Playing with steering boxes. SPA S fixed ratio, SPA AF variable ratio. Firebird 12.7

Bentworker

VIP Members
Joined
Jan 17, 2015
Messages
1,465
Reaction score
179
Location
California
My Car
71' Grande project.
Intro... 

So you want a quick ratio box in your Mustang?  Better yet a quick ratio box with feedback that feels like a modern car instead of the "pinky finger" power steering it came with?  It can be done, with wrecking yard parts and a moderate level of tools.   Best yet it can be done with no change in the appearance of the steering box, and no modifications to your car.  The GM A-body guys have it easy, since the Jeep Grand Cherokee box will bolt right up in their cars.  However the Mustangs use a different casting, with different mounting points.  There were no applications that used the 71-73 Ford mustang style Saginaw 800 casting with the 12.7:1 ball screw and piston.  So if you want a quick ratio box you must swap in the 12.7:1 ball screw and piston out of a GM or Jeep vehicle that had one into your casting.  The thread below is a general guide to what has to be done.

I started building up a steering box today.  My 71' Grande had the super slow fixed ratio box.  The variable ratio box came from another member on the forum.  Add in a 91' Firebird 12.7:1 fixed ratio box and I have a mountain of mix and match parts.  Goal is to use the Mustang casting, with the quick 12.7:1 firechicken ball screw and piston.  Also going to use the firechicken input since it has a much larger T-bar (Torsion Bar).  We'll see how it turns out, I was thinking of using the Mustang input shaft, but the T-bar (the thin little shaft I'm measuring with a caliper in a photo below) on both of the Mustang boxes was so tiny that I decided to go with the Firebird input.  That means I will have to get an adapter rag joint since the splined input shaft is smaller. Hopefully it will be worth the trouble to get more feedback that the larger T-bar will offer.

These are all Saginaw 800 series boxes and the parts interchange minus the input shaft and the casting itself.  This is a pretty neat DIY project and the 12.7:1 quick ratio gears are plentiful in many 1980's GM F Body (Camaro & Firebird) along with many of the Jeep Grand Cherokees.  If you are go to a pick-n-pull yard you should be able to walk out including tax and core charge for less than $75.00 and have the parts you need minus a $30.00 rebuild kit from Rock Auto.  The info on what exact models to harvest from is posted a few pages ahead.

Pictures...

You can see the differences in the internals.  

Ball Screw.  Quick ratio 12.7:1 ball screw in the bag on the far left,  stock variable ratio in the center, slower fixed ratio on the right.  Note the two lines between each "thread" on the 12.7:1 screw.  This is unique to the 12.7:1 screw and can be used to identify it in a wrecking yard.  Just remove the pitman arm, then unscrew the four bolts on the sector shaft cap.  Make sure the steering is in the center of it's travel and pop the entire sector shaft and cap out (mallet from the bottom).  With a flashlight you should be able to turn the junkyard box to full lock in one direction and see the ball screw.  If it has the two lines like the one in the photo you are good to go!

20160429_152715-853x480.jpg

Variable ratio sector shaft and piston.  Note the deeper center tooth for the variable ratio.

20160429_152620-853x480.jpg

Fixed ratio sector shaft and piston.  Notice that all the teeth are the same depth.  The fixed ratio teeth seemed to be identical to the GM F body ones.

20160429_152528-853x480.jpg

.185" diameter torsion bar out of the SPA S fixed ratio box.  This is pretty small and is why the stock steering boxes take so little effort to turn with next to zero feedback.  Larger torsion bars = more feedback.  You should never take apart an input assembly this far if you intend to reuse it.  I took it apart for learning.

20160429_164208-480x853.jpg

Slightly larger .190" torsion bar out of the variable ratio SPA AF box.  Still small but better.

20160429_163454-480x853.jpg

 
Last edited by a moderator:

Bentworker

VIP Members
Joined
Jan 17, 2015
Messages
1,465
Reaction score
179
Location
California
My Car
71' Grande project.
More pictures.  

This shows the difference between the GM Saginaw box and the Mustang Saginaw box.  I blasted the casting, cleaned it up and installed new seals for the sector shaft.  

Notice the mounting points on the castings are different between the Mustang box and the GM one

20160430_115556-480x853.jpg

Got the casting all cleaned up with new sector shaft bearing and seals pressed in.  An arbor press is awesome for this if you can get your hands on one.

20160430_114734-800x450.jpg

20160430_115606-480x853.jpg

 
Last edited by a moderator:

Bentworker

VIP Members
Joined
Jan 17, 2015
Messages
1,465
Reaction score
179
Location
California
My Car
71' Grande project.
More pictures.

I got the new o-ring and Teflon seal on the piston. Compressed the new seal with electrical tape and a hose clamp, then baked it at 200F in the toaster oven. Finished it off by chilling it in the beer fridge and made a seal protector out of a plastic water bottle.

Sweet success the firechicken 12.7:1 piston is now in the Mustang box.

Piston with the new o-ring in the groove, along with the stretched teflon seal on top.

20160430_153314-480x853.jpg

Took a bunch of good electrical tape and firmly wrapped it around the piston over the teflon seal to compress it.

20160430_153027-480x853.jpg

Next I tossed a rag over the tape and used a hose clamp to compress it. You may want to chill it afterwards so it does not try to expand before you get it in the casting. The o-ring underneath acts as a bit of a spring to push out the teflon ring in the bore.

20160430_153021-480x853.jpg

Note the small bit of a thin plastic water bottle used as a seal protector to avoid damaging the teflon seal on the sharp edge of the oil port.

20160430_153325-800x450.jpg

Done! This piston is in the bore. Sometimes you may have to tap it a bit with a wooden dowel or a plastic mallet. Teflon seals can be tricky. It is probably worth buying two kits just in case you destroy a seal.

20160430_153607-480x853.jpg

 
Last edited by a moderator:

Bentworker

VIP Members
Joined
Jan 17, 2015
Messages
1,465
Reaction score
179
Location
California
My Car
71' Grande project.
More pictures...

Got the ball screw loaded up. Transmission assembly goo is critical for this. Got the balls all lined up in alternating colors, and loaded them carefully in the nut making sure to load them correctly. (If you do it wrong you will fill up the end of the ball nut and the first time you turn it will go crunch destroying your box)

1st step. Rotate the piston like this so you can load the balls. The ball screw with torrington bearing and race must be installed in the input shaft end of the housing. Take the balls one by one and carefully place them into the hole closer to the piston cover end, the ball must go down...NOT over the screw. The idea is to load them one by one, alternating colors as you go until you can see the first one you loaded in the other hole. You will have to give the ball screw a wiggle and help the ball bearings down with a non marring tool like a pencil eraser. If you make a mistake and accidentally place one ball over the wrong side of the screw it will end up in the cap of the piston and you must remove the ball screw, dump out the balls and start again.

20160430_160829-800x450.jpg

I organize them before I load them one bright, one matte.

20160430_161558-480x853.jpg

So once you have the piston loaded where you can see the balls in both ports you take the remaining ones and place them into the two half sections of the channel and hold them in place with transmission assembly goo. Then just invert and insert into the piston, keeping the orientation of the ball bearing colors in mind so the alternating pattern is correct. Place on the retainer strap and tighten the two bolts that retain everything. You really want to take the time to do this right, and be sure to check it when you are all done before you put the rebuilt box in the car.

20160430_162117-480x853.jpg

Once the ball screw and nut (Piston) are loaded correctly just turn the piston in the bore so the the teeth that mesh with the sector shaft are centered and aligned in the hole. If you have the input shaft assembly and cap installed you can turn the input until the piston reaches the limit in both end of the bores to check for smooth operation.

20160430_162511-640x360.jpg

 
Last edited by a moderator:

Stanglover

VIP Members
Site Supporters
Joined
Sep 12, 2015
Messages
5,406
Reaction score
621
Location
SW Ontario
My Car
1971 Mustang Mach 1, M code, 4 speed.
This is very interesting and you have taken considerable time to present your changeover. You may have read previous posts from me about rebuilding my SPA-T V/R box, which I will soon be testing once I get my motor back in. I found your idea to compress the rack piston Teflon seal interesting. One of your pictures shows the fluid return hole and you did what I ended up doing by placing a piece of plastic film over it. This hole has a very sharp edge that needs to be trimmed. That edge cost me a complete new kit as I shaved a chunk right out of the Teflon seal. (can't buy just the seals!) The second attempt went much better and I was able to install the piston with the aid of lots of lube!!

Along with many others, I will be very interested in the results. I may be looking at the same modification in the near future. Question: where did you find a 12.7:1 worm and rack piston? Were they new parts or something from the wrecking yard?

Good work,

Geoff.

 

Bentworker

VIP Members
Joined
Jan 17, 2015
Messages
1,465
Reaction score
179
Location
California
My Car
71' Grande project.
Quick Ratio box application pdf link

I just looked at the pdf files that are avaliable at the above link. Then I wondered around the pick-n-pull wrecking yard until I found a car on the list that hadn't been wrecked. $50 later I had a complete steering box to harvest with 12.7:1 ratio and one of the largest T-bars offered. Mine came out of a 1991 Pontiac Firebird.

It is true that the Teflon seals are an epic pain to install. Honestly the tape and clamp trick works pretty well. Sometimes a piston ring compressor also works well.

 
Last edited by a moderator:

Stanglover

VIP Members
Site Supporters
Joined
Sep 12, 2015
Messages
5,406
Reaction score
621
Location
SW Ontario
My Car
1971 Mustang Mach 1, M code, 4 speed.
Quick Ratio box application pdf link

I just looked at the pdf files that are avaliable at the above link. Then I wondered around the pick-n-pull wrecking yard until I found a car on the list that hadn't been wrecked. $50 later I had a complete steering box to harvest with 11.7:1 ratio and one of the largest T-bars offered. Mine came out of a 1991 Pontiac Firebird.

It is true that the Teflon seals are an epic pain to install. Honestly the tape and clamp trick works pretty well. Sometimes a piston ring compressor also works well.
Thanks for the pfd link. I do know where I can get a steering box or two from a couple of 73's. Just got to get the owner to sell one of them!! When I did my rebuild, I watched a few YouTube videos that were a great help, but nowhere did I see the mention of the T bar you talk about. Did I miss something critical??? I stripped the box completely and replaced everything, or so I thought and did not see anything that looks like the one in your pictures. Also, did you need to replace the sector shaft as it is a 1.25" and if so, what pitman arm were you able to find that has the correct length and arc?

For me in Canada, the current exchange rates are high, so just ordering one gets to be an expensive proposition. As I love messing with mechanical things, a better ratio rebuild may be a fun alternative.

Thanks and great work,

Geoff.

 

Don C

Fords Forever
Joined
Jan 1, 2012
Messages
7,902
Reaction score
689
Location
Springfield, OR
My Car
1971 Mustang Sportroof M code
He's referring to the torsion bar, which is a part of the stub shaft (input shaft) assembly.

 

Stanglover

VIP Members
Site Supporters
Joined
Sep 12, 2015
Messages
5,406
Reaction score
621
Location
SW Ontario
My Car
1971 Mustang Mach 1, M code, 4 speed.
He's referring to the torsion bar, which is a part of the stub shaft (input shaft) assembly.
I see! How could I have missed that unless there are different box types. Mine is an 800 box. I'll go back and check the video's, but I know I placed everything in order on disassembly. Hmmm!

 

Bentworker

VIP Members
Joined
Jan 17, 2015
Messages
1,465
Reaction score
179
Location
California
My Car
71' Grande project.
You didn't miss anything. For whatever reason the steering gear rebuild kits do not include the small o-ring that you need to replace if you knock out the pin and remove the T-bar. The exploded diagram included with the kit I bought did not even show that the assembly could be broken down further. As best as I can tell you can't mix and match used T-bars and stub shafts, because they are cross drilled for a retaining pin, and it seems like no two are drilled exactly the same. If you could somehow dig up a new T-bar you could drill & ream it to match your used input. If you want to swap to gain steering feel you need to swap the assembly.

I really want a more modern steering feel, so I am going from my current T-bar which is about .185" to the firebird one that is .210" that should give me about a 50% increase in the effort required before the power assist kicks in. I will have to build some sort of Frankenstein rag joint since the box will have the newer 30 spline 3/4" input.

As for what pitman arm I will run, the stock one. The radius that the sector shaft will travel is controlled by a snap ring inside the casting, and the depth of the aluminum cap. They act as stops for the piston and only allow it to travel so far. Since I am using my Mustang casting with Mustang snap ring and cap it will have exactly the same arc as stock. The pistons in that family of box are all the same length.

Amazingly enough the fixed ratio Mustang and the Firebird sector shaft are exactly the same. The good thing about this is that if you had a variable ratio box and needed a fixed ratio sector shaft your GM donor will have just what you need.

 
Last edited by a moderator:

Don C

Fords Forever
Joined
Jan 1, 2012
Messages
7,902
Reaction score
689
Location
Springfield, OR
My Car
1971 Mustang Sportroof M code
Thanks for posting this, there's some great information here, some of which can only be gained by experience. I know I've learned from it (old dogs CAN learn).

Maybe one of the Admins can move it into the tutorials.

 

Bentworker

VIP Members
Joined
Jan 17, 2015
Messages
1,465
Reaction score
179
Location
California
My Car
71' Grande project.
Took some pictures of the snap rings and caps to show the diffrences.

SPA S Fixed ratio mustang sector shaft on the left, Firebird one on the right. Teeth and splines are identical. The mustang pitman arm will go right on the Firebird / Camaro shaft.

20160501_103222-480x853.jpg

.080" deep snap ring at the bottom of the bore. This is in the Mustang box and is what controls the travel of the piston, and therefore the arc in degrees that the pitman arm will travel in one direction, Other direction is limited by the depth of the piston cap.

20160501_103451-480x853.jpg

.260 worth of snap rings stacked up in the bottom of the bore on the firebird box.

20160501_103647-480x853.jpg

Piston caps to show how they limit the piston travel in the other direction. You want to use the cap that came with your mustang box. Mustang cap on the left that was .330" tall, firebird one the right was .500"

20160501_104012-800x450.jpg

 
Last edited by a moderator:

Bentworker

VIP Members
Joined
Jan 17, 2015
Messages
1,465
Reaction score
179
Location
California
My Car
71' Grande project.
There is about .170-.180" diffrence on the stops between the Mustang and Firebird box.

 
Last edited by a moderator:

Stanglover

VIP Members
Site Supporters
Joined
Sep 12, 2015
Messages
5,406
Reaction score
621
Location
SW Ontario
My Car
1971 Mustang Mach 1, M code, 4 speed.
You didn't miss anything. For whatever reason the steering gear rebuild kits do not include the small o-ring that you need to replace if you knock out the pin and remove the T-bar. The exploded diagram included with the kit I bought did not even show that the assembly could be broken down further. As best as I can tell you can't mix and match used T-bars and stub shafts, because they are cross drilled for a retaining pin, and it seems like no two are drilled exactly the same. If you could somehow dig up a new T-bar you could drill & ream it to match your used input. If you want to swap to gain steering feel you need to swap the assembly.

I really want a more modern steering feel, so I am going from my current T-bar which is about .185" to the firebird one that is .210" that should give me about a 50% increase in the effort required before the power assist kicks in. I will have to build some sort of Frankenstein rag joint since the box will have the newer 30 spline 3/4" input.

As for what pitman arm I will run, the stock one. The radius that the sector shaft will travel is controlled by a snap ring inside the casting, and the depth of the aluminum cap. They act as stops for the piston and only allow it to travel so far. Since I am using my Mustang casting with Mustang snap ring and cap it will have exactly the same arc as stock. The pistons in that family of box are all the same length.

Amazingly enough the fixed ratio Mustang and the Firebird sector shaft are exactly the same. The good thing about this is that if you had a variable ratio box and needed a fixed ratio sector shaft your GM donor will have just what you need.
Thanks so much for your clarification on this "T" bar matter. I guess a normal re-seal and clean up doesn't go that far and why it was not mentioned on any of the YouTube video's I watched, Saginaw 800 steering gear box , parts 1 -5. Perhaps the guy doing the video wasn't aware of it either!! Hmmm. wonder what else he wasn't aware of.

Obviously you have good knowledge and experience which I am sure many will benefit from. I may never have the desire of need to go back into my s/box, but if I do, guess where I'm going for my info!!

Well done on a very good post. I have enjoyed reading it, but you will have to post later how it all worked out.

Thanks again,

Geoff. (Stanglover)

 

Bentworker

VIP Members
Joined
Jan 17, 2015
Messages
1,465
Reaction score
179
Location
California
My Car
71' Grande project.
Franken box is done.

I'll clean it up, and hit it with some cast spray paint. I replaced the rest of the Teflon seals, compressed them with electrical tape and a hose clamp. I had to dig into one of my GMC kits to get the correct seal for the 30 spline shaft. Took pictures of the kits with part numbers. I will be a while until I get to give it a try. The Mustang is in about a million pieces right now. Going to paint it from the firewall forward.

Input / control valve assembly with new o-rings installed under the new teflon rings. Had to stretch the teflon rings a bit to get them on. Did the same trick as the piston, wrapping them tightly with quality electrical tape to compress them, then a scrap of cloth and a hose clamp. Be sure to replace the o-ring that goes between the input / control valve assembly and the ball screw. It will be shown in the exploded diagram included in the rebuild kit. 20160501_114028-480x853-480x853.jpg

Installing the input shaft bearing, seal and dust shield with an arbor press. It is easy to over insert the parts, be careful.

20160501_125747-480x853.jpg

Cleaning up the sector shaft and sector shaft cap. They just unscrew from each other.

20160501_133940-480x853.jpg

Assembled steering gear!

20160501_142324-800x450.jpg

Various rebuild kits with application written on top near the part number. Rock auto is where I get mine. Because I built a frankenbox with the smaller GM input shaft I had to use two kits. If you elect to retain your mustang input and only go with the quick ratio gears out of a Firebird / Camaro or Jeep Grand Cherokee you will only need the mustang kit. 20160501_142558-480x853.jpg

 
Last edited by a moderator:

Bentworker

VIP Members
Joined
Jan 17, 2015
Messages
1,465
Reaction score
179
Location
California
My Car
71' Grande project.
The Edelmann 7858 and the Gates 350350 are correct for the Mustang box.

The Edelmann 8524 and the Gates 350440 are for a Chevy square box pickup and are totally wrong except for the smaller input seal needed for firebird box. I would not buy this kit if you are doing the same swap, just buy the seals alone.

Also an arbor press turned out to be a much better seal installation tool than a drift. You want to install the seals just deep enough that you can install the snap ring.

 

Stanglover

VIP Members
Site Supporters
Joined
Sep 12, 2015
Messages
5,406
Reaction score
621
Location
SW Ontario
My Car
1971 Mustang Mach 1, M code, 4 speed.
Took some pictures of the snap rings and caps to show the diffrences.
I have another question. The rings you show pictures of, where are they located?? I did not see anything like this on the Saginaw 800 box I rebuilt. Are you working on an 800 box, or is this another type. I don't want to come across as a dumbass, but I missed the "T" bar and also these rings. If you can clarify this, it would help no end if and when I do another. I stripped my casting to the core and did not see anything like these items. I guess I'll need more info before I attempt another box rebuild. I was only replacing old seals and bearings, so other than a good clean up, there was no need to pull everything apart. That's my excuse and I'm sticking with it!! lol.

Geoff.

 

Bentworker

VIP Members
Joined
Jan 17, 2015
Messages
1,465
Reaction score
179
Location
California
My Car
71' Grande project.
The two castings I took pictures of were pretty dirty, so the snap rings are camouflage. They look like beefy piston rings. The picture below should help out. The rings don't go into a groove, they are just spring loaded and pressed into the end of the bore. If you look closely at the firebird picture above in the thread you can see that there are two rings stacked on top of each other to get the total size needed.

The torsion bar is something I don't think most people fool with. The only reason I could see the need to remove one was if the steering box was leaking out of the shaft where it steps from the splines for the steering coupler to the smooth section (3/8"ish in dia that protrudes about 3/4" past the splines). That smaller protruding part is actually the end of the torsion bar. There is an o-ring in the bore of the splined shaft where the torsion bar goes through it. There is no other reason I can think of to take it apart, unless you like really small roller bearings going everywhere.

Also, with 100% certainty all three boxes I was working on are 800 series.

2016-05-04 16.34.40-480x853.jpg

 
Last edited by a moderator:

Bentworker

VIP Members
Joined
Jan 17, 2015
Messages
1,465
Reaction score
179
Location
California
My Car
71' Grande project.
Critical instructions on how to set the input (Thrust bearing) preload. I trust these, there are a bunch of other goofy methods out there on the net involving counting threads etc that don't match up with any Saginaw publication like the one below I have ever seen. Just follow these, the only special tool needed is a spanner socket that you can make and a torque wrench.

image.jpeg

Made up a spanner socket today to set the bearing preload. Found the instructions above online and figured they were worth posting.

Got it torqued to 20ftlb and then backed off 1/2".

Should be good to go, Except for the custom rag joint.

The socket was just made out of a spare steering box input nut (you can do the same, you will have a GM or Jeep box to harvest one from), with some drill rod pressed into the holes, and a socket welded on the back.

20160506_133422-240x427.jpg

20160506_133430-240x427.jpg

Using a torque wrench to tighten the nut to 20 foot pounds, mark its location, back it off 1/2" then tighten the lock ring.

20160506_134011-640x360.jpg

20160506_134147-480x853.jpg

Checking the amount of torque it takes to turn the input shaft. This is for the "over center" adjustment on the above sheet. This type of torque wrench is great to have, but is expensive. Might be better to borrow, or guess depending on tool budget. No matter what set this while the box is off the car. I don't think you can judge the force when it is on the car feeling it through a giant steering wheel and are probably much more likely to set it too tight.

20160506_134827-640x360.jpg

 
Last edited by a moderator:

Latest posts

Top