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PostPosted: Wed Oct 31, 2007 5:29 pm 
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This is going to be a strange request but..........

Does anyone recognize what lower ball joint my suspension has? The chassis was built by CMC using a 1983 RX-7 GSL donor. But the lower ball joints don't seem to be any RX-7 item that I can identify.

The attached picture shows a close up of my lower ball joint and the drawing is what the parts fiche shows what the 1 generation RX-7 has.

The joint mount on mine uses 3 bolts to hold it to the lower A arm. One bolt is hidden behind the joint in this picture. The steering arm above the joint has a hole that the ball joint is bolted through. The stock joint is pressed into the A arm. Mine has some sort of a 3 bolt adapter that the joint is in.


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File comment: Mystery ball joint
Ball joints.jpg
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PostPosted: Wed Oct 31, 2007 6:26 pm 
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It doesn't have a part number stamped on it anywhere?


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PostPosted: Wed Oct 31, 2007 8:15 pm 
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Auto-X Fil wrote:
It doesn't have a part number stamped on it anywhere?

Nothing that shows through the powder coat. I haven't taken it off the A arm though.

The strange thing is that one of them has a grease fitting on the bottom and the other one doesn't. Otherwise they are the same. It looks like the ball joints are pressed into the adapters but I cant be sure.

I would guess that they are off some small Japanese car. But which one?

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PostPosted: Wed Dec 26, 2007 6:43 pm 
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I think this ball joint looks like a '74-'78 Mustang II piece (upper ball joint). I also have CMC control arms and am using this ball joint on the lower end of the spindle (see photo).

A good referance document is the Lefthander Chassis catalog - available at Phone 815-389-9999 and www.lefthanderchassis.com. This catalog show pictures of most common ball joints that are used in oval track racing, and has the Moog part numbers for cross-reference.

Jim


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PostPosted: Wed Dec 26, 2007 10:53 pm 
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jrs7s wrote:
I think this ball joint looks like a '74-'78 Mustang II piece (upper ball joint). I also have CMC control arms and am using this ball joint on the lower end of the spindle (see photo).

It certainly looks like mine. I'll look for a Mustang next time I'm at the junk yard to make sure. Thanks for the info, that really helps me.

A good referance document is the Lefthander Chassis catalog - available at Phone 815-389-9999 and www.lefthanderchassis.com. This catalog show pictures of most common ball joints that are used in oval track racing, and has the Moog part numbers for cross-reference.

Jim

I found the Mustang one in the catalog. The catalog joint appears to be a one piece affair. When I look at my ball joint from underneath, it appears to have a housing with a ball joint installed into it. The ball joint itself isn't rounded like the catalog picture.

Is the ball joint itself replaceable in the housing or is it a one piece assembly?

One of my ball joints has a grease fitting and the other doesn't. Both appear to be new. Naturally the one with the grease fitting is so stiff that you really have to work at it to move the spindle back and forth when it is disconnected from the steering link with the car jacked up.

The car doesn't have ANY self centering affect when driving. That doesn't inspire a lot of confidence when you have to use some effort to steer OUT of turns. I need to find one that is just "sort" of worn in. :wink:

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PostPosted: Wed Dec 26, 2007 11:48 pm 
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olrowdy_01 wrote:
jrs7s wrote:
I think this ball joint looks like a '74-'78 Mustang II piece (upper ball joint). I also have CMC control arms and am using this ball joint on the lower end of the spindle (see photo).

It certainly looks like mine. I'll look for a Mustang next time I'm at the junk yard to make sure. Thanks for the info, that really helps me.

A good referance document is the Lefthander Chassis catalog - available at Phone 815-389-9999 and www.lefthanderchassis.com. This catalog show pictures of most common ball joints that are used in oval track racing, and has the Moog part numbers for cross-reference.

Jim

I found the Mustang one in the catalog. The catalog joint appears to be a one piece affair. When I look at my ball joint from underneath, it appears to have a housing with a ball joint installed into it. The ball joint itself isn't rounded like the catalog picture.

Is the ball joint itself replaceable in the housing or is it a one piece assembly?

One of my ball joints has a grease fitting and the other doesn't. Both appear to be new. Naturally the one with the grease fitting is so stiff that you really have to work at it to move the spindle back and forth when it is disconnected from the steering link with the car jacked up.

The car doesn't have ANY self centering affect when driving. That doesn't inspire a lot of confidence when you have to use some effort to steer OUT of turns. I need to find one that is just "sort" of worn in. :wink:


It sounds like you need to introduce more caster by moving the upper balljont back or the lower one forward.

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PostPosted: Thu Dec 27, 2007 1:01 am 
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chetcpo wrote:
olrowdy_01 wrote:
One of my ball joints has a grease fitting and the other doesn't. Both appear to be new. Naturally the one with the grease fitting is so stiff that you really have to work at it to move the spindle back and forth when it is disconnected from the steering link with the car jacked up under the lower A arm.

The car doesn't have ANY self centering affect when driving. That doesn't inspire a lot of confidence when you have to use some effort to steer OUT of turns. I need to find one that is just "sort" of worn in. :wink:


It sounds like you need to introduce more caster by moving the upper balljont back or the lower one forward.

Normally that would be the first thing I'd try but toe and camber are the only adjustments you have with a stock CMC. I've got about 6° caster right now. The A arms don't have any spacer washers at the mounting brackets. The nylon bushings fill up all the gap.

But that one wheel is very tight. You really have to brace yourself to turn the wheel itself. The steering doesn't seem tight at all at the steering wheel though.

All the parts on my front end are new and everything is very tight. Nothing is really binding though.

For instance, the steering links from the rack are very tight when trying to move them back and forth when they are disconnected from the spindles. And there's no adjustment to loosen them up.

I think if everything was worn in and a little loose that it would have self centering. There's another CMC in town and his self centers OK. But he has a lot more miles on his than I do. (Including track time.)

I'm ordering some parts to redo my Ackermann, steering ratio and upper A arm angle so while I have it apart I'll see if there's anything that can be done to loosen things up. Maybe just driving it more will be the answer.
---
On a side note: something I've noticed is that practically all the pictures I've seen of two piece Heim joints being used on suspensions don't have grease fittings. The fittings are optional on many Heim joints and some female ones have an internal grease passage way from the inside of the female threaded mounting area.

My Aurora Heims have a groove inside the retaining ring around the ball, but no lubricant. All my Heims have NO grease and I plan on dribbling some 90wt on them.

I've seen some ads that claim that the polished ball is "oil impregnated" but I really wonder how you can have a "highly polished" piece of hardened metal that is porous enough to retain oil. Sounds like an oxymoron to me.

This might be a topic for discussion if anyone has information to add.

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PostPosted: Thu Dec 27, 2007 9:07 am 
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Scrub radius?

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PostPosted: Thu Dec 27, 2007 10:39 am 
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That's a good idea, have you tried it with less offset/zero offset wheels?

Quote:
I'm ordering some parts to redo my Ackermann,


How are you going to do this short of hacking the steering arm off of the spindle and repositioning it?

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PostPosted: Thu Dec 27, 2007 3:00 pm 
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Olrowdy
Ackermann
Just from looking at the picture, I would guess that the spindles you are using are from a rear steer car. The steering arm position for the rod end attachment should be going in towards the disc on a front steer vehicle for the correct effectiving ackerman. I would also bet that 95% of all locosts will not have 100% Ackermann unless they are built with machined steering arms that give you some kind of adjustment or with a replaceable arm design that can be made at a new correct angled. As long as you are in the ball park it should be OK, unless you are racing for big money.

Selfcentering
It sound like something is binding. Start disconnecting the system one part at a time working your way back to the steering column until you find the cause of the binding. These cars are so light that you should not have any difficulty in turning them once you are going 5 MPH. By the way I have more caster and a lot more KPI then the book but my locost steering does not return like a big American sedan, but has nice straight line tracking. I think binding is probably the real problem.

Good luck on the suspension Dave W


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PostPosted: Thu Dec 27, 2007 3:42 pm 
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If your having to lift over center to turn out of the turn, you have plenty of caster already, maybe too much.

For more self-centering, since your stuck with the SAI, you need slight toe-in and some negative camber. If your toe-out, it would be darty even if everything else was good.

The rack can be moved aft for more ackermann as long as there is no binding.

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PostPosted: Thu Dec 27, 2007 11:41 pm 
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chetcpo wrote:
That's a good idea, have you tried it with less offset/zero offset wheels?

It's hard enough to find any wide rims that fit the 1st generation RX7 bolt pattern. Actually the rims came with the car so I'm going to stick with them as long as I can.]

Quote:
I'm ordering some parts to redo my Ackermann,


How are you going to do this short of hacking the steering arm off of the spindle and repositioning it?

I've been thinking about this whole front suspension setting part of any home built car and this response is just putting into words what I've come up with after many years of building cars. The worst handling one being a 1940 Ford dune buggy with 48" cut out of the w/b!!! But it was the most fun to drive.
---
To answer your question:
I've been playing around with two suspension programs for months now and I've come up with two easy to do things that hopefully will help correct/improve my bump steer, steering geometry and steering wheel turn ratio quite a bit.

The steering arms right now are the stock RX7 ones which had a different track and w/b as compared to a Locost. My CMC as delivered, bump steer right now is ~1/2" toe out for 5/8" dive!! My friends CMC has about the same amount with his CMC Toyota suspension. Both are rear steer and the racks can't be moved far enough to the rear to correct the link angle.

That's what happens when the original "designer" just throws various spindles onto various length A arms and doesn't take into consideration track and w/b. And then add in the fact that the the spindle tubes aren't long enough and ............. [ouch].

Surprisingly, I don't notice much affect of the bump steer when driving the car. If one wheel runs over a sewer lid in a turn the car will dart about just a little. But that's running at about 1/10 and not 10/10s.

My CMC stock setup right now has the outer ends of the upper and lower A arms closer together than the mounting ends. By using the suspension programs I found that I can get some camber gain in dive by raising the outer end of the upper A arm 1". I should be able to make a 1" thick steel spacer [more unsprung weight] to raise the upper A arm studded Heim joint.

I can correct the Ackermann by repositioning the mounting points for the outer ends [tie rods] of the steering links from the rack closer to the "kingpin line" and moving them 1° closer to the center line of the car. I'll leave the original tie rod mounting points on the steering arms until I know that this all works.

The bump steer right now is caused more by the incorrect vertical angle of the steering links than the also incorrect RX7 Ackermann angle. I will also lower the tie rod ends DOWN to the correct point. And they will be adjustable in height for small adjustments.

I've done quite a bit of measuring and staring at the front end and it looks like I can take a 1"x1" by 1/4" thick piece of angle iron and bolt/weld it to the underside of the steering arm to provide a new mount for some Heim rod ends that will change the Ackermann steering angle etc.

By moving the tie rod end mounting points closer to the spindle I'll also change my over all steering ratio [for the same amount of tire angle] from 3-1/8 turns to ~2 turns. Measuring the small angle change is going to be the fun part! Luckily the RX7 the steering arm is removable and the two mounting bolts are on the 0° reference line.
-----------
Has anyone made a scale model of the steering links etc of their Locost to draw out the "100%" Ackermann crossing lines? I did and I seem to have found that the Ackermann lines cross the rear axle extension line at only ONE particular steering angle! Any other steering angle causes the cross over point to be ahead or behind the rear axle line. The line of crossing is at about a 30° angle to the rear axle.

I am also able to confirm this by making a series of Ackermann drawings at different steering angles in Acad.
---
This is hard for me to explain, but I've found that Wishbone gives agreement between the "theoretical and actual" Ackermann if you input some steering rack change [1" for instance] and then change the amount of Ackermann angle to cause the theoretical and actual Ackermann to be equal [correct]. BUT the amount of Ackermann may be way above or below 100% when the tires are aimed straight ahead.

I think there is a big interaction between the "correct" suspension settings [having the ends of the rack in alignment with the A arm mounting points] changing to be NOT correct as the rack is moved to cause a turn.

That's when I decided to just make a scale model out of cardboard and DRAW the Ackermann lines to see what was going on.

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PostPosted: Fri Dec 28, 2007 12:02 am 
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davew wrote:
Olrowdy
Ackermann
Just from looking at the picture, I would guess that the spindles you are using are from a rear steer car.

Yep, a 1st generation RX7. They are being used as rear steer on the Locost too.

The steering arm position for the rod end attachment should be going in towards the disc on a front steer vehicle for the correct effectiving ackerman. I would also bet that 95% of all locosts will not have 100% Ackermann unless they are built with machined steering arms that give you some kind of adjustment or with a replaceable arm design that can be made at a new correct angled. As long as you are in the ball park it should be OK, unless you are racing for big money.

Another yep. :)

Selfcentering
It sound like something is binding. Start disconnecting the system one part at a time working your way back to the steering column until you find the cause of the binding.

I did that and found that one wheel is very hard to turn. I would guess that it is the lower ball joint that I wanted to find out what car it came from. The other wheel turns much easier. Also all the steering rod ends etc are new and very stiff.

These cars are so light that you should not have any difficulty in turning them once you are going 5 MPH.

Actually my car is very easy to steer with the low ratio rack I have. It just doesn't have self centering. I'm tempted to do what Renault did on some of their light cars. They used two "centering springs" inside the rack. Sneaky cure. At one point I was eying my front end to see where I could mount two screen door springs. :lol:

By the way I have more caster and a lot more KPI then the book but my locost steering does not return like a big American sedan, but has nice straight line tracking. I think binding is probably the real problem.

Good luck on the suspension Dave W

Could be, I also think I need to wear in that lower ball joint more.

My "real" car is a Honda CRX which is listed as weighing 1700 lbs. It has a LOT of self centering. When I go around a turn all I have to do is let go of the steering wheel and grab it again when the wheels are pointed straight ahead.

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 Post subject: suspension changes
PostPosted: Fri Dec 28, 2007 1:15 pm 
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OK The racers will kill me but, I would not really worry about the 100%ackermann that much. If you look at the truck market they have 3 or 4 different wheel bases, and they all use the same spindle in the same gross Wt series.

Your bump steer can not be that bad! a 1/2" bump in 5/8" travel, are you sure you are not adding in the scrub. How did you measure it.

From the picture is appears that your steering rack is close to being level with the tie rod end, have you try adjusting the rack in the vertical plane to reduce the bump.

It does sound like you are going in the right direction for increasing the steering ratio, can improve the ackermann at the same time.

I think you would be wise to install a new BJ first before you try a hole lot of different fixes, if in fact there is that much fiction in the current joint.

My 2 cents on the geometry, it would probably be better and easier in the long run, to re-position "lower" and make new upper control arm brackets then to try work around a compromised design.

Keep plugging at it :lol: Dave W


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 Post subject: Re: suspension changes
PostPosted: Fri Dec 28, 2007 6:19 pm 
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davew wrote:
OK The racers will kill me but, I would not really worry about the 100%ackermann that much. If you look at the truck market they have 3 or 4 different wheel bases, and they all use the same spindle in the same gross Wt series.

I agree, especially after I found that there seems to be only ONE turning angle that results in truly "correct" Ackermann. Besides, once you start sliding and drifting all bets are off anyway as to what 100% is (in addition to the rank ends then not being lined up correctly in relation to the inner A arm mounting points). It's all a great big compromise.

Your bump steer can not be that bad! a 1/2" bump in 5/8" travel,

Not only is my bump steer that bad. My friends CMC built chassis with a Toyota front spindles is just as bad! See the gory pictures of a head on view of his red car car and a top view of my car below. Both racks are mounted so low on the frames that the steering links angle UP to the spindle attachment points. Really gross.

are you sure you are not adding in the scrub. How did you measure it.

I don't think scrub would be a factor in this measurement. But maybe it is. I haven't seen much description of what excessive scrub does to handling. I know that my ultra wide rims for a dune buggy with about 5" of scrub would try to rip the steering wheel out of your hands if you hit something at speed!!

I made the measurement with the car sitting on it's wheels with the toe in set to 1/8". I then pulled up on the chassis as far as I could, measured the toe in at that point as a reference and then pushed down on the chassis as far as I could and measured the changed toe in/out.

This pushing and pulling on the chassis gave about 5/8" change in height (dive). The toe in/out had changed by ~1/2". I didn't roll the car(s) for the measurements since the chassis would have settled back down. The bump steer is VERY noticeable when you do this even without measuring it.

The change in bump steer is explainable by looking at the steering link angle. When the chassis moves up and down the rack is pulling/pushing on the spindle attachment points and changing the toe in/out.

Truthfully when the original owner sent me pictures of the front end I immediately was concerned about the front end geometry. A arms at wrong angles, rack positioned too far forward and too low etc etc.


From the picture is appears that your steering rack is close to being level with the tie rod end, have you try adjusting the rack in the vertical plane to reduce the bump.

The picture of the Toyota car shows the relative difference in height of the rack to spindle on our CMC built cars. Amazingly his Toyota spindle and my RX7 spindle are so similar that you have to have the cars sitting next to each other so you can see the differences. The major difference is that his brake calipers are in front of the axle and mine are behind the axle.

I really don't want to have to rebuild the front end any more than I have to. The rack is as far back as it can go right now since it's just clearing tubes FU1/FU2. By moving the ends of the steering links FORWARD I can correct a large amount of the horizontal mismatch. I can correct the vertical mismatch by lowering the ends of the steering links in my planed changes.


It does sound like you are going in the right direction for increasing the steering ratio, can improve the ackermann at the same time.

I think you would be wise to install a new BJ first before you try a hole lot of different fixes, if in fact there is that much fiction in the current joint.

That was my plan but a didn't even know WHAT the ball joint was from. :)

My 2 cents on the geometry, it would probably be better and easier in the long run, to re-position "lower" and make new upper control arm brackets then to try work around a compromised design.

In affect I can either lower the upper A arm mounting points ~1" or raise the outer ball joint (Heim rod end) ~1".

I plan on raising the ball joint for two reasons:

1. it's easier to do with a spacer welded to the top of each spindle cap (centered with a long bolt while welding)

2. lowering the inner mounting points will increase the suspension loads going in to the vertical chassis tubes with no side to side cross bracing at the new inner mounting points.


Keep plugging at it :lol: Dave W

Actually I have as much fun doing the computer designing as working on the car. At least I'm more confidant that when I start beating on metal that the computer says "go for it!".

What has been holding me back was that I couldn't get the two suspension programs and Acad to all agree on what to do. Once I made my scale model I finally realized that the way Ackermann is drawn may not be what it's cracked up to be. :roll:

I appreciate the conversation. If anyone is interested I'll post a picture of my scale (cardboard) front end that I was able to draw out the Ackermann lines etc. If my changes work as expected I'll post the results here and on my website. If they don't work, I'll .................... :cry:


Attachments:
File comment: Notice that steering links angle UP to the spindle. CMC Toyota spindles.
H-Front View-sml.jpg
H-Front View-sml.jpg [ 44.88 KiB | Viewed 6054 times ]
File comment: Top view of my RX7 steering link. This extreme angle seems to mess up Ackermann more than bump steer. CMC RX-7 spindles.
P8040005.JPG
P8040005.JPG [ 20.65 KiB | Viewed 6056 times ]

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