Awwe Crap!

[ford38v8]

Cap, the "spring scale" referred to was a KRW tool made for Ford. When I used it on mine, the reading on the scale bounced radically while turning, preventing any kind of accurate measurement. After fooling with it for several hours, I did get the preload set by guesswork on the scale, but had no confidence in the value achieved. I took it to a flathead guru who used the vise/spin test, and told me I had indeed achieved the desired value, which surprised me.

[Capt Kirk]

I did a test. 10 pound dumbbell with a shoelace tied around it and wrapped around the splines. Released the weight and it didn't move. A little twist with my fingers and it moved some and then stopped...did this same thing repeatedly with the same result. In my previous post I figured I'd need 9.3 pounds hanging from the shaft to get 17 in-lbs of torque. My bearing pack is flooded with Lucas and for those that don't know, it's stringy and like honey. Before the Lucas, I did the spin test (bearings lubed with WD40) and got about a turn and a quarter. I feel comfortable where it's at now and the proof will be in the pudding as I drive it.

[Mart]

I think you may be out on your calcs.

If you had 17lbs at a 1" radius, you would need a heavier load at the radius of the spline, which is less than 1". 1" radius is 2" diameter.

I just measured the spline at 1.1" diameter so that's a .55" radius. 17/.55 is pprox 31.

I reckon you would need about 31 lbs acting at the radius of the splines to give an effective 17 lbs in.

I have not figured the radius of the string or the fact that the diameter is smaller between the splines. Not sure how relevant they are.

Mart.

[Capt Kirk]

LOL...Mart, you're absolutely correct! Smaller diameter more load to equate the same torque. I thought about the string thickness and the reduced diameter of the groove area of the spline but didn't think the difference would amount to much. Thanks for the correction...I went the wrong way with the calc...may have been the couple beers and/or the distractions here. Next time I'll think before I type. My pinion now has a firm but free feeling to it and the bearing pack has been mated forever. It's certainly tighter than it was and I have no doubt that it would spin with 30 pounds on it. Now I need to figure out how to recover from the embarrassment of a reversed numerator and denominator in my calc.

[V8COOPMAN]

Originally Posted by Capt Kirk

Now I need to figure out how to recover from the embarrassment of a reversed numerator and denominator in my calc.

You can always blame it on getting older. Plus, I'd bet that QUITE A FEW folks wouldn't have a clue where to even begin calculating such. DD

[Capt Kirk]

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With Mart's revelation that I screwed up my calcs, I had to go out and check with more weight. I have a 10lb and 8lb dumbbell available. I tied both of those together and wrapped the splines. Turned the weights loose and it didn't move. Gave little encouragement and the weights went all the way to the floor at a very gradual speed. So, it's looking like 9.9 in-lbs. I'm fine with that with mated bearings.

[Capt Kirk]

Originally Posted by V8COOPMAN

You can always blame it on getting older. Plus, I'd bet that QUITE A FEW folks wouldn't have a clue where to even begin calculating such. DD

Thanks Coop. It's simple math and I made a rookie mistake...and I'm embarrassed and thankful to Mart for correcting that mistake. I am getting older and things aren't working like they use to. I'm finding, as I go through this rebuild (my first), that there has been some debate/confusion over the ft-lb and in-lb topic and exactly what the number should be for pinion pre-load. Apparently, the "spin test" has worked forever but for the new guy, they might be looking for something a "little" more scientific. My wife couldn't get a half turn out of it and Hulk Hogan could get 2 turns. There isn't any talk about if the bearing pack should be dry, lightly oiled or coated in axle grease. A shoe lace and some dumbbells whittles down some of the uncertainty I think. I'm comfortable where mine is at now but just throwing other ideas out for the younger crowd that may find themselves in the position I'm in now.

[JSeery]

I think we are starting to mix things up again, there is a difference between 12 - 17 lbs of pull at .55 inches of radius and 12 - 17 in lbs.

Inch pounds is defined as 17 lbs at a distance of 1 inch. Your test is interesting and seems valid to me (and ingenious) but the numbers you are using do not equate to 12 - 17 in lbs. The numbers you are using would be 22 to 32 lbs of weight at the spline and 12 - 17 in lbs with a torque wrench.

The original Ford numbers were 12 - 17 lbs at the spline or 7 to 9.4 in lbs. I'm NOT saying that is the correct values to use, just pointing out that's how the math works out.

It would be interesting to know the history of this reference to 12 to 17 in lbs that keeps popping up, but I would be willing to bet that it is based on a misunderstanding of the original specification and transferring the pounds of pull at a distance of .55 inches to an in-lb value. This is an interesting topic (well at least to me it seems interesting).

[Mart]

Good point, J. Working out how to do an effective test is one thing, having the correct numbers to work from is another. I know how my used bearing assembly felt when I removed it, I will try and achieve the same feel when I reassemble with a different pinion. Are the lower numbers you quote traceable to a Ford publication or document? I might try and measure the drag just for the fun of it.

Mart.

[Capt Kirk]

[QUOTE=JSeery;1356587]I think we are starting to mix things up again, there is a difference between 12 - 17 lbs of pull at .55 inches of radius and 12 - 17 in lbs.
QUOTE]

That is correct. Van Pelts spec is 12 - 17 in-lbs of torque. This is 21.8 - 30.9 pounds of weight hanging on a 1.1" diameter shaft.

I could only find 18 pounds of weight to do this test. The shaft did not rotate when I let the weight hang on it but it slowly went to the floor once
I started it. So, 18 pounds hanging off a 1.1" diameter shaft is 9.9 in-lbs of torque. A little on the low side but I'm guessing OK because the bearings have already been mated.

[Capt Kirk]

[QUOTE=
The original Ford numbers were 12 - 17 lbs at the spline or 7 to 9.4 in lbs. I'm NOT saying that is the correct values to use, just pointing out that's how the math works out.
QUOTE]

Van Pelts says 12 - 17 in-lbs.

[JSeery]

I know what VanPelt says, just curious where it comes from. Doesn't match the original Ford spring pull spec at all and appears to be a confused transfer of the spring spec into in-lbs. It would be cool if someone with an original tool would set a pinion and then check it with a torque wrench.

[JM 35 Sedan]

I would suggest doing the banjo housing spin test as Alan mentioned in post 221, with splined end of pinion clamped in a soft jaw vice. You do not want the preload set too high on those used pinion bearings that would likely cause too much heat.

[deuce_roadster]

I have the KRW tool and the numbers on it are exactly the same as inch pounds, I checked it with a calibrated inch pound torque wrench. This may have already been mentioned as I haven't read all the threads.
Also, after setting up a banjo with the KRW tool, it verified the "spin test" as accurate.

[JSeery]

Good info deuce, but I'm not totally clear yet. I haven’t tried it myself but I would think 15 in-lbs of preload would not allow the pinion to spin as stated. If Ford wanted to call out the preload in in-lbs then I think they would have done so. Just some thoughts on my part.

[Talkwrench]

I set my preload with the spin in vice technique, no problems. You will soon get a 'feel' for how good your bearings are too. I had one NOS bearing that I felt wasn't quite right when I assembled it you could feel straight away , it was binding and was hard to 'break' the resistance..

[Capt Kirk]

Originally Posted by Talkwrench

I set my preload with the spin in vice technique, no problems. You will soon get a 'feel' for how good your bearings are too. I had one NOS bearing that I felt wasn't quite right when I assembled it you could feel straight away , it was binding and was hard to 'break' the resistance..

Talkwrench, I'm comfortable where I have my preload set and did the spin test and got a bit over a turn out of it. It's certainly better than the free-wheel that it was when I took it apart. There's no binding and there was an initial "break" required but that stands to reason. The question is inch-pounds, foot-pounds or pounds and what those numbers are...the answer to which makes a huge difference to the setting. I'm leaving mine at about 10 inch-pounds on mated bearings and will either have success or will have to spend some money for a bad decision. I'm not a bearing expert but feel that if a bearing is too tight it excludes the oil/grease that lubes and cools and the bearing will overheat and eat itself up. Too loose, it will allow misalignment of the gears which will also eat themselves up. My pinion was free wheeling but there was zero slop in any of it and the bearings and gears were great. I hope I didn't make a good situation worse by adding preload to a diff that has been happy for 76 years.

[Capt Kirk]

All of my parts came in yesterday including the axle...which looks amazing. I will be hitting it with dye penetrant this weekend before reassembly.

I'm sure I'll have some questions and will share some assembly pictures starting Saturday. One of the questions will be with respect to lube. I plan (unless told otherwise) on using some red grease that's in a container that says for disk and drum wheel bearings for gear assembly. I'll need to find out what kind of pump grease to use for the front and center driveline bearings and the wheel bearings. Thanks for all your help Barners!
Kirk

[JSeery]

Looks like progress!

[V8COOPMAN]

Hey Kirk.....You've got a whole sack-full of clean parts there, and it's gettin' late on a Saturday afternoon. We're wonderin' if you got that thing glued-together yet, and if maybe you've done a few do-nuts to see if it's gonna stay in one piece! DD