Manual steering rack
11-21-2020, 02:46 PM
#62
Instructor
I'm also latching onto this thread as it mentions some points of interest to me.
I have to point out that many seem to be missing the fact that driving with a broken/disconnected PS pump is NOT the same as correctly de-powering the rack. If still full of fluid, trying to steer will be trying to force fluid around the system and probably drive the pump too, so it will be unnaturally heavy. Whereas removing all the internal seals and blocking up the hose connections should result in the correct feel for a non-powered rack of that ratio. Still probably quite hard as the ratios in PS systems will be lower, so higher geared and harder to turn, but fewer turns lock to lock. Maybe obvious but I still so many quotes of how hard the steering is when the PS fails, so i thought it worth mentioning again. Anyway…
Main reason for posting was the idea of using a different rack, specifically one with electric assist and not hydraulic. I saw mention above of 'Anderson' having an electric rack? Who he?
What about the electric rack from a 991? Looks very much like Bosch's current EPSapa, but although no doubt both are available for L & RHD, is the 991 rear steering like the 928? Although does that really matter? Pinion position (in front of or behind rack) and spindle drop link/arms direction (in front or behind wheel axle pivot) must go hand in hand. So rear pinion and rear links would be the same as front pinion and front links? Not fully thought that through, but pretty sure it's correct.
Anyone any ideas on electric racks? There are reasons why that would be preferable and I hoped a solution had already been worked out by those with years of 928 experience, compared to my meagre few months.
I have to point out that many seem to be missing the fact that driving with a broken/disconnected PS pump is NOT the same as correctly de-powering the rack. If still full of fluid, trying to steer will be trying to force fluid around the system and probably drive the pump too, so it will be unnaturally heavy. Whereas removing all the internal seals and blocking up the hose connections should result in the correct feel for a non-powered rack of that ratio. Still probably quite hard as the ratios in PS systems will be lower, so higher geared and harder to turn, but fewer turns lock to lock. Maybe obvious but I still so many quotes of how hard the steering is when the PS fails, so i thought it worth mentioning again. Anyway…
Main reason for posting was the idea of using a different rack, specifically one with electric assist and not hydraulic. I saw mention above of 'Anderson' having an electric rack? Who he?
What about the electric rack from a 991? Looks very much like Bosch's current EPSapa, but although no doubt both are available for L & RHD, is the 991 rear steering like the 928? Although does that really matter? Pinion position (in front of or behind rack) and spindle drop link/arms direction (in front or behind wheel axle pivot) must go hand in hand. So rear pinion and rear links would be the same as front pinion and front links? Not fully thought that through, but pretty sure it's correct.
Anyone any ideas on electric racks? There are reasons why that would be preferable and I hoped a solution had already been worked out by those with years of 928 experience, compared to my meagre few months.
11-21-2020, 03:12 PM
#63
Drifting
I'm also latching onto this thread as it mentions some points of interest to me.
I have to point out that many seem to be missing the fact that driving with a broken/disconnected PS pump is NOT the same as correctly de-powering the rack. If still full of fluid, trying to steer will be trying to force fluid around the system and probably drive the pump too, so it will be unnaturally heavy.
I have to point out that many seem to be missing the fact that driving with a broken/disconnected PS pump is NOT the same as correctly de-powering the rack. If still full of fluid, trying to steer will be trying to force fluid around the system and probably drive the pump too, so it will be unnaturally heavy.
My experience is that it feels incredibly dangerous to drive on track, and tedious to drive on the road
11-21-2020, 04:11 PM
#64
Instructor
I have a desire though to change to electric only assistance and I'd really like to hear from anyone who has had a go at that.
11-21-2020, 05:14 PM
#65
Former Sponsor
I don't doubt what you say, although there are others on here happily using their 928 without power assistance for steering and think it's fine. However, that was not really my point. Just that there will be a difference between a failed system and one that has been re-engineered into a manual system. The latter will of course still be hard to turn due to the ratio being lower to suit power assistance. For sure, I wouldn't want to have to drive without assistance, either way. In fact I would like to increase the assistance as I find the 928 relatively heavy.
I have a desire though to change to electric only assistance and I'd really like to hear from anyone who has had a go at that.
I have a desire though to change to electric only assistance and I'd really like to hear from anyone who has had a go at that.
11-22-2020, 06:29 AM
#66
Instructor
Anyway, still hopeful I'll find someone who has thought about or ideally done this. Otherwise, I guess I'm on my own.
A couple of quick questions. Anyone know the lengths (ball joint to ball joint) of the 928 and/or 991 racks? Also, do they use the same ball joint? By which I mean is the ball joint taper the same?
I'm not expecting a direct or even simple swap, but looking into what would be required. Early days.
11-22-2020, 10:46 PM
#67
Burning Brakes
I've have some experiences with a 928, on the track with various power steering configurations, some intentional, some not.
1. Stock power steering with normal alignment setting.
Not ideal Too heavy and numb, difficult to make quick corrections and my arms went numb and started to burn at the end of a 20 min session. I'd descride it as a wrestling match.
2. No assist, with normal alignment settings. (closest to manual rack)
Extremely heavy. Unsafe on the track, cant make any sort of meaningful course corrections necessary for track duty. I had this experience at Limerock this year for 1 lap. My Porsche 944 100 Bar power steering pump failed. Clearly over heated, when I pulled into the pits and checked the reservoir I open it to make sure I didnt leave any oil on the track and the oil was smoking. When I got back home, I took the pump apart, it was badly scored and too far gone to be rebuilt. Fluid smelled like burnt clutch, had to rebuild the rack, lots of metal from the pump was visable in the oil. FAIL!
3. Modifed rack with thinned quill and 100 Bar pump. Stock alignment settings.
Much better for the 8 laps it lasted. Car was far more pointable, controllable, no arm fatigue, felt light on its feet, almost nimble and tossable. Totally different car. I could quickly transfer the weight and complete my turns. I ran my fastest time ever in the wet with wipers on at some points, a 1.07 and was easily doing 1.08's repeatable in traffic. Last track day with stock steering configurations was exhausting and the best I did for 1 lap was 1.08 with a clear dry track.
I dont think a manual rack it right for a 928. Based on my experience... a modified power rack is best. If you look at Modern Porsche, from a drivers perspective where you can see the hands ripping around the ring it's its very clear the steering is light and no doubt precise. That makes for less driver fatigue and better feel over all.
I got to drive a Miata with a full manual rack. Since I was only 1/2 way though my track day when the PS pump failed, I rented a fully race prepped Spec Miata, I also ran low 1:08's repeatable. The Miata with a manual rack really works. Miata's are brilliant and very slideable and I didnt get the Miata thing until I drove one on the track. It was a great learning experience and a benchmark I can use to tune my 928's feel. On the Miata, as speeds increase the steering lightens, almost rewarding you as you drive faster. Eventually it gets light and feels right if you're going fast enough
My current configuration is a highly modified rack completely reworked for reduced friction points and more assist. Now with a large fluid cooler. I'm also running 1/2 the toe spec and just 3.5 degrees of caster. ( 4 to 5 is spec). These setting were arrived at after much trial and error. Since my 928 is lowered I had some bump steer with 5 degrees of castor and almost none with 3.5. I also carefully went through every ball joint and tie-rod end and checked them for friction, a few needed to be replace not for wear but for stiffness. All this this makes for very light and very precise steering , even with less caster and more assist the wheel still snaps back to center quickly. This transforms the 928. The point-ability, precision, control and quickness are welcome changes from the stock configuration.
1. Stock power steering with normal alignment setting.
Not ideal Too heavy and numb, difficult to make quick corrections and my arms went numb and started to burn at the end of a 20 min session. I'd descride it as a wrestling match.
2. No assist, with normal alignment settings. (closest to manual rack)
Extremely heavy. Unsafe on the track, cant make any sort of meaningful course corrections necessary for track duty. I had this experience at Limerock this year for 1 lap. My Porsche 944 100 Bar power steering pump failed. Clearly over heated, when I pulled into the pits and checked the reservoir I open it to make sure I didnt leave any oil on the track and the oil was smoking. When I got back home, I took the pump apart, it was badly scored and too far gone to be rebuilt. Fluid smelled like burnt clutch, had to rebuild the rack, lots of metal from the pump was visable in the oil. FAIL!
3. Modifed rack with thinned quill and 100 Bar pump. Stock alignment settings.
Much better for the 8 laps it lasted. Car was far more pointable, controllable, no arm fatigue, felt light on its feet, almost nimble and tossable. Totally different car. I could quickly transfer the weight and complete my turns. I ran my fastest time ever in the wet with wipers on at some points, a 1.07 and was easily doing 1.08's repeatable in traffic. Last track day with stock steering configurations was exhausting and the best I did for 1 lap was 1.08 with a clear dry track.
I dont think a manual rack it right for a 928. Based on my experience... a modified power rack is best. If you look at Modern Porsche, from a drivers perspective where you can see the hands ripping around the ring it's its very clear the steering is light and no doubt precise. That makes for less driver fatigue and better feel over all.
I got to drive a Miata with a full manual rack. Since I was only 1/2 way though my track day when the PS pump failed, I rented a fully race prepped Spec Miata, I also ran low 1:08's repeatable. The Miata with a manual rack really works. Miata's are brilliant and very slideable and I didnt get the Miata thing until I drove one on the track. It was a great learning experience and a benchmark I can use to tune my 928's feel. On the Miata, as speeds increase the steering lightens, almost rewarding you as you drive faster. Eventually it gets light and feels right if you're going fast enough
My current configuration is a highly modified rack completely reworked for reduced friction points and more assist. Now with a large fluid cooler. I'm also running 1/2 the toe spec and just 3.5 degrees of caster. ( 4 to 5 is spec). These setting were arrived at after much trial and error. Since my 928 is lowered I had some bump steer with 5 degrees of castor and almost none with 3.5. I also carefully went through every ball joint and tie-rod end and checked them for friction, a few needed to be replace not for wear but for stiffness. All this this makes for very light and very precise steering , even with less caster and more assist the wheel still snaps back to center quickly. This transforms the 928. The point-ability, precision, control and quickness are welcome changes from the stock configuration.
Last edited by icsamerica; 11-22-2020 at 10:52 PM.
11-23-2020, 08:39 AM
#68
Instructor
I've have some experiences with a 928, on the track with various power steering configurations, some intentional, some not.
1. Stock power steering with normal alignment setting.
Not ideal Too heavy and numb, difficult to make quick corrections and my arms went numb and started to burn at the end of a 20 min session. I'd descride it as a wrestling match.
2. No assist, with normal alignment settings. (closest to manual rack)
Extremely heavy. Unsafe on the track, cant make any sort of meaningful course corrections necessary for track duty. I had this experience at Limerock this year for 1 lap. My Porsche 944 100 Bar power steering pump failed. Clearly over heated, when I pulled into the pits and checked the reservoir I open it to make sure I didnt leave any oil on the track and the oil was smoking. When I got back home, I took the pump apart, it was badly scored and too far gone to be rebuilt. Fluid smelled like burnt clutch, had to rebuild the rack, lots of metal from the pump was visable in the oil. FAIL!
3. Modifed rack with thinned quill and 100 Bar pump. Stock alignment settings.
Much better for the 8 laps it lasted. Car was far more pointable, controllable, no arm fatigue, felt light on its feet, almost nimble and tossable. Totally different car. I could quickly transfer the weight and complete my turns. I ran my fastest time ever in the wet with wipers on at some points, a 1.07 and was easily doing 1.08's repeatable in traffic. Last track day with stock steering configurations was exhausting and the best I did for 1 lap was 1.08 with a clear dry track.
I dont think a manual rack it right for a 928. Based on my experience... a modified power rack is best. If you look at Modern Porsche, from a drivers perspective where you can see the hands ripping around the ring it's its very clear the steering is light and no doubt precise. That makes for less driver fatigue and better feel over all.
…
My current configuration is a highly modified rack completely reworked for reduced friction points and more assist. Now with a large fluid cooler. I'm also running 1/2 the toe spec and just 3.5 degrees of caster. ( 4 to 5 is spec). These setting were arrived at after much trial and error. Since my 928 is lowered I had some bump steer with 5 degrees of castor and almost none with 3.5. I also carefully went through every ball joint and tie-rod end and checked them for friction, a few needed to be replace not for wear but for stiffness. All this this makes for very light and very precise steering , even with less caster and more assist the wheel still snaps back to center quickly. This transforms the 928. The point-ability, precision, control and quickness are welcome changes from the stock configuration.
1. Stock power steering with normal alignment setting.
Not ideal Too heavy and numb, difficult to make quick corrections and my arms went numb and started to burn at the end of a 20 min session. I'd descride it as a wrestling match.
2. No assist, with normal alignment settings. (closest to manual rack)
Extremely heavy. Unsafe on the track, cant make any sort of meaningful course corrections necessary for track duty. I had this experience at Limerock this year for 1 lap. My Porsche 944 100 Bar power steering pump failed. Clearly over heated, when I pulled into the pits and checked the reservoir I open it to make sure I didnt leave any oil on the track and the oil was smoking. When I got back home, I took the pump apart, it was badly scored and too far gone to be rebuilt. Fluid smelled like burnt clutch, had to rebuild the rack, lots of metal from the pump was visable in the oil. FAIL!
3. Modifed rack with thinned quill and 100 Bar pump. Stock alignment settings.
Much better for the 8 laps it lasted. Car was far more pointable, controllable, no arm fatigue, felt light on its feet, almost nimble and tossable. Totally different car. I could quickly transfer the weight and complete my turns. I ran my fastest time ever in the wet with wipers on at some points, a 1.07 and was easily doing 1.08's repeatable in traffic. Last track day with stock steering configurations was exhausting and the best I did for 1 lap was 1.08 with a clear dry track.
I dont think a manual rack it right for a 928. Based on my experience... a modified power rack is best. If you look at Modern Porsche, from a drivers perspective where you can see the hands ripping around the ring it's its very clear the steering is light and no doubt precise. That makes for less driver fatigue and better feel over all.
…
My current configuration is a highly modified rack completely reworked for reduced friction points and more assist. Now with a large fluid cooler. I'm also running 1/2 the toe spec and just 3.5 degrees of caster. ( 4 to 5 is spec). These setting were arrived at after much trial and error. Since my 928 is lowered I had some bump steer with 5 degrees of castor and almost none with 3.5. I also carefully went through every ball joint and tie-rod end and checked them for friction, a few needed to be replace not for wear but for stiffness. All this this makes for very light and very precise steering , even with less caster and more assist the wheel still snaps back to center quickly. This transforms the 928. The point-ability, precision, control and quickness are welcome changes from the stock configuration.
11-23-2020, 03:43 PM
#69
The Parts Whisperer
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11-23-2020, 05:14 PM
#70
Burning Brakes
Interesting to read that. I had decided that modifying the Quill was the way to go if keeping the OEM hydraulic rack, and I may well do that until I figure out an all electric solution. Maybe convert the rack to manual (remove all hydraulic parts) and add a powered column if I cannot find a suitable replacement rack.
Specifically...
1. The small and far inward bushing on the non-driver side
2. There is only a partial bushing on the driver side.
PM me if you want help re-doing the OE rack.
11-23-2020, 09:42 PM
#71
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Ah, I was wondering what he had done. That's the fall-back option. Plan B. However I'd really like to find a full electric solution. Perhaps a rack from a LHD 991/981 (and maybe other Porsche models), flipped for my RHD car so the pinion is on the correct side of the rack. That should work, although not sure where the electronic control is. Or maybe the Bosch equivalent EPSapa rack.
Anyway, still hopeful I'll find someone who has thought about or ideally done this. Otherwise, I guess I'm on my own.
A couple of quick questions. Anyone know the lengths (ball joint to ball joint) of the 928 and/or 991 racks? Also, do they use the same ball joint? By which I mean is the ball joint taper the same?
I'm not expecting a direct or even simple swap, but looking into what would be required. Early days.
Anyway, still hopeful I'll find someone who has thought about or ideally done this. Otherwise, I guess I'm on my own.
A couple of quick questions. Anyone know the lengths (ball joint to ball joint) of the 928 and/or 991 racks? Also, do they use the same ball joint? By which I mean is the ball joint taper the same?
I'm not expecting a direct or even simple swap, but looking into what would be required. Early days.
I ended up following a 944 manual rack conversion with stripping, lubing, remaking the oil lines to cycle the fluid, then filling and plugging the unused ports.
I bought an EPAS system by Ultimate Power Steering in the UK, which although quite a challenge to fit in there, does tuck in nicely. It can be switched off, switched to manual assist or switched to variomatic using speed pulse input from the diff.
Not cheap but totally silent and no belts, oil, hoses or reservoirs. As my project is not road ready I can't say what it's like driving but pushing it around the yard/shed with the bride at the helm. it's very pleasing.
Current draw measured well under 10 amps, closer to under 5 amps mostly
steering and about 20 amps when it hits the lock [full turn].
11-23-2020, 11:04 PM
#72
Burning Brakes
I've been down this path. I couldn't find an electric rack that would come close to fitting into the 928 without 'serious' cutting and shutting, if at all.
I ended up following a 944 manual rack conversion with stripping, lubing, remaking the oil lines to cycle the fluid, then filling and plugging the unused ports.
I bought an EPAS system by Ultimate Power Steering in the UK, which although quite a challenge to fit in there, does tuck in nicely. It can be switched off, switched to manual assist or switched to variomatic using speed pulse input from the diff.
Not cheap but totally silent and no belts, oil, hoses or reservoirs. As my project is not road ready I can't say what it's like driving but pushing it around the yard/shed with the bride at the helm. it's very pleasing.
Current draw measured well under 10 amps, closer to under 5 amps mostly
steering and about 20 amps when it hits the lock [full turn].
I ended up following a 944 manual rack conversion with stripping, lubing, remaking the oil lines to cycle the fluid, then filling and plugging the unused ports.
I bought an EPAS system by Ultimate Power Steering in the UK, which although quite a challenge to fit in there, does tuck in nicely. It can be switched off, switched to manual assist or switched to variomatic using speed pulse input from the diff.
Not cheap but totally silent and no belts, oil, hoses or reservoirs. As my project is not road ready I can't say what it's like driving but pushing it around the yard/shed with the bride at the helm. it's very pleasing.
Current draw measured well under 10 amps, closer to under 5 amps mostly
steering and about 20 amps when it hits the lock [full turn].
11-24-2020, 05:17 AM
#73
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I did put a spare stock one through some very nasty testing to see when it would fail but it didn't.
The stock U-joint must be able to operate in manual mode. Porsche would not design a component that would break if used with a failed hose or belt.
The other U-joints are from the US and are stainless steel. Luckily they are available with the weird Porsche spline count on one side!
11-24-2020, 02:13 PM
#74
Instructor
What was the Audi rack you were thinking of using? Did you check any measurements, or how you would interface the control unit with the 928's electrics?
Bearing in mind that there will be no engine sitting on the crossbeam onto which the rack is mounted, I can pretty much modify that however is required to suit mounting the rack and although a powered column (as just mentioned in this thread) is obviously a real possibility, a dedicated EPAS rack would in fact be superior in my opinion and doable in my case as I can modify the cross beam to suit whatever rack is used.
But there are certain restrictions. Length can be adjusted with different track rod ends, but column pinion needs to be ahead of the rack and ratio and assistance level would be important as well. Did you ascertain a particular Audi rack as suitable? Did you consider the 991 rack at all?
11-24-2020, 02:25 PM
#75
Instructor
I've been down this path. I couldn't find an electric rack that would come close to fitting into the 928 without 'serious' cutting and shutting, if at all.
I ended up following a 944 manual rack conversion with stripping, lubing, remaking the oil lines to cycle the fluid, then filling and plugging the unused ports.
I bought an EPAS system by Ultimate Power Steering in the UK, which although quite a challenge to fit in there, does tuck in nicely. It can be switched off, switched to manual assist or switched to variomatic using speed pulse input from the diff.
Not cheap but totally silent and no belts, oil, hoses or reservoirs. As my project is not road ready I can't say what it's like driving but pushing it around the yard/shed with the bride at the helm. it's very pleasing.
Current draw measured well under 10 amps, closer to under 5 amps mostly
steering and about 20 amps when it hits the lock [full turn].
I ended up following a 944 manual rack conversion with stripping, lubing, remaking the oil lines to cycle the fluid, then filling and plugging the unused ports.
I bought an EPAS system by Ultimate Power Steering in the UK, which although quite a challenge to fit in there, does tuck in nicely. It can be switched off, switched to manual assist or switched to variomatic using speed pulse input from the diff.
Not cheap but totally silent and no belts, oil, hoses or reservoirs. As my project is not road ready I can't say what it's like driving but pushing it around the yard/shed with the bride at the helm. it's very pleasing.
Current draw measured well under 10 amps, closer to under 5 amps mostly
steering and about 20 amps when it hits the lock [full turn].
What other racks did you consider and why did you reject them? As I mentioned before, modifying he cross beam to mount a different rack would not be an insurmountable problem for me. So if the only issue was the actual mounting of an alternative rack, that might still be the way to go for me.
I guess I'm keen on the 991 rack idea. It's the right sort of rack, A LHD rack flipped over would provide the correct physical movement required for the 928 and I think it should still work and it would keep it Porsche.
We could take it private if of no interest to others, but there's a huge amount I'd like to know about this.