All right, I know I’m going to get flack about this. Like, that is totally brain-dead, why in the world would anyone want to do that? Well, it’s because I love driving my car. But I’m old now, and driving isn’t what it used to be for me. I don’t race every other car on the road (although the urge is still there) or drive the fun, twisty roads at the highest speed possible so much anymore. All too much I find driving taking me to various shopping centers to do battle with the SUVs finding and pulling into and out of parking spaces. This, and the unfortunate near-demise of the 15” performance radial tire, which caused me a few years ago to start using DOT- approved racing tires, mostly Kumho Victoracers, on my car (they wear faster, but then I drive a lot less, and the grip is terrific), have conspired to make me long for power steering. Those 205/50 racing almost-slicks on 7” rims that I have on the front are no fun to muscle around at low speed in a parking lot with limited clearance all around, and getting even less so as I get older and more arthritic.

There is another reason, but one not strong enough by itself to make me do such a thing. I’ve wanted to get rid of the bump steer my car has ever since I found out about it many years ago. It turns out, going to a ‘90s era power steering rack allows adjusting out the great majority of the bump steer because the PS rack is much smaller in diameter than the stock ZF rack, and it can consequently be mounted enough higher in the car to null out the bump steer. The effectiveness of doing this is shown in the graph below:

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I described the measurements and data behind this graph in a previous thread. In that thread, I mentioned that the PS rack I wound up using is 40mm longer than the stock rack between the inner tie rod joints and so the tie rods have to be 20mm shorter than stock if it’s used on a 914. This actually makes the bump steer worse (note the greater curvature of the green curve in the graph), but it’s something that gets swamped by the much larger improvement available from placing the rack high enough to make the tie rods parallel to the A-arms (which tilts the curves down to horizontal). I know there are less extreme ways of reducing the bump steer than changing the steering rack, but it represents an additional benefit to something I wanted to do anyway, and, now that I’m retired, the car is my hobby, so….

Selecting a power steering rack to use seemed like a good starting point. Like many others, perhaps, I’d seen these photos on the web about a V8 car someone built using a PS rack from a ’92 VW Corrado.

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Fitment with this kind of rack didn’t seem to be a big problem, the rack is readily available, and the number of turns lock-to-lock was essentially the same as the stock 914 rack, so I decided I’d risk $50 and buy a used one on e-bay to get an idea of what I was up against. I figured, once I’d used it for dimensions and making all the necessary pieces for the adaptation to fit, I could turn it in as a core on a freshly rebuilt rack that I’d actually install in my car. I’d gotten to this point before I wrote that previous post. Having the measurements on the PS rack was necessary to get the results I posted there. Getting from there to ready to bolt the thing into my car, however, was something else again. This was going to take a lot of trial fitting and measuring on a very difficult to get to part of the car. To make it more inconvenient, my agreement with my wife was, and is, that my 914 is never un-drivable for longer than 2-3 days at a time. Anything more and I have to send it to my mechanic and pay to have it done, which in this case would probably be hugely expensive. So, how to do this? And before anyone suggests it, the answer is not to get another wife. What I did was to go to Rich Bontempi’s High Performance House in Redwood City and find a 914 tub that was being cut up for various repair parts. I got the entire cavity that contains the gas tank from 6” behind the pedals to 6” into the front trunk, less the fenders, to use as a test-bed, and built a jury-rigged rotisserie to hold it, using a ¾” steel rod through the mounting holes for the front stabilizer bar as the pivot.

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I found a used 914 front suspension cross member on eBay for $25, and I had all the pieces I needed to insure that everything would fit. I could cut the holes needed for the new rack in my test-bed with abandon since this wasn’t my car, and I could take careful measurements once I had everything fitting properly so I could cut the minimum amount of metal when it was my car. Rather than modify the cross member by welding on the attachment points for the PS rack, I decided to make an intermediate piece that picks up the factory mounting points on both the rack and the cross member. This piece would have to hold the rack at the optimum height that I calculated previously would minimize the bump steer. To insure this, I made some simple jigs to hold the rack at the correct height relative to the mounting holes for the A-arms in the cross member, and then did the final welding of the intermediate bracket with everything bolted up in place.

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Two new access holes were required for the PS rack, one in the top of the hump formed into the floor pan to contain the stock rack necessitated by the fact that the input shaft on the PS rack isn’t in the center, and one in the firewall between the interior and the cavity that contains the gas tank for the shaft to connect directly to the steering column. The first one needs to be right where the tubes that supply brake fluid from the reservoir to the master cylinder, the wires that connect to the brake failure warning switches, and the overflow drain for the brake fluid reservoir go through the top of the hump. All these can be passed through the larger hole, once it’s cut.

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After I had this hole cut and enlarged to clear the new rack, I looked at locating the perforation in the front firewall. This one was tricky because of the compound angle at which the input shaft points relative to the plane of the firewall. I felt it was also important to maintain a good seal here, so that the interior is at least as well-separated from the area around the gas tank as it is in the stock configuration. I wound up with an arrangement like this:

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I found that a piece of 3”OD exhaust tubing mounted as shown would clear the U-joint that attaches to the input shaft of the rack. So, I carefully measured and cut the tubing at the required angle, made and welded on a sheet metal washer to form the end, and then fitted it into place to allow me to trace its outline to define the required hole in the firewall. Once I’d cut the oddly-shaped hole in the firewall, I made a transfer jig out of plywood to allow me to duplicate its location when I installed the rack in my car. Rather than try to weld this tubular shield into the firewall, I welded it into a flat piece of sheet metal that I could then secure to the firewall with stainless pop-rivets, subsequently sealing all the edges with seam sealer. The semi-circular area machined away on the bottom inside of the shield in the picture below was added to allow getting a wrench on the clamp bolt of the input shaft U-joint, which turned out to be otherwise inaccessible.

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That took care of the basics of mounting the rack in the car, but a great deal more hardware is required to operate it as a power steering unit. To stay as close to Porsche design practice as possible, I used 944 parts for the other bits and pieces: the pump, reservoir, the multiple loop fluid cooler in the return line from the rack to the reservoir, and two of the short low pressure lines. I used 3/8” stainless tubing for the main pressure and return lines , which I ran under the passenger-side rocker below the -12 lines for the front-mounted oil cooler, and Swagelok compression fittings for all the various joints.

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I managed to get all the 944 parts on e-Bay, and bought a new high pressure hose for a ’92 VW Corrado to get the correct end fittings to mate with the rack. I mounted the return line cooler in the rear of the front passenger side fender well where it would catch windage from the tire. How I routed the lines from there to the rack is easiest to see in these pictures of them trail-fitted on the test-bed:

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With the line routing settled, I finalized the size and shape of the cutout I would need to make when I installed the rack in my car, and produced a paper template to use as a guide.

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I leveraged the already-scheduled removal of the engine in my car by my mechanic for various other updates, and got the pieces that go in the engine compartment ready for installation at the same time. The reservoir mounted neatly next to the battery on one of the uprights that mount the drain tubes on a four cylinder car. You can see where the lines enter the engine compartment just in front of the battery, and the return connection to the bottom of the reservoir in this photo:

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I mounted the pump on the right side of the engine using the mounting holes that originally supported the smog pump, and drove it from the outer groove of the two-row fan pulley that also was originally for the smog pump. The stock 944 supply line from the reservoir to the pump was just long enough, and a braided Teflon hose from the pump output to the end of the pressure line completed the necessary connections.

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Once I had the engine back in, I lacked only the shortened tie rods in the way of parts to be able to install the rack in my car.

The stock VW tie rods are much longer than those for the 914. Taking the difference in rack length into account, it turned out each VW rod needed to be shortened 6”. On the bottom in the following photo is a stock VW tie rod, the rod in the middle is a 914 tie rod with a “turbo” inner joint (note that the same style joint is standard on the VW parts), and on top is a VW tie rod shortened for use with the PS rack in my 914.

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To shorten the rods, I first tried simply cutting off 6” and then re-threading the end with a die. This produced a rather poor result because the threads on the stock rods are rolled rather than cut, and the diameter of the bare rod is consequently less than the OD of the threads, leading to a low percentage of thread when you try to re-thread them the way I did. Fortunately, the tie rods are readily available from aftermarket sources at reasonable prices, so I got a second set and shortened them by cutting the 6” out of the middle and welding the rod back together. The VW rods are long enough to do this while still preserving the sealing area for the end bellows, the threads, and the hex section next to the threads for engaging a wrench to adjust the tow. To make the joint, I chucked both pieces in a lathe after cutting out the 6” and drilled and tapped a ¼”-20 hole just over ½” deep down the center on each of the cut ends, and also beveled the outer edges ~1/4”. I screwed a 1” long ¼”-20 set screw into one hole until it bottomed, and then screwed the other piece onto the exposed end of the set screw until it ran up against the first piece. The set screw was then completely enclosed and holding the two pieces in alignment, while the two bevels formed a “V” groove for a weld bead. Filling this groove with weld bead produced a good high-penetration weld and a tie rod with good threads and wrenching hex.

Armed with the shortened tie rods, there was nothing left to do but install the rack in my car. I pulled the gas tank and first used my jig and pattern to locate the two holes I would need to cut. The circles on the paper pattern locate the guide holes for hole saws at the corners, which had to be used from the bottom because of the curvature of the hump.

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Once these were located, it was time to pull the stock rack out and actually cut the holes. This shows the holes cut, the bottom hole edged with rubber “U” channel, and the rack, the input shaft shroud, and some of the lines trial fit into place:

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It was at this point that I made an unfortunate discovery. Since I finally had both racks out of the car and sitting on the ground in front of me, I decided to carefully repeat some of the measurements I had experienced trouble in making with the stock rack in the car. While it wasn’t something I measured before, I decided to measure the total travel of both racks, and to my horror the stock rack’s travel going from lock-to-lock was 170mm while the corresponding travel of the PS rack was only 140mm, even though both racks were three turns lock-to-lock. This meant that the steering would be ~18% slower with the PS rack, and the turning circle would be about four feet larger. Not what I had in mind. Thinking about it a bit more, I didn’t see how I could’ve found out about this in advance. The total rack travel isn’t specified anywhere I could find in any of the factory service manuals or spec. books for the 914, and isn’t specified in any listing I could find for replacement PS racks. What’s more, looking at the diagrams in ZF’s brochure on their PS racks, it’s fairly clear that the power assist mechanism requires some fraction of the rack’s length while the manual rack has no such requirement. So, if I were to find a PS rack with the correct total travel, there’s a good chance the rack’s overall length would just be that much larger, which would require even shorter tie rods and give back a great deal of the bump steer correction. Besides, I was already pretty well committed to this rack, having made so many things to fit it. I resolved to complete the installation and see just how bad this reduction in the steering sensitivity and increase in the turning circle was before contemplating any major modifications to correct it.

The finished installation in the area under the tank is shown below:

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This routing of the lines made for a very compact package in a crowded area of the car. Note that there’s even plenty of room for the fuel pump in the stock ’75 location, right across from the rack’s input shaft. The hook-up to the steering column is an almost-straight shot from the universal joint at the back of the shaft that holds the steering wheel to the u-joint on the rack input shaft, as you can see in this photo:

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Some adaptation was required, not only because one u-joint is Porsche while the other is VW, but also to allow the shaft connecting them to be installed without having to remove either the rack or the steering column. The VW joint came with a short (~3.5”) shaft with flats on opposite sides attached, while the 914 shaft was much longer and smaller in diameter with a spline on its end. Since I couldn’t measure the length of shaft required to connect the two very accurately in advance, I elected to connect them with a sleeve that I could slide up over the 914 shaft to allow the two shafts to be aligned, and then slid down over the VW shaft and be anchored with ¼-20 set screws on both sides. I machined flats on both sides of a spare 914 shaft I got on eBay (so I could preserve my entire stock rack and shaft set-up, in case I ever wanted to reverse the installation), and made the sleeve with a bore on each end to fit the appropriate shaft. When the PS rack was in place I attached the VW joint to it, clamped the modified 914 shaft into the steering column joint and slid the sleeve onto it, then aligned the two shafts and slid the sleeve down over the short shaft on the VW joint and tightened all the set screws.

Attaching the tie rods to the outer joints at the struts was simple because of the “turbo-style” inner joints. It was unnecessary to remove the former, just loosen the jam nuts and unscrew the tie rod until the end is free of the joint, replace the rack, and then thread in the new tie rods. With everything fitted into place, you can see from this photo of the front suspension how the tie rod is now close to parallel to the A-arm:

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After filling the system with fluid, checking for leaks, and having the suspension aligned, I set out to see what I’d done to the handling of my car. I was gratified that the 914’s light, precise steering hadn’t gotten much lighter under normal driving conditions. At speed, the power boost becomes noticeable only when you turn the wheel more than 20-30 degrees. You can certainly feel it when turning through a right angle corner, but it isn’t obvious when changing lanes or even swerving to avoid road hazards. The improvement in the effort required for slow-speed maneuvering in parking lots, however, is dramatic, as you might expect. My favorite test for bump-steer is to run over a small, approximately two-inch high bump in the pavement on a nearby street with only one of the front wheels and see if the car is pulled one way or the other. Prior to installing the new rack, I’d typically get a very noticeable tug to the left if I ran over the bump with the left wheel. With the power steering, however, there is little or no perceptible tug to either side when doing the same thing.

These results were basically what I had set out to obtain, however after driving the car for a month or so with the new rack in place, I came to the conclusion that I wasn’t going to be happy long-term unless I could restore the original steering sensitivity and minimum turning radius. Since finding another rack with a longer total travel was an unattractive option, as I explained earlier (in addition to being something I didn’t know how to do), I began to look at the other possible solution, which is to shorten the effective length of the 914 steering arms by 18%. This turns out to not be as difficult as one might think. The tie rod end joints hang down below the strut steering arm far enough that there is room to securely mount rod ends at a reduced distance from the strut axis while maintaining the correct height to minimize the bump steer. So, I designed and fabricated some pieces to accomplish this:

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Which, when installed on a strut, look like this:

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The rod end, a 14mm x 1.5mm fine thread part to match the threads on the tie rod, is straddle-mounted for safety and has its center of rotation held at the same distance below the steering arm as that of the stock tie rod end. The pivot point, however, is moved a little less than an inch along a straight line toward the center of the strut. Lots of careful CAD layouts verified that this position will give very close to the original steering sensitivity, minimum turning radius, and ackerman correction. It was difficult to find 14mm rod ends with the 1.5mm instead of the more common 2.0mm thread pitch. I did find some on McGill Motorsports’ UK website, but these were standard rod ends that have a fairly short shank with only about an inch of threads. My layout predicted that there would be only about ½” of threads engaged when everything is properly aligned if I used these, which, although probably safe, made me a little uneasy. I didn’t want to take any chances with something as fundamental as the steering, and also didn’t want to limit the adjustment range so severely, so I elected to buy and use the joints that Elephant Racing has custom-made for their bump steer kits with extra-long 2” threaded shanks. These took care of that problem, and now, with the parts installed and the suspension aligned yet again, the car handles very much like it did before I started this project, only with dramatically reduced effort required at low speeds and no discernable bump steer.

Was this a real factory 6 ??? I noted the front motor mount,which is OE six. .

his profile list a conversion 4 - 4702904577

Awesome write up!

Not an original six. I did my conversion in 1980, however, and all the conversion parts, motor mount, oil tank, etc. were still available from Porsche.

nice job on this procedure! I've never even thought at all about power steering in a 914 but I enjoyed reading about it!!

Excellent write up !!!!! Gives another dimension to steering , with the needed mods well thought out and presented .

Jack

Your profile says "doesn't post much" and hopefully after this wonderful writeup you will post a lot more!

Paul

Truly a great write up. If someone decides to do this in the future they are golden. You've mapped it out pretty well. Probably not something I will do but who knows. When I'm a little older I might

Ricardo Gonzales who I auto x with up here in Indiana took an electric steering motor from a POLARIS atv.

I drove it last year and it was very impressive

Nice work and really great write up. Nice fabrication!

You could have Changed tires and raised it. But fun to watch.

Nice!

I've read some folks threads here saying they've got BIG tires on the front and have no problem turning at low speeds- I don't really think that's the case unless they took the Charles Atlas course- but then I'm just a skinny guy. The power steering addition makes sense to me if the rest of the suspension doesn't get ripped out by big tires. A true GT car is just that- made for Grand Touring!

But light weight makes a sports car. I don't parellel park often
Depends on the outcome desired. But true gt's have a purpose and cutting weight helps

This thread has motivated me to get going on my next project. EPS, electronic power steering.
I found out a Saturn Vue EPS and custom control box can be grafted into any car. If you have fabrication skills... I will post a new thread as I get going on the project.
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Does this upgrade kill steering altogether if it loses electrical power?

There is an internal clutch that disengages toe worm drive so you can steer manually if power is lost.