Steering rack centering bushing

Aluminum for the steering rack bushing is not ideal. SAE 660 Bearing bronze is better in many ways. This is a material specifically designed as a bearing material, holds oil-lubricant due to porosity, tough and a LOT stronger than aluminum (depending on the grade-type of aluminum) in these applications. There should be only one tension screw for this bushing, the other two retention devices should be pins. This is due to the fact the rack housing is sheet steel which is not really round and will change dimension when loaded. If three screws are used, they can work loose as the loading changes on the sheet steel rack housing and rack gear. Some years ago, made a batch of these for a few Xweb folks, to date including the original one used for years and years and many race hours in the LeMons car, the original SAE660 bronze bushings has been completely problem free.

Here is the original Xweb post.
https://xwebforums.com/forum/index.php?threads/steering-rack-project.12184/#post-92233

If there is enough interest in this bushing, it might be possible for me to make a CAD drawing and get a local CNC shop to run up a bunch, then make up a kit with parts and instructions.


Bernice
 
Thanks. I'd love to have one of the bronze ones ...or maybe 2 or 3...and i can compare with the lifespan of this one if I am living right enough to actually log a LOT of good miles on my SOHC family Fiats (2 X1/9s & a 128 presently).

so, would you replace 2 of the small bolts with a long grub screw to act as a pin?

this is interesting. a bit luxurious, actually...considering the hell my '85 went through before I owned it, I can still put a lot of parts on it backward & be improving :)
 
So, the staked ball joint rack end also (a CM or so) slides into the bushing at full lock? This one had some sloppy staking on it & that may begin to explain the demise of the old bushing in the first place (along w/ being cut & slid in place at some point also....)
 
I'll look into to finding a CNC shop that can do this. Problem with sending parts out to be made, set up charge can be stiff. The CAD drawing is far less of a problem.

Grub or set screws make hideous pins. they have threads, the threads act as a slow saw blade slowly grinding away at the internal sides of the hole. On this replacement bushing, the screw is a M3, grade 12.9 socket cap screw, the two pins are M3 roll pins pressed into a holes on the bushing to a specific depth to never touch the rack gear even if the bushing is worn.

The pictures have disappeared since the image host_er changed their usage policy. Could try to re-post them at a different image hosting location.


Bernice
 
I'd be in for 3 bushings.
Might be worth reaching out to Matt and asking if he would be interested in selling the bronze style ,that could make a production run more affordable.
 
Rupunzell said:
I'll look into to finding a CNC shop that can do this. Problem with sending parts out to be made, set up charge can be stiff. The CAD drawing is far less of a problem.

Grub or set screws make hideous pins. they have threads, the threads act as a slow saw blade slowly grinding away at the internal sides of the hole. On this replacement bushing, the screw is a M3, grade 12.9 socket cap screw, the two pins are M3 roll pins pressed into a holes on the bushing to a specific depth to never touch the rack gear even if the bushing is worn.

The pictures have disappeared since the image host_er changed their usage policy. Could try to re-post them at a different image hosting location.


Bernice
Click to expand...
You can post the pictures directly to Xweb now, no need for a hosting site.
 
Rupunzell said:
Aluminum for the steering rack bushing is not ideal. SAE 660 Bearing bronze is better in many ways. This is a material specifically designed as a bearing material, holds oil-lubricant due to porosity, tough and a LOT stronger than aluminum (depending on the grade-type of aluminum) in these applications. There should be only one tension screw for this bushing, the other two retention devices should be pins. This is due to the fact the rack housing is sheet steel which is not really round and will change dimension when loaded. If three screws are used, they can work loose as the loading changes on the sheet steel rack housing and rack gear. Some years ago, made a batch of these for a few Xweb folks, to date including the original one used for years and years and many race hours in the LeMons car, the original SAE660 bronze bushings has been completely problem free.
Bernice
Click to expand...

The literature I've seen on SAE 660 lists tensile and yield strength as ~35 ksi / 20 ksi respectively. I would not characterize that as a lot stronger than aluminum (not typical machinable bar/tube extrusions that are tempered). For example, ASTM lists 6061-T6511 tube as 38 ksi / 35 ksi. Were you thinking of aluminum bronze perhaps? At any rate, no disagreement that the 660 bronze would be a fine material to use.

On the aluminum version, three button head screws are used for servicability and to make it easy to install the boot. The platic bushings are frustrating enough to remove, without having to pull roll pins, etc. But the great thing about engineering is the abundance of choices and trade-offs! :)
 
Could small shoulder bolts be used to locate the bushing? That way the smooth shank would ride against the housing rather than threads.
 
Here are a couple of photos to show the rack end as it reaches the end of its travel.

SOHC%20Rack%20End%20at%20Almost%20Full%20Lock.jpg


SOHC%20Rack%20End%20at%20Full%20Lock.jpg
 
Dr.Jeff said:
Could small shoulder bolts be used to locate the bushing? That way the smooth shank would ride against the housing rather than threads.
Click to expand...

I don't see why not. They're about $4 or $5 a piece from McMaster though. You end up with an M2 x 0.4 thread on the end, as if the M3 wasn't small enough... To do an M3 screw with a 2 mm unthreaded shank you'd probably have to get them custom made.
 
Rupunzell said:
If there is enough interest in this bushing, it might be possible for me to make a CAD drawing and get a local CNC shop to run up a bunch, then make up a kit with parts and instructions.


Bernice
Click to expand...

I received one of Bernice's initial run. Excellent fit, installation was straight forward, and it has lasted well. I have not had it apart and inspected it though. I recommend it.
Paul Davock
 
Bernice, if you end up doing up some of these bushings in an appropriate bronze units I would appreciate the opportunity for two. Belt and suspenders as it were.
 
You must log in or register to reply here.
Back
Top