Manual steering rack
11-05-2011, 07:11 AM
#32
I'm talking about the fact that the 928 steering pinion sets in front of the rack and the outer tie-rod on spindle is trailing behind the ball-joint (rear steer).........(completely opposite the 944 front-steer configuration)
To mod a different rack for the 928, you would need a rear-steer rack, that's all I'm saying. Sorry If I sounded incoherent, it's early, I need coffee and I'm already in the shop modding some Late 944 struts for coilovers and inserts, they are rebuildable now.
I'm surprised that no-one has actually modded a 928 spindle.
To mod a different rack for the 928, you would need a rear-steer rack, that's all I'm saying. Sorry If I sounded incoherent, it's early, I need coffee and I'm already in the shop modding some Late 944 struts for coilovers and inserts, they are rebuildable now.
I'm surprised that no-one has actually modded a 928 spindle.
11-05-2011, 09:57 AM
#34
Nordschleife Master
This is a good idea but, I think, gets bogged down in the facts of how a 928 is.
The 928 is a heavier car than a 944 or a 911 and the double-wishbone suspension along with big caster numbers requires more force to turn and hold the wheel.
I've driven both my 928s and my 944 with no power assist and the 944 is much easier. I think that shows the basic difference in the need to put torque on the rack. (Torque, not power, sports fans.)
A viable solution, technically, is to make a rack and pinion with a higher mechanical advantage. A smaller pinion gear is what is needed. That'd take considerable work and the dimensions are already set by the rack housing. Getting a rack from another car is the best option.
I've tried to track my car without power assist. Actually only for brief instants after killing the engine and I ended up in the grass both times. It's too stiff to make quick adjustments.
The 928 is a heavier car than a 944 or a 911 and the double-wishbone suspension along with big caster numbers requires more force to turn and hold the wheel.
I've driven both my 928s and my 944 with no power assist and the 944 is much easier. I think that shows the basic difference in the need to put torque on the rack. (Torque, not power, sports fans.)
A viable solution, technically, is to make a rack and pinion with a higher mechanical advantage. A smaller pinion gear is what is needed. That'd take considerable work and the dimensions are already set by the rack housing. Getting a rack from another car is the best option.
I've tried to track my car without power assist. Actually only for brief instants after killing the engine and I ended up in the grass both times. It's too stiff to make quick adjustments.
11-05-2011, 10:09 AM
#35
Rennlist Member
I've got a 944 manual rack in the basement.
Can offer it up for one of you for 928 use, but it doesn't sound like its a viable alternative.
Its a tube with brackets, less complicated and substantial than 928 piece.
Can offer it up for one of you for 928 use, but it doesn't sound like its a viable alternative.
Its a tube with brackets, less complicated and substantial than 928 piece.
11-05-2011, 12:08 PM
#36
Here is the post from the 944 site describing the 944 steering rack.
Coming from a recently reassigned hydraulic power steering engineer of 4 years...
How to turn a power rack into a manual rack and actually live with it:
1. Piston chamber - must remain filled with POWER STEERING FLUID in order to keep seals sealed and bearings/bushings lubricated. Proper way to do this would be to remove the stock lines and plumb them one into the other. Since nothing will be pressurized, you could literally cut the lines and just use a ps friendly hose and clamps to connect. The chamber must be 100% bled free of air, or else you will get a nasty feel as the trapped air rushes across the piston seal and froths up your fluid making it spongy. Running both lines to a common resevoir would be the best way to keep it bled properly. If you don't disconnect the piston ports from the valve ports, you must force the fluid through the valve before it can get back to the low pressure side of the piston. This is about half of what makes a PS system with the belt disconnected feel mushy and overly heavy. That is as long as you still have fluid of course.
2. Pinion tower - 4 ports on this. Plug up three of them and run the fourth (highest one) to your resevoir. This area also needs to be kept full of fluid to properly lube the bearings. There is no "pumping" action up in the valve tower when unpowered.
3. Valve/pinion drive flats shim - the pinion (gear that engages the rack) and the valve (part connected to the input shaft) are two separate parts that are joined by a torsion bar. With the pump running, when you twist the wheel, the valve senses the amount of torque you're inputing to the rack and provides an increasing amount of assist as the angle of twist in the torsion bar increases. There's usually about 15 degrees of twist allowed before the valve reaches a mechanical stop on the pinion called the drive flats. This mechanical stop is there to limit the max amout of twist in the event of a pressure loss or torsion bar failure. When you disconnect your PS pump, you obviously loose all assist and must now twist the wheel through that 15 degrees or so in either direction before you can apply anything more than a few ft-lbs of torque on the steering wheel. This is a large factor in the "mushiness" felt by those running PS racks without the belt connected. The easy fix is to just take up the free rotation between center and each drive flat. This can be done with shims relatively easily.
4. Boots/rack teeth/equalizer line - Boots must be intact and sealing properly. Their entire job is to protect the inner tie rods, and they need to do this on both manual and power racks. Slather the rack teeth with a healthy amount of sticky grease (moly works fine), but definitely don't pack it in. And you must keep the equalizer line installed and intact. This is the line that transfers air from one boot to the other as the rack is stroked. If you leave this off, you may as well just run without boots and plan on replacing your tie rods every few months.
And that's it. Summary: you must keep fluid in the rack to keep it from eating itself to bits unlubricated, disconnecting the piston ports from the valve ports will lower turning efforts, proper steering maintenance items must still be attended to, and install shims to remove the free play in the valve/pinion assembly.
After you do all that, you should have a "true" manual steering rack (probably with a heavier ratio), that should last for a long time.
Coming from a recently reassigned hydraulic power steering engineer of 4 years...
How to turn a power rack into a manual rack and actually live with it:
1. Piston chamber - must remain filled with POWER STEERING FLUID in order to keep seals sealed and bearings/bushings lubricated. Proper way to do this would be to remove the stock lines and plumb them one into the other. Since nothing will be pressurized, you could literally cut the lines and just use a ps friendly hose and clamps to connect. The chamber must be 100% bled free of air, or else you will get a nasty feel as the trapped air rushes across the piston seal and froths up your fluid making it spongy. Running both lines to a common resevoir would be the best way to keep it bled properly. If you don't disconnect the piston ports from the valve ports, you must force the fluid through the valve before it can get back to the low pressure side of the piston. This is about half of what makes a PS system with the belt disconnected feel mushy and overly heavy. That is as long as you still have fluid of course.
2. Pinion tower - 4 ports on this. Plug up three of them and run the fourth (highest one) to your resevoir. This area also needs to be kept full of fluid to properly lube the bearings. There is no "pumping" action up in the valve tower when unpowered.
3. Valve/pinion drive flats shim - the pinion (gear that engages the rack) and the valve (part connected to the input shaft) are two separate parts that are joined by a torsion bar. With the pump running, when you twist the wheel, the valve senses the amount of torque you're inputing to the rack and provides an increasing amount of assist as the angle of twist in the torsion bar increases. There's usually about 15 degrees of twist allowed before the valve reaches a mechanical stop on the pinion called the drive flats. This mechanical stop is there to limit the max amout of twist in the event of a pressure loss or torsion bar failure. When you disconnect your PS pump, you obviously loose all assist and must now twist the wheel through that 15 degrees or so in either direction before you can apply anything more than a few ft-lbs of torque on the steering wheel. This is a large factor in the "mushiness" felt by those running PS racks without the belt connected. The easy fix is to just take up the free rotation between center and each drive flat. This can be done with shims relatively easily.
4. Boots/rack teeth/equalizer line - Boots must be intact and sealing properly. Their entire job is to protect the inner tie rods, and they need to do this on both manual and power racks. Slather the rack teeth with a healthy amount of sticky grease (moly works fine), but definitely don't pack it in. And you must keep the equalizer line installed and intact. This is the line that transfers air from one boot to the other as the rack is stroked. If you leave this off, you may as well just run without boots and plan on replacing your tie rods every few months.
And that's it. Summary: you must keep fluid in the rack to keep it from eating itself to bits unlubricated, disconnecting the piston ports from the valve ports will lower turning efforts, proper steering maintenance items must still be attended to, and install shims to remove the free play in the valve/pinion assembly.
After you do all that, you should have a "true" manual steering rack (probably with a heavier ratio), that should last for a long time.
Depending on how many pieces my 928 ends up in this winter I might give this a shot.
Getting a rack from a different car and getting it to fit/ fabricating mounts is just too much work for something the factory rack will do just fine. However a quicker rack would be nice.
Around parking lots and tight spaces no PS is tough with these cars but Ive driven my (2600lb) hybrid around town many times before I added PS with no issues at all. As long as you are on the move the steering is extremely communicative and not overly heavy at all.
11-05-2011, 12:48 PM
#38
Administrator - "Tyson"
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Thread Starter
Not at all, I think heinrich had the same initial thought I did which was a car with rear wheels that steer (Prelude / 3000GT etc..)
It's a very valid point that needed to be addressed.
The 79 spindle in my car has been modified to hold an S4 caliper. No adapters, my friend Todd cut off the factory mount and made a new one.
I only see this "mod" being performed on dedicated track cars. Most fall under the weight of your typical 944. Hell, I haven't even begun fully stripping my 79 and it's already 3,040lbs.
I knew this might be an issue, I have no idea the full limit of caster adjustment on a 928. This alone could easily kill the idea.
It's a very valid point that needed to be addressed.
The 79 spindle in my car has been modified to hold an S4 caliper. No adapters, my friend Todd cut off the factory mount and made a new one.
I only see this "mod" being performed on dedicated track cars. Most fall under the weight of your typical 944. Hell, I haven't even begun fully stripping my 79 and it's already 3,040lbs.
I knew this might be an issue, I have no idea the full limit of caster adjustment on a 928. This alone could easily kill the idea.
11-25-2011, 05:43 AM
#39
Administrator - "Tyson"
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Thread Starter
Found this post interesting from the 944 world on how to "depower" the steering rack. In other threads people who have driven 944's with a true non-power rack and a de-powered rack preferred the modified power steering rack due to the quick ratio:
https://rennlist.com/forums/8363705-post22.html
https://rennlist.com/forums/8363705-post22.html
well...
you need to accomplish 2 things:
1st. keep fluid in the rack but make some external hoses looped back to the rack (both going to and coming from the rack)OR cap off all the ports (no external hoses except for those fixed metal ones...)and fill with grease and remove the piston on the rack.
the reason you need to remove the piston on a sealed rack without looped hoses is because the piston creates pressure when moved left or right. external hoses fix this because air/fluid has a change to escape to the other side of the rack via the external hose when the piston moves(when the steering wheel is turned) i used standard axle/moly grease in my rack and sealed the rack with some threaded plugs.
2nd. and this is optional, but remove the two springs in the steering valve that allow for 15% rotation in either direction. with power steering in place, this acts as a dampener, with out power steering it will just make your steering feel mushy... you replace these springs with solid replacements so there's no give. i used an old allen key that i cut to fit.
hope this makes sense, i think it will when you get down there and see what everything looks like...
you need to accomplish 2 things:
1st. keep fluid in the rack but make some external hoses looped back to the rack (both going to and coming from the rack)OR cap off all the ports (no external hoses except for those fixed metal ones...)and fill with grease and remove the piston on the rack.
the reason you need to remove the piston on a sealed rack without looped hoses is because the piston creates pressure when moved left or right. external hoses fix this because air/fluid has a change to escape to the other side of the rack via the external hose when the piston moves(when the steering wheel is turned) i used standard axle/moly grease in my rack and sealed the rack with some threaded plugs.
2nd. and this is optional, but remove the two springs in the steering valve that allow for 15% rotation in either direction. with power steering in place, this acts as a dampener, with out power steering it will just make your steering feel mushy... you replace these springs with solid replacements so there's no give. i used an old allen key that i cut to fit.
hope this makes sense, i think it will when you get down there and see what everything looks like...
11-25-2011, 05:56 AM
#40
Racer
This is a good idea but, I think, gets bogged down in the facts of how a 928 is.
The 928 is a heavier car than a 944 or a 911 and the double-wishbone suspension along with big caster numbers requires more force to turn and hold the wheel.
I've driven both my 928s and my 944 with no power assist and the 944 is much easier. I think that shows the basic difference in the need to put torque on the rack. (Torque, not power, sports fans.)
A viable solution, technically, is to make a rack and pinion with a higher mechanical advantage. A smaller pinion gear is what is needed. That'd take considerable work and the dimensions are already set by the rack housing. Getting a rack from another car is the best option.
I've tried to track my car without power assist. Actually only for brief instants after killing the engine and I ended up in the grass both times. It's too stiff to make quick adjustments.
The 928 is a heavier car than a 944 or a 911 and the double-wishbone suspension along with big caster numbers requires more force to turn and hold the wheel.
I've driven both my 928s and my 944 with no power assist and the 944 is much easier. I think that shows the basic difference in the need to put torque on the rack. (Torque, not power, sports fans.)
A viable solution, technically, is to make a rack and pinion with a higher mechanical advantage. A smaller pinion gear is what is needed. That'd take considerable work and the dimensions are already set by the rack housing. Getting a rack from another car is the best option.
I've tried to track my car without power assist. Actually only for brief instants after killing the engine and I ended up in the grass both times. It's too stiff to make quick adjustments.
Puyi
11-25-2011, 02:12 PM
#42
Captain Obvious
Super User
Super User
Found this post interesting from the 944 world on how to "depower" the steering rack. In other threads people who have driven 944's with a true non-power rack and a de-powered rack preferred the modified power steering rack due to the quick ratio:
https://rennlist.com/forums/8363705-post22.html
https://rennlist.com/forums/8363705-post22.html
11-25-2011, 02:42 PM
#43
Rennlist Member
In the 944 world there is a factory manual steering rack with a different turn ratio for less effort without the power assist.
I've driven both of my 928's with the belt off a few times, not bad but definitely too much effort for regular driving.
This may be in the realm of impossible, but what would it take to modify a 928 rack to be more like a traditional manual rack? Has anyone ever changed the rack to pinion ratio before on any make / model of car?
I'm thinking for my track car, just one less thing to worry about not having that pump, the lines, fluid etc.. on there and less weight.
I've driven both of my 928's with the belt off a few times, not bad but definitely too much effort for regular driving.
This may be in the realm of impossible, but what would it take to modify a 928 rack to be more like a traditional manual rack? Has anyone ever changed the rack to pinion ratio before on any make / model of car?
I'm thinking for my track car, just one less thing to worry about not having that pump, the lines, fluid etc.. on there and less weight.
that could be a dangerous proposition. as it is now, the responsiveness of our racks are not optimal compared to most race cars, even those without powersteering. there is a reason that even a cup car has power assist.
you can always go electric like anderson.
11-25-2011, 02:50 PM
#44
Rennlist Member
Erik,
Why not just fit an electric pump. I have a setup in the garage on the shelf from an MR2 I was going to fit to my Audi SCCA project... but that looks like it may be liquidated to make room for more 928 stuff. Anyhow, with an electric pump, you can use a controller to adjust the speed of the pump, and hence total line pressure. So, you can dial in the amount of assist you want, or even have it adjust in relation to speed or steering angle.
Just a thought.
Hans
Why not just fit an electric pump. I have a setup in the garage on the shelf from an MR2 I was going to fit to my Audi SCCA project... but that looks like it may be liquidated to make room for more 928 stuff. Anyhow, with an electric pump, you can use a controller to adjust the speed of the pump, and hence total line pressure. So, you can dial in the amount of assist you want, or even have it adjust in relation to speed or steering angle.
Just a thought.
Hans
11-25-2011, 03:04 PM
#45
Perhaps something a little more involved is needed, much like the guy's at re-speed did for the first generation RX-7. Their kit includes a completly different cross member and mounts the engine directly to the front cover (not ideal for our cars though).
But with the RX-7's crappy itman arm steering there was a need for it, not sure if our cars really have enough owners that would want a manual rack.
http://mrcmfg.com/catalog/index.php?cPath=112_133
But with the RX-7's crappy itman arm steering there was a need for it, not sure if our cars really have enough owners that would want a manual rack.
http://mrcmfg.com/catalog/index.php?cPath=112_133