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What it is:
I'm using a power steering rack out of a '88 Thunderbird ( quick rack out of the turbo version ) in my '73 Capri,
( changed geometry to eliminate bumpsteer, etc )
I believe the rack is the same as the ones in the High Performance Fox Body Mustangs.
I hooked this up to a Electric pump out of a Volvo S40.
( pump is made by Ford, and according to several internet posts, compatible pressure to the T-Bird rack in limp home mode, as it is when hot wired )
Rack in the usual place for a Capri ( in front of the Axle line ), pump behind the RHS front wheel under the fender.
What it does:
When you steer the car, the power assist reacts too slow.
At first it is unassisted, and when it comes on ( since you are already cranking on the steering wheel without any help ) it suddenly goes light and you overshoot.
( probably less than a second of delay, but long enough to mess everything up )
My questions:
- Because of where the pump is the lines going to it and back are fairly long.
Could this be a reason for the delay?
( I thought it wouldn't be a problem, since fluid doesn't compress.
So any spike in the system would instantly go from one side of the line to the other, but I'd like to hear what you guys think )
-The rack is low mileage used, but original equipment made by Ford.
Could the long time it wasn't used be a factor?
-It is angled a couple of degrees back ( about 15 or 20 deg ) from how it is mounted in the T-Bird to create space between it and the Dry Sump pump.
Could that have trapped air in the rack?
-Should I buy a Power steering pressure test kit and start measuring?
Probably better than randomly replacing pumps and racks, right?
Only other option I see is starting over with a conventional belt driven system, but that would mean a complete redesign of everything on the front of the engine, as well as the stutbars ( which extend in front of the engine )
I'd really like to hear your thoughts on this.
Thanks in advance.
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The wiring is hooked up like it is in this vid.
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Nov 10, 2020 10:14:46 GMT
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It sounds like there is a fault with the Torsion bar or valve in the rack, if there is no play it's probably the valve sticking or has air trapped in it.
I would try cracking the uppermost connection to the valve body to see if any air can be bleed out, if not it might be worth putting some additive through it and keep cycling the steering lock to lock until it all gets hot to see if it frees off.
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Nov 10, 2020 10:38:24 GMT
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Could this be a reason for the delay? I've seen much longer lines as OEM, so it seems unlikely. Could the long time it wasn't used be a factor? Always possible. Gummed up with grease? Worth giving it a clean or flush through. Could that have trapped air in the rack? Could you jack the rear of the car up to make the rack level? It would reduce the number of questions you have! -Should I buy a Power steering pressure test kit and start measuring? Seems a good idea, unless you can find a power steering specialist who is able to test each item in isolation first? This is always the frustrating thing when creating something from scratch from components borrowed from many sources. You can never be sure how is is supposed to behave as you don't have anything to compare it to. |
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Nov 10, 2020 14:03:20 GMT
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It sounds like there is a fault with the Torsion bar or valve in the rack, if there is no play it's probably the valve sticking or has air trapped in it. I would try cracking the uppermost connection to the valve body to see if any air can be bleed out, if not it might be worth putting some additive through it and keep cycling the steering lock to lock until it all gets hot to see if it frees off. I've compared the rack with another Ford rack I have, and the degrees of "free" twist and resistance ( I assume that is the torsion bar?) seems the same. I will try cracking the connections. All fluid is new, and it seems clean. But I'll check that too. Thanks for the comments. |
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Nov 10, 2020 14:08:37 GMT
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Could this be a reason for the delay? I've seen much longer lines as OEM, so it seems unlikely. Thats what I thought. I've seen some home brew versions with the pumps in the trunk as well ( online pics ) Nice to take that one off the list . Could the long time it wasn't used be a factor? Always possible. Gummed up with grease? Worth giving it a clean or flush through. It seemed like a good unit. And clean. But you never know... Could that have trapped air in the rack? Could you jack the rear of the car up to make the rack level? It would reduce the number of questions you have! I thought about that, or have the rackhang loose underthe car while it is on the lift. -Should I buy a Power steering pressure test kit and start measuring? Seems a good idea, unless you can find a power steering specialist who is able to test each item in isolation first? I could, but sending a garage on a wild goose chase on my dime scares me. Also there is the humiliation of not understanding what is going on with something I built... This is always the frustrating thing when creating something from scratch from components borrowed from many sources. You can never be sure how is is supposed to behave as you don't have anything to compare it to. Yeah... It really is... Thank you for the reply, and thinking with me. |
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Nov 10, 2020 15:20:50 GMT
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So does the pump run all the time or does it cycle via a pressure switch? If the latter I’d be wondering about the pressure switch.....
Nick
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1967 Triumph Vitesse convertible (old friend)
1996 Audi A6 2.5 TDI Avant (still durability testing)
1972 GT6 Mk3 (Restored after loong rest & getting the hang of being a car again)
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Nov 10, 2020 15:39:40 GMT
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So does the pump run all the time or does it cycle via a pressure switch? If the latter I’d be wondering about the pressure switch..... Nick I have a switch on the dash to turn it on ( flip the switch and the pump starts to run about 2 seconds later ) After that it just runs at a steady RPM ( by the sound of it ), putting in steering effort doesn't seem to change the RPM much, but it does change the intensity of the pumping sound. About the pressure... I was wondering about the pump itself. I assume there must be an internal bypass valve that gets activated to bleed off pressure when the speed, throttle position, greenwich mean time, and the moon gravitational pull call for it on a stock Volvo. Maybe that one is stuck open? Thanks for the reply Nick. |
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Nov 10, 2020 15:47:54 GMT
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Yes, if the pump runs all the time, there must be some kind of internal relief - probably a simple spring loaded pop-off valve. That has to pass the full pump flow when you are not doing any steering, which is somewhat wasteful. I thought that most of these pumps had something a bit smarter to reduce power draw when cruising along in a straight line?
Nick
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1967 Triumph Vitesse convertible (old friend)
1996 Audi A6 2.5 TDI Avant (still durability testing)
1972 GT6 Mk3 (Restored after loong rest & getting the hang of being a car again)
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Nov 10, 2020 15:59:59 GMT
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Yes, if the pump runs all the time, there must be some kind of internal relief - probably a simple spring loaded pop-off valve. That has to pass the full pump flow when you are not doing any steering, which is somewhat wasteful. I thought that most of these pumps had something a bit smarter to reduce power draw when cruising along in a straight line? Nick I bet it does on a stock Volvo, it reads all the parameters and adjusts the power assist according to the situation. But when you use it like this, you bypass all of that by hotwiring the pump to work in limp home mode. And then it works at 80% pressure, which works out to be the exact pressure the rack needs ( about 1000PSI, if I remember correctly ) (all this according to Info I've found online) |
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Nov 10, 2020 16:25:04 GMT
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So just to make sure I understand power steering correctly...
( I've never played with it before.
My only other car with power steering is my daily driver latemodel truck, which is stock so I don't have to mess with it)
On a regular ( belt driven) pump, the fluid constantly circulates, right?
And when you need power assist the rack feeds the flow into ram part of the rack, which restricts the flow & increases the pressure?
And the bypass on the pump is just the failsafe to prevent the whole system from going over the max pressure?
And that is the configuration you re-create with a hot wired electric pump, right?
If I got any of that wrong, please let me know.
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Nov 10, 2020 19:29:22 GMT
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Belt driven pump has an internal relief valve which passes full flow when you are at full lock. Full flow will vary with engine rpm and the pump has to be sized to give enough from idle so even more wasteful than the electric scenario.
For your purposes, if you have bypassed any electronic controls, I would expect your electric pump to work the same way with full flow passing through the rack position valve when no steering input is made, a proportion of it diverted to the appropriate end of the rack when a steering input is made and all flow going through the pump relief valve when held at full lock.
I’d be surprised if the operating pressure is anything like 1000 psi, except possibly when held at full lock.
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1967 Triumph Vitesse convertible (old friend)
1996 Audi A6 2.5 TDI Avant (still durability testing)
1972 GT6 Mk3 (Restored after loong rest & getting the hang of being a car again)
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Nov 10, 2020 20:44:42 GMT
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Yeah, thats what I meant. The 1000PSI is the peak pressure, which happens at full lock. From what I understand, all other situations are metered down from that. Thanks for explaining the parts I wasn't completely sure of. I think I need to go look for a gauge setup, because it would be interesting to see what the actual pressure is when the pump is just running without any steering input. If that press is low enough, I guess the energy to run it would be reasonable as well? Either way, I'm not too worried by those losses. It wouldn't be the only component on this car to generate heat...  The stumbling block, right now, is the slow transition from low ( or no ) press to the higher press. And how to find out if the problem is in the pump or the rack. |
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Nov 10, 2020 20:57:30 GMT
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Thank you all for the input.
I have some things to think about, and I have to decide what to try next.
I think a gauge is first, so I can get a better picture of what is going on.
Next is to try and bleed the rack, because that would be the least work, if successful. ( maybe that should be first...)
Next to replace the pump ( I got a couple identical ones from the junkyard when I got this one, so I can swap them out )
And then order a new rack. ( rebuilt original or aftermarket, I believe both are available )
I actually have one that looks like it has never been used, but it has been outside in the weather for a long time ( without the press lines on it ) so I'm not sure I trust it,
I'll let you know what I'll find out.
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Nov 10, 2020 21:48:57 GMT
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Have you found this already?
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1967 Triumph Vitesse convertible (old friend)
1996 Audi A6 2.5 TDI Avant (still durability testing)
1972 GT6 Mk3 (Restored after loong rest & getting the hang of being a car again)
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I found some stuff, but that one is really helpful. Thanks |
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It was the rack. I bought it because it was supposed to be a low mileage/good as new/ original Ford ( US T-Bird ) PS Quickrack. But I guess it was not that good as new. I replaced it with an actual new one, and the problem seems to be solved ( haven't driven it yet, but sitting still with the car's weight on it I can not feel any delay). So that makes me very happy. ( as long as things are still OK when I take it for a test drive... ) |
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Without having driven it yet, but going by feel of the steering wheel and the sound the pump makes as it ramps up pressure, this seems to be the difference between the used and the new rack.
The new rack builds up pressure immediately, but ramps up to not as high of a pressure when you turn the wheel.
The old rack would do nothing at first, and then after some delay suddenly go to high press/ high assist.
Which made the car very hard to drive.
So my guess is that whatever measures the amount of force on the steeringwheel, and has to translate that to the correct amount of assist, is broken/stuck/clogged..
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Jul 13, 2021 21:05:30 GMT
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Good to know it’s working now and get feedback on what the problem was.
I reckon Kevins had it nailed with his first reply. Probably fixable if you know what to do (I don’t, but I’d have go anyway!)
Nick
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1967 Triumph Vitesse convertible (old friend)
1996 Audi A6 2.5 TDI Avant (still durability testing)
1972 GT6 Mk3 (Restored after loong rest & getting the hang of being a car again)
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Good to know it’s working now and get feedback on what the problem was. I reckon Kevins had it nailed with his first reply. Probably fixable if you know what to do (I don’t, but I’d have go anyway!) Nick Yeah, kevins did nail it right away. For me there were too many unknowns to be able to figure it out. Mixing used parts from several brands, and this being my first racer with power steering ( so I had nothing to compare it to ) Thanks to everybody that posted, and for trying to figure this out with me. |
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