Steering shudder on braking

mvcoller
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Re: Steering shudder on braking

Post by mvcoller » 11 Mar 2018 11:40

Clem, which are the bolts/nuts you tightened? Mind placing a picture of it and a description of how to reach it?

I can feel there is a tendancy towards that wobble on my Patrol. When I first got it, with the 16" steel wheels and BFG ATRs 265/70 LT 16s is was really bad. On a trip to Nelspruit, down Schoemanskloof it was so bad, it felt like I was going to loose control of the vehicle as I needed to slow down for a corner. I could not get off the brakes at the time. When I got off the brakes, all returned to normal.

Not long after that, I replaced the rims and tyres with 17s, and it has nearly all gone away. I can't say why, but at times when going slowly, I can feel a movement starting to develop on the steering, but as I get to about 40kph, it goes away, and that same slight movement sometimes comes back under braking.

Thanks

Malcolm

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Re: Steering shudder on braking

Post by Clem » 11 Mar 2018 12:20

Hi Malcolm,

If you stand in front of the vehicle, directly in line with the steering wheel (looking towards the windscreen) and you look down, you will see the steering box just behind the headlight (which is the right hand side headlight of the vehicle as you sit in the driver's seat). On the underside of that steering box, you will see the Pitman arm, from which the steering rod runs through to the left wheel. On the opposite side of the Pitman arm (in other words, the top of the steering box, which you are looking at) you will see a nut (size 17) in the centre of which is a slotted screw (it sits in the centre of four bolts that hold the top cover down). That is what you use to adjust the steering box. You will probably find it easiest to get at the nut if you loosen the rubber shield which runs around the steering box behind the right front wheel. If you pop out the forward three retaining plastic plugs, you should be able to fold the rubber screen back such that you can access the nut. If you loosen the nut about half a turn, you should be able to rotate the centre screw with a flat bladed screwdriver. Everything is normal right hand thread. By tightening the screw, you tighten up the steering box, by loosening the screw you loosen the steering box.

I first tested the amount of play in the steering shaft running from the steering wheel through to the steering box. This I did simply by grasping it in my left hand and rotating it quickly backwards and forwards in order to ascertain the amount of play. There was a fair bit but not what I would consider totally excessive but certainly enough to create a little bit of slop. I tighten the steering box to reduce this so that there is now still only a very small degree of play. Once this has been done, then obviously the locknut needs to be tightened. I must warn you though that you may need somebody to hold the screwdriver and hold the slotted screws in place while you tighten the locknut through the wheel arch.

Be very conservative as to how you progress the tightening of the screw. I would not recommend under any circumstances progress in more than half a turn (180°) at a time before test driving the vehicle, preferably less. Remember that what you are effectively doing is reducing the lash between the gears and forcing the internal gears more tightly together; as a result, excessive tightening will increase the wear rate on the steering box. If one gets silly, you can literally break things. The correct way to do it is on a bench with the correct torque measuring tools and so forth; doing it the way that is reflected in this series of posts is really a little bit of an "bush mechanic's approach".

As I say, I tightened mine about 75°. Probably 90° may have been enough but it seems fine with 75°. The steering feels a little bit tighter (just noticeably, not significantly) and as I say, I am still able to easily steer the vehicle when there is no power assistance. I probably would not have done this without first eliminating every other possibility but for the fact that (a) the car is very low mileage (46,000 km), (b) the issue with the vibration feedback (in other words minor death wobble) has been present in the car since brand-new and (c) since brand-new there has been a noticeable amount of free play in the steering wheel – with the engine off, you could with one hand move it backwards and forwards and hear the "knock knock" on either side of the range of movement, which strikes me as rather unusual when I compare it to other modern vehicles. Peter's note really triggered this point in my mind at a different level by connecting the two dots for me, viz. the play in the steering wheel and what I was occasionally experiencing uncertain road surfaces. After adjustment now I can still rock the steering input shaft with my left hand through an arc of a few degrees, which tells me that there is still a very little bit of lash between the gears, so they should not be binding.

I also suggest you note the position (perhaps mark it) of the adjustment screw before you tighten it so that you can return it to the original position should your adjustment not solve the problem you are looking to solve. Should my adjustment not solve the problem in question once I have tested matters over a more meaningful period of time, I will definitely be returning the adjustment screw to its original position (which in my case is absolutely parallel with the wheel arch).

I hope this helps.
Last edited by Clem on 12 Mar 2018 17:50, edited 6 times in total.

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Re: Steering shudder on braking

Post by Clem » 11 Mar 2018 12:28

Malcolm, here is a site with a useful explanation that will give you a mechanical understanding of what is going on. See the discussion about "sector shaft" and "gear mesh load". From this you will also understand why I am expressing the need to be conservative. Your Nissan patrol GU steering box may not be absolutely identical but it is sufficiently similar for the principles to be applicable.

http://www.stangerssite.com/HowItWorksSteeringBox.html

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Re: Steering shudder on braking

Post by Clem » 11 Mar 2018 13:37

I've just taken the car for a spin on the freeway and the problem persists. So I've returned the steering box to its original setting. Next thing is to skim the discs.

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Re: Steering shudder on braking

Post by mvcoller » 11 Mar 2018 16:27

Thank you Clem for that detailed info. I have just checked my steering with the engine turned off, and the play on the steering is negligible. I won't fiddle with the steering box as am am convinced the problem does not lie there.

It may just cause more problems rather than rectify anything. :biggrin:

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Re: Steering shudder on braking

Post by Peter Connan » 11 Mar 2018 20:50

Sorry to hear that Clem.

I must say, I find it a bit strange that the problem still persists after all you have done.

I have found that the steering box in my car (I am not entirely sure if they are all the same) has a "tight spot" in the straight-ahead position. Because this is exactly where the wear should be greatest, I believe this is a "design feature", and it should be set up that you can just feel this "tightness" when turning the wheel with the front wheels jacked up and the engine not running (IE no power assistance).

Note that, if you do over-tighten it, it becomes almost impossible to un-screw the screw. I have found that, if this happens, get somebody to turn the steering wheel while you apply rotary pressure to the screw.
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Re: Steering shudder on braking

Post by Clem » 12 Mar 2018 18:00

Well Peter, at least we're eliminating possibilities. But it's strange to me that this all only became apparent after the ARB and OME 20mm lift fitment though it could be coincidental or I simply wasn't paying enough attention before.

The GQ and GU steering boxes are essentially similar but from what I read GQs are often upgraded with GU boxes.

The tighter centre point is indeed a design feature of various steering boxes it seems. From what I read I deduce that this is to create a more firm steering setup in the dead ahead position. This would make sense on the open road for example while one wants lighter steering while navigating corners etc at low speed. In fact cars without this feature can be a bit scary on the open road - in.my experience anyway!

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Re: Steering shudder on braking

Post by Pieter B » 13 Mar 2018 20:53

For what it's worth, the steering box for the Hardbody is similar in dimension and mounting points as the one for a Patrol

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