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Power Steering Rack Installation Question

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Power Steering Rack Installation Question Empty Power Steering Rack Installation Question

Post by Jeff Richards on Thu Feb 08, 2018 9:37 pm

Hi,

I'm converting from manual to power steering in my 5000. The build manual talks about adding 3/4" spacers between the rack and frame cross member when installing a power rack. Anyone know why?
Jeff Richards
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Post by Derson on Wed Dec 26, 2018 11:42 am

Jeff,
I'm trying to replace my manual steering to power like you were last Feb. I came across the same note in the manual. Did you ever resolve the question?
Thanks.

Derson

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Post by johnhappley on Wed May 22, 2019 3:03 pm

I'm replacing my manual rack and pinion with power steering. The manual R & P has three
attachment bushings. The outermost are about 15 3/4" center to center. Most R & Ps are 15 1/2 with just two bushings. I can buy offset bushings to handle the 1/4" difference.

My question is what did my three bushing manual R & P come off of? I'd search for a power version if I knew where it came from. Otherwise, I'll go with a two bushing power rack.

Thanks,
John

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Post by Derson on Wed May 22, 2019 6:03 pm

I think I've discovered why the 3/4" spacers are needed. The spacers move the rack and pinion forward enough so you can get the belt(s) between the crank pully and the hydraulic line coming out of the rack.

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Post by Hotrod on Wed May 22, 2019 6:16 pm

I believe the 3 bolt units are original Mustang II.  The later Fox body Mustangs lost the extra boss on the inside.

I'm at work right now and answering on my phone. I'll try to comment more after I get home.
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Post by Hotrod on Wed May 22, 2019 10:36 pm

According to the info I have, the MII racks are 16" center to center.

The Fox units are 15.5" C to C.

I recommend you use a Fox body unit.  These were used on Mustangs and Thunderbirds in the 1980's and into the 90's.  They can tolerate higher pump pressures than the MII spec units.  To use a Fox rack on a MII spacing you will need the offset bushings.

I don't know what engine you're using, but if it's a Chevy, the common GM pumps put up too much pressure for the MII racks.  I know from experience with my 46 Coupe.  The high line pressure results in way too much power assist and makes the steering very sensitive with little road feel.  Combine this with the fast 2.5 turns lock to lock steering ratio and you have a dangerous combo.

Even if you are using a Ford engine and pump, you may still have too much pressure.  The MII/Pinto platform was very light weight and Ford used a low pressure system.  I think it was only around 600 or 700 PSI.  A pump off of a heavier Ford car will most likely have a much higher pressure calibration than a MII pump.

The Fox rack was designed for a higher pressure from the start and is said to tolerate the GM pumps much better.  But, this doesn't mean that you can't still have an overboost situation.  The front end on a Sebring probably only weighs about 1100 LBs  and I'm sure that's a lot less than the front end of a T-Bird or Fox Mustang.

If you do have overboost, the street rod industry has a couple of solutions available.  There are recalibration kits for GM pumps that lower the pressure, but you need to know how much you want to lower it.  Considering that the pump will have to come off for every adjustment and how difficult it will probably be to remove the pump on a Sebring, you might want to consider another route.

The better solution (IMO), is an adjustable bypass valve made by Heidts (street rod supplier).  It plumbs into the hoses between the pump and rack and allows you raise or lower the line pressure just by turning a nut.  It can be mounted anywhere you have room for access and can get to with the hoses. Very handy and is the solution I used to solve my overboost problem.  BTW - My 46 coupe weighs about 2000LBs on the front end and still suffered from too much assist.  Of course, main downside to the Heidts valve is that it's the most expensive fix.  

You will need a hose kit, too.  You can usually have hydraulic hoses made locally, but my experience is that these tend to be very stiff as they are made using hose with a very high pressure rating. Heidts also sells a plumbing kit with -6 stainless braided teflon hose that you can make up yourself.  Way more flexible and easier to route.  The kit is available for the in-line valve or without.

One more issue you will encounter.  The splines on the manual rack are 9/16-26 where the steering shaft attaches while the power racks are 3/4-36.  If go with a mid 90's era sn-95 rack, they have an unusual triangle shaped input shaft.  The good news is that aftermarket steering u-joints are available to fit all of these input shafts.  The bad new is that they are not at all cheap. Stick with Borgeson, Flaming River or Sweets for these joints.  Good quality stuff that I will bet my life on (and have).

Sorry for the long post.
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