FJ80 Stock Front Pinion Angle - Tips On A Cut And Turn

[vwhammer]

This is going to be wordy so i appologize in advance.
Can anyone tell me what the stock front pinion angle is on an FJ80?
I'm going to be up front.
I am not building an FJ80 but I am using the front axle from one.
However, I need to rotate the pinion down for my use.
This will require that I cut and turn the steering knuckles to correct caster.
The real issue here is that, without taking a lot of time to build a fancy tool or jig, there is no simple, accurate and/or repeatable way to measure caster.
So what I would like to do is simply measure the stock pinion angle, which is a lot easier, then derive a caster number from that.

My main problem is that I do not have an FJ80.
I only have an axle so I can not measure the stock pinion angle.
After I have the stock pinion angle I can set my axle up on the bench and set the pinion angle to the factory setting.
The plan after that is to put some of those exhaust U bolt things around the axle just inboard of the steering ball on the axle housing.
I would then adjust these until the reading across the flat part of the saddle (or whatever you want to call it) reads zero as measured with my angle finder.
I would then rotate the pinion angle down to zero.
Then I would cut and turn the knuckles until the reading on my U bolt saddles reads zero again. (Well I may add a degree to help with high speed stability)

Does anyone see any flaws with this method?
Does anyone have a possible better method?

I would like to get a few "stock" pinion angle measurements so I can get a good average to use for my process.
So if you are bored and have a stock 80 series and an angle finder would you mind going out and measuring the front pinion angle to the best of your abilities.
Thanks

 

[Stoffregen Motorsports]

Caster and pinion angle are relative measurements, so not knowing the caster won't matter for what you're doing. I don't have the exact numbers, but I do know the caster is in the 5-6 range and the factory pinion angle does not tip up much at all. I bet it's only 2 or 3 degrees.

I hope this is an off road rig, as welding the balls on without a jig leaves a lot of room for error.

 

[krazytoy]

Yeah, stock pinion angle is typically between 5* to 6*. You can obtain the caster angle accurately and repeatedly with a digital level across the steering arms. Keep in mind that you want some cross caster for alignment and to account for the crown in the road. Here is a write up I did when I did my C&T http://forum.ih8mud.com/threads/knuckle-cut-turn.753203/. Really though if you are turning the pinion down this is only going to increase your negative caster number which, to some point, will help with drive-ability. I usually try and set my caster at around 6*, in my experience anything past 7* starts to have a negative effect.
There are a lot of different variables to consider such as tire size, Ackerman angle and steering degree movement in the horizontal plane, if that not enough for you you can also start looking into caster and pinion change throughout the movement of the suspension dependent upon how much travel you have and suspension design, its really not all that difficult though. I had a good article on how the factory determines what the proper caster angle should be, but I can't find it now.

 

[vwhammer]

Ok I had a guy (or girl maybe? I don't know) on Ih8mud measure their pinion angle and it came out to about 5.5* so that sounds like a pretty good place to start.

According to this image from Slee it looks like the stock caster is about 3*


I think I am going to carry on with my plan as described above.
I will set it up on the bench and set the pinion angle to 5.5*.
Then I will bolt on my exhaust U-bolts and set the flats to 0*
At this point I can rotate my pinion down to 0* (thus rotating the knuckles another 5.5* positive giving us 8.5* total positive caster)
Now, with the U-Bolts still tightened down where they were when this whole thing began, I cut and rotate the balls forward 3.5*-4.5* (have not decided yet).
This will net somewhere in the neighborhood of 4-5 degrees total positive caster.
Bing bang it's all done.

As far as the concern of screwing up the front end, it is not likely since the balls have a sleeve that fits pretty tightly in the axle housing.
To ease all concerns I am currently having an alignment jig made for my rear axle build for which I am also having parts made to work on the front housing
I can put the jig on it before I do any welding.

Well that nearly wraps this up.
I will post some pics once I have something to post.

In the meantime if anyone else has time and means to measure their pinion angle please do so so I can have a few more numbers to smooth out my average pinion angle measurement.

 

[ChuckB]

You guys are way over my head, but I'm following your build. I wish I had 1/10 of your skills. Looking forward to the end product!

 

[krazytoy]

The factory spec is 3* to 5* on the castor and for what you are doing (which is very cool) I would stay right in the middle and shoot for that 4* range. What you have planned will work just fine, grab the grinder and get to work! Just a few pointers on cutting the knuckles, make sure you cut on the 3rd member side of the weld, pay attention to how deep you are going, you only need to go about 1/8", the ball are a tight fit (that sounds weird), when I am comfortable with my cut depth I usually stick a bar through the trunion bearings and hit it with a hammer rotating the balls and breaking them loose. Other than that its fairly simple and honestly pretty hard to screw up, just don't cut too deep.

 

[vwhammer]

Well I did the cut and turn today.
Have not welded it yet.
However I posted it in my van build so rather than post it all here again you can check out what I have done on page 4 of my build
http://www.expeditionportal.com/forum/threads/162055-Volkswagen-Vanagon-4x4-Conversion/page4

 

[Stoffregen Motorsports]

Even though the balls have a tight press fit, they can still tweak during welding. Plan your welding. Maybe tack it first with a couple good, strong tack welds and then check for movement, then burn it in place. Do the same welding sequence on both sides for consistency.

 

[vwhammer]

Yeah I've read that is is generally a good idea to tack it at opposite sides.
Then let it cool to the touch.
Then do the other two sides and let it cool.
Then start with a more substantial short weld and the same on the opposite side and let it cool.
So on and so forth until the whole thing is welded.
I'm pretty confident in my welding ability (aren't we all) so I am not too worried about the welding part.
With my jig I will also have the ability to put some tension on everything to hold it as tightly as possible.