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Hydraulic Steering


najw
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There still seems to be some uncertainty about the legality of full hydro steering.

As there are some MOT bods around here is there anything that states that a vehicle must have a constant mechanical link between steering wheel and wheels?

In other words is full hydro really legal on an ordinary PLG vehicle?

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my take on it for what its worth is based on the hurdles Ive jumped to get petal a legitimate ticket with a seriously officious tester.

as far as our MOT tester is concerned the test called for checks on play and operation. It doesnt call for the tester to make engineering assessment - merely follow a bouncing ball. Ive subsequently been told by another source that there is a specific sentance in the MOT testers manual that calls for a "mechanical link throughout" but oddly I cant find it in the manual and neither can my Testing guy - can someone please tell me what page this is on?

construction and use regs call for a mech link but these arent taken into consideration for an MOT. Previous incarnations of hydro steer meant that in the event of motor or belt failure you were left with no steering - an offroad expert confirmed this to me and even after turning my motor off and cycling the steering to prove the point that its not the case with modern systems he still told me it doesnt work with a dead engine. thwack.

agricultural and construction vehicles limited to 26mph do pass construction and use with full hydro.

wierd when you think just how feeble "ultra tough" landrover pas boxes are that a system exerting over 2.7 tonnes or steering force isnt classed as robust enough..

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I remember the SA chap at Bling who told you it doesn't work with the engine dead - even when he tried it himself I think he thought you were playing some sort of elaborate trick on him :lol:

Mind you the same day Mr Bowyer also told you Petal would explode and kill thousands of children because of the hydro winch :hysterical:

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I guess the big issue is that a blown hose means no fluid means no steering.

People have been killed when hydraulic steering systems in boat outboard motors have failed due to fluid loss and the steering has gone to full lock instantly at high speed, flipping the people out of the boat and sometimes running over them on the return circuit. Not sure I'd want that in the middle lane of the M25... mind you I'm not sure I'd want it in a tractor with a trailer full of bales on the back at 25mph either!

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I'm not selling anything just an observation ;)

With sufficient over-engineering I am sure it would be fine and the risk no greater than the risk of a ball joint shearing off without warning (seen that happen before on a Shogun, fortunately without serious consequences as he was going slowly at the time)

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Or breaking the master cylinder of the vacuum booster, due to the nuts not been done up. My father had this on his then brand new disco 200tdi.

I suppose we can argue forever whether it is save or not, I have no doubt Jez did a good job on it and it wont fail BUT; not everyone works to those standards, hence the ruling.

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or bent tie rods folding up..

or egged panhard rod mounts leading to death wobble

or bump steer

hey ho... :lol:

would be good if someone could point out the section in the MOT testers handbook though?

I went to see a customer about some work tonight, he runs a garage where he is the chief tester, I quizzed him about full Hydro after reading your posts earlier. He couldn't remember anything in the testers handbook refering to full hydro steering, but what was interesting was he remembered testing a Citroen a while ago where the engine had to be running for the steering to work it was an old Citroen, he seemed to think that was full hydro. Back in the 60's and early 70's some of the stuff on Citroens was years ahead of its time.

Andy

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or bent tie rods folding up..

or egged panhard rod mounts leading to death wobble

or bump steer

hey ho... :lol:

would be good if someone could point out the section in the MOT testers handbook though?

Or a drop arm falling off.....

A mate had that happen out in Malasyia while driving at 40 mph - vehicle went up a 20 ft bank and stopped just before going over the edge of a 100+ ft steep drop.

Slightly OT, how would this relate to a new build? Could a vehicle be SVAed as a tractor to allow this sort of thing? I mean, if you left it in low range for the test there would be no problem exceeding 60 km/h......

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There still seems to be some uncertainty about the legality of full hydro steering.

As there are some MOT bods around here is there anything that states that a vehicle must have a constant mechanical link between steering wheel and wheels?

In other words is full hydro really legal on an ordinary PLG vehicle?

Hi Neil,

Have we opened a can of worms with the scrutineers

my MOT bloke as been tested my car for the past 12 years and if i am thinking of moding somthing i ask him first if its ok

asking about hydro steer he got the book out and couldn't find anything that said not, so i went ahead and it passed

and after using it its far more accurate that landrover steering and less to brake/bend

and as for speed on comps the speed limit is 15 mph

is it going to be a problem for the comps, are we with hydro steer going to be stopped from entering

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Presumably rear wheel steer HGVs' can't have a mechanical linkage.

Neil, what I did with my hydraulic handbrake was ask a couple of testers, one said no, one said no problem.

Hydraulic handbrake is a definate no no. Many rallycars have got it, but they are indeed all illegal. You have to have a mechanical backup for brakes.

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Don't worry John, I am on your side with this one.

I just want to get some facts for when I need to go on the defensive.

Still waiting for a definitive answer...

Hi Neil,

Have we opened a can of worms with the scrutineers

my MOT bloke as been tested my car for the past 12 years and if i am thinking of moding somthing i ask him first if its ok

asking about hydro steer he got the book out and couldn't find anything that said not, so i went ahead and it passed

and after using it its far more accurate that landrover steering and less to brake/bend

and as for speed on comps the speed limit is 15 mph

is it going to be a problem for the comps, are we with hydro steer going to be stopped from entering

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Hydraulic handbrake is a definate no no. Many rallycars have got it, but they are indeed all illegal. You have to have a mechanical backup for brakes.

Yes, but I have a tester who doesn't mind. I understand they are legal everywhere else but the WRC boys have to fit a cable for GB :unsure:

I don't have a problem with it as I use the park on the autobox rather than the handbrake and it's far better than most Landy handbrakes.

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Presumably rear wheel steer HGVs' can't have a mechanical linkage.

not sure how these are operated, I suspect hydraulically, but rear steer axles only operate at low speeds [when turning corners/manouvering] & auto lock into the straight ahead position above a set speed.

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not sure how these are operated, I suspect hydraulically, but rear steer axles only operate at low speeds [when turning corners/manouvering] & auto lock into the straight ahead position above a set speed.

the rigid volvo,s i have driven with rear steer have a mechanical linkage down the side of the chassis connected to the rear wheels which work in conjunction with the front axle to turn the rear wheels

the artics have a linkage system from the rear trailer wheels to the fifth wheel connection on the trailer, this is activated by the tractor units coupling turning against the trailer and working the linkage

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Full hydro would certainly solve my current design problem!

One could possibly 'get around' the issue by fabricating a lever on the steering column which pulls on each of two handbrake cables (one in either direction) the other ends of which are connected to the wheels. So long as there is a 'track rod' and the cables are tensioned, you could get some steering out of the thing. For the MOT, there is a direct mechanical link - eve though in reality it would do little!

Si

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long load trailers with steering a steering dolly have no mechanical link - and if they go wonky its gonna be just a entertaining as if the tractor unit lost steering :blink:

anyone found the magic sentance in the MOT testers manual yet or is it still eluding us? :huh:

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anyone found the magic sentance in the MOT testers manual yet or is it still eluding us? :huh:

I don't think its there - because of the Citroen system

I think its in construction and use which post-dates the Citroen system

Andy

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