Steve 90 Posted November 13, 2008 Share Posted November 13, 2008 As some of you will know I have a Hydro assist steering setup on my truck. Its brilliant, Feather light steering even when the boggers are aired right down. Only problem is I have reasonable large bore hoses, Steering box is drilled and tapped with good size holes and there is a high output (ZF74) pump but I dont think the steering box will flow enough oil when going lock to lock through the trees. Its fine on the normal challenge events and on the road but when it comes to the special stages that require speed through tight and twisty woodland the steering just isnt fast enough. I think I might look for a smaller capacity ram which will hopefully (at the expense of some power) speed the steering up. I did think about moving the mounting back along the drop arm to speed it up but I would like it so I can swap the ram for different types of event. Keep original for slower stuff as the light steering is brilliant and new/faster ram for the higher speed stuff. I cant work out what size of ram is needed as the steering box is an Unknown quantity. So considering the ram I have now is 40mm dia, 25mm shaft, and a 248mm stroke, Anybody who's in the know like to make an educated guess of what I should get made? I want it faster but still to have a reasonable level of assist (the boggers make std steering &$%*&%% heavy) How much do you think I will have to alter it to see a difference in speed? The difference in displacement from one direction to the other with my present ram is noticable but not hugely so whatever ram I get now I'd like to keep the difference to a minimum if possible. Certainly no greater than it is now. Sorry, I know I have not given a lot of info but theres unknown values mixed up in it all so Its going to be a bit of trial and error, Hence the plea for an "Educated guess"! Any help much appreciated Cheers. Steve. Quote Link to comment Share on other sites More sharing options...
custom-conversions Posted November 13, 2008 Share Posted November 13, 2008 Hi, Sorry I don't have any experience with Hydro-Assist but am interested to know the solution as I'm going full hydro steering when I get a chance to fit all the parts. And it'll be good to know what you conclude. Anyway, I wondered why you have concluded that the box is causing the restrictions & that its not the pump reaching its flow limitations. I guess you need to measure the presure at different points in the system to find out. Are the holes tapped in the box quite a small bore? Smaller than the high pressure pipe internal diameter?? Quote Link to comment Share on other sites More sharing options...
Steve 90 Posted November 14, 2008 Author Share Posted November 14, 2008 Hi, Anyway, I wondered why you have concluded that the box is causing the restrictions & that its not the pump reaching its limitations. I guess you need to measure the presure at different points in the system to find out. I dont know for sure, But my guess is its the box as the same pump as I use runs fast, full hydro systems using larger rams without any problems. So I guess its probably the restrictions through the box. No more scientific than that really. Are the holes tapped in the box quite a small bore? Smaller than the high pressure pipe internal diameter?? Yep, The holes ive tapped in the box are much bigger than the pipe. Wherever the restriction is the basic fact of the mater is im lacking oil flow so I need to either reduce the stroke of the ram or the cylinder bore (or increase flow which would be much harder) So im looking to go down the smaller bore route and hopefully still be able to use the existing ram on slower events. So anyone any advice????????? Im tempted to go with a 25mm bore, Is that likely to make a huge difference or not enough to make a difference????? Quote Link to comment Share on other sites More sharing options...
Hamish Grundy Posted November 14, 2008 Share Posted November 14, 2008 I dont know for sure, But my guess is its the box as the same pump as I use runs fast, full hydro systems using larger rams without any problems. So I guess its probably the restrictions through the box. No more scientific than that really. Yep, The holes ive tapped in the box are much bigger than the pipe. Wherever the restriction is the basic fact of the mater is im lacking oil flow so I need to either reduce the stroke of the ram or the cylinder bore (or increase flow which would be much harder) So im looking to go down the smaller bore route and hopefully still be able to use the existing ram on slower events. So anyone any advice????????? Im tempted to go with a 25mm bore, Is that likely to make a huge difference or not enough to make a difference????? hi, i wouldnt have thought pipe size will make much of a difference, if you go smaller then the presure will be increased but there will be no gain in flow, what size pipe are you using at the moment? id have thought 3/8 or 1/2'' hose would be ample. hamish Quote Link to comment Share on other sites More sharing options...
zim Posted November 14, 2008 Share Posted November 14, 2008 steve, does it work faster one way than the other ? Quote Link to comment Share on other sites More sharing options...
disco_al Posted November 14, 2008 Share Posted November 14, 2008 why not use a quick ratio streering box from somewhere like bearmach? Quote Link to comment Share on other sites More sharing options...
Bush65 Posted November 14, 2008 Share Posted November 14, 2008 ... the ram I have now is 40mm dia, 25mm shaft, ...The difference in displacement from one direction to the other with my present ram is noticable ... ... so whatever ram I get now I'd like to keep the difference to a minimum if possible. ... Steve. Given a fixed flow for the ram, the speed of the ram will be proportional to the effective area. From what you have said, I conclude that your ram has a single rod. Then the area at the end with the rod will be 765.7 mm2, and the area at the other end will be 1256.6 mm2 (64% larger). IMHO you should not go much smaller than 40mm. You should be able to find 1-1/2" dia (38.1 mm), which will make a small difference but still be ok. The next common bore is 25 mm, which is too small - you may be able to find something about 32 mm, but that is still on the small side. The best solution is to get a double rod cylinder of 38 or 40mm with the 25mm rod. Obviously, since you already have found, this gives you enough assistance. The advantage will be the reduced flow demand when steering in the direction where the ram is extending. It is going to save about 64%. The other advantages are that you won't need to swap rams for different events and the steering will feel the same in both directions. A double rod ram will cost more. You might also try increasing the setting of the pressure relief valve a little, in case it is spilling fluid over the relief in those situations when you are running out of flow. I'm sure I have posted pics on this forum for adjusting the relief valve and a mod to increase flow from the P.S. pump. Edit: sorry I just re-read where you have a ZF74 pump. The pics I posted were for the stock PS pump, not the ZF74. I haven't had anything to do with the ZF74, but wouldn't be at all surprised if the same principles cant be applied - they are certainly applicable to some other PS pumps such as the Saginaw style. Quote Link to comment Share on other sites More sharing options...
Steve 90 Posted November 18, 2008 Author Share Posted November 18, 2008 Thanks John. Excellent advice, just the sort of ideas I was looking. I think thats the way I will go. Will need some re-engineering of the setup for a double acting ram but should be worth it. Steve. Quote Link to comment Share on other sites More sharing options...
will_warne Posted November 19, 2008 Share Posted November 19, 2008 Steve, why not go double acting and use the ram + a pair of short rods to replace the track rod? ie basically a system that looks like a full hydro setup but with a mechanical linkage to fulfill the C&U requirements. Quote Link to comment Share on other sites More sharing options...
Steve 90 Posted November 20, 2008 Author Share Posted November 20, 2008 Steve, why not go double acting and use the ram + a pair of short rods to replace the track rod? ie basically a system that looks like a full hydro setup but with a mechanical linkage to fulfill the C&U requirements. Thats pretty much the way id like to go. Something like Tim Bently runs. Anybody know what steering box he is running??? Quote Link to comment Share on other sites More sharing options...
Simon Smith Posted November 20, 2008 Share Posted November 20, 2008 hi, i wouldnt have thought pipe size will make much of a difference, if you go smaller then the presure will be increased but there will be no gain in flow, what size pipe are you using at the moment? id have thought 3/8 or 1/2'' hose would be ample. hamish I have found with tractor stuff that increasing the pipe diameter can make a huge difference to flow rates, so it's worth a try, especially as hoses can be made up so cheaply. Quote Link to comment Share on other sites More sharing options...
will_warne Posted November 20, 2008 Share Posted November 20, 2008 Thats pretty much the way id like to go. Something like Tim Bently runs. Anybody know what steering box he is running??? Yep. He's using a Saginaw unit built by Howe. Quote Link to comment Share on other sites More sharing options...
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