions, irrespective of which way the rack is pointing.

[Addiston]

Thanks to all have responded.

I had wondered about the camber of the road issue, so I think the first thing is a trip down to the M9, which should generally have less of a camber.

After that, I'll have a look at the centering of the rack, which I hadn't realised could go off centre over time, which would explain why I feel I'm fighting the car a bit, particularly if the PAS is kicking in. I presume ther'e something in the manual about centering the rack?

The strut top bearings were renewed in the last few years and the car doesn't do much mileage, but if all else fails will open up for a look

If it has the decency not to rain, I'll know in the next few days... but the forecast suggests it might take longer.

Regards

[Jonathan Lewis]

Hi David,

I think that you will find that the issue of the rack going off-centre usually tends to be one of disturbance (either caused by unequal adjustment of tracking, as suggested by Alec, or by removal and refitting of the rack itself) rather than any progressive deterioration, hence my comment that I thought that it might not be the cause of your problem unless something has been adjusted or disturbed.

There is a procedure for checking rack centralisation by removing the small screwed plug in the centre of the thrust plunger on the bottom of the rack casing (i.e. diametrically opposite the steering column tower) and using something like a centre punch to align the drilling in the thrust pad with a dimple in the rack itself. I think I'd try the other obvious possibilities (especially road camber) first, however!

One other possibility - especially if the steering action has become in any way 'lumpy' - could be a stiff or binding universal joint in the upper steering column causing the linkage to attempt to realign itself; in my experience, the presence of the rubber joint can sometimes mask the onset of problems with its mechanical equivalent.

Good luck!

[Mike Stevens]

I used to think that if the PAS rack wasn't centralised you'd get a pull, but I'm not so sure now. The control valve works by correcting a difference between its input and output shafts. So if you put a bit of turn into the steering wheel, there is a difference between it and the control valve output shaft so some power assistance is applied to the rack itself to bring the control valve shafts back in 'step' again. Because of this, I don't think it matters (pull-wise!) if the rack isn't centralised.

My PI rack is not centralised. I get more turning circle one way than the other but it doesn't pull. It's come about due to some oddity that shows itself as the outer ball joints not screwing onto the steering rods the same number of turns each side. I've not got to the bottom of it and my expert next door (ex-garage owner) set it up for good tracking alignment and 'feel' on turns. I still think it's wrong though!

A stiff steering column as mentioned by Jonathan will often give a tight feeling every 180 degrees of steering wheel turn. Been there and done that!

Road camber and/or a stiff upper or lower strut bearing would be one of the first things I'd look at!

Cheers,
Mike.

[Addiston]

After monumental rain all day Sturday, it dried up early Sunday evening. Did a short trip with the PAS discosnnected. Yes - it is very heavy at low speeds! This made no apparent difference and the pull was replicated, but not so pronounced when driving up the wrong side of the road. So looks like a little bit of camber influence, but something else is up.

Poking around underneath, the PAS rack mount bushes have definitely been adversely affected by weeping over the years and a little side to side movement could be obtained with a pry bar.

The plan now is to re-check all brakes / bearings and joints, rule out a stiff stering column joint (evry 180 degrees), fit new PAS rack bushes and then get wheel alignment checked. We'll see how it develops from there.

Thanks again for all your comments / guidance.

Regards