MII Directional Stability

. I raced cars and set up my own for over 10 years. I read several books and countless articles on suspension. I needed some help on this one because I had no history. Like you, I've been amused by some of the posts.

I still appreciate the well intentioned suggestions.

 

I will be as kind as i can.
The crossmember does,nt look like its weilded on just bolts.Thats not the problem.
The crossmember is drilled wrong.
You have a few choise.
Raise the rack holes,lower the a arms holes.
You can twist turn do what ever to crossmember.
Last post "the crossmember is drilled wrong"
George

 

I will be kind, too. The cross member is welded in, not bolted. I do not believe that with the crude pictures I took, you can ascertain that things are wrong with the geometry of the stub. I was told it is a FatMan stub but don't know how to verify that. I am not removing and reinstalling the crossmember.

 

I used a Flaming River rack and pump on my 41 Chevy with MII frt end. I have 0 camber, 3.5 pos caster .15 toe in and it drives great. The rack isn't cheap, but you get what you paid for.

 

Rode around with old hot rodder and friend, Bill Hampton today. He confirmed what I thought I knew. Mainly, I am dealing with roll steer now. The car tracks straight and true but roll steer, especially from the rear is a the real culprit that I need to further tame. This car, even in its lowered state, still has a pretty high center of gravity.

I will report back as I make additional improvements.

 

Wouldn't rear anti sway bar be a place to start?
I've found KYB gas adjust shocks seem to have helped in my case as well.

 

Front sway bar first, someone mentioned it a long time ago. Put one on....every decent IFS ever manufactured, oem or otherwise, uses one.

Don't go barking up the roll steer tree. Leaf springs roll steer, 4 bars roll steer. I doubt very much that you are feeling roll steer from your rear end.

I will bet a bag of donuts that a front sway bar fixes 95% of your issues.

 

Front bar is definitely the place to start. A rear bar would make it oversteer more.

 

A front bar definitely won't hurt handling, but I don't think that it'll be the magic bullet your looking for. I'd love to be wrong though.

 

After talking to Brent at FatMan and George at Chassis Engineering, I'm going to put sway bars on it. I ordered both front and rear. I'll try both.........and I will likely try it with one unhooked at either end. That's three combinations. Either way, it's cheaper than changing out the rear spring setup. I really think sway bars will improve it now that I have it where it tracks straight and comes off center predictably.

 

I hope I'm right, perhaps if nothing else the bar will mask some of the symptoms.

I just put a rear bar on my 40 wagon and the difference is notable, but a 40 woodie is a great deal taller than A 53 chev...

I hope that you continue to report on the ultimate solution to this problem.

 

Bars did not arrive yesterday, so it will be next weekend before I get them installed. I'll keep you posted.

 

I have sway ( or roll ) bars front and rear on mine. It does make a big difference in the handling. I have skipped over a bit of this thread and so I apologize if I'm repeating something already said. If the twitchy /quick handling is your issue, I'm convinced that after trying shims ,etc that too much pressure is not the cause. I believe that as has been said by some, there is just too much flow from the GM pump and when on the highway while trying to go straight the result of the excessive flow is a quick movement of the rack which you end up chasing. If you remove the flow valve from the pump ( not the pressure valve that involves the shims ) you will see a hole about 1/8 inch diameter in the side of the tube section away from the threaded end. This is the flow orifice that allows fluid to flow from the pump to the discharge port. But there is also another smaller hole that is between the threads and the O-ring. This hole is drilled to allow some of the fluid to bypass the discharge port directly back to the tank.

My theory is that shims aside, to reduce flow to the rack you can do one or both of the following. Reduce the size of the flow orifice and , or increase the size of the bypass orifice.

John

 

Shazam! The Chassis Engineering bars made a big difference in the handling of the car. No more jumping and steering itself all over the place and you can drive with much more confidence. I will play with them a little this weekend and see if just one is better than both. Right now it is a big improvement over what I've had. Pictures this weekend.

 

Just to close the loop on this thread, the Chassis Engineering sway bars made more difference to the handling of this car than anything else I did. It now drives and handles great!

 

Thanks for the update. I have a 1939 ford with mII and have not installed my sway bars.
Sounds like I should off my ass and install my sway bars !!

 

After driving this car for a year, it is better but not where I want it to be. A cross wind will move it around pretty good and a bad bump in the road will make it jump around and change direction.

Additionally, the steering is really quick. The biggest reason it is so quick is that the rear steers itself. When you turn, say to the right, the outside rear leaf spring compresses and lengthens. The inside rear leaf arches and shortens. This causes the rear axle to steer itself. Additionally, the 1 3/4" wide springs are highly arched plus I think they probably deflect some when you turn.

My next move is going to be the Chassis Engineering rear spring kit. Anybody got experience with this and how it will impact my "rear steer" problem?

 

If a bump on a straight road will make it " jump around and change direction" how does that translate to a rear steer problem?

Still sounds like a mismatched pressure problem, if all the front end geometry is correct.

 

Not to argue with you, but unless your leaf springs are shot and/or the bushings and shackles are totally worn out they should not be messing with it that much.

I have a '53 Chevy with a MkII front suspension with a sway bar, 1978 GM ps pump, 1982 T-Bird power steering rack, and a 17" steering wheel, no rear sway bar and I drove it for a couple thousand miles with the stock leaf springs de-arched with nylon shackle bushings that I made. It handled like a fricking slot car. As you can see in my avatar, the car is lowered about 4-5 inches front and rear from stock ride height. I also have radial tires.

Adding the front sway bar made very little difference.
Changing from the temporary 15" steering wheel to the 17" DID make the steering feel slower and better. (And one-finger parking!)

Then I replaced the rear springs with new Posies Super Slides because 2 guys I know had original leafs break on their cars. The Posies springs have a reversed eye at the rear but non-reversed eye at the front, which changed the angle of the leaf springs and added rear-steer understeer in corners but the car still tracks straight and true on the highway. Always has. That's with the front end aligned to FoMoCo 1976 Mustang II specs.

So I would guess the problem is with something worn out in your car or a less than ideal steering rack choice. I think my car is about 3-4 turns lock-to-lock but didn't drive it to work today so I can't confirm. The problem is not that you have leaf springs in the rear of your car. Changing to the Chassis Engineering spring kit might solve your problem but if it does it's because you're replacing something worn out with something new.

 

I just read my own thread and I'm not sure I was very clear! What I meant to say is that if your rear end is shifting around that much I suspect you have worn or missing bushings in the springs and/or shackles.
The original shackles bushings are soft rubber that flexes like crazy and they crumble when they get old. Replace them with new rubber in the front spring eye and buy or make some solid bushings for the shackles and I think you'll find the car much more stable. I personally just bought new shackles that came with rubber bushings and then made nylon bushings on a lathe to match the rubber ones.
(I think it was nylon - I just went to my local plastic supply dealer and said I wanted something that would work well for suspension bushings. It's white plastic-like stuff with just a little flex to it and a slightly slippery feel. It's been 12 years so I don't remember what he said it was.)

 

I don't think you ever told us what type of tires your running. If the're bias plys try a set of radials, or vice-versa. After all these replys and everyone's help, my opinion is bump-steer or tires. Any way good luck with solving it. Ralphie

 

You could well be right. The bushings are the first thing I'm going to check when I get back. My steering pump has the pressure relief shims and I have the rack with the most turns I could get from napa. I need to check exactly what it is but I've been through that. I can literally feel the rear steer the car when I hit a cross wind or even when I turn the wheel. It makes for a very twitchy ride back to NC from Kansas!

Thanks for the input. Good to know your stock springs worked well for you.

For the record I have radials, not bias plys. Bias plys would be even worse!

 

Just bumped the thread up a couple of stars .

I mean really, does 1974-78 IFS technology blow your panties up that much? Very informative thread, and the reality is that there is a shipload of MII front ends on HAMB friendly rides.

You haters might do well to take in the fact that guys like Ray Erickson, who was building bitching '34 hot rods and shoebox customs in the early '50s, was one of the first to adapt the Pinto/MII IFS technology to a street rod, back in the late '70s.

Now, granted, it is post-'65. Get over it.

 

I read this whole thread and there's some great stuff here. One thing that wasn't mentioned is the human driver. I believe the OP is perhaps more sensitive to slight handling quirks that other drivers might overlook.....Kinda like a race car,one driver goes like hell,the other driver is all over and says it handles like shit.
Be interesting if 10 cars with a similar suspension were available to drive for a comparison

 

I raced sports cars and even Legend cars. I am definitely sensitive to the inputs on the car but when a cross wind hits the car and it moves over a foot or two and I have to catch it and redirect it, my wife nearly jumps out of her skin.

 

I do remember contributing to this thread last year when it popped up, but not what I contributed. I probably told you to go back to non power and a stock sized 17" steering wheel, 'cause that's my fix for this situation 9 times out of ten... Hell, just did that with a friends '40 Ford last month. That's kinda beside the point right now.

What are you running for a caster setting on this front end? I know stock Mustang II is kinda wimpy at a degree and a half or so, if I remember correctly. I know when I have my Plymouth aligned, I always beg them to dial in as much caster as they can get. Matter of fact, when ElPolacko and I made the upper arms for my car I vaguely remember adding a degree or two more into the mix in the arms themselves.

 

Don't blame leaf springs! I owned a 74 mustang II new and it was designed and built with leaves in the rear. If it is moving around in a cross wind you have something loose and/or broken, check each element of your suspension carefully before you kill yourself.

 

My 86 Silverado has leafs and handles great. I know they can be made to work.

Need louvers, this is not a front suspension problem. That part is working well. I may very well have some bushings shot in the rear springs. I have not checked them yet. I will after I get back home.

 

I'm gonna bet your shackle bushings are totally gone. That would allow a LOT of movement and shifting of the rear end.

The shackles are supposed to be hanging between the bracket and the frame. A lot of times they flip when the car is jacked up and wind up pointing down at the ground, which raises the rear of the car 3 or 4 inches and I would guess totally messes with the handling as well, so check that while you're looking! And don't rule out a broken leaf - one of the friends I mentioned drove around with a broken leaf for a week or two before he even realized he had a problem.
(That's why I replaced my springs: I didn't want one to break when I was on the highway with my kid in the car.)

 

Got it up on the lift and, sure enough, my bushings are crapola. Ordered some new ones from Summit today. I will let you know if that fixes it. If it does, I feel like a dumbass for not checking that one myself. Thanks!