Bump Steer Problems with Mustang II

[sirelesar]

I have a Mustang II front suspension, and have a considerable amount of bump steer. Does anyone know a bump steer package for the Mustang II front end? I see them for the 79-93 Mustangs, but not for the II.
Thanks,
Darren

[Mike Simard]

I asked the same question recently but never did find out what thread the late Mustang kits have. The taper part is prbably the same. I did feel uneasy about them because the spherical bearing would be unsheilded from dirt and if you had to shim alot you could wind up with your bearing waving around on a flag pole. I was lucky in that my car has a steering rack that adjusts up and down. I made billet mounts with even more even more travel (and rigid!) but it wasn't necesarry. I was suprised how little movement affected bumsteer. .020" vertical movement made very measurable differences. How does your steering rack mount to the frame?

[DaveR]

sirelesar,

I have the same setup and am curious how you are measuring bump steer, by feel, or with instruments?

[cobrashoch]

sirelesar- 99% of the time when a M-2 setup has bump steer it's because it's been narrowed and they are using a stock rack. The rack arms pivot on a arc, and that arc does not match the arc at the hubs attachment point. The answer is to buy a custom rack that is designed to match that cut down hub to hub width, at the hubs attachment points.
If you still have bump steer you will need to unhook the rack arms, and take out the springs so you can raise and lower each hub in turn conditions that simulate bump conditions. What you are looking for is bind. Sometimes the guys that narrow those things don't do such a good job. For example the arms have to be mounted perpendicular to the frame for the hubs arcs to be even front to back in turn situations. If the arms are mounted forward or towards the rear the hubs travel arc will be uneven and cause bump steer. None of it is that hard to find but it does take some time and measurements. The fix however may be complex or need welding, so I would find someone that can straighten things out. Bump steer in a narrowed M-II setup can be 100% done away with, but you will have to play with it to get it there. I know of no neat bump steer kits that address the type the problems created by cutting down a M-II incorrectly either.
Good luck,,,,,,,
cobrashock

[tpiini]

Not to hijack this topic, but while we're on it, do y'all use regular Mustang II alignment specs? So to say, if I were to take my Shell Valley to a regular alignment shop, would I just ask them to align it like it was a stock Mustang, or is there something else to it?

[cobrashoch]

tpiini - Nix on the stock specs. They aren't that close anyhow. What I found that works was found through the trial and error method. For example, in my case, for me to get enough camber adjustment I had to go to a adjustable upper control arm.
Each setup is different, and each alignment is different in some respect.
cobrashock

[tpiini]

Any thoughts on a starting point for a stock wheelbase/track width?

[cobrashoch]

tpiini - Stock MS-II/Pinto setup is too wide for a Cobra, esp. if you run big tires. It will have to be cut down, either that or you will have to make the whole body wider. We are talking body, hood, trunk lid, e.t.- all. Then you would have a body that is out of proportion, sorta like a Devin. I made my car a bit wider and longer and did a lot of wheel- well work, but in the end I had to cut down the stock Pinto front end 8 inches too.
Using a cut down stock setup can be done, but you will still have to buy a rack and retain it's crossmembers heavy weight . In the end, using a low end (price wise) hot rod assembly makes more sense. All of the geometry problems are worked out and they are much lighter. Not to mention you will get brand new bushings, ball joints, etc. Try "Fatman" or some of the low cost rod front end producers.

cobrashock

[sirelesar]

Thanks for all the feedback.
Mike, the 79-93 Mustangs have 9/16" - 18 tpi rods. My rack is mounted directly to the front cross member, and is pretty stationary. I think the MII rods are 1/2" fine thread. I will be measuring them today. If I could find an adaptor for the rack rods to a self-lubricated ball joint, I would use it in combination with Maximum Motorsports bump steer kit for the 79-93 using the tapered pins. I am hesitant to drill out my spindles, but anything goes. They were used spindles anyway, and I am beginning to believe they may be part of the problem. Who knows how close they are to tolerance, or if they were bumped/bent by the previous owner.

Dave,
I have a measurement set-up, but it is unnecessary, as the yaw in the car is quite noticeable. I will use the instrumentation for actually setting the anti-bump, but I need to know what my options are before I begin.

cobrashoch,
Good feedback. I had a standard MII setup a week ago, and as you say, there was contact with the fiberglass (ouch). At this stage, there was a slight amount of bumpsteer - still an irritation, and caused some yaw. So in an attempt to fix the contact, I narrowed my lowers by 5/8", and the uppers by 1/2". I did that to keep some length ratio, but in retrospect I should have done both by 5/8". That would have given me the -1.0 degree of camber that I was looking for. As it is, I could only get to 0.0. I will probably wallow out my slots at the upper A-arm attachments to get the rest. Once I did the shortening, the contact problem is gone but as you stated, the bumpsteer became significant. My rack is pretty stationary, so I dont think that I will have a chance to alter its position. I need to cogitate on what you are saying with the shortened rack. I don't know how readily available a shortened rack is, or if you are suggesting an at-home modification. If you could, please expound on this.

tpiini,
The MII alignment is OK, but the camber range from OEM is between -0.3 to +1.3. For any performance, I would want to be around -0.5 to -1.0. I don't see that the shortened A-arms are adversely affecting the instant center.

[cobrashoch]

serelesar - I find interesting that you choose to shorten the arms and thus limit wheel travel. That's a old school way of thinking that runs current to current thinking, but has indeed been done through the years many, many times. The only problem I see is when you shorten the arms, the mount points on the hubs have to be pulled down to to keep the stock geometry. (stock upper arm angle) Shorter hubs are sold thru Speedway and others for use on shortened arms that restores stock geometry. It looks to me like you are trying non stock arm geometrys as I did several years ago, always leading me to compomised results. I played with mounting points on the frame, shorter arms, even used a hub off of a old T-Bird (for big brakes) reversing the right side to left and vice versa to get the the steering arms forward for a forward rack.
Through it all I returned to stock type gemetry stuff for several reasons. For example, I too ran into the upper arm slot adjustibiliy problem you mentioned. My solution: to buy adjustable upper arms. Thats not a option for your custom upper arms. See where this is going? We are talking about down the road easily had modification stuff, as apposed to modified custom everything stuff.
Running a narrowed front is the answer, together with the stock stuff IMHO. I tried all of the other stuff and finally switched back to stock for several reasons.
As for the rack, all you have to do is measure from ball joint eyehole to ball joint eyehole on the hubs, with a narrowed front end. Send some money to Flaming River (or others) together with that measurment and in about 3 days you will get the right rack. Then you will have to figure out what it will take to mount said rack exactly dead even and straight across to your cars frame. Each car is different but it is really pretty simple in most cases, requiring hand made spacers or washers, whatever. A few times it may require welding, as was in my case, but most cars in my experience don't have to go there.
cobrashock

[sirelesar]

Thanks ron, If I read what you are suggesting, it is two-fold for retaining my shortened A-arms:

1) Get modified hubs for the shortened arms to maintain the stock upper a-arm angle (to maintain the same instant center with shorter arms)

2) Get a shortened rack from Flaming river (or equal) based upon the ball joint-to-ball joint length. Mount to ensure vertical rods.

Did I read you right?

Thanks,
Darren

[DaveR]

sirelesar,

Thanks for the response, I haven't driven my car enough to evaluate steering, but I have noticed yaw a couple of times, and wasn't smart enough to know it was caused by bumpsteer.

I have the B&b tube arms which are shortened 5/8 inch and am also having tire-to-fiberglass contact, caused partly by my backspacing decision. My original backspacing resulted in a 3 piece wheel where the inner piece actually extended about 1/2 inch beyond the face of the outer rim. When I looked at other Cobra's, I was surprised to see that this is not uncommon, but I just couldn't live with the appearance, so I had the backspacing decreased 1 inch, and now I have contact problems.
I don't have a solution yet, but I will either limit upward travel with bumpers and/or fabricate custom hubs which move the wheels inboard. Then I will deal with bumpsteer. Seems like the custom rack is an attractive solution, I'm wondering if I can also get a faster ratio. However, I have seen one B&B with a flaming river rack, and if memory serves me correctly, the mounting required considerable change to the setup.

[sirelesar]

Dave,
You may not want to put cripples in your shocks. I tried it, and bent the stuffing out of the rod at the lower a-arm after a bump. There is no good way to limit the movement without setting up a dangerous and possibly damaging situation. It really requires that the tire can move within the wheel well. Bumpsteer I can deal with, wrecked a-arms, fiberglass, a-arm connection points etc. I cannot.

Hope this helps.
Darren

[cobrashoch]

YEP , You've got it right. Only thing is those shortened hubs are for the shortened arms that they sell. They most likely won't match the cutdown you did to your arms. Also, those new hub arms may or may not change the stock length of the rack span, I dunno, but could also have longer arms away from the hub. I DUNNO. That would effect the steering radius adversly. The closer in to the hub the more leverage to the hub results in a tighter steering radius. I dunno what's out there. One things for sure though. If your overall balljoint to balljoint lenth is the same as stock plus or minnus say a half inch or so then I would use the stock power steering rack. When you cut down the arms you are in the wonderfull world of custom stuff and everything is up for grabs. That's why it's better to stay with the stock spec stuff I found. I don't know where this is going because your project is not in front of me and you are doing non-stock stuff. Maybe you can peice together something, maybe not. But whatever you do requires past experience in this area. That's why I went to a rod fab car guy that raced sprint cars, that did this type of stuff. He's why I retured to the stock arm stuff more than anything.
Cobrashock

[DaveR]

Darren,

I was planning to fab a bracket off of the top spring mount, down to the lower A-arm with a nub bumper similar to the one used on the rear of a B&B. This same system has been used on many of the OEM cars I have owned, and is where I got the idea. I don't have many options other than moving the wheels inboard by fabbing custom hubs (not spindles). I suspect that I would still have some rubbing. I am also running a fairly high ride height, which is possible because I modified this setup to use shocks with 7 inches of travel. This helps to minimize contact.

[grumpy]

sirelesar,
As noted the custom bmpstr kit is less than $50, but look at the fact, the rack is causing more of the problem by it's location than adjusting the vertical travel of the steering arms on the spindle.
Installed you will still have the wrong geometry.
grumpy

[sirelesar]

Dave,
That sounds like a better alternative than what I tried. Plus you have some travel to play with, where I was going with the 3-1/2 travel shocks, and limiting them a whole 1-1/2". Let me know what you find. I am still fighting the bump. We are on our way to New Orleans tonight, so I will get the whole picture on that drive.
Good Luck,
Darren

[sirelesar]

Well, lots of interesting developments since yesterday.
I took a trip to New Orleans, yawing all the way. On the way back, we hit a big pothole (in Louisiana? go figure), and it felt like the rear end came out. The yaw was dangerous at this point. So we pulled over to discover that the bolt going thru the bottom of the right rear coilover (into the live axle) had sheared off and rattled away. I had used a single grade 8 bolt thru the lower eye hole. After towing her home, I went to the u-pull-it and got the two brackets that go on the '94 rear end that mount the stock shocks. These put a bolt in double-shear with no chance of any bending loads. I drove her today, and halehluyah! all of the bump-steer went away! So it was rear-end compliance that was causing it all along.

Anyway, thought you might like to know, that the rear live-axle can cause a bump-steer effect if there is any compliance in the bushings, brackets, etc.

Darren

[Jack21]

Go to heidts.com and read the tech article on Mustang II front suspensions. Bump steer and all.

Although the MII was a POS when it rolled off the assembly line, the front suspension off the thing is extremely popular with street rods. So check it out.

[DaveR]

Darren,

Glad you got your problem resolved. I was aware that the rear can cause steering issues. I have a copy of Carroll Smith's book about racing and it is quite informative. One section talks about anti-squat and it's effect on rear axle pivot (one side moving forward, the other side moving rearward) during cornering, which obviously has a major impact on steering, similar to the new Chevy trucks with four wheel steering.

You broke a grade 8 bolt! What size? Mine are 1/2 inch. I wonder if I'm at risk of breaking one?

I'm not using the stock B&B mounts, I fabricated a bracket that has about 1/4 inch clearance on each side of the bolt, between the bracket and the hiem joint on the shock. This means that it's not in shear, but in theory could bend/bow slightly. The top mount is even worse, with close to 1 inch on each side. Please describe your setup in detail so I can determine if I need to make a change.

Dave