Boothy Posted September 14, 2009 Share Posted September 14, 2009 After now going through 2 brand new ZF74's including mod's I have come to a bitter conclusion they are not man enough. I'm using them on a V8 Challenge truck to power my twin ram hydrosteer using a "Danfoss" type valve fed off a RR resevoir to an 80cc/rev steering unit to a pair of 200mm single actuators. My mate has more or less the same set up which works great, but he is rear engined so a bit lighter at the front. The steering OK except when stationary it will simply not turn the wheels, which was the sole point of fitting it in the first place, even if rev'ved up it will not produce enough pressure/flow to move, or will move a small amount before giving up. It has had a cooler fitted just in case to overcome heat which made no difference, all the pipes (which were all new) have been cleaned and checked, the resevoir has been cleaned and checked, the "Danfoss" has been swapped for another unit (just in case), and the ZF74 was replaced for another brand new unit, and still lack of good strong effort, also the hydraulic rams have been changed for a much bigger set which are now 50mm diameter. One of the pumps has been drilled bigger and had the spring washered out by about 10mm in an effort to help but it didn't cure the problem it just makes the relief noisier. So whats the alternatives lads, a bigger pump that can be made to fit?, will stand the rev range of a V8 and is available somewhere (not some obscure Yank V8 that I will never find", I have been looking at geared stage 2 pumps but think I will struggle with the rev range. The HGV route, i.e. Ford Cargo etc is a massive option but I'm not sure of pressure or flows and are struggling to find info out on them and ideas there also would be massivly appreciated. Cheers lads. Quote Link to comment Share on other sites More sharing options...
zim Posted September 14, 2009 Share Posted September 14, 2009 Chris, This is from the pirate4x4.com technical section....so if you've got a spare day to sit and read it all might point you in the right direction : http://www.pirate4x4.com/tech/billavista/PR-Hydro_Steering/index2.html The interesting part : The most common pump used in 4x4 Hydro steering setup is an automotive power steering pump. This makes sense since they are cheap, readily available, easy to mount and run, are designed for the environment, are relatively cheap, and produce reasonable flow while being capable of developing sufficient pressure for our needs. The exact make and type of pump used will likely depend mostly on what fits the engine application easily. The most popular pump is the venerable Saginaw pump, which generally comes in 2 broad styles, the "P" style pump and the "TC" style pump. Regardless of the exact style or part number of automotive power steering pump you use, it will be a fixed displacement type. That means that it always produces flow (as opposed to a variable displacement pump that only produces flow in response to demand) and the GPM output (flow) can be changed only by varying the drive speed of the pump. If the flow is not required (i.e. the hydraulic circuit is in the neutral position - that equates in a hydro steering system, to the steering wheel being centred and there is no steering input from the operator), fluid flow is internally bypassed back to the reservoir. This type of pump (fixed displacement) can be used in an open-center system - the "open-center" means that the control-valve spool (in our case, the steering unit) must be open in the center to allow pump flow to pass through the valve and return to the reservoir. This will become very important later, when it comes time to understand / select the steering unit for the system, as the type of pump and type of steering unit MUST be compatible. (i.e. you cannot use a fixed displacement type pump with a steering unit designed for use with a variable displacement pump). There is a load of pics and information after this on that link... As you know i don't run hydro, but found this and thought it might possibly help Regards Gordon Quote Link to comment Share on other sites More sharing options...
Boothy Posted September 14, 2009 Author Share Posted September 14, 2009 Nice one G that will give me a bit of quality reading and a bit of brain food. Cheers Chris Quote Link to comment Share on other sites More sharing options...
Bush65 Posted September 14, 2009 Share Posted September 14, 2009 If you have a large scrub radius, have you considered if it can be reduced? Quote Link to comment Share on other sites More sharing options...
ciderman Posted September 15, 2009 Share Posted September 15, 2009 If you have a large scrub radius, have you considered if it can be reduced? Good shout there , Thats the problem I have with mine. Quote Link to comment Share on other sites More sharing options...
Boothy Posted September 15, 2009 Author Share Posted September 15, 2009 What the bl**dy hell's a scrub radius?????? Quote Link to comment Share on other sites More sharing options...
ciderman Posted September 15, 2009 Share Posted September 15, 2009 Basicly its effects of large offsets on wheels that change the Ackerman angle . There ya go fella Quote Link to comment Share on other sites More sharing options...
BogMonster Posted September 15, 2009 Share Posted September 15, 2009 your ackerman is knackered man and it's scrubbing your radius Que? wibble! Quote Link to comment Share on other sites More sharing options...
Boothy Posted September 15, 2009 Author Share Posted September 15, 2009 I'm running 4.5" offset Mach 5's with a 35/10.5/16" Simex ET's on, nothing to stupid or to much of an offset I would think. What I did was use a smaller diameter actuator which was not very successful so then I increased this to a larger one at the same time a modding the pump out a bit more, so tomorrow hopefully I will refit the smaller dia to see how that works now. I also have a portable hand type pump capable of driving these actuators which is used on a set up at work with a manual overide in the event of failures, power cuts and mtce tests, so is an ideal match and will try to see if that will move the steering with more success. If I lift the front wheels of the floor onto axle stands the steering moves superbly from lock to lock with just the steering unit moving the fluid (no engine running) which leads me to think there is no real problem with the actuators or steering unit,but possible with the amount of flow or fluid pushing on the actuator. Which again makes me think fit the smaller diameter actuator about 1.5" piston size and there may be more effort. At the moment once the motor is moving the steering is cracking, its just when its stationary there is little or no effort exerted by the hydraulics. Surely an offset of only four and half inches will not cause that much extra effort to move the steering, not the worlds best on steering geometry is Boothy. The only way I could see was to increase the flow without increasing the pressure so as not to damage the steering unit. Any ideas welcome lads. Quote Link to comment Share on other sites More sharing options...
ajh Posted September 16, 2009 Share Posted September 16, 2009 Did you try putting a pressure/flow gauge on the system to see if you are actually making the expected pressure and getting enough ltr/min flow? Quote Link to comment Share on other sites More sharing options...
Bush65 Posted September 16, 2009 Share Posted September 16, 2009 What the bl**dy hell's a scrub radius?????? Nothing to do with Ackerman steering as others have suggested. When you turn the wheels to steer, they pivot about the axis through the swivel pins. The theoretical axis if extended to the ground should ideally coincide with the centre of the tyre contact patch on the ground. Stock steering will be close to this. However if you change wheel offset these points can be different - the difference is the scrub radius. As scrub radius increases several adverse things happen: 1. Resistance to forward (or backward) motion (rolling resistance etc.) at the vehicle is applied at the tyre contact patch and because of the scrub radius it wants to pull the tyre around the swivel (in other words steer the wheel away from straight ahead). On the road, this is not a great problem because the left wheel wants to pivot opposite to the right and they counterbalance each other. But offroad where for example one wheel is in the air or has little contact pressure, steering becomes more difficult. 2. When trying to steer while the vehicle is not rolling (what you described), the tyre has to be dragged across the ground (this is where 'scrub' comes into it), it doesn't pivot about the contact patch. This increases the force required for steering. 3. Because of the inclination of the axis through the swivel pins, large scrub radius causes the vehicle mass to be lifted vertically. Part of the steering force is going into lifting the weight of the vehicle. Quote Link to comment Share on other sites More sharing options...
zim Posted September 16, 2009 Share Posted September 16, 2009 Quote Link to comment Share on other sites More sharing options...
Boothy Posted September 16, 2009 Author Share Posted September 16, 2009 Lads the information your providing makes perfect sence and sounds about right for what is happening. But it leaves me with a problem, With Saleys motor which the exactly the same set up as mine but he has 7" offset and a 1" wheel spacer as well plus 37" Boggers on which have a greater footprint the my Simex'es do, so much so that his motor barley fits on his ramp due to the width or the axle/tyre but mine flies on, yet his steering is absolutely effortless when stationary, so what's the difference ?? So using that theory his should be far worse than mine but he uses same valve, same actuators and same ZF74 pump, so it leaves me completly puzzled. I have a single pressure guage that I can try but have not (yet) got a flow guage, so lots more testing and keep the theory coming please, I find it a great help. Cheers lads. Quote Link to comment Share on other sites More sharing options...
RangeyRover Posted September 16, 2009 Share Posted September 16, 2009 Boothy, Check the pressure first. You can have as much flow as you like, but if you dont have the pressure to do the work, the work wont get done. Does the PRV blow off when you try to move when stationary? If it does then pressure needs increasing, if possible. Use the hand pump and gauge to see what pressure you need to move it when sitting. I think that it is relieving pressure early for your application. RR Quote Link to comment Share on other sites More sharing options...
BogMonster Posted September 16, 2009 Share Posted September 16, 2009 Increased offset makes steering easier. My old 1987 90 with "Armstrong" power steering (non assisted...) was a pig to park on 7.50s but on offset rims with 33x12.50R15 on the steering was much, much lighter even with the footprint of the tyres being nearly twice as wide. I assume it was because as you turn the wheels, if the rims are offset then the wheel will rotate slightly rather than just scrubbing on the spot. May explain why Saley's is easier than yours? Quote Link to comment Share on other sites More sharing options...
dirtydiesel Posted September 16, 2009 Share Posted September 16, 2009 I run a stock 300tdi pas pump on a 80cc danfros with a 50mm bore single ended ram with a 30mm shaft. i have a 6ltr res i normally use hydraulic oil but i have once used landrover genuine parts cold cilimate pas fluid. (i couldn't tell the difference between them) I have feather light steering at all times, (enough to bend unimog steering components without knowing about it!) What is you steering like with the engine off? This will give you an indication of whether you've over-geared the danfoss. Mine is about the same weight as a conventional non pas landy. What is the the bore of your rams and the od of the piston? Quote Link to comment Share on other sites More sharing options...
Boothy Posted September 18, 2009 Author Share Posted September 18, 2009 Right here goes, The steering effort as I said earlier without the engine running wheels off the ground is OK bit nochy but not a massive effort required, 3.5 turns lock to lock. Steering engine off with wheels on concrete garage floor is ridicously heavy, with engine running a bit better but not much, certainly not one handed. Actuator piston is solid and measures 34mm, it extends 214mm, I've measured the pressure on the actuator (in line gauge) and it only gets to about 1100psi which is about 80bar and well short of what I was expecting this is when the actuator is trying to move the steering or is at the end of the steering travel and does not go stupid high when I rev the engine, the noise from the pumpis high, almost that I've got air sound. I also have a old (9 months old) ZF74 pump and a Vauxhall Elite one as well which is dead ringer and have been playing with stretching the spring, washering the spring, washering the internal spring in the bung thing, and different bores of output hole to try to find the best combination of effort and pressure and I think I've got it now. I realise there may be a slight amount of air in the system because of keep draining it and refilling everytime I alter the relief valve so it takes a while to settle. But I also know its not right, so here are a few questions if anyone is kind enough to answer, how does the pressure relief valve workin the ZF pump, will streching the spring or washering it UP the pressure and what is the smaller internal plug sort of things part in all this and it relationship to the main spring, and what effect will stretching/washering the bungs spring have ????? Who can repair reservice etc the ZF pump but will be able to modify/improve the pump and will test and tell me the rating/flow afterwards ??my localfactor sends themaway for reservice but its only standard and no mods sort of service ?? I've read the pirate 4X4 write up on pumps and how to mod them but its a different type of pump really and still leaves me asking questions, I am really tempted to buy another but have already bought 2 this year already and don't think another will improve things massively. Saley and myself are going to look at the angle the actuators act on the hubs and try to and staighten them slighly, they sort of come from slightly behind the centre line of the axle, but Saleys are at a worse angle than mine and work fine. Thanks again lads, sorry but I'm struggling here. Quote Link to comment Share on other sites More sharing options...
TOR4x4 Posted September 18, 2009 Share Posted September 18, 2009 Actuator piston is solid and measures 34mm, it extends 214mm, You need to know the piston diameter and the piston rod diameter to be able to work out the surface area, I would be surprised if the piston rod is the same diameter as the piston, if it was it would only be able to extend, as there is no surface to apply pressure to too retract it. Quote Link to comment Share on other sites More sharing options...
Boothy Posted September 18, 2009 Author Share Posted September 18, 2009 Piston diameter is 34mm, the actuator is single acting and there are a pair or them acting oposite one another i.e. as one opens it pushes the other one shut, the outside diameter of the actuator body is 50mm. Exactly the same as Saleys, works a treat when moving. Quote Link to comment Share on other sites More sharing options...
landmannnn Posted September 18, 2009 Share Posted September 18, 2009 Just wondering, why don't people use pumps off trucks? 7.5 tonners must have high volume pumps since you can turn the wheels easily while they are stationary. Quote Link to comment Share on other sites More sharing options...
dirtydiesel Posted September 18, 2009 Share Posted September 18, 2009 Piston diameter is 34mm, the actuator is single acting and there are a pair or them acting oposite one another i.e. as one opens it pushes the other one shut, the outside diameter of the actuator body is 50mm. Exactly the same as Saleys, works a treat when moving. I think you've overgeared the system, to my mind a 50cc danfoss should sort it. Quote Link to comment Share on other sites More sharing options...
Boothy Posted September 19, 2009 Author Share Posted September 19, 2009 Hey'up DD I've just swapped off my original 40cc for the present 80cc the only difference in effort was the amount of turns, I also swapped the actuators for a smaller dia as well. I don't think there is anything left to try its proper "doin me head in". Of to the scrap yard to attemp to find a cargo or similar and have a mooch at them. Cheers Quote Link to comment Share on other sites More sharing options...
WHO? Posted November 26, 2009 Share Posted November 26, 2009 have you sorted this? Quote Link to comment Share on other sites More sharing options...
Boothy Posted November 26, 2009 Author Share Posted November 26, 2009 Yes, I've found a person whocan supply a pump that does what it says and will adjust the pressure and flow test it for me and supply the results. Quote Link to comment Share on other sites More sharing options...
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