Super-fast ratio Corvette power steering rack in '88 Fiero

[The Dark Side of Will]

Depowering a power rack is a common mod to Mjatas.

[Series8217]

Speaking of Miatas, has anyone looked into running a Miata rack in a Fiero? They're front-steer..

[The Dark Side of Will]

Hadn't yet, but I'll check it out... a friend is putting a 1st Gen Mjata together with a bored/stroked 1.8 (2.0) in the next couple of weeks.

[Series8217]

Got everything pretty much bolted together now except coolant pipes and the steering column. I pulled the column so I could remove the dust guard and check clearance. Rick had to grind a bit of the firewall to get the steering shaft to fit on his car, because the pinion angle of the Corvette rack is different than the Fiero rack and it moves the shaft over a bit.

Tomorrow I plan to finish fitting the column, and then Thursday I'll put the rest together and align it. I got some Longacre toe plates, so between those and some string I should be able to get it pretty close.

[Series8217]

For reference, the AC Delco part number for the passenger side steering rack boot is 45A7055.

It's available from Amazon:
http://www.amazon.com/gp/product/B000C9 ... 05_s00_i00

On the driver's side, I used the Fiero boot or the Corvette rack boot; whichever one stretched longer. I think it was the Fiero one. IIRC the Fiero one is rubber, but the Corvette one is plastic.

[Series8217]

The steering wheel is not centered... it's about 120* off. This was not expected based on others' experiences shared in the thread on Old Europe. They said the stock shaft worked as-is. It's possible that my rack is slightly different. I didn't check super accurately if the rack was centered; I just followed Rick's dimensions and eyeballed it to see if it was in the ballpark. I'll have to double-check tomorrow.

The steering shaft hole in the firewall needs to be clearanced a few mm like on Rick's car.

The driver's side tie rod hits the swaybar when approaching full lock while the car is in the air (full droop). I don't recall this being an issue on the stock 88 front suspension, but maybe it was.

I'm going to clearance the steering shaft hole and then put the car on the ground tomorrow with wheels on it so I can set the toe to 0 and confirm if I actually have a problem with rack fitment and left side travel.

[Series8217]

I have a 6-bolt Sparco wheel, I was able to recenter my steering wheel by clocking it 120* to the left. This gets me pretty damn close to center.

I remeasured and it looks like my rack ended up 3/16" too far to the passenger side. It may just be down to chassis manufacturing tolerances. One tie rod is going to end up being 3/16" longer than the other in order to center the steering wheel. I don't think that's significant enough to cause any noticeable problems, so I'll go ahead and center the wheel.

[The Dark Side of Will]

Should have just bought this and a steering quickener: http://www.ebay.com/itm/200800748316

[Series8217]

That front suspension looks like it's been through hell. I bet the rack is all rusted out inside, and there aren't going to be parts available.

[Series8217]

Drove the car around the block and on the highway today. I'm running the rack dry (full of air) with the fluid ports capped of with AN fitting caps on the port adapters. My caster is at the mechanical maximum for an 88 suspension with stock geometry. I haven't fully clearanced the steering column firewall hole yet so the steering shaft still rubs. I have a small steering wheel (and inch or two smaller diameter than stock) so this increases steering effort.

Effort is OK when moving but not ideal -- its pretty hard. Highway effort and response is good in a straight line. Tire force feedback is strong.

Effort with the ports looped may be better. I may experiment with that after I finishing clearancing the column (which should help a lot).

I'll probably hook up the fluid lines but the car is driveable as it is.

[Series8217]

I forgot that reclocking the steering wheel means that all of turn signal cancel geometry is going to be messed up. One direction is now hard to set and the other doesn't cancel.

If I disassemble the column can I reclock these components?

Otherwise I guess I will have to pull the rack pinion and rotate it. Actually, that makes me wonder if the rebuilder just clocked it wrong during reassembly.

[Series8217]

Reclocking the pinion looks really easy: http://www.vetteweb.com/tech/vemp_1106_ ... index.html

I think I'll just do that.

[VF1SkullAngel]

I wouldn't mind doing this to my 86. I'm starting to think the steering rack is going and I might as well get something worth the while.

[Series8217]

The F-body power steering rack conversion is well developed for the 84-87 suspension. As far as I know, there are no 84-87 cars running around with the 'vette rack yet; only 88s. The front suspension (and crossmember) is completely different.

[Series8217]

I hooked up the pump and lines...

I ruined the car. I can't take it on the freeway like this. The W-body pump that goes with the 3.4 DOHC is NOT matched to this rack. It's so overboosted it's hilarious to drive. 2 turns lock-to-lock also makes it frightening as well.

I'll need to restrict flow somehow, or adjust the pressure bypass valve in the pump.

Also, how do I fill the system so the fluid doesn't just foam up like it has done now?

[Series8217]

Foam seems to be going away now. It was just all the initial air getting stirred up. The pump has quieted down. No leaks yet! I'll take full pics of the system once I have all the bugs worked out.

The twitchiness seems to be alignment-related. It's more twitchy when turning slightly to the right than to the left. Still too much assist for my taste though.

[The Dark Side of Will]

The assist is in the spool valve, not the pump. I think all GM systems use the same pressure. This is one of the gotchas of a GM/BMW swap, as the BMW steering gear wants a higher pressure than the GM pump delivers.

Anyway, there *should* be someone in the Corvette and/or muscle car community who can recalibrate the spool valve. This requires machining a new spring rod.

The C4 Corvette--especially the ZR1--has something like twice the weight over the front end as the Fiero, as well as different steering and suspension geometry--most notably caster... some tuning will be necessary.

Have you measured the bump steer yet?

[FieroWanaBe1]

You can check the pump output in pressure and flow on AllData or the GM factory manual for the LQ1 and the Corvette, even if the assist is controlled at the spool valve, if youre flow and pressure are reasonably in the range of the rack, lowering the relief spring force in the pump will help lower the assist. The gain remains the same, except the input force is lowered, so the output is lowered. Just dont outflow the rack's capacity, since it will blow out the seals. It looks like the Corvette and early luminas had the same style pump bodies. Im fairly certain that the corvettes had pressure compensated pumps as well. Swapping to a corvette pump may be a solution, mostly likely not though, given the size of corvette tires and the weight of the iron or 32v engines.

Edit: found these interesting articles, but useless for you at this point:

http://www.corvettefever.com/howto/16638/
http://www.vetteweb.com/tech/vemp_1106_ ... ewall.html

[Series8217]

I found a place out in the valley that can modify the spool valve to change the assist: http://lee-powersteering.com/

I'm going to go through my alignment settings more thoroughly to see how that affects the twitchiness.

Have you measured the bump steer yet?

No, but I don't see why it would have changed. With the adapters on, the rack is the same length as the stock 88 rack.

[The Dark Side of Will]

Mounts are different, though. If they are out (mostly up or down) just a little bit compared to stock, then you'll get bump steer.