Power steering build, MR2 Electric Pump Options

[turboman808]

Let me know when you make a power brake system. I can live with the steering. but power brakes and even ABS would be killer.

[byndbad914]

Do you intend to measure the bump steer? That will be critical in either rack placement and/or tie rod mounting at the strut... given limitation in rack location possibilities you will likely need to machine tie rod spacers and use rod ends to mount the setup, drill the spindle "arm" out to match the rod end size, etc.

After relocating the stock rack in the race car, I did fine tuning of bumpsteer after converting over to 14mm rod ends for tie rod ends, and drilled the strut out to 14mm instead of the 12mm-14mm taper they have. Works ver' nize and is a nice, solid interface (no rubber whatsoever)

[drive-ability]

Do you intend to measure the bump steer? That will be critical in either rack placement and/or tie rod mounting at the strut... given limitation in rack location possibilities you will likely need to machine tie rod spacers and use rod ends to mount the setup, drill the spindle "arm" out to match the rod end size, etc.

After relocating the stock rack in the race car, I did fine tuning of bumpsteer after converting over to 14mm rod ends for tie rod ends, and drilled the strut out to 14mm instead of the 12mm-14mm taper they have. Works ver' nize and is a nice, solid interface (no rubber whatsoever)

The P/S rack was installed higher, closer to the body in the tunnel. It looks like about 1/2 inch. I'm sure I'll need to fine tune the bump. I didn't plain to use rod ends but I see how it would be nice. I'll have to look at that, since I'm not there yet your advise is appreciated. Each time I move forward I have more things to work out. I did see that the main steering shaft (914) is bent a bit, so I need to address this as well.

This is a lot more than I expected but I say why-not.. (IMG:style_emoticons/default/biggrin.gif)
(some day I'll build a car that has all the parts per-made (IMG:style_emoticons/default/lol-2.gif) )

[byndbad914]

(some day I'll build a car that has all the parts per-made (IMG:style_emoticons/default/lol-2.gif) )

hey, I am waiting for you to science this puppy out so I can copy it! With the big scrub radius with the fat front tires and struts in the way, I need PS for the track. The car wears my shoulders out pretty quickly.

[drive-ability]

I have set up one tie-rod, the rack is 48" to the end of the inner tie rod. That's about
8" longer than the old rack. As it sits at riding height the rod has a small rise as it leads out to the spindle. Looks like a 1/4 inch. Like most of us the term bump steer is a bit fuzzy to me. (IMG:style_emoticons/default/icon8.gif)




(IMG:http://members.cox.net/altjamy/Power%20steering%20tie%20rods.jpg)

[drive-ability]

Here is one tie-rod,
The end is 930, seems the thread/size is the same as the Jetta rack I'm using.
The tie-rod had to be shortened 4 inches. I put some threads on the male and female to lock in place and will weld the peaces up next. (IMG:style_emoticons/default/welder.gif)

(IMG:http://members.cox.net/altjamy/Tie%20Rod%20914.jpg)

[byndbad914]

I have set up one tie-rod, the rack is 48" to the end of the inner tie rod. That's about
8" longer than the old rack. As it sits at riding height the rod has a small rise as it leads out to the spindle. Looks like a 1/4 inch. Like most of us the term bump steer is a bit fuzzy to me. (IMG:style_emoticons/default/icon8.gif)

Bump steer is basically what it sounds like, when you hit a bump, the car wants to steer itself off center.

So, if you had perfect, zero bump steer, you could set the tire straight and move the tire up and down thru full travel and it would never turn and remain perfectly straight. This happens when you have perfect rack length to A-arm spacing, etc (a lot to explain but it is easy to google and read up on).

In short, because the rack is so much longer (taking 4 inches out of 930 tie rods is a LOT) you have pivot points for the tie rods that are way wider than the suspension geometry would need, so you are going to have a LOT of bump steer unfortunately. That means as you are rolling down the road and you hit a dip, etc that causes the suspension to compress and rebound, you can hold the wheel perfectly straight and the car will toe in and/or toe out like crazy. If they both compress perfectly the same amount you won't notice anything more than aggressive tire wear, but the typical case is one side moves more than the other, and in a straight line holding the wheel perfectly centered, the car will steer itself in the direction of the largest tire displacement.

I am not sure even aggressive rack relocation could fix that much difference in overall length with a strut suspension. What you might find is a spot that has such an aggressive tie rod angle you would have small bump over a small range of motion (1" each direction maybe) but then it would start getting aggressive.

You really should check out some website searches and make up some simple tools, buy a dial gauge (or two depending on tool design) and check it. Honestly. That car could be scary if you hit a dip on one side on the freeway and it steers in 1/2" on one side.

[andys]

drive-ability,

+1 to what byndbad914 said.
Yup, 4" is a lot.

Andys

[Wilhelm]

So the Jetta rack is 8" longer than the 914? Regarding bump steer.... I suspect the Jetta's wheelbase is no wider than 914's and so it must not be that much of an issue running a wider rack and shorter tie rods.

[drive-ability]

drive-ability,

+1 to what byndbad914 said.
Yup, 4" is a lot.

Andys

I took 4" off the Jetta tie rods and am using the 930 tie rod ends. The Jetta ends were longer to start with.

[byndbad914]

ahh, misunderstood. What is the length of the new, welded up tie rod v. the stock 914 you took out?? Measure the distance between the points of rotation, not overall length... what is the difference in that length?

[drive-ability]

ahh, misunderstood. What is the length of the new, welded up tie rod v. the stock 914 you took out?? Measure the distance between the points of rotation, not overall length... what is the difference in that length?

The inner tie rod is only 1" shorter, I suspect since I'm using the same tie rod
end that will be about it.

[charliew]

Someone will have to say but is the 914 perfect on bump steer to begin with? And at what ride heigth?

The ideal situation would be that the pivot at the end of the rack, where the tierod fastens on, is exactly even with the shaft that the lower a-arm pivots on so that the radius of their arc is identical out at the spindle. And the two are parallel, the tierod and the a-arm. If the rack tierod is longer or shorter the wheel will only be straight at one ride heigth. Also the length of the spindle arm is the same length as the distance the rack is from the centerline of the axle.

[byndbad914]

1" longer is still a pretty good amount, which means that it might be hard to get the bump out of it, but I think it is more doable at 1" than, of course, 4" like I thought before (IMG:style_emoticons/default/smile.gif)

charlie - I don't know about a stock 914 but I think it is rather low - the rack sits just above the lower arm pivot point and pivots at the same width and lines up decently with the upper mount locations, but when I built my tube chassis car I relocated the rack up, etc and have measured my bump - I have 0.005" on the first 1" of compression and an additional 0.007" on the second 1", so 0.012" overall for the max compression I expect on a race car, which is essentially what one would call "zero bump".

So, back to drive's issue, if the rack were in stock location then I can guarantee the 1" difference per side in tie rod length would have a strong effect for creating bump steer, like 1/4" in the first 2" of motion I would hazard to guess, and a street car should expect 3" of compression travel at minimum so the bump could be significant. Just being a bit off can cause 1/8" per side.

However, the rack is relocated a bit, so I dunno what effect that would have - it might be even worse. I suspect that an aggressive rack relocation and/or tie rod offset might fix it over a small range of motion but it will never be a "zero" bump setup because within just a couple inches of motion the difference in pivot locations will never want to zero out over 3" of travel (or more). But if it were an 1/8" even on 2" of compression, it isn't optimal but on a street car it probably wouldn't be that noticeable for most people (I would notice it cuz I am used to recognizing it). On a racer with really sticky and wide front tires, it would be very noticeable.

[drive-ability]

1" longer is still a pretty good amount, which means that it might be hard to get the bump out of it, but I think it is more doable at 1" than, of course, 4" like I thought before (IMG:style_emoticons/default/smile.gif)

charlie - I don't know about a stock 914 but I think it is rather low - the rack sits just above the lower arm pivot point and pivots at the same width and lines up decently with the upper mount locations, but when I built my tube chassis car I relocated the rack up, etc and have measured my bump - I have 0.005" on the first 1" of compression and an additional 0.007" on the second 1", so 0.012" overall for the max compression I expect on a race car, which is essentially what one would call "zero bump".

So, back to drive's issue, if the rack were in stock location then I can guarantee the 1" difference per side in tie rod length would have a strong effect for creating bump steer, like 1/4" in the first 2" of motion I would hazard to guess, and a street car should expect 3" of compression travel at minimum so the bump could be significant. Just being a bit off can cause 1/8" per side.

However, the rack is relocated a bit, so I dunno what effect that would have - it might be even worse. I suspect that an aggressive rack relocation and/or tie rod offset might fix it over a small range of motion but it will never be a "zero" bump setup because within just a couple inches of motion the difference in pivot locations will never want to zero out over 3" of travel (or more). But if it were an 1/8" even on 2" of compression, it isn't optimal but on a street car it probably wouldn't be that noticeable for most people (I would notice it cuz I am used to recognizing it). On a racer with really sticky and wide front tires, it would be very noticeable.

I normally learn as I go and it seems nothing has changed (IMG:style_emoticons/default/dry.gif) I'll just have to start with evaluating the basic P/S operation. If it works well I'll relocate the rack, why should this be any different than many of my projects..
I did take some measurements using a laser, moving the wheel up and down. It looked like I had some toe in but not much maybe 1/8 inch over 6 inches or so of movement. I did mount the rack higher, closer to the body and forward a bit as well. This was a crude test / measurement at best.
Nobody said this would be easy (IMG:style_emoticons/default/hissyfit.gif)

Here is the set up I used. The laser is level and the suspension is hanging down as I jack up the control arm the laser line should twist if the toe changes. I can't see it move much. I did it a few times and didn't see any real difference, less than the thickness of the laser line for sure. I see less than I mentioned above, looks like less than 1/16 or so.
What I did see is a lot of change in caster, honestly I don't know if thats normal or a big deal.

(IMG:http://members.cox.net/altjamy/Power%20steering%20Laser%20shot.jpg)

[byndbad914]

I normally learn as I go and it seems nothing has changed (IMG:style_emoticons/default/dry.gif) I'll just have to start with evaluating the basic P/S operation. If it works well I'll relocate the rack, why should this be any different than many of my projects..
I did take some measurements using a laser, moving the wheel up and down. It looked like I had some toe in but not much maybe 1/8 inch over 6 inches or so of movement. I did mount the rack higher, closer to the body and forward a bit as well. This was a crude test / measurement at best.
Nobody said this would be easy (IMG:style_emoticons/default/hissyfit.gif)

Here is the set up I used. The laser is level and the suspension is hanging down as I jack up the control arm the laser line should twist if the toe changes. I can't see it move much. I did it a few times and didn't see any real difference, less than the thickness of the laser line for sure. I see less than I mentioned above, looks like less than 1/16 or so.
What I did see is a lot of change in caster, honestly I don't know if thats normal or a big deal.

I believe I figured out your setup from the pic... depending how far away you take your measurement, the more toe you will see... so that can be all over the place.

BTW my first track day with the tube chassis setup when the front arm broke in half that Kanna Motorsports sold me, I called my friend and said "nobody said it would be easy, they just never said it would be so damn hard!" so, yeah, the projects never seem to end and the more you do the more you find you need to fix (IMG:style_emoticons/default/dry.gif)

Here is how a typical bump steer setup works - you mount a flat plate where the wheel mounts and the flat plate can be marked at your tire diameter (1/2 the diameter forward, half back) or the dial gauges set at a width of the tire diam. You would set up dial indicators front and rear at those points (or some now have a roller at one end and a single dial indicator) and you would be measuring the toe change at the tire's diameter.

A way you could more or less do this using your laser and a nice flat piece of plywood is

1. cut the piece of plywood to be say 8" tall (enough to fit a 130mm bolt pattern at 5.119" diameter) and to a length of around 24" overall (so 12" each way from center) which more or less mimics your tire's diameter (close 'nuf).

2. drill a bolt circle, at the center of course, using one of your spacers for a template.

3. mount the piece of plywood and get it level to ground.

4. set your laser up to run parallel to the board (you would be perpendicular to the board with your current setup), with the steering of course centered like you are driving forward in a straight line. Get the laser parallel by taking a measurement front and rear (should be the same value if the laser is parallel to the board). So if the plane of the laser is 4" away, you should measure 4" front and back... whatever the value, write it down.

5. jack the hub up ~ 1" and measure now from the front edge of the board to the laser and see what the difference is. the diff between the new value and the value you wrote down in step 4 is your bump at 1" PER SIDE. If the value got bigger, you toe'd in and smaller, then obviously toe'd out.

6. Take measurements every inch for 3" up and 3" down and you will get a bunch of different values that will be your toe curve.

This is way crude, but IMO if you can't measure the diff with a tape measure with 1/16" hash marks (.062") then I wouldn't worry about it. If you can see a measurable difference with the tape then that can't be considered "zero" bump.

Measuring perpendicular like you did will include noise due to scrub radius, etc.

You are on the right path to checking it tho'!!

BTW, as for caster, it isn't a big deal, but because the lower arm moves the bottom of the strut up and down in a truly vertical plane and the strut is actually angled back and hard mounted at the top, you should indeed get a slight increase in caster thru compression and less thru rebound.

[charliew]

Something a little easier might be to go to home depot and get a 36x1x1 alum.angle and drill two holes in it to go on the studs on the hub. Set the lazer straight up at the outer edge of the wheel dia. and like bad says make it a distance 1,2 or whatever and do the 1 inch measurements. I'm not sure the angle will clear the bearing housing on the hub though but it might. When you get through you can show everyone your bs tool.

[drive-ability]

I did get things going, first test drive was nice. I haven't done any measuring as yet, just wanted to see how the power part felt. My first impressions are its so cool !! The car is so easy to move around in tight places and feels good going down the road. I haven't driven it enough to evaluate the bump but I will do what I can to minimize it. Just driving though my neighborhood making 360 turns is so easy and with a V-8 its really helpful in first and second gear. My steering shaft under the dash the original part seems to be a bit bent, using a block bearing exposed something I wasn't aware of prior to this project.. I'll need to fine tune things but, its a success !!!! (IMG:style_emoticons/default/smilie_pokal.gif)

[Wilhelm]

Doncha love when a plan comes together? (IMG:style_emoticons/default/14.gif) Are you letting the power steering pump run all the time or are you modulating it down with speed or perhaps simply shutting it off at a preset speed?

[drive-ability]

Doncha love when a plan comes together? (IMG:style_emoticons/default/14.gif) Are you letting the power steering pump run all the time or are you modulating it down with speed or perhaps simply shutting it off at a preset speed?

I haven't graduate to that level as yet, it would be nice to have a computer that could PWM the motor. I am now looking at slowing down the motor in 3 & 4th gear if needed. I could or may get the guts out of an MR2, the steering wheel sensor, computer etc... I don't know if I can run that because I won't have all the inputs the MR2 had. Its likely the system would go in to limp and run the pump all the time or at a given percentage according to its programing but for now its working well. and the pump doesn't get hot at all.......