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: Magnasteer on 2006 Z06?


GrantG
06-15-2005, 10:21 AM
I read the 12 page list of std and optional features of the new Z and it says that it comes standard with speed-sensitive power steering. Does this mean that we can infer Magnasteer or do you think some other speed-sensitive PS has been specially developed?

CorvetteInfo
06-15-2005, 10:47 PM
By all accounts the Magnasteer II has been carried over into the '05 C6. It is possible the system has been updated and recalibrated, but it remains basically the same as C5.

MAGNASTEER
General motors used EVO variable-assist steering over the years. In 1996, a more sophisticated type of variable-assist power steering, developed by Delphi Saginaw Steering Systems, called "Magnasteer" was introduced on the Corvette and other GM lines.

Unlike EVO variable-assist power steering systems, Magnasteer does not use an orifice valve to reduce pressure to the steering gear. There’s no solenoid or stepper motor involved. Instead, Magnasteer uses magnets to assist or resist steering input.

The Magnasteer control valve assembly is mounted on the steering rack in the same location as a regular control valve assembly on an ordinary power rack. Inside the base of the Magnasteer unit is a large electromagnetic coil. Just above the coil is an inner and outer pole assembly with a permanent magnet in the center. Steering feel is varied by changing the strength and polarity of the magnets, which in turn, is controlled by changing the pulse width and direction of the current to the coil.

On 1996 and 1997 applications, Magnasteer has its own separate control module. But on the 1998 and newer applications, the Electronic Brake Control Module (EBCM), which also oversees the operation of the anti-lock brake system, handles the Magnasteer control function.

Control input to the Magnasteer is via the vehicle speed sensor. At zero mph, a negative current of approximately two to three amps flows to the Magnasteer coil. This causes the magnets to repel each other, which in turn allows more deflection in the torsion bar inside the spool valve assembly. This increases fluid flow through the spool valve to the steering gear for maximum power assist when it is needed most.

As vehicle speed increases, current flow to the Magnasteer coil is gradually reduced. At about 45 mph, current flow to the coil hits zero and Magnasteer has no effect on the amount of power assist (which is determined only by the torsion bar and pump flow).

Above 45 mph, the direction of current to the coil is reversed and continues to gradually increase up to a maximum of about three amps at 75 to 85 mph. Reversing the polarity of the coil causes the magnets to attract each other, which has the effect of stiffening the torsion bar. This reduces the amount of deflection in the torsion bar that normally occurs when the wheels are steered and causes an increase in steering effort for better road feel and high speed steering stability.

The Electronic Brake Traction Control Module (EBTCM) looks at input from a steering wheel position sensor to determine if more or less steering assist is needed under certain driving conditions. Oversteer is reduced by reducing assist, when excessive lateral G-forces are detected.

Compared to conventional power steering systems, Magnasteer gives the driver a broader range of power assist with a smooth transition from low to high speed. The system can be recalibrated to modify steering feel using a Tech 2 or equivalent aftermarket scan tool. There are three settings: Factory, More Firm and Less Firm.

MAGNASTEER II
In 1998, a second generation "Magnasteer MAGe" system was introduced. This version eliminates the permanent magnet, using a redesigned electromagnet that has one pole mounted on the input shaft and the other on the pinion shaft.

At low speed, there is no current flow through the electromagnetic coil. The level of steering assist depends solely on the calibration (stiffness) of the torsion bar. As speed increases, current flow to the coil is gradually increased up to a maximum of several amps to decrease assist and increase steering effort. Magnasteer MAGe uses vehicle speed as its only input, so there are no changes in steering effort during sudden steering maneuvers.

Magnasteer Servicing
Magnasteer is vulnerable to the same kinds of problems as any other power steering rack, including leaks, center wear, excessive play, or sluggishness at cold startup or with high mileage.

Magnasteer needs repair/replacement when there is:

Noticeable change in the amount of steering effort (all speeds)
Stiffer than normal steering (low speed), or lighter than normal (high speed).
Erratic steering feel at various speeds.

The Magnasteer system has a self-diagnostic capability, with one fault code: C1241 (Magnasteer Circuit Malfunction). The code sets when the module detects an OPEN or SHORT in the coil circuit. If this code sets, Magnasteer is disabled and there is no variable steering effort with vehicle speed changes.

The DTC C1241 will set a DIC warning, and can be read with a Tech 2 or equivalent scan tool. Tech 2 can also perform a Magnasteer function test. Current to the coil is varied to test for changes in steering effort, when turning the steering wheel. A road test also confirms any problems with the system. At low speed, the steering should require minimal effort and feel the same in both directions.

As speed increases, steering effort should gradually increase. If the steering feels lighter than normal at high speed and/or unusually stiff at low speed, Magnasteer isn’t working. If the steering feels stiff at all speeds, the problem may be hydraulic. Noise indicates air in the system or a bad pump valve.

Magnasteer Electronics
With electronic problems, check the electrical connection to the coil on the Magnasteer unit. Coil resistance between terminals A and B should read 1.6 to 3.1 ohms. An infinite (OPEN) reading indicates a bad coil (requires replacing the rack since the coil is not serviceable). Also check for SHORTS between both sides of the coil assembly and rack housing.

If the Magnasteer coil is within range, check the wiring between the coil and control module, and at the control module itself for continuity for grounds, shorts, and opens. Check the control module for voltage when the key is ON (Terminal F on the EBCM or EBTCM). If there is NO voltage at the module, check the module FUSE and wiring.

Separate fault codes (VSS Circuit P0500, P0501, P0502, P0503, P1501) and Check Engine Light, indicates a problem with the vehicle speed sensor circuit which provides control input to the Magnasteer.

Magnasteer Hydraulics:
The Magnasteer rack can be tested using a high pressure gauge to check pump output and the operation of the steering gear. Systems operate at about 1,500 psi (maximum), with a flow rate of 2-1/2 gallons per minute. A weak pump, bad pump valve or a restriction, can have an adverse effect on steering effort.

When inspecting the rack, check the bellows on both ends for the presence of fluid. Large amounts of fluid in either bellow means the seals are leaking and the rack needs to be replaced. Leaks around the input shaft also requires replacement.

Magnasteer Rack:
When installing a new rack, make sure the pump and hose have been completely drained before reconnecting the lines to the rack. Refill the system with new power steering fluid that meets GM service specifications #9985010 (GM part number 1050017 or equivalent). Old fluid contains abrasive particles that can damage new steering gears and pumps. Installing an in-line fluid filter can also help protect new components and prolong service life.

Always check the condition of the power steering hose. Old hoses become brittle and leak, and can deteriorate internally, releasing small flakes of rubber into the fluid that can cause problems in the pump and control valve. Replace any high mileage hoses to minimize the risk of future problems. Inspect the pump drive belt and replace as needed.

Once the system has been filled, bleed off any trapped air inside (discolored or foamy fluid indicates air bubbles). Bleeding is also necessary if the fluid level in the pump reservoir has gotten low and allowed air to enter the lines. Air can cause noisy operation as well as reduced power assist.

After filling the pump reservoir with the new fluid, raise the wheels off the ground and slowly turn the steering from lock to lock with the engine OFF. When you reach the stop at one side, wait five seconds before cranking the wheels to the opposite stop. Continue cranking the wheels back and forth 10 to 12 times while adding fluid to the reservoir as needed to keep it full. This will purge most of the air out of the system. You may have to use a special power steering pump air evacuator to purge all of the air from the system.

With the power steering pump air evacuator, cycle the steering from lock to lock every 30 seconds for approximately five minutes while maintaining 15 inches Hg of vacuum. Do not hold the steering wheel at the stops while cycling because this increases pressure. Repeat the vacuum procedure as many times as necesssary.

When servicing is complete, short test drive to ensure the system is changing the amount of steering effort required as vehicle speed changes, and that the system is operating quietly with no fault codes reappearing.
Ref. (http://www.motortrend.com/future/spied/112_0304_c6/index2.html)
Ref./Credits (http://www.babcox.com/editorial/bf/bf20224.htm)

C'ya
D

theflinger
06-16-2005, 09:23 AM
that was pretty fun to read...especially after taking my physics final including electromagnetism :drink:

Thanks D!

GrantG
06-16-2005, 09:53 AM
I enjoyed reading that too. It certainly is impressively engineered, but it's my understanding that Magnasteer is largely responsible for the less than tactile steering feedback on the Vettes:(

fgordon
06-16-2005, 01:06 PM
Originally posted by GrantG
I enjoyed reading that too. It certainly is impressively engineered, but it's my understanding that Magnasteer is largely responsible for the less than tactile steering feedback on the Vettes:(

Where did you get that info? "Less than tactile steering feedback on the Vettes"

GrantG
06-16-2005, 01:23 PM
Originally posted by fgordon
Where did you get that info? "Less than tactile steering feedback on the Vettes"
Well, I am a longtime Porsche owner and I can tell you honestly that there is a huge difference. I really want to like the Vette (and maybe buy a Z06), but the C5Z and C6 Z51 are lagging far behind in steering feedback, precision and involvement. Some folks point to the Magnasteer as the culprit (along with run-flat tires), so I was hoping that the C6Z addressed this "problem".

CorvetteInfo
06-16-2005, 03:12 PM
Originally posted by fgordon
Where did you get that info? "Less than tactile steering feedback on the Vettes"
The M/T link above:

"The Corvette's version of Magnasteer variable-effort power rack-and-pinion steering is a more-than-adequate system for commuters driving Olds Auroras. Even with a lot of tuning by the Corvette group, it's never quite provided the kind of linear, accurate feedback that Porsche and BMW owners appreciate."

Roadkillz
06-16-2005, 03:30 PM
Easy fix for the run flats, get new tires.

GrantG
06-16-2005, 03:51 PM
Originally posted by DOC7000
Easy fix for the run flats, get new tires.
Doc - I'm with you on that one :thumbsup: Not hard at all, except there are no other tires currently made in those sizes, AFAIK. I'm sure there will be soon though...

k wright
06-16-2005, 05:17 PM
There is alot of tire and weight out front on this car to go without power steering. I think the magnasteer system presents an opportunity not seen with conventional hydrallic systems, an opportunity to adjust the amount of assist easily.

I have no experience with this system but look forward to using it. If it needs tuning I'll explore it then.

ken

GrantG
06-16-2005, 05:38 PM
Originally posted by k wright
There is alot of tire and weight out front on this car to go without power steering. I think the magnasteer system presents an opportunity not seen with conventional hydrallic systems, an opportunity to adjust the amount of assist easily.

I have no experience with this system but look forward to using it. If it needs tuning I'll explore it then.

ken
Ken - When I drove the C5 Z06 and C6 Z51, I didn't find the power assist over-boosted that much. The system (maybe the Magnasteer and maybe something else) just seemed like it was filtering out feedback from the front tires. Sort of felt like a video game instead of an intimate connection to the road (which allows you to push the car near its limits and have confidence where you are relative to the limit).

k wright
06-16-2005, 08:13 PM
I know exactly what you mean about feedback. I'm hoping that the feedback on the new car will be exactly what I'm after and if so will not think about changing anything.

Setting up this chassis offers us alot of opportunity to change the "feel" of the steering: toe-in and caster have a massive impact on sterring responsiveness. RE: less feedback, I've got to assume that if magnasteer was "cut back" then the torque that the steering rack feels would be transmitted directly back to the steering wheel. There is a solid link between the rack and the steering wheel and likely no significant mechanical friction. The dampaned feeling is from the amount of assist provided by the magnasteer. How cool would it be to have selectable amounts of assist with this system? Probably not hard to do.

The 911 has little mass in the front of the car and is quite willing to make quick changes in direction. I've seen this make a big difference in the 355 and the 550. It will be more of a challenge for the Vette.

Again, I'm hoping that we will get in the car and fin that the experience in something that we are not likely to be capable of improving.

ken

The article that details the function of steering rack above reports that with a Tech 2 scan tool the original version of magnasteer may be recalibrated to one of three settings. It also reports that the rack has hydrallic assist, magnasteer is used to vary the amount of assist dependent on vehicle speed.

ken