Steering Rack Disassembly and Refurb

[wheee!]

If we don’t hear from Jim by noon MST, I might have to drive down to Calgary and check on him!
.... dibs on all his Z stuff if the band saw ate him!

[zKars]

No such luck Mark, I survived. Stay put. I was repairing a broken bottom right corner of a L20B front cover. Welding (torch brasing actually) aluminum is fun. I had to build up new metal then file it back into shape. The busted out corner was long gone. PO had just put a large blob of RTV in the hole.... Sheesh

Ok, I hacked it off just between the flange and the pinion housing. This is past where the end of the steel inner tube seats in the aluminum.

Then I couldn't resist trying to separate the aluminum housing off of the steel tube. I drilled out the remaining metal in the two holes and heated the housing. Had the MAP torch out from doing the front cover repair. It came right off.

A point of note here, as I was heating the aluminum housing to expand it, molten plastic stuff began boiling out of the two  holes. Well after it came apart (easy, quite loose), it was apparent where that molten plastic came from.

Both the steel tube and the inside of the housing have a groove, that was filled with that plastic stuff. Here is the picture with the remains of it in the groove after I picked at it.

Here is the groove on the steel part.

This leaves me a bit perplexed. I drilled through metal for sure in both holes to get to the ID. But to fill that groove with plastic, you would have to have the outer hole open to the OD and groove of the steel tube to fill it. So maybe the groove space is injection filled, then some metal is pressed in to the holes lock the two metal together. I think the plastic is a moisture seal between the two. I would have just used a dang o-ring.... 

The aluminum housing was not a tight fit onto the steel tube. I can tap it back on now that it's off with just a little effort. It would definitely rely on the pin/metal in those holes to prevent rotation.

And here is the remains of the metal pin/plug after I drilled it out.

So I suppose for Mark's Powder coating melted plastic, there may be a moisture path in or grease path out if the plastic filled groove is not full anymore. Just a little silicon at the housing/tube junction might prevent anything from going either way.  No rotation prevention is likely comprimised though. 

Edited January 21, 2018 by zKars

[wheee!]

I’m sure that only a small portion of all that plastic came out of mine so I will seal the remaining openings.
Very interesting results Jim!

[Captain Obvious]

Thanks for the autopsy! I've been dying to know. 

After seeing the grooves in the gearbox and the tube, and after hearing how loose the two pieces fit together now that they have been disassembled once... I stand by my original analysis!!

I think those two parts were aligned on a jig and then "glued" together with that plastic material to lock them in place. They were designed to be a little sloppy so the correct position could be achieved, and then locked into place with the plastic. I don't think there were any metal pins. I think it was all plastic injected under pressure into that groove until it came out the other side.

On ‎1‎/‎16‎/‎2018 at 9:22 PM, Captain Obvious said:

My theory is that they have something to do with the fitting and alignment of the two major components of the rack tube. The rack housing body is made up of two parts... 1) A cast iron piece that houses the pinion gear and one end bushing, and 2) a steel tube that reaches over to the other end of the housing. I believe those white plastic nubs are some sort of epoxy used to align and lock the two pieces of the assy together.

I'm thinking that since the alignment of the long steel tube into the cast portion that houses the pinion gear is important, maybe they loosely fit the two parts together, locked them in an alignment jig, and then used a hard setting thermoplastic to lock the two together. Inject it into the hole until it comes out the other side, and then let it cure in place locking the two parts in alignment.

 

[Zed Head]

Just a nomenclature note, and a maybe/guess on what Nissan was doing with the plastic.  Thermoplastics don't set, they just solidify from the melt, and can be remelted.  Thermosets are the ones that cure and can't be remelted.  So if the material melted and flowed it would be a thermoplastic, not a two part thermoset.

It might be that Nissan put a ring of thermoplastic in that groove then pressed the parts together.  Maybe as a sealant and/or alignment aid, prior to locking it all together with the holes and pins.  Some subsequent heat treatment process might have allowed the plastic to flow.  Maybe just the paint drying/curing oven.  

[240260280]

17 hours ago, Captain Obvious said:

Thanks for the autopsy! I've been dying to know. 

After seeing the grooves in the gearbox and the tube, and after hearing how loose the two pieces fit together now that they have been disassembled once... I stand by my original analysis!!

I think those two parts were aligned on a jig and then "glued" together with that plastic material to lock them in place. They were designed to be a little sloppy so the correct position could be achieved, and then locked into place with the plastic. I don't think there were any metal pins. I think it was all plastic injected under pressure into that groove until it came out the other side.

 

I agree.  It looks like the concentric grooves were filled to maintain alignment and to prevent the aluminum mounting flange from sliding up and down the tube (left/right relative to cars direction).... not to prevent rotating.

[Zed Head]

I overlooked hot melt, or glue gun material.  That would be an injectable thermoplastic.  Fits all of the necessary criteria.  It would even set up faster than a two part material.  Once the heat is gone it's set.

[wheee!]

On 1/16/2018 at 2:16 PM, Mike W said:

I actually don't know the purpose of the plug that you point out on the rack although I had the same on the racks that I have rebuilt.  I guess that it may have been something used in manufacturing for perhaps the initial greasing of the assembly but needed to be plugged for actual use.

Having said that I have powder coated multiple racks like this without any issue. I just left the plug in tact during the powder coat process.

Mike.

SO any issues after a powder coated rack has been put back into use? No slippage etc?

[74_5.0L_Z]

I would be interested in knowing the force it takes to overcome the plastic bond holding the pinion housing to the rack tube without heat being added.  I have a custom crossmember in my car that supports the rack around the rack tube.  The force of the pinion on the rack will try to separate the pinion housing from the rack tube.  I have ran it this way for several seasons of autocross and two seasons of track days without issue,  but I think I will add an end support to keep the pinion housing attached. 

crossmember.pdf

[Captain Obvious]

5 hours ago, wheee! said:

SO any issues after a powder coated rack has been put back into use?

I doubt it. If you only bubbled out a drop or two, you should still have 95% of the original material still in there. I'd run it.

I wouldn't do it again on the next rack though.  

[Captain Obvious]

1 hour ago, 74_5.0L_Z said:

The force of the pinion on the rack will try to separate the pinion housing from the rack tube.  I have ran it this way for several seasons of autocross and two seasons of track days without issue,  but I think I will add an end support to keep the pinion housing attached. 

I suspect the amount of force to pull those parts apart cold is pretty high, but I agree... I'd fasten to the pinion housing as well.

Send me a rack and I'll pull it apart for ya.   Haha!!

[Zed Head]

I didn't really grasp what the pictures showed.  Just to summarize, it sounds like we/us/the Z world is saying that the two metal parts are assembled, maybe fixtured, a pin is driven in to lock them together, then a molten plastic is injected in to the two grooves (which are apparently aligned).  

I could see the plastic as a longitudinal lock, and the pin as a radial/rotational/locational lock.  Without the pin the tube can spin.  One probably came before the other.  A proper design might have the two functions combined.  "Dang it, this tube keeps spinning"...translated from Japanese.