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Ok, I am near finishing final assembly on my car...here is the dilemna.

 

The steering rack (Woodward) cannot go any higher because it will hit the oil pan.  Everything has been clearanced as much as possible.  I "could" raise the engine, which of course would introduce negative fallout in terms of CG and other issues.

 

I have an Apex crossmember with multiple front suspension pivot points.  I am using the pickups in the stock location height wise, and matching the width of the inner tie rod pivots on the rack side to side.

 

My understanding is that the tie rods have to have basically the same angle as the control arms or I will have bump steer problems.  This is doable, but it requires using a long bolt on the steering knuckle and spacing the outer tie rod Heim joint approximately two inches below the steering knuckle.  This is the part that bothers me.  It is a single shear joint, I cannot conjure a practical way to convert it to double shear, and that seems like a lot of stick-out and lever-stress on the bolt.

 

Am I missing something?  Is there an easy solution here or is this just something that people modifying a Z front suspension have to live with?

Edited by Ironhead
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Couple pieces of advice from personal experience. Moving the rack forwards or back makes very little difference in practice. I moved mine back as tight to the xmember as possible, then decided to do a Woodward rack and the ps servo is right in the way, so I had to move it forward to fit. Had moved the rack back purposely to add Ackerman, and then a year or so later found a link that showed how to sketch it out on graph paper. Did that and found that the difference was tiny, so then when I had to move the rack forward, did it again, graphed again and ended up with something close to parallel steer. Not ideal for autox, but hey, throw some static toe out at it and it's just not a big enough difference to sweat over.

As to using a lot of bumpsteer shims to move the tie rod down, I was running my car like that for a while, it was good enough. Bolt is better than a tapered pin though, according to an engineer friend of mine. He said the tapered pins move around more and are more likely to break, and also that the thin circle track bumpsteer shims that I was using are not the best. He suggested running a really thick walled tube tapered down to fit on the rod end. I don't have a lathe, so I welded a rod end spacer to some thick wall tubing and then ground it to the right length with my belt/disc sander. Took a while, but it worked. Here's a pic of the old and new versions.

I have an extra length of this tube so if you want to do this give me $8.30 for flat rate shipping and I'll mail you a chunk.

holyscrubradiusbatman.jpg

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Maybe I'm missing something here, but can't you move the inner mounting points for the LCA to match the angle of the outer tie rods?  Or are you not wanting to do that because of roll center concerns?

 

@JMortensen, Jon, what adjustable front sway bar is that?  Have been going through mental gymnastics to design an adjustable bar for the front (with little success).   Did you move the frame mounting points forward of the stock mounting points?  That's the only way I would think you could use a straight center-section bar, true?  (Or minting bracket drop-downs, which does bad things to the end-link geometry).

Edited by jhm
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9 hours ago, JMortensen said:

Couple pieces of advice from personal experience. Moving the rack forwards or back makes very little difference in practice. I moved mine back as tight to the xmember as possible, then decided to do a Woodward rack and the ps servo is right in the way, so I had to move it forward to fit. Had moved the rack back purposely to add Ackerman, and then a year or so later found a link that showed how to sketch it out on graph paper. Did that and found that the difference was tiny, so then when I had to move the rack forward, did it again, graphed again and ended up with something close to parallel steer. Not ideal for autox, but hey, throw some static toe out at it and it's just not a big enough difference to sweat over.

As to using a lot of bumpsteer shims to move the tie rod down, I was running my car like that for a while, it was good enough. Bolt is better than a tapered pin though, according to an engineer friend of mine. He said the tapered pins move around more and are more likely to break, and also that the thin circle track bumpsteer shims that I was using are not the best. He suggested running a really thick walled tube tapered down to fit on the rod end. I don't have a lathe, so I welded a rod end spacer to some thick wall tubing and then ground it to the right length with my belt/disc sander. Took a while, but it worked. Here's a pic of the old and new versions.

I have an extra length of this tube so if you want to do this give me $8.30 for flat rate shipping and I'll mail you a chunk.

 

My Woodward rack is one of the manual ones, so I had a bit more freedom about where to mount it fore/aft.  But, at Woodward's suggestion I just mounted it slightly behind the imaginary line between the tie rod pivots on the steering knuckles and have no plans to mess further with that.

 

I think I'm OK on the bolt/bump steer spacer thing....I am using an AN10 (5/8") bolt spaced down with 1" OD  stainless steel spacers.  I guess my main concerns were:  How much total height of bump steer spacers is too much?  Also, are there any workarounds that I am missing.  Having the tie rod end cantilevered so far downward in a single shear joint just seems like bad practice, but so far I don't see any way around it. 

 

9 hours ago, jhm said:

Maybe I'm missing something here, but can't you move the inner mounting points for the LCA to match the angle of the outer tie rods?  Or are you not wanting to do that because of roll center concerns?

 

@JMortensen, Jon, what adjustable front sway bar is that?  Have been going through mental gymnastics to design an adjustable bar for the front (with little success).   Did you move the frame mounting points forward of the stock mounting points?  That's the only way I would think you could use a straight center-section bar, true?  (Or minting bracket drop-downs, which does bad things to the end-link geometry).

 

I can do that.  I would still need some bump steer spacing but the total amount would be much less.  My concern would not only be roll center, but the angle of the LCAs.  The LCAs would then be canted upward toward the outer ends when the vehicle is sitting at ride height.  For ideal suspension geometry, don't we want the LCAs pivoting as close to horizontal as possible?

 

I know trade-offs are part of the deal when we go modifying our cars....I guess I am trying to figure out which trade offs have the least/smallest downside.

 

Thanks for the help gents.

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As far as how much is too much on the spacers, I think fox body mustang guys run a lot, IIRC it's like 2 or 2.5 inches on that chassis. The other common solution would be to bend the steer knuckles. DP Racing does this for 510 knuckles to give Ackerman and to fix bumpsteer, no reason it couldn't be done to lower the tie rod attachment. Friend of mine had some bent for his 510, IIRC they heated them red hot with a torch, bent, then heat treated for strength.

Alternatively could just take a huge chunk of billet steel and make a forked end so you'd get double shear on the tie rod, which would be better but is a huge PITA and wheel clearance is a real problem on the Z. I've even seen sheet metal used in boxed structures that are welded for strength, and I'm sure that could be done if you were so inclined. I'm skeptical that it would be worth the effort on a 50 yo Nissan strut front end. My guess is that there's enough flex in the other bits that the gains probably wouldn't be noticeable.

The angle of the arm itself is kind of deceptive. You want the angle through the joints to be parallel. Since the ball joint sits entirely on top of the arm, that means that the arm will need to angle down to get the pivots level. A stock tie rod pivot is much closer, but still the angle of the tie rod isn't the the same as the angle of the joints. So if you line up the arms, you'll still be significantly off. Best way to fix bumpsteer is to measure it. I don't know if the guy who wrote the JTR manual that said to move the LCA pivot up 3/4" and out 1/4" actually measured anything, but when I measured on my stock(ish) front end 20 years ago, up 7/16" was what minimized it best. I suspect maybe he was looking at the arm angles, but that's a guess.

 

11 hours ago, jhm said:

Jon, what adjustable front sway bar is that?  Have been going through mental gymnastics to design an adjustable bar for the front (with little success).   Did you move the frame mounting points forward of the stock mounting points?  That's the only way I would think you could use a straight center-section bar, true?  (Or minting bracket drop-downs, which does bad things to the end-link geometry).

I'll make another thread. Those pics were taken when I was still figuring things out. Got it all done and then couldn't put the splitter on, redid the front mounts over the summer and haven't touched the car since then, but it looks significantly different now and the drop downs are... different.

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I am using the T3 LCAs, where in the pivot point is pretty much dead in line with the arm, so it's a bit easier to compare the angle with that of the tie rod.  I know I am going to have to wind up measuring bump, I just want the starting point to be as close as possible.

 

Thanks again for all the help.

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I have Baer bump steer kit on my 68 Mustang.  When I purchased the kit from Street or Track the owner Shawn told me don't bother testing amount of shims just use them all.  The total height of all shims is about 1".  Don't know the amount of shim you need or if this info helps but plenty of people have been using the Baer bump steering kit over the years of various racing and street cars so it has proven the test of time.

 

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Comparing the control arm angles and tie rod is the starting point.  Actually measuring bump steer is the logical next step.  I'm not sure what ends you have on the Woodward rack, but perhaps you could also add an adjustment there?  You can do the larger spacers (2"?) at the steering knuckle, but you might end up having interference with the tire/wheel.  Keep an eye on that.  If you are using a 5/8 bolt or tapered bolt at the knuckle, it should be plenty strong enough.  

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On 1/29/2021 at 8:42 AM, 280Z-LS3 said:

Sorry, I skimmed over the part where you wrote 2" needed.

 

Maybe a combination of something like Arizona Z Car Bump steering spacer can work or possibly using it in conjunction with Baer type spacer at rod end can work to get you 2".

 


knucke4.jpg

 

 

 There are two versions of these spacer/steering arm out there.  The old version has too much of a pocket in the steering arm and can break if you use them on track days and autoxs.  The other problem is they are flat.  So any spacers under them aim for the wheel.  A friend tried these and they wouldn't work when we went for enough of a spacer to lower bump steer.  Personally this is one item I don't think I'd use aluminum for.

 

One other general item I'd add around the spacers is to weld it to the steering arm and then use thin spacers to finish of the bumpsteer.  This is stiffer then adding a spacer to the top and a long bolt torques down.  

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  • 4 weeks later...

I have been trying to get all the suspension adjustments dialed in for the past couple of weeks.  Kind of frustrating in front, as I'm sure you all know.  Making one change affects everything else.

 

Once I made all the changes necessary to get 6 degrees of caster, I found that all the angles changed sufficiently that it appeared to change the relative angles between the LCAs and the tie rods.  So I had to quit dicking around and finally actually measure bump-steer.

 

I found that my eye-balling of the relative angles of the LCAs and tie rods had been pretty close.  To achieve "zero" (or close to it) bump steer required 1.83" of spacers between the bottom of the knuckle and the Heim joint.  More than I would have preferred, but it is what it is.  So, when accounting for the thickness of the Heim joint, steering knuckle, a couple of washers, and lock nut, I ordered 4.77" UHL AN10 (5/8") bolts.  McMaster-Carr had an assortment of 5/8" ID/1" OD stainless steel spacers.  I will probably do as tube80z suggested and weld a long one to the knuckle, then just fine tune with smaller spacers to get the 1.83" needed.

 

I had looked at the Arizona Z car knuckle with integral bump steer spacer, and at first thought it would be an ideal solution.  But, I too was bothered by it being aluminum, and it comes with the OEM style tapered holes when I needed straight 5/8" holes.  I spent the money on the AN bolts just because they are critical parts, and the AN bolts are fairly high strength while being designed to not be too brittle.  So if they are overstressed some bending should be visible before they fail.  Probably overkill, as I cannot imagine even in the long-spaced single-shear application I have conjured that a 5/8" bolt is going to bend/break steering a Datsun around. 

 

Thanks for all the input.

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14 hours ago, Ironhead said:

I had looked at the Arizona Z car knuckle with integral bump steer spacer, and at first thought it would be an ideal solution.  But, I too was bothered by it being aluminum, and it comes with the OEM style tapered holes when I needed straight 5/8" holes. 

 

So which steering arms (knuckles) did you end up going with?  (Personally, I agree with your assessment of the aluminum arms from AZC; and I believe that they are still machined "straight", i.e. no "twist" in the geometry like the OEM knuckles have.)  Both Apex and T3 offer nice quick-steer knuckles, machined from steel, with the requisite twist.  You could use either of these with standalone bump-steer spacers.

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45 minutes ago, jhm said:

 

So which steering arms (knuckles) did you end up going with?  (Personally, I agree with your assessment of the aluminum arms from AZC; and I believe that they are still machined "straight", i.e. no "twist" in the geometry like the OEM knuckles have.)  Both Apex and T3 offer nice quick-steer knuckles, machined from steel, with the requisite twist.  You could use either of these with standalone bump-steer spacers.

 

I'm using the Apex ones and selected the straight 5/8" holes.  Just gives me way more options for spacing than the tapered design.  It is often said that the tapered design is "safer".....but I dunno.  The straight 5/8" bolt, with a proper first-time-used locknut, is not coming apart.  MS365 locknuts are reasonably priced, and when installed the first time are hard to turn with a wrench.

 

So many of these aftermarket parts are made of aluminum not to save weight or even because aluminum is appropriate, but rather simply because aluminum is VASTLY cheaper to CNC machine.  IMHO aluminum hubs are in the same category.

Edited by Ironhead
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58 minutes ago, Ironhead said:

So many of these aftermarket parts are made of aluminum not to save weight or even because aluminum is appropriate, but rather simply because aluminum is VASTLY cheaper to CNC machine.  IMHO aluminum hubs are in the same category.

 

Yep...completely agree with you there.

 

I like the straight 5/8" hole as well, vs the standard tapered design.  Have been using the Apex arms, with straight 5/8" hole for three years now with no issues.  They are much easier to work on IMHO.

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5 hours ago, Ironhead said:

 

I'm using the Apex ones and selected the straight 5/8" holes.  Just gives me way more options for spacing than the tapered design.  It is often said that the tapered design is "safer".....but I dunno.  The straight 5/8" bolt, with a proper first-time-used locknut, is not coming apart.  MS365 locknuts are reasonably priced, and when installed the first time are hard to turn with a wrench.

 

So many of these aftermarket parts are made of aluminum not to save weight or even because aluminum is appropriate, but rather simply because aluminum is VASTLY cheaper to CNC machine.  IMHO aluminum hubs are in the same category.

I think I already said it in this thread, but an old racing buddy and engineer made a point of saying that the straight hole with a thick spacer preferable to a tapered hole stud that uses spacers. It makes sense. The diameter at the large end of the tapered hole is quite a bit smaller than 5/8" so it's only going to get weaker from there.

As to the aluminum vs steel, never underestimate the selling points of BILLET aluminum: 1) OMG it's BILLET!!1!!1!!  and 2) its legitimately lighter weight.

Edited by JMortensen
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Posted (edited)
3 hours ago, JMortensen said:

I think I already said it in this thread, but an old racing buddy and engineer made a point of saying that the straight hole with a thick spacer preferable to a tapered hole stud that uses spacers. It makes sense. The diameter at the large end of the tapered hole is quite a bit smaller than 5/8" so it's only going to get weaker from there.

As to the aluminum vs steel, never underestimate the selling points of BILLET aluminum: 1) OMG it's BILLET!!1!!1!!  and 2) its legitimately lighter weight.

Another point about the 5/8" bolt vs tapered stud:  If you buy a quality bolt from a reputable manufacturer, you have a very reliable idea of the heat treating and strength vs brittleness of the bolt.  With a tapered stud, I would probably trust one from Nissan, but do any come from Nissan anymore?

 

Aluminum has its place for sure...however...

 

I bought a set of 5-lug aluminum front hubs from one of the....uh....two places that sell them.  They came with no-name (probably Chinese) bearings, and I had quality SKF bearings on hand, so I figured I would swap them before install.

 

When I installed the hubs, they had so much run-out as to be completely unusable.  Something like .015" on the hub face and .040" on an installed brake disc.  Now, I realize it is highly unlikely that they came out of CNC that way.  It would be like turning something on a lathe and having it come out not-round.  Almost impossible...

 

I can only conclude that the hubs were so soft that just the process of pressing out the bearings and pressing in new ones permanently distorted the bore of the hubs.  I will accept blame I guess for changing the bearings...but...damn.  Who's to say they weren't already destroyed when the Chineseium bearings were pressed in at the manufacturer?

 

Maybe 7075 hubs would be more long-term usable, I dunno.  But since this is mostly about making cool looking parts at the lowest possible cost, I know that will never happen.

 

I'm pretty sure that no OEM manufacturer has ever sold a car with aluminum hubs...in fact I have seen plenty of high-end racing cars...with magnesium uprights and all that....but they still used steel hubs.  Since these sorts of manufacturers hate weight as much as anyone, I figure there has to be a reason.

 

After talking all this shit....I looked at some F1 hubs before posting.  They are either steel alloy or ti, but definitely not aluminum. 

 

I know you weren't arguing with me.  I'm just venting.

Edited by Ironhead
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Akshully, since you brought it up... ;)

Same engineer suggested I ditch my aluminum hubs because he said the hub and bearing expand at different rates and it's pretty common to spin a bearing in the hub at high temps. Most people who buy this all this blingy stuff just drive on the street, but for those of us who really push it it's a different story. I have a completely separate front brake setup with steel hubs and I'm going to get it all prepped and take it with me when I finally do a track day, and I'll be prepared to swap hubs if I have problems at the track.

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+1 on not mixing metals on rotating parts, unless one is intended to be a wear surface (like a bearing), or it’s an activity oiled bearing like the forged cam in the aluminum tower in your head. 

 

ME here, but I don’t work in rotating equipment. Mostly process design (oil, gas, and alt. Energy). 

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Posted (edited)
10 hours ago, calZ said:

Ironhead, were you pressing out the races or the bearings? All the S30 front hubs I know of, including my T3 hubs, use tapered bearings that don't press in. 

 

The "cup"...or bearing race...whatever you call it....has to be pressed in.  That's what I was talking about.

12 hours ago, JMortensen said:



Same engineer suggested I ditch my aluminum hubs because he said the hub and bearing expand at different rates and it's pretty common to spin a bearing in the hub at high temps. Most people who buy this all this blingy stuff just drive on the street, but for those of us who really push it it's a different story. I have a completely separate front brake setup with steel hubs and I'm going to get it all prepped and take it with me when I finally do a track day, and I'll be prepared to swap hubs if I have problems at the track.

 

Your engineer friend sounds like a wise dude.  Keep quoting him, I'm going to do what he says.  If you're the least bit curious, check the brake disc runout with your aluminum hubs.  I wager there's more than you want.

Edited by Ironhead
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