D-44 steering knuckle to brake caliper mount interface???

[Turdle]

I have a set of d 44 parts to powdercoat. I am in the school of thought here that the surface between the disc brake cailper mount plate and steering knuckle should be bare metal, as the friction between these 2 surfaces is what actually keeps the caliper mount from spinning off during braking. The bolts merely keep this friction there with their clamping force. There should be no sidways load on these bolts, in other words-

Sort of like how the friction between the high steer arm and knuckle work. It is this friction area which does the work and it has to be machined carefully.



Or am I wrong? It would be best to coat the entire surface to prevent rust, but if this surface should stay bare I can deal with it by coating the 2 parts "mated"
Help?

 

[IZwack]

I agree that the two clamped surface is what provides most of the torsional resistance during braking but plenty of people have painted both surfaces w/o any issues so I say go ahead and coat these surfaces.

I think the problem with coating the two parts mated is that if the backing plate ever has to come off of the knuckle, the coating has to be parted/split which means the likelihood of the coating flaking off in that area is greater than if they were coated separately.

 

[Turdle]

Exactly. Thanks IZ.

 

[rookieshooter]

FWIW, I've never had a problem doing the whole part on D35s when I PCed.

 

[Turdle]

FWIW, I've never had a problem doing the whole part on D35s when I PCed.

Dmm I wish MLB wouldn't have left our camera at her sister's house--I need to show what I am talking about I guess. Not the caliper--I Am speaking of the bracket, held on to the knuckle by 5 studs---I believe the "spindle" bolts in between em anyway--If memory serves-

 

[IZwack]

You're talking about the interface between the spindle, the brake caliper's mounting/backing plate, and the steering knuckle itself:

 

[Turdle]

:d

 

[rookieshooter]

Ok, I'm thinking about the friction thing you mentioned. I think you make a good point about bare metal to bare metal. The bolts that I think you mentioned have to sustain a lot of shear force not clamping force or should I say pulling away force. Therefore once the friction is lost by the bolts losing their pre load or what ever, then the shear force which is perpendicular to the axis of the bolt could have some bad effects. Just as in the shear force put on a high steer arm. In fact I welded extra metal on one of my knuckles so it would have a larger surface (friction) area. Of course I machined the welded area. This was on the passanger side.
I would leave it bare metal. Once the the two pieces loose their friction then it's Shear City. That's why on my D70 axle flange to hub I make sure they're torqued properly to handle all the shear force that is put on them. Case in pont. Read on another site that this guy had so much HP that all eight of his hub bolts broke. I call that BS. What happened is those bolts were not torqued properly and lost their preload then got sheared off.

 

[Turdle]

Hmmm, I think I will try this.

I will carefully cut and place some high temp tape between the 2 surfaces and use a couple nuts to hold the "assembly" in place during the baking (curing). This "should" allow the 2 parts to separate clean, and, get most of the surface coated as possible.

 

[rookieshooter]

A wise choice Grasshopper. I gave it some more thought, which is a scary thing in it's self. If all parts were coated then the parts that were bolted together might just start cracking the PCed surfaces which would then surly loose a lot of the friction coefficient necessary to keep the shear forces from acting on the bolts. An irregular surface area would not make for a good fastening area that has to deal with shear.
I really don't have the numbers as far as the force applied in shear, but better safe then sorry or even worse.

 

[Turdle]

A wise choice Grasshopper. I gave it some more thought, which is a scary thing in it's self. If all parts were coated then the parts that were bolted together might just start cracking the PCed surfaces which would then surly loose a lot of the friction coefficient necessary to keep the shear forces from acting on the bolts. An irregular surface area would not make for a good fastening area that has to deal with shear.
I really don't have the numbers as far as the force applied in shear, but better safe then sorry or even worse.

I forgot to mention the color of choice requires a second clear coat, so, this means adding about 5-6 mils minimum to both surfaces. It would not be "machine smooth" either.

These knuckles take a lot of masking, I had to fabricate ball joint hole plugs, and then the snap ring grove plugs.--ah, good times. Between blasting and masking, I have about 6 hours into em already. I must admit I blasted the coil buckets, radius arm caps and some smaller brackets also, but the knuckles have proven to be a challenge. Since I have so much time into them, do you reckon all other surfaces are safe to be coated?

The bummer for me is after curing the color, most tape will fall off, requiring a second tape off for the clear. Lots of Television time.

All the parts will be toxic green. Someone we all love is swapping a d44 into a blue ranger---

 

[rookieshooter]

I think you have all the bases covered. I don't know if adding those mills would make it harder to drive the hardware in that holds the caliper in place, probably not.
Hope to see pics of this when done or on the Ranger.
Just preparing the metal alone is so time consuming. Do you chemically treat it fist? I used to use Acetone.

 

[Turdle]

I think you have all the bases covered. I don't know if adding those mills would make it harder to drive the hardware in that holds the caliper in place, probably not.
Hope to see pics of this when done or on the Ranger.
Just preparing the metal alone is so time consuming. Do you chemically treat it fist? I used to use Acetone.

Usually it goes ,,,,
Degrease, bake real hot to cook out oils, blast, wash with hot water, blow off, preheat then coat. That makes handling while taping very tricky, so I use a rubber glove on the handling hand, leaving one hand free to play with tape.

 

[Turdle]

I clamped the 2 parts as mentioned with a tape between, trimmed very tight. Then After coating and baking, I let them cool a bit, loosened the acorn nut 2 turns and using a block of wood to the caliper bracket, smacked it with a hammer while still over 300 degrees. The paint split looked real clean, so, after cooling I re torqued them, shot the clear and then after baking did the same "split". Looks clean, but I have to let it cool completely before handling. i will do what I can for a picture.

 

[Turdle]

That is what I came out with. I like it.

 

[rookieshooter]

Looks great. Now the friction should be greater then the clamping force on the two parts preventing shear.

 

[Turdle]

Thanks guys for the help. It was a combined solution.

 

[IZwack]

Looking smashing as always JT!

 

[Turdle]

Thanks. It is a cruddy cell phone picture after all.