Can I move Mustang II rack out 3/4"

joems · Jun 26, 2013

Hi All.
My car is a 41 Chevy sedan with an inline (261.) We've put a CE crossmember in front with a Mustang II kit (manual rack). I've already cut the front motor mount off of the 261 but the rack still will not fit under the oil pan. All the research I did before hand mentioned that once the motor mount was cut off of the front plate, the rack would fit fine. In my case, it doesn't. I can raise the motor a little, but not enough to fit the rack under it. My plan durring mock up was to move the rack out 3/4" with spacers, but have been told now that that's a no-no.
Any suggestions would be greatly appreciated.
Thanks.
Joe

Bad Bob · Jun 26, 2013

Since when is a Mustang II traditional? Depends on how wide your billet wheels are...

KevKo · Jun 26, 2013

I assume by "out" you mean move the rack forward, not up, down, or to the side. In theory, as long as the inner tie rod pivots are in line with the lower control arm pivot point, it would work. In practice there is a limit to how far forward you can go. 3/4" doesn't sound excessive. I think a redesigned bracket would be better than a spacer as the rack will see high loads.

need louvers ? · Jun 26, 2013

No, as the fore to aft location of your rack controls the Ackerman in your steering linkage. Why can't you raise the engine a bit?

davidbistolas · Jun 26, 2013

This ^^^

In fact, I went up 1/2" on my mounts to clear the steering/exhaust.

joems · Jun 26, 2013

Thanks to all with the helpful resonses.
The engine is at the firewall now. If I raise the front of the motor any more, I'd have to do something with the firewall.
As you probably know, the older inline 6's have rear mounts on the bellhouse house that I used to position the engine, so that's not something I could have messed up. The more I tilt the engine up in the front, the closer the top (valve cover) gets to the firewall, and it's almost touching now.

Again, thanks for the help. I am a "FNG" and this is my first build, so I do appreciate that there are those willing to help, even if I have to wade through the A-Holes...

davidbistolas · Jun 26, 2013

Ok- so, I'm comparing things to my '51, and I know damn well they're different- but I think you're saying you won't have clearance at the firewall to tilt it motor back- but can it go straight up? It sounds like you don't need very much? - as long as there's room in the transmission tunnel, then the whole assembly should be able to slide up an inch or so without any negative impact to the driveline (IANAE).

What part of the rack is interfering? Pics will help...

joems · Jun 26, 2013

The oil pan hits the middle of the rack.
I probably could raise the whole engine up. I didn't really think of that. I would just have to come up with some spacers for the rear bellhouse mounts.
I will try to get some pics tonight.
Thanks.
Joe

Crazy Steve · Jun 26, 2013

Is there a reason you can't notch the oil pan?

jcapps · Jun 26, 2013

I had an issue on an off topic car. I notched the pan and moved the rack out 3/8 with no issues. If you can get away 3/8 or less I cannot see a problem. As long as the pivot points remain the same.

joems · Jun 26, 2013

Crazy Steve said: ↑

Is there a reason you can't notch the oil pan?
Click to expand...

Lack of skills.

NashRodMan · Jun 26, 2013

Joe,
can you move the engine forward and then up? When I put the 292 Chevy 6 in my chevy I used the CE frame mounts and just positioned the engine forward or back as I needed it in order to have clearance for everything (fan, rear of valve covers, etc). I dont have a MII rack so i didnt have the same problem you have but maybe this will help.
Paul

need louvers ? · Jun 26, 2013

Easy way to handle that is find someone with the right skills to do it! That might sound over simplistic, but it will solve the problem once and for all. even in my shop at 50.00 per hour I couldn't see simple oil pan notch taking more than 2 hours total. Once that is solved drop the engine back down to where it belongs and don't think about it ever again. If you start raising the engine at one end or another you are then messing with driveline phasing and that can get goofy real fast too.

badlefihand · Jun 26, 2013

I installed 1/2" tapered shims between rack and c/e cross member for clearance problem,no change in operation. Easy way is blocks to bring fwd.Maybe Elpacko will chime in if he sees this.

terryble · Jun 26, 2013

Instead of moving the rack forward and effecting the steering geometry can you move it down just enough to clear but still have the tie rod ends square to the steering arms? If you move it forward it may bump steer when your suspension goes up and down.

need louvers ? · Jun 26, 2013

Moving it forward won't effect bump steer within certain limits, it will alter the Ackerman effect, but moving it up or down very most certainly will!

Why is it that the absolute of some thing as complicated as steering geometry is so "fluid" around here? The rack needs to stay where it is, notch the pan and be done with it.

If you have moved your rack forward and had no ill effects until now, did you get away with it? How about when you're rolling down the freeway through a long sweeping turn at 75 and an animal steps out in front of you? Is it gonna just be okay when your compromised Ackerman lets your car under steer to the point where you go straight off or worse hit the family in the car next to you? THIS STUFF MATTERS FOLKS! Do it right and make the other stuff fit the suspension and steering geometry.

brigrat · Jun 26, 2013

Take this for what it's worth, FatMan say's you can move their rack (rear steer) a certain amount horizontaly BUT not up and down. Ran into same problem on a '34 Ford P/U, 351 Cleveland, front sump pan .............................

Jalopy Joker · Jun 26, 2013

oil pan notch idea sounds good, as long as it will not mess up clearance required for oil pickup at bottom of pan. moving rack forward will also mess up having the wheels centered in wheelwell. just raising front of engine will alter final trans angle and you will have to change rearend pinion angle too. have you checked with company that made the Must II crossmember as what would be best?

joems · Jun 26, 2013

I was just at Back to the 50's and CE was there. I don't know why it didn't occur to me to ask them........

So, I just got off the phone with CE and he said I could move the rack out with a spacer as much as 3/4" without any issues.

Pitt Grease Monkey · Jun 26, 2013

I like notching the pan.

I ran the numbers to see what impact moving my rack 3/4" forward would have on the front suspension I designed (not MII). The results for anyone interested:

Baseline @ 1" rack travel:
Outside Wheel Angle -13.1 deg
Inside Wheel Angle - 16.3 deg
Ackerman - 3.2 deg

3/4" Forward @ 1" rack travel:
Outside Wheel Angle - 12.9 deg
Inside Wheel Angle - 15.6 deg
Ackerman - 2.7 deg

So you can see that ackerman will decrease when making these kind of changes. This means one of your tires will scrub more, mostly at lower speeds. In high speed corners, the compliance of the tire will contribute much more to how much your tires scrub (tires can develop more than 6 deg slip angle at higher speeds).

So will you really notice the change from moving the rack? Probably not. Also, ackerman is considered in relationship to the rear axle as well. So unless a 41 Chevy has the same wheelbase as a stock MII, the ackerman is already off.

need louvers ? said: ↑

Moving it forward won't effect bump steer within certain limits, it will alter the Ackerman effect, but moving it up or down very most certainly will!

Why is it that the absolute of some thing as complicated as steering geometry is so "fluid" around here? The rack needs to stay where it is, notch the pan and be done with it.

If you have moved your rack forward and had no ill effects until now, did you get away with it? How about when you're rolling down the freeway through a long sweeping turn at 75 and an animal steps out in front of you? Is it gonna just be okay when your compromised Ackerman lets your car under steer to the point where you go straight off or worse hit the family in the car next to you? THIS STUFF MATTERS FOLKS! Do it right and make the other stuff fit the suspension and steering geometry.
Click to expand...

So, while I agree with this conclusion to keep the geometry unchanged, I would argue that it is not absolute. Engineers and designers make compromises all the time when it comes to suspension geometry for many reasons; time, money, quality, available space, regulations, desired handling characteristics, etc.

Flat-N-Low · Jun 26, 2013

I'm with Chip on this one. The rack should stay in it's intended, engineered position. You have two reasonable options:

1): Notch the pan. If all the rack needs to do is come forward 3/4" of an inch, I have to think that the notch in the pan is going to be very minimal.

2): Raise the engine/trans to gain clearance. Just remember that if you do this, you need to address the rear trans mount as well. You may even need to add a tapered shim to the rear axle perch to keep the driveline geometry within spec.

I'm a real stickler about suspensions and brakes because I have seen some unbelieveable abortions out running on the streets that are poorly engineered. Some guys only care about clearance and appearance and give NO consideration to engineering and safety. I'm not bashing the OP for asking his question. Actually, I applaud him for asking it, because too many guys just assume it's no big deal and do whatever they want.

hotroddon · Jun 26, 2013

joems said: ↑

Lack of skills.
Click to expand...

An Honest Man - I like that!

hotroddon · Jun 26, 2013

terryble said: ↑

Instead of moving the rack forward and effecting the steering geometry can you move it down just enough to clear but still have the tie rod ends square to the steering arms? If you move it forward it may bump steer when your suspension goes up and down.
Click to expand...

Assuning it was designed right in the first place, moving it DOWN as you suggest WILL effect bump steer, unless you can move the tie rod ends down the same amount. Moving it forward, not so much. The ackerman will change but only slightly. In fact I think from plotting this, so slight you will never know the difference.

need louvers ? · Jun 26, 2013

Pitt Grease Monkey said: ↑

I like notching the pan.

I ran the numbers to see what impact moving my rack 3/4" forward would have on the front suspension I designed (not MII). The results for anyone interested:

Baseline @ 1" rack travel:
Outside Wheel Angle -13.1 deg
Inside Wheel Angle - 16.3 deg
Ackerman - 3.2 deg

3/4" Forward @ 1" rack travel:
Outside Wheel Angle - 12.9 deg
Inside Wheel Angle - 15.6 deg
Ackerman - 2.7 deg

So you can see that ackerman will decrease when making these kind of changes. This means one of your tires will scrub more, mostly at lower speeds. In high speed corners, the compliance of the tire will contribute much more to how much your tires scrub (tires can develop more than 6 deg slip angle at higher speeds).

So will you really notice the change from moving the rack? Probably not. Also, ackerman is considered in relationship to the rear axle as well. So unless a 41 Chevy has the same wheelbase as a stock MII, the ackerman is already off.

So, while I agree with this conclusion to keep the geometry unchanged, I would argue that it is not absolute. Engineers and designers make compromises all the time when it comes to suspension geometry for many reasons; time, money, quality, available space, regulations, desired handling characteristics, etc.
Click to expand...

Thank you for running those numbers! A slight or minor change does multiply into a bigger change down the line, especially when a simple notch in the oil pan will solve the original problem with an afternoon's worth of work.

As far as the "absolute" in my little tirade, I agree with you too, that the engineers do make compromises frequently. But with street rod stuff, it is so frequently already modified in the name of making it fit something that it was never intended to fit, why push it further? I do agree though that "absolute" is a more powerful word than I should have used...

davidbistolas · Jun 26, 2013

I'd still like to see some pics, if you can. I'm sure we can collectively come up with a solution to match your skillset.

Pitt Grease Monkey · Jun 26, 2013

No problem on the numbers. I agree that sometimes as hot rodders we must be aware of how the modifications we make will effect the car as a whole. It is easy to overlook.

For those interested, or who may be more visual, you can see the effect moving the rack 3/4" has on the linkages in the screen shots here. Baseline at left, moved forward 3/4" on the right. Again, this is not MII geometry, I am simply using it for illustration.

You can see it has little effect on the instant center (the imaginary center of your turning radius, which should ideally be along your rear axle line); it stay just about 122 1/4". It does however effect the ackerman angle (shown as "NetStr") of the inside wheel relative to the outside wheel.

need louvers ? said: ↑

Thank you for running those numbers! A slight or minor change does multiply into a bigger change down the line, especially when a simple notch in the oil pan will solve the original problem with an afternoon's worth of work.

As far as the "absolute" in my little tirade, I agree with you too, that the engineers do make compromises frequently. But with street rod stuff, it is so frequently already modified in the name of making it fit something that it was never intended to fit, why push it further? I do agree though that "absolute" is a more powerful word than I should have used...
Click to expand...

porknbeaner · Jun 26, 2013

joems said: ↑

Thanks to all with the helpful resonses.
The engine is at the firewall now. If I raise the front of the motor any more, I'd have to do something with the firewall.
As you probably know, the older inline 6's have rear mounts on the bellhouse house that I used to position the engine, so that's not something I could have messed up. The more I tilt the engine up in the front, the closer the top (valve cover) gets to the firewall, and it's almost touching now.

Again, thanks for the help. I am a "FNG" and this is my first build, so I do appreciate that there are those willing to help, even if I have to wade through the A-Holes...
Click to expand...

Hmmmmn doing something with the firewall has been hot rodding 101 since before i was born and I'm getting pretty long in the tooth.

terryble · Jun 26, 2013

I may be misunderstanding terminology here but my suggestion of move the rack down a bit would be the same as moving the spindles up, like when we put in shorter springs to lower a car, truck or what ever and yet we condone and recommend that all the time on here. What is the difference if you lower one end of the tie rod or raise the other end? As for notching the pan there is not a lot of room between the pan and the spinning crankshaft, rods etc. in the front of a stock 261 pan.

porknbeaner · Jun 26, 2013

terryble said: ↑

I may be misunderstanding terminology here but my suggestion of move the rack down a bit would be the same as moving the spindles up, like when we put in shorter springs to lower a car, truck or what ever and yet we condone and recommend that all the time on here. What is the difference if you lower one end of the tie rod or raise the other end? As for notching the pan there is not a lot of room between the pan and the spinning crankshaft, rods etc. in the front of a stock 261 pan.
Click to expand...

On a rack if your geometry is wrong you get bumpsteer. Moving up or down can be done but it is not for a novice to try unless said novice is willing to do his homework and deal with the problem accordingly.

here is the deal and I have said this before and no one paid any attention so I will talk to the wall once again. Hot rods and Customs are not bolt together, they take a lot of finessing of the parts that are to be used to make them all work together. It is going to make you dirty no mater how hard you try to stay clean, or you can pay someone else to do it. Then it will be their car and not yours.

VoodooTwin · Jun 26, 2013

I love PnB's way with words....lol.

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Can I move Mustang II rack out 3/4"

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