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Discussion Starter · #1 ·
this isnt a dodge specific question, but i thought some of you guys may know the answers. what causes bumpsteer exactly? in my project car i dropped my steering rack 5/8 of an inch all around to allow for more room for my big block dodge motor to fit better. i dont really care to be doing 70 and veer off to the right or left suddenly.
 
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At the bottom of that page is a diagram - that's the best way to look at it.

From the front of the car, look at the spindle. As it goes up and down, it travels in an arc. The upper and lower arms both travel in their own arcs, but because the spindle is attached to both of them, and they're different lengths, the steering arm travels in it's own arc. The tie rod has to be adjusted so it will exactly match the steering arm's arc.

In reality, the steering arm travels in an eliiptical pattern, not a true arc, but the tie rod DOES travel in an arc, so you can't adjust it perfect, only very close.


If you look at the longacre diagram, notice that if you raise or lower the rack location, the width of the inner pivots needs to change, as does the length of the tie rods, to match the intersecting lines. You only need to be close, so don't worry about custom-width racks and stuff, just take care in measuring the bumpsteer with what you have, and then adjust something and check it again. It only takes a few tries to get a feel for what's happening and then you can make smaller and smaller adjustments until you're as close as possible. For the most part, you're probably not far off to begin with, and chances are your only option is to adjust the height of the outer end, so you won't have much trial to get it whittled down.

It's kinda like adjusting carb jetting - make a single change and see what happens, then go from there.
 

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I'm thinking about modifying my outer tie rod ends for more wheel clearance... I've got 17x8's up front on my Valiant, and with 5.7" of backspace, I've got maybe 0.2" clear between the wheel and the OTRE.  If I swap the OTRE for a good Heim joint, and modify the LBJ for a straight stud rather than tapered, I can probably gain a couple more tenths of clearance.  However, if I TOP LOAD the OTRE, the clearance issue essentially goes away.  Potential bump steer issues are really the only thing keeping me from trying this at the moment.  Well, that, and actually researching what Heim it will take to do the job.  Is anyone here already using Heims for their OTREs, and has anyone already tried top loading the OTRE on the LBJ?  Were talking 73+ A-body parts...

Clair
 
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Mounting the heim on top will cause huge amounts of bumpsteer. However, if you just switch to a heim in the same location you'll gain quite a bit of space - that's why the alterk has a heim tie rod end - it's much smaller than a normal end. Drag cars mostly use 1/2" ones. I use 5/8" ones and they have held up to some unbelievable stresses - A 5/8 size is definitely safe to beat on.
 

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That's how I was thinking of starting out, on the bottom, so if I wanted to I could try it on top and go back easily if it got ugly. 5/8" is also the way to go, 1/2" just seems too spindly... like running with one lug nut on...

I know that QA-1 makes nice Heims, is there somewhere else I should be looking, too?

BTW, what constitutes "huge amounts"? If it's in the same ballpark as the taller spindles, I can probably live with that...

Thanks for the reply, Bill!

Clair
 
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Moving it that far would be like 1/2" of steer - excessive.  When I play around with the alterk on the stand, raising or lowering the end 1/8" changes the bump numbers more than 1/16" in each direction - the height is fairly sensitive.

I swear by QA1's X-series - they're chrome-moly, but instead of a full teflon liner that can pound out, they have a teflon "ring" inside the end - so it's lubed, but still metal to metal. There are suspensions out there for over 4 years on heavy street use and they're not worn out yet.

If you need more clearance and mis-alignment angle, try the PCM series - they're pretty tough too, but have 26 degrees of travel versus the X-series 16 degrees. They don't look as beefy as the X series, but the strength is there.

http://www.colemanracing.com also has neat little shim packs you can buy to adjust the height - VERY useful.
...I just checked their website, it's alittle confusing. The shim pack is like $10. It's part no. 808-900.
 

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That's awesome, Bill, thanks again! I'll agree that 1/2" of steer is a tad more than the difference between 0.040 and 0.020... That's good to know. Time to get my hands on one of those Heims and see how the size compares to the OTRE. Depending on how thick they are, that might gain me a thin half inch, and that might make the difference in fitting a 17x9 comfortably or painfully...

Clair
 
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You'll probably have to make your own adjusting sleeves with the correct threads, but that'll be a simple machine shop job once you figure out what you need.
 
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Actually, now that I think about it. The ones I have made are 9/16" right-hand threads on one side and 5/8" left on the other. If they're the thread sizes you do, I already have the correct ones handy...
 

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Heck, I don't know what thread sizes I have... it's all aftermarket replacement parts for an OEM 74 Dart suspension.  Tie rod sleeves are TRW's that are thicker in the middle, but taper down to the smaller A-body ends.  Kind of a hybrid C-body tie rod end arrangement.  I need to go measure some of that stuff, since I think I have a lot of it on the shelf already.

This might be as good a time as any to upgrade my tie rods, although it's all new stuff with only a couple thousand miles on it.

Here's a shot of the OTRE / wheel interface:


Looking at it, I think if the Heims are significantly thinner than the OTRE (up-down, not just side to side), that alone might let the wheel sneak past the OTRE...  Curiouser and curiouser...

Clair
 
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Now that I think about it some more, my sleeves would be too short. You'll probably need sleeves that are 8" long or so. I believe the A-body tie rods are 9/16" threads, and the bigger c-body(heavy duty) ones are 11/16". The kicker is that you can't get a 9/16" or 11/16" heim, so the adjuster sleeve will have to have different threads on each end.  Simple to make though if you're not worried about wrench flats. Just use a piece of DOM tubing and thread each end to your needs. Put a jam nut on each end to lock it in place.

Looking at your picture, you'll probably gain 1/8" or better by switching. The diameter across the middle is about the same, but it's only about half as high, so it'll be up tighter to the steering arm - it looks like that's what you need to get the tie rod away from the wheel....
 

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I'll go talk to my machine shop buddy to see what that would take. I do my own alignments, so no worries on anything funky that might be going on with the sleeves. As long as I know what's up, that's good.

The height is the magic dimension. That may have just solved the problem right there! tnku I'll mention this thread to the autoXers I've been talking with... this is good stuff!

Clair
 
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I considered making a tie rod with heims on both ends, so both ends of the link could be height-adjustable. The Mopar suspension has a one-way toe curve - I'd have to look again at the charts to remember which way it goes, but for instance, at full compression it's at a toe-out condition, and as the wheels fall, it toes inwards all the way to full rebound - it may be the opposite of that. So from ride height to compression, the wheels hit a toe-out condition, but during rebound, they toe-in.

In contrast, just to clarify the picture in your mind, the Alterk is at the apex of it's toe curve at ride height - the toe curve is toe-in from that point, in both directions.

I was thinking if both sides of the tie rod were height-adjustable, you may be able to cancel some of the goofy in and out curve the stock stuff had. I haven't had a chance to try it in the software to see what changes would straighten it out, if it even would help at all... I'm SLOWLY getting more tests done on the stock suspension, but I have to fit it in between the welding, so it's taking time. Definitely worth it though. Just the spindle tests alone have been immensely interesting.
 

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Bill,
One more question regarding the heims... when you talk about a 5/8" joint, that's the threaded end, not the hole end, right? I'm guessing that the 1/2" end is going to be sufficient as well? Pricing the stuff up in Coleman's on-line catalog, it looks like I can do heims on all 4 tie rods, with some sort of sleeve/lock nut situation for something in the $120-130 ballpark. The only "machine" work I may have to do is cut down their stock sleeves, and MAYBE find a bushing for the bolt end. Not bad, if it'll let me sneak that 17x9 under the front of the car...

Thanks again,
Clair
 
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Coleman also has that stud adapter to convert a taper, but it sticks down enough that I don't think it would help your clearance any. It's a useful piece if you have the room to fit it.

Use 5/8" X 5/8" - the big end of the taper is just about 5/8", so that's the smallest size you can go by simply drilling it out. If you machine a little tapered bushing you could go to 1/2" hole, but then there's the added expense of that. If you put the bolt up through from the bottom it's just the bolt head under the heim - that's about the tightest package. The only smaller option would be to use a 5/8" button-head fastener so the head isn't so big. Don't forget to grab some tapered spacers so the heim doesn't bind during travel. You could also use those shims I mentioned above - one on top and one below the heim so it has plenty of room to angle - the stock suspension travels pretty far and if you don't use the spacers, the heim can reach it's limit.
 

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Discussion Starter · #17 ·
i completly forgot about this, until i had to look up some info. thansk for all the tech bill, ive asked a few other sites (like rx7 specific, and v8 rx7 boards) and all i got was a bunch of beating around the bushes, no actual help.

i think im dropping my engine cradle 5/8 of an inch and buying the bumpsteer correction kit from a guy that makes them for the 3rd gen rx7. im still debating on pulling the engine cradle forward an inch or so.

here is a picture of my setup so far.

ignore some of it, still a work in progress. thats with it dropped ~5/8 of an inch, moving it forward an inch or so would give me much more room i think room for ear where starter bolts to and probably brake booster room) .

 
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