Steering, Suspension, & Brakes

I finally built an EPS system for my car (Toyota based). I have not driven it yet since there seems to be a problem with the compatibility between the ECU and steering motor, but that will be worked out. however, it might be interesting to see my approach. Basically, I avoided any welding on the steering shafts and was able to keep about 2 1/2 inches of collapse distance.
I have more pictures that I can post but am at the limit for now...

Choosing a steering motor:
The most readily available speed varying units are Toyota Prius 2004 – 2007 and Yaris 2006 -2014. The rest of the discussion will be confined to these units. Both have separate ECUs which makes them more compact, and the Yaris has a smaller pinion gear which makes it even more compact. I used a Yaris unit and the following text and pictures are specific to the Yaris, but the general principles apply to the Prius. Yaris steering motors are most often found in Europe (but listed on US eBay). I got one from a Yaris 1.4 diesel from Lithuania. There are many Yaris motors available from the UK, but these motors are arranged in the mirror image from the left had drive units from continental Europe, so do not get one from the UK. Also, the 2012-2014 Yaris unit has the Toyota mounting bracket cast as part of the gearbox, before then the bracket was bolted on. I used the bracket bolt holes to attach my motor plate. For the later unit, the cast bracket would need to be cut off and mounting holes drilled and tapped. If possible, et a unit with its original ECU. There are differences in ECUs and not all are interchangeable. I have a compatibility problem with my ECU and motor that needs to be resolved before my steering will work properly…
Used assist units usually come with the original steering column and sometimes an output shaft extension. The first step is to remove everything and get down to the base unit. The inner steering column on the Toyota units is (somehow) securely fastened to the gearbox and should be left in place, but eventually cut to the desired length. I put a small set screw in mine to make sure it does not begin to move and so start to loosen.

Fitting the upper MGB column:
In addition to the steering, unit a spare MGB steering column and steering column support are nice to have so the originals will still be available as a back-up. Begin by taking the column and shaft apart (look in an MGB workshop manual – hint, the bearing cup at the bottom of the column is just a press fit and the entire inner shaft except for the upper bearing can be pushed out the bottom of the column once the upper bearing lock ring is removed). The next step is cutting the steering column just in front of the upper mounting hole slots (I used a cut-off disc in an angle grinder). When this is done, the mounting plate becomes held to the column by only two plug welds at the outer end. I added three more plug welds to make sure it will not come loose. Then I took the column to a machine shop and had the first 1 ¾ inches of the column machined out so it would be a press fit on the Toyota column (I shortened the Toyota column to a length of 1 ¾ inches, again with a cut-off disk). I chose this length so the area under the original plug welds would not be disturbed.

Fitting the upper MGB shaft:
The next step was to shorten the Toyota input shaft so only a small part of the splined area remains. The original MGB steering shaft has a “3/4 inch double D” configuration. The Toyota splined section is almost ¾ in in diameter, and I ground it down to a double D using a bench grinder. Before I did this I bought a Borgson double D coupler, [www.borgeson.com], and used it to check how the grinding was coming along. As well getting a tight fit to the coupler, I was careful to keep the double D flats centered on the shaft. I actually practiced on the intact Toyota shaft to get the grinding technique down before I cut the shaft to its final length and made the final double D. I fastened the coupler in place, then took it off and drilled recesses where the setscrews marked the shaft. For the final assembly, I got shorter screws that went in almost flush with the coupler outer surface because of the very limited clearance inside the column.

It is important to be able to fasten and unfasten the MGB upper shaft from the double D coupler. To make this possible, I drilled a hole in the column at the exact place where the set screw would be located in the assembled column holding the upper MGB shaft in place. It is then easy to put in or take out the set screws (assuming they are the type with a recessed Allen drive). Of course, the upper MGB shaft must be shortened to length. It is also possible not to use set screws on the MGB shaft portion but there is a slight amount of free lay which might become annoying. As described, the cut MGB shaft extends well beyond the steering lock slot so all functionality is retained.

Coupler set screw access
Once the MGB steering column is finally in place, it can be locked in position by drilling and tapping a hole through the MGB column and the Toyota column, and inserting a retaining screw. Do not do this until you are sure what angle you want the motor to be in relation to the column mounting flats (slightly up to the left worked for me).
Note, if the upper column is separated from the motor with the MGB shaft still connected to the Toyota shaft with set screws, the shaft torque sensor section will be torn apart and destroyed.

Modifying the steering column support:
The steering column support must be cut out to clear the motor/gearbox. It will be obvious what to cut once the MGB column with its mounting pads installed on the motor. Try to minimize the metal removal to retain as much strength as possible. I also reinforced some of the cut areas as shown in the picture. Tis support is designed to transfer the rearward force on the steering column in a collision to the firewall, otherwise, the force goes into the flimsy bar that runs behind the dashboard. Cutting open the bottom of the support to fit the motor removes much of the strength. With the smaller Yaris or Prius gearbox it is possible to put a support across the bottom of one side of the bracket as James Johanski showed in the post on his Prius conversion.
The final modification was welding nuts to the bracket for the bolts holding the gearbox support plate to the bracket.
Lower steering gearbox support:
The gear box support bracket is held to the gearbox with the original Toyota support bracket bolts. It is made from 16-gauge steel sheet, but a heavier gauge would have been better; I did add an additional reinforcing piece to the right side of the plate made from 12 gauge steel. Any flexing in the support bracket will probably lead to uneven steering assistance.
This support serves two functions: 1) it stabilizes the steering column because the lower collapsible column is quite flexible and the three mounting points on the original column provided the necessary stability (but now one is gone); and 2) it resists the turning torque of the EPS unit; the upper column is not intended to resist the steering torque and so it should not be relied on for that.

Lower MGB collapsible column:
The lower collapsible MGB column is cut to length and welded to the gearbox support bracket. To facilitate this, I drilled holes in the bracket that the cut ends of the column structure could fit into before welding. I also ground down the cut ends to make them better suited to going into the drilled holes.

MGB lower collapsible shaft modifications:
To prepare the lower shaft, I first cut off the splined end and took it to a machine shop to have it machined out from the shaft tube so it could be inserted again into the hollow lower shaft once the shaft is cut to length. I recommend cutting the shaft so there is just enough of the round section to insert the splined end in. I brazed (silver soldered) the spline plug in place (using two MAPP gas torches capable of heating the shaft to a dull red color) and also added some set screws inserted in drilled and tapped holes, and ground down flush with the outside surface (really not needed but to provide peace of mind).

A Double D to Toyota 17 mm, 36 spline shaft coupler is available [www.unisteer.com] to connect the MGB double D shaft to the gear box. The coupler has to be ground down to fit inside the MGB column but it is possible. I also replaced the Allen clamp screw with a button head screw for more clearance, and the mesh can be slightly “expanded” if needed. It is also very important to shorten the coupler behind the splined area so that the clamp bolt can fit in the groove between the two splined sections on the shaft.

Shorten coupler to match Toyota u-joint length
The shaft after the splines have the same OD as the splines so the coupler cannot be pushed on beyond the splined area. Compare to the original Toyota U joint if available. Cut the inner and outer MGB shafts so they engage but leave some collapse length (about 2 1/4 inches in my case). It will not be as much collapse length as the MGB had originally because the motor is in the way, but some collapse space is better than none. My setup has about 1.5 inches of overlap in the shafts, reducing this can gain more collapse space.

Note: there are recesses on the MGB double D shaft for plastic pieces to take up play between the inner and outer shafts. These are often broken and/or missing. They can be replaced by drilling a small hole in the outer shaft and injecting hot melt glue into the recess while heating the shaft with a heat gun. It is recommended to cut the shafts so the recess closest to the shaft end is inside the outer shaft section holding the relocated MGB splined end.

The original MGB shaft plastic inserts also keep the shaft pieces from sliding except in a crash, and so prevent the spring in the lower bearing cup from pushing the shaft out.

Installation:
First bench test the motor, ECU and controller. The first step is to connect power and make sure the motor does not run. Then turn just the upper shaft and see again that the motor does not run. Finally, twist the upper and lower shafts in opposite directions with pliers and make sure the motor starts to apply assist in the proper direction in proportion to the force applied. If one or more tests fail, help can be found online or from Buno. (My unit goes to full output at the slightest input force so I need to solve that problem.)
Remove the dashboard and install the column support and the new motor/column assembly. Note that the original MGB steering column can be reinstalled at any time without removing the dash again. Find a place to install the ECU and the control box and connect the power. For this unit all that is needed is a positive wire to the battery (probably off the starter motor), a ground and then a ground and an ignition hot wire to the Buno controller. Maximum current draw is 30 amps, but only when there is steering input. Most of the time the unit draws no power so the standard alternator (or even generator) should be sufficient. There is plenty of room in the car since the unit is so compact.
Note: I built in slots in the mounting holes to allow positioning of the unit in the car. The goal was to allow some “wiggle room” once it was installed to achieve optimum positioning.
[attachment 22994 uppercolumnoverviewcopy.jpg]

Thanks, Larry. Great writeup!

Every new option gets us closer to the ideal swap, if there could be such a thing. For now, for those with the bucks, Mike Moor's offer is about as good as it gets.

I'd like to see someone take on the MX5 EPS unit and let us know how that performs since they reportedly went to some trouble to retain road feel. What we seem to lose the most is the natural return to center, as most EPS units have enough rotational resistance on the output shaft to pretty much eliminate that. On my Toyota unit I even went so far as to install caster shims to INCREASE the stock caster and still got no really noticeable return to center action.

Even at that I wouldn't go back. Having power steering is great.

Jim

I just got my unit working with a new ECU. I ended up buying another Yaris EPS but this was compete with its original ECU, model 89650-52330. This worked for both my original, and the new EPS as well as a Prius unit I had. ECUs 89650-DD120 and DD190 did not work. The bad ones activated the motor from only from the torque required to turn the drive gear, using hand pressure. The correct one required resistance applied to the output shaft with pliers. With the bad ECUs, the motor went to full force as soon as the steering wheel was touched. If the wheel was let go of, the steering oscillated back and forth to full lock rather violently. Not good…
The car drives very well. I set the Bruno unit to reduce assist with speed as quickly as possible and the reduction in assist is quite noticeable. My next step is to remove the caster wedges and put the caster back to 6 degrees from 3 degrees. But even with the reduced caster there is a reasonable centering effect.

The Yaris unit is also quite compact and only a small opening will be needed in the under dash cover. I even suspect self centering is better with this than with larger units because the gear reduction is less and so there should be less resistance when the steering is driving the motor.

Larry my memory is less than perfect but the unit I used is either a Yaris or Prius, Yaris probably but could be either one. At the time I was under the impression they were both the same. It's pretty small and mounts similarly to yours but I have a short telescoping universal shaft going to a firewall mounted passthrough bearing block. I'm using the stock control box in limp mode which gives about 50% boost and that seems to work rather well. Not sure if it's worth buying the GPS Bruno control. I think that Mike uses the GM unit, I forget which one. Also the wheel offset plays a part, I do have custom hubs so the hub offset could be a little different, I'm not real sure about that. I have drawings that show 4-1/4" from the wheel mounting surface to the back end of the hub. My wheel offset should be somewhere around 15 but I'm not sure where I put the receipt.

With the reverse installed caster wedges there is a *little* self centering maybe? I have plans to switch to sealed timkens in the kingpins if I can ever get a line on the bearings I want to use and that should free things up a bit more. We'll see how it works then.

Jim

The Yaris gear box is considerably smaller than the Prius gear box (I have one of each). See the attached picture of the under-dash cover in place.

After driving the car more, it feels very natural and I no longer notice the power assist.

The following describes how to calculate the lower shaft lengths in relation to the collapse space available:
The first step is to find the total distance from the inside end of the hollow shaft to the outer end of the Toyota shaft coupling (with the parts laid out in their final positions). Divide the distance by 2 to find the middle. If the lower hollow shaft is cut to that length, and the upper solid shaft is cut to that length plus the length the upper shaft goes into the Toyota coupler, the two shafts will meet in the middle with no overlap. The next step is to decide on what overlap you want, and add that amount to each shaft length (such as one inch to each to get a 1 inch overlap). This will give the maximum possible collapse length. Be sure to shorten the end of the solid shaft so that the lower groove goes into the hollow section but do not worry about the upper groove.

Quote:

Larry my memory is less than perfect but the unit I used is either a Yaris or Prius, Yaris probably but could be either one. At the time I was under the impression they were both the same.

Deep back in this thread, Jim, you said that you used a 2009 Corolla EPS unit.

OK then that would be correct. Wonder how it compares to the Yaris in size? It's a good unit and is smaller than the GM version but the lower universal shaft makes it more difficult to mount. OTOH, it makes it less capable of converting itself to a spear in the case of a head-on collision so that's a plus. Maybe not the best choice though.

Jim

Some comparison pics at the link below.

[www.forabodiesonly.com]

More installation notes:

The distance from the center of the shaft to the bottom of the gearbox is about 2 inches for the Prius and 1.5 inches for the Yaris. Also, the internal gear in the Prius unit probably has about twice the number of teeth (circumference is proportional to the square of the radius) and so twice the reduction to overcome when driving the gear from the steering shaft.

The ECU for the Yaris/Prius has several different mounting configurations which can be quite awkward. But the sheet metal boxes are only held to the aluminum heat sink plate the computer is attached to by bent tabs, so it is easy to remove the box to alter its attaching points by welding or installing bolts as studs without damaging the electronics. I used a DD190 box with my 52330 computer after cutting off one mounting stud/bracket. The ECU now fits perfectly on the back of the console above the radio and the motor wires easily reach it (and plug right in). The ECU retaining stud also serves as a ground for the ECU wiring.

I liked keeping the original MGB spring loaded lower bearing. It seemed like a very ingenious design in that it can compensate for some steering shaft misalignment, at least compared to a rigid bearing. But with careful set-up, a rigid bearing is also fine as it has worked for Jim and others.

Hint: it is much easier to install (and remove) the stock MGB dashboard if oversize nuts are put over the mounting studs to act as spacers for the retaining nuts. There is much less turning to get the nuts tight and a 7/16 socket with a ¼ inch drive ratchet fits on most of the studs.

I will look for the Yaris gearbox next time I go to the pick-n-pull. Probably be a few years before the Miata ND begins to show up there. Hopefully there will be at least a little commonality between that and the Corolla box in terms of mounting and shaft connections. I did not alter the Corolla box in any way IIRC.

Carl, thanks for that link, it was a good one.

Jim

Comparison of Prius and Yaris steering motors:

The Prius gear is about 3 15/16 inch in diameter while the Yaris gear is about 3 1/16 inchers in diameter. However, both have 44 teeth, the pitch is just finer on the Yaris.

The output shaft diameters and splines are identical, but the input shafts, while similar, differ in that the Prius has coarser splines. The column stub outside diameters on the input side are identical so a modified MGB column will fit either one.

The Prius motor housing is about 5/8 inch longer and about 1/8 inch larger in diameter than the Yaris motor housing.

Good info Larry.
Wonder if the Prius and Corolla are the same.

Will you be going to Townsend? Maybe we could swap test drives.

Jim

Hi Jim;

I am not sure if I will be going, but it would be great to compare cars if I do go.

Larry

Steering feel is personal, and one system will not satisfy everyone. But after getting experience driving the car, I found an improvement in most conditions, not just parking. Especially impressive is the improvement in sharp, medium speed corners such as turning on to a side road or going through tight S turns (very common in the Midwest since secondary roads closely follow farm boundaries) at speeds of 30 to 45 mph. With unassisted steering, the steering becomes very heavy and makes the car feel ponderous. With power assist the car feels like the lightweight performance car it actually is. This alone justifies the EPS in my opinion. Of course, this assumes spirited driving; much faster than I would drive with my dog in the car, but not up to a competition level.

At highway speeds I sometimes get a periodic shimmy between 65 and 80 mph caused by slight tire imbalance. I always get the tires road force balanced, but with wear, rebalancing is sometimes needed due to an imbalance as small as ¼ oz. Currently, the shimmy is starting to return, but it has been completely damped out by the slight drag of the steering motor. The reduced assist at highway speeds is also much appreciated as the car feels just as stable as always. This was a concern because I am using the Moss quick ratio steering rack.

While the constant assist level of the fail-safe mode of the Prius/Yaris steering may be satisfactory for many people (all reviews I have read are positive), the speed sensitive feature is worth experimenting with. Especially since the Bruno box only costs about $100 including shipping (from Portugal) and can be installed in a few minutes.

"I am not sure if I will be going, but it would be great to compare cars if I do go."

What the heck were y'all doing in Monticello?! I am sure there were, at least a half a dozen conversion with EPS in attendance. We should have set up a parking lot demo somewhere.


Alan Hendrix of British Wire Wheel in Greensboro, NC maintains that much of the steering wheel shimmy on our LBCs is caused by out of round tires. He specializes in truing wire wheels & shaves tires every day.

Yes, a parking lot demo,aka autocross, would have been informative.

I did drive some cars with EPS but I was gentle with them since they were not my car. However, a parking lot demo session is much better controlled than driving fast on public roads, and I agree it would be an excellent thing to do. If I had known about the true advantages of an EPS system I would have installed one much earlier.

What is your opinion of the reduced road feel, Larry?