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For those who haven't been following the saga of me replacing my overpowered '93 L.E. with a Xida/FMII-equipped MSM which, while mostly reliable and capable of punching well above it's weight (price) class, has a predilection for tossing its power steering belt during extended high-rpm use. Short recap: Several track days have been ruined when the PS belt unceremoniously shredded during a track day. Carrying a spare wasn't always the answer, as there was about a 25% chance that it would take out the Crank-angle Sensor and/or toothed wheel when it came off. There was no apparent misalignment of the pulleys and several members posited that sometimes it was "just one of those things". At the end of last season, frustrated by lost track days, I did the ol' "loop the hoses" trick and found it fairly awful. The steering effort was extremely high, there was a lot of slop in the steering (through the torsion bar) and an unbelievable amount of kick-back. Not fun to drive at all.
Over the winter, I purchased a used MSM rack from a wrecker and sent it to Miatacage for their depowering service (which, IMO, is a great value). It was here in lots of time for the first scheduled track day this Spring but, of course, coronavirus spoiled the fun for all of us. Our province is opening up some more now and we can now hold track days again (albeit with no passengers and strict social-distancing guidelines). I had the rack installed by my local shop last week and the alignment touched up.
The first problem arose with the alignment. The previous owner, unbeknownst to me, installed offset bushings in the upper control arms. I, cleverly, had extended lower ball joints added, which resulted in a minimum camber number of -3.8 degrees. Not terrible for a track-mostly car, so I didn't sweat it at the time. However, it also means (I think) that I cannot reduce the caster number to the desired range of 4-4.5 degrees (current setting is just over 6).
Our first track day was today. Driving on the street is just fine, with the steering heavy at parking speeds but lightening up with any speed and exhibiting zero slop. However, once the suspension loads up (either a high-g corner or even a 90-degree corner requiring significant steering input), the effort becomes onerous. Not nearly as bad as when I had the lines looped, mind you, but still tiring enough that I didn't complete a full 20-minute session at any time today. There is also significant kick-back through the wheel with any mid-corner bump - enough to shock my wrists. Result: Big grins from being able to hit the track again after a pretty boring Spring, but sore shoulders and wrists. On the other hand (pun intended), I didn't lose the power steering belt once today.
So, other than to update progress on my car, my question is this: Is the offset bushing the cause of the limited caster? If I change it out should I be able to get things within the desired range?
I don't know the answer to that question. But, isn't part of the answer to try rotating the bushings to a less aggressive position?
I've only ever used one in the LCA, but with two in the upper you should have a lot of scope to differentially adjust them to get the upper BJ exactly where you want it. Not a quick job though.
Separately, I'd look at bumpsteer. That kick you describe shouldn't be that severe if bump steer is minimized. A Longacre bump steer gauge is money well spent considering how many cars you modify. ELBJ do raise steering effort. On our ELBJ equipped cars, we run a bit less caster to compensate.
Thanks Emilio. If I understand bump steer correctly, it's the toe changing as the suspension moves through its arc - a function of the geometry between the control arms, upright and tie rod ends. Since the offset bushings in the FUCA are pulling the top of the wheel inboard (while the ELBJs are pushing the bottom outboard), would this exacerbate bump steer? I'd certainly like to get the caster down to about 4 degrees and maybe getting rid of those offset bushings will allow me to kill two birds with one stone. Would it be worth shimming the rack and/or installing the R-package tie-rod ends at the same time?
The Longacre BSG isn't in the cards, unfortunately. My '93 is gone to help pay for the 30AE (which, other than the one day at Laguna Seca, isn't going to see any track duty), so the MSM is my only "project car", although I'd be happy to just be changing tires and pads for as long as I can. My modification days are pretty much done.
Not sure if you even have a bumpsteer issue. The symptom you describe does sound like it though. There might be some way to DIY a bumpsteer gauge using a laser pointer or something.
I agree with Emilio, on my car with a depowered rack and ELBJ’s I need less caster to lighten up the steering some. I’m currently running 3.8 degrees caster and could probably even stand a touch less. The offset bushings probably need to go, 6 degrees is a ton.
re: the other problem, how low are you running your suspension? If significantly lower than stock, you probably have a bump steer issue also. You can address it (partially at least) with the R package tie rod ends, but I think shimming the steering rack up is a better/more powerful solution. The shims from 5x racing are good.
The combination of ELBJ’s and shimmed depowered steering rack without offset bushings, running 4.75” or so ride height, is a pretty tried and true formula. Basically every Spec Miata runs that way.
Last edited by Schroedinger; 06-21-2020 at 11:54 PM.
Thanks Schroedinger. The previous owner definitely had the car set up too low. When I had the ELBJs installed, the car was corner-weighted and the ride height set at 4.3" front and 4.4" rear (before was 3.7" front and 4.3" rear). With the power steering working properly, it was absolutely marvelous. So, from what you're saying, in addition to removing the offset bushings, I should raise the ride height even more and also add shims to the steering rack. Checking out the 5X Racing shim kit, it states that it will not fit the NB. Any other options?
I've ordered I.L.M. FUCA bushings as well as the R-package tie-rod ends (which, surprisingly, are available from my local dealer) and will get the caster and bump-steer issues sorted once and for all.
We had another track day on Wednesday (Canada Day) and there was epic, borderline torrential rain for most of the day. First observation is that steering effort does decrease in lockstep with traction (which one would expect). The other is that I'm loving the feel of the manual rack. It faultlessly communicates everything the front wheels are doing, with no ambiguity whatsoever. I went faster in the rain that I've ever before dared, with the chassis just dancing around the limits of adhesion. This car is just so awesome - no vices at all. Also, another day with no power steering belts being shredded is a good day.
Car was at my mechanic's for parts installation and re-alignment. The good news is that the deletion of the FUCA eccentric bushings fixed the caster issue. They were able to reduce caster to 4.5 degrees, while keeping the Supermiata track alignment settings (front negative camber was reduced from -3.9 to -3.8, but that's pretty minor). Track day this Friday, so I can see how it all works together. Will report afterwards.
In case anyone's interested, here's the alignment report:
It seems the offset bushings provide over 2 degrees more negative camber, which is why they're not exactly ideal when combined with ELBJs. Driving the car home this morning, I noticed that the kick-back through the wheel over bumps is pretty much gone, so the R-package tie-rod ends are working as intended. No opportunity for hard cornering, so final assessment will have to wait until Friday.
I promised an update. Long story short: Steering effort is reduced, as expected. Still harder than with PS but much more tolerable. I'm an instructor and, due to all the social distancing in place, no in-car instruction is allowed - lead/follow only. The bad news, for my arms, is that (with two student) I did 12 twenty minute sessions today, one hour on and 20 minutes off. I'm completely knackered as a result. The steering effort is quite tolerable for a session at a time, spread out throughout the day, but perhaps not ideal for an endurance race.
The bump steer is pretty much banished with the R-package tie-rod ends. What was a mule kick through the steering wheel is now merely information (albeit very unfiltered information). There seems to be less front end grip than before, which might be a function of reduced camber gain from the reduced caster. A trade-off I'm willing to make, I think. Still no power steering belt failures to report.
Glad to see you're making progress. 4.5 degrees of caster is still quite a bit, you could probably dial it back to 3.5 or so. May depend on the tracks you're running; I like my steering quick at AMP and Barber but I like more caster at Road Atlanta because the car can get skittish on long straightaways. I'm running 3.8 which seems like a pretty good compromise.
Pre ELBJ, all our cars were maxed out 4.5 to 5 degrees. With ELBJ, we dial that back to about 3.5. Keep in mind that the main reason to a dial in all that caster was for the camber gain when turning. That is obviated with the ELBJ.
Either my front suspension is slightly bent or I just have a collection of parts on the skinny end of the Bell Curve, but 4.5 degrees is the minimum caster my shop was able to dial in (the shop owner, who worked on my car, is a top Spec Miata driver who knows his way around setting up our cars). Otherwise, I would be all over your suggestions. Would raising the front ride height allow for more caster adjustment, perhaps? I don't want to just try it, since the car is currently nicely corner-weighted and the recent shop bills have tapped me out. Thanks for all the input, fellas.
06-19-2020, 10:54 PM
Depowered steering rack installed
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