Mustang II Rack and Pinion
 

OK - I'm thoroughly confused and I need enlightenment.
I'm about to redo the front end on my Cobra with bigger brakes , special Trigo hubs ( to fit my Sunburst wheels), new a-arms, balljoints etc. And since I do not know the history of my Mustang II manual rack I thought I would replace it with a new one.
Here's the confusion : Having followed countless threads on the subject, looked at countless web sites and catalogues, I still can't get a clear picture of what rack is what.
Here's what I think I know.
Mustang II is '74 to '78. Right? Summit calls it in their catalogue '72 to '74 and on their website '77 to '78, Flaming River calls it '74 to '78, and Speedway dosen't give it a year.
So let's call it 74 to '78.
Now what about ratio? Flaming River's website dosen't talk about ratio, but if you call the they say 16:1. Many discussions on this website talk about 18:1. Higher number - easier to turn but more turns lock to lock ( good for slow speed and parking , but not for performance driving) and lower number, harder to turn but fewer turns lock to lock ( harder to steer at low/parking speeds but better at high speeds and performance driving).
Am I right so far?
So what ratios and lock to lock turns come from what source?
Flaming River 1502 : 16:1 ratio and 4.15 turns (3.92 or 4.0 depending on who you talk to when you call)
Summit 770601 : ? ratio and 3.75 turns (catalogue) or 4.0 turns (website)
Speedway 91034340 : no ratio or turns info.
Where does the fewer turns rack come from?
Sooooo, is the 18:1 a stock Mustang II rack (one you'd get from a NAPA etc) and is the 16:1 (Flaming River) the only aftermarket rack avilable?
I can handle the steering effort on my car now for normal driving and don't plan on any "performance" driving, but I would like fewer turns ( my current rack is just over 4 turns).
Should I be thinking a later model rack with offset bushings? (Or does this take me into the power steering relm where I'd rather not go?)
What's the answer? (No power steering tangents please.)
When I can get enough info , I'd be happy to create a rack selection spreadsheet to help those of us that need enlightenment.
Thanks for any input you all might have.
Greg

Everything you said about steering effort etc is true.

As far as lock to lock, let me take an educated guess here.

Regardless of ratio, the rack will have to have a certain amount of travel to accomodate the steering geomotry. With a higher ratio (easier effort), you would have to turn the steering wheel farther in order to to move the rack the same distance. And visa-versa. It's the same concept as pulley ratios except that rotating motion is being transfered to linear motion.

I've actually done something similar at work with a motor turning a gear to move a linear shaft. We used a high ratio which translated to finer control on positioning the shaft and it also meant we could use a smaller motor, ie. less torque load on the motor or in human terms, less effort in turning the wheel.

As in all things life, there has to be some compromise.

Good luck in your decision.

I went through the same process of trying to get a straight answer from Flaming River. Seems that the ’74 thru ’76 MII rack used a three hole mount. The ’77 and ’78 MII rack uses a two hole mount. Even though you can use the three hole mount (same outside centers) the two hole mount is preferred.

Flaming River's MII, GT and Quick ratio racks all have the same tie rod centerlines (45"), but the mounting center is 16" for the MII, whereas the newer Mustang racks mounting center is 15 1/2". I was unable to get any dimensional infromation on the MII rack and was concerned that using offset bushings would cause bump steer.

MII racks use a 9/16-26 input shaft, so if you opt to go with a GT rack, you would use a power rack without the power in order to match your existing u-joint or rag joint. As to lock-to-lock turns, this is a function of both the ratio and rack travel. Flaming River's catalog calls out 4 turns lock-to-lock for their MII rack, Shell Valley used to carry a 3.5 turn lock-to-lock rack and according to one of the parts stores, the original MII's were somewhere around a 4.15 lock-to-lock. Hope this helps.

Thanks for the response and info guys. Regarding using a power rack with no power (pump and lines), I've never seen any magazine articles or read any threads on the tech aspect of doing this and I am curious:
1) Do you fill the power rack with grease or power steering fluid?
2) Do you plug the line ports or "loop" the lines?
3) What is the ratio and turns for a power rack?
Thanks all.
Greg

Greg,

I don't know much about the power steering set ups but you might contact Bill Emerson of Emerson Motorsports. He is in the club and I know that he has put several different power steering combinations in Cobras.

Ron

Did you ever try steering a power steering car when the engine (and power steering pump) stopped running? Doesn't work too well, does it. So, don't put a power rack in a manual steering car. Use a manual rack.

The most popular manual rack seems to be the Flaming River '74 - '78 MII.

For a complete treatise on the MII front suspension, go to Heidts.com and read their tech section.

I'm using a power steering setup with a '79 - '85 (Fox body) high effort, standard ratio power rack. (And I love it.) The later rack has a slightly shorter mounting bolt hole c/c width, and the mounting bolt centerline to the rack centerline is slightly shorter. Used offset rack bushings to position the late rack to more closely match the MII original rack centerline position. This was done to minimize any potential bump steer problems.

Since this is a manual rack question, I won't elaborate on MII power steering setups for Cobras other than say, It can be done, and it works quite well. Start a new thread and we'll go into it.

Thanks to all who posted. Flaming River it is.
Greg

With regards to using a power rack without power, this is possible with one of the the GT racks (can't remember which year). This let's you stay with a manual setup and still have quick steering. If you check the FFR forum, I believe this is a common setup.

Hi Guys,
I currently have a power rack installed , but it is not connected to a pump.
I like the steering response, but there is some slack in unit. I'm wondering if filling with PS fluid will solve this problem. Is there any trick to filling a rack? Does the unit need to be bleed.

BTW:
Here is a reply I got from flaming river. I was considering going to a manual rack but 19:1 is way too slow.

Dear Roger,
Our power Mustang II rack has a ratio of 15:1,however, our manual rack will have a 19:1 ratio only.
We do offer a ' 79- ' 93 Mustang rack with a 15:1 ratio,but the mounts are 15 1/2 inches on center,instead of the 16 inches on center that the Mustang II racks have,other wise there is not any difference between the two racks.
This rack has a part number of FR1520,and a cost of $279.00.

Best Regards,
Tech Dept.
Flaming River Ind.
800-648-8022