Sometime over 10 years ago I did a modified B code spring swap on the rear of my Ex and it lifted it about 2.5". i put on V code springs on the front. The rear is about 2" higher than the front. This was by design, as the truck is used mostly for towing a Travel Trailer. It will sag about 2" with the 1250 lb tongue weight and a Weight distributing hitch. It runs perfectly level with this setup and the ride is excellent while towing, and a bit stiff when not towing. I never 'thought' I noticed any odd vibration or shimmy from the driveshaft. The spring setup that I have now uses the OEM Excursion blocks.

Anyway, I wanted to change my U-joints and after reading Tom Woods site and the BillaVista pages about Driveline geometry, Using one of the analog angle finders you can get from Home Depot, I decided to go and check the angles.. Then the slapping of the forehead and calling myself stupid for a half hour ensued.

As far as the angles,, whoo boy, are they off. Now I realize that a hard shudder that I feel sometimes when braking hard is the dang driveshaft geometry. i had always assumed it was due to brake or tire issues. It seems that there is a 9 degree included angle at the transfer case/driveshaft, and a 0 degree angle at the driveshaft/pinion. The dang pinion is directly inline with the driveshaft at rest !! Af far as I can tell, the geometry would only get worse when the trailer is attached and it drops that 2". The shaft has single cardan joint at teach end.

I used to have Landyot radius rods on there, but found after the spring swap that they did not do much for the feel when driving. (boy was I wrong.) I still have them in the garage.

Any suggestions as to how to handle this? I can machine my own shims of any angle if needed. What I was originally thinking to do was to put on the W codes, get another inch up front, and add F350 tapered blocks out back ( I have them already). With a minor leaf deletion, I would gain about a inch in the rear and all would be as before, so I thought. I see the tapered blocks would only cause it all to get even worse, unless I swapped sides on them to reverse the taper. That is a pretty big angle back there. I think I need to hook up the trailer and see what the angles are when towing too.

BillaVista page
Tom's driveshafts pageworse,

Edit: another website to read http://www.4crawler.com/4x4/CheapTri...l#Measurements

 

Hard braking will cause the differential to turn downward at the u-joint causing more shaft alignment issues. My guess is that you have too much flex in your new springs. Guess is the word.

 

 

 

I'll go out and get pics now. Will take a little time as I will get hook up the trailer and get those angles, too..

 

Here is some pics as it is without a trailer. I laid a 6 foot level on the driveway in 4 spots and put the angle gauge on it. Zero angle at all four, driveway pretty level. I remeasured the angles and this time I wire brushed the flanges and clamped a flat metal ruler to them to make sure of the readings.
Transfer case output flange 1 degree up
driveshaft down angle 7.5 degrees down
Pinion flange angle 7.5 degrees up
The OEM blocks are tapered. 2-1/8" in front, 2-5/8" in rear.

 

Jees. I made the calculation as to the angle on the blocks. That freaked me out so much I went back and re-measured them. Works out to be 5.71 degrees by calculation. Given probable measuring error, give it anywhere from 5 to 6 degrees.

So the pinion has 5 to 6 degrees up just from using the original blocks.

 

i guess I could switch the blocks and turn them backwards to get the pinion down. Adding a angled shim would probably help.. I wonder how many others that have done the rear spring swap with or without modding the springs have had this issue. (and not even realized it)

The only other thing I can think of to fix this is to go for a CV driveshaft. Heck, with the inch or so height from the tapered F350 blocks, that would probably put the pinion down a degree or so from the driveshaft, making it perfect. Only problem is that is in the ballpark of 500 bucks.

I also found another website for further reading http://www.4crawler.com/4x4/CheapTri...l#Measurements

 

 

The PMF blocks could work., But now I'm concerned that lowering the pinion down will increase the angle of the top cardan too much. The top cardan angle is already 8.5 degrees, and that is getting to the reasonable limit. I need to get out my drawing software and start making measurements in various configuration positions, then draw them up and see what happens.

I need to figure out:
Configuration when towing
Configurations with the front W springs and different blocks on the rear, both with and without the tongue weight.

Then I would know what the best is. Blocks or double cardan driveshaft. I have a feeling that it is going to end up getting a driveshaft. But the numbers will tell.

 

When single cardin driveshafts are used than the OEM block should be flat. The angled blocks are for double cardin shafts.

I would look for a used double cardin shaft from an X, and swap it in.

 

Well, the blocks that are in there are tapered and they are the original blocks and the original non CV driveshaft from Ford.

 

Ok, but I would like to know what the approx 1" block is on top of your oem block, or am I seeing things?

Irregardless the geometry seems to be pointing toward a double cardin setup, almost perfectly so.

What is also odd is the rust difference between the sterling rear end yoke and the driveshaft. Most of the time both will rust the same.....Unless a new yoke was installed.

At this point I recommend a double cardin driveshaft.

 

That 'Block' is not a block. The original OEM Exccursion springs had a anti wrap leaf with a large snubber on it that stuck out the back of the leaf pack. I took that leaf and cut off the rear of it, leaving it as a spacer for just a bit more height. It is part of the spring pack held by the bolt. It is 5/8" thick. If I went with a 3.5" F350 block, that is the leaf I would leave out to just give a total of 1" of extra lift to the rear.

Yeah, for some reason the driveshafts have rusted up good, and they used to have a good layer of paint on them.. I'm thinking that it is from getting cooked by the Catalytic converter and the muffler right next to it. Rust is not too deep yet. The tubing is only .086" thick.

The front axle is rusted as bad. I think it gets heated from the Exhaust manifold right next to it.

If I get a new driveshaft, I might paint it with high temp exhaust manifold paint. It would probably last longer.

 

I'm still in the middle of my build and spring swap, but had concerns regarding driveshaft angles and vibration. So I'm using double cardan front and rear driveshafts from a 2002 V10 4wd Excursion - just finished rebuilding them. Fingers crossed.



CR