I am building a custom lift for my 1975 highboy f-250. I am having difficulty finding information on maintaining correct pinion angle when using large lift blocks on the rear axle. As far as I can tell, (after spending several days surfing and calling around), noone sells a 10-12 inch lift kit for my truck or for any other 75 F-250 for that matter. I want to raise the rear 10 inches and the front 12 in order to clear the 44x18.5-16.5's I have purchased. I have already designed my traction bars, (front and rear), and am using 12 inch lift springs in the front. I was in the process of building the 10 inch blocks for the rear when it ocurred to me that if I didn't taper the block, it would cause problems down the road with pinion bind. But how much to taper? Is there a formula, for example, x amount of degrees per x number of inches of lift? If anyone can help, I would greatly appreciate it.
Thanks,
Eric
By the way, I am a new user here and so far this site rocks!!!

 

It really depends on how bad the axle twist when you accelerate. If you haven't torn it apart yet, measure the angle now, then unbolt the driveshaft and drop the rear of it down 12" then you can kinda eyeball about how much you would need to get close to where it is now. I know it's not a very scientific way, but it's just an idea.
Have you tried to contact the guys that built Bigfoot? They may have a formula that might help ya.

 

Check the driveline section of the links in my Club FTE webpage.

 

Thanks for the info...I was kind of hoping that there was a scientific method for determining the proper angle, but then again I guess "proper" is where FoMoCo had it set in the first place! Anyway I'm gonna use the "eyeball" method and see how it turns out. The only thing I was really concerned about in doing this is that with a zero degree alignment it could wrap up during hard accelerations, (I forgot to mention that I have a 460 in the machine shop I'm expecting to be able to get a solid 400hp out of once installed ahead of the stock T-18 tranny...but that's a whole different hole in my wallet.) I'll post pics when I'm done but it may be awhile...a long while.
Again...Thanks, and I'm guessing that since my post was moved, I must have put it on the wrong board...sorry.

 

I just took the 2 1/2" lift blocks off my 78. The PO added them to the stock blocks and I had some minor problems with them. The stock block has a solid bottom but the lift blocks had big holes in it (looks like a square 8). From off-roading, the lift blocks started smashing the perches around the edges and caused my axle to wrap a little and make the problem worse.

If you're making blocks, make at least the bottom solid and flat.

Also, if you spend about 30 minutes drilling out the rivets on the rear shackles and flipping them over, you'll get about 2 1/2" - 3" of lift (assuming it's similar to the F150). That will reduce the size of the lift block and that's a good thing.

I'll measure the taper on my blocks and the angles I have and post back later.

Kevin K.

 

OK. I measured the stock blocks and the lift blocks that were on my 78 F150. If you extended the angled planes of the blocks towards the front of the vehicle, you'd get a radius point of 4'-4" for the lift block and 3'-8" for the stock block. If you average that out you'd get 4'-0". So, if you draw a triangle with two 4' legs and a 10" leg (for your 10" lift), you'll get and angle that should work.

I did notice that the top surface is at a right angle to the front and back of the block, meaning that only the bottom surface is angled. If they were both angled, the axle would move further forward the higher you went.

Using these primitave calculations, here's a drawing of what a 10" lift block might look like.


Ok, so I have a little time on my hands.

Hope this helps.

Kevin K.

 

A 4" long degree block that is 1/2" high to nothing, is a little bit over 7 deg. My 79 F250 is tipped 14 deg, in the rear with a 6" lift. I have no vibration problem.

 

Thanks for the info...I think I've decided on a little different block design, however, it seems that as long as I roll the axle to raise the pinion an inch, I should be in good shape. The difference I mentioned is still in the planning stages, so I haven't figured any angles yet and I'm not completely sure it can be done, but: The block should be 10 inches long at the top, (where the spring rests), 13 inches tall in the front and the rear but angled toward each other so as to almost make a 10x13x13 triangle. At the point where the the front and rear sides come within 3 inches of each other, (it should be 10 inches below the top of the block), I'll cut a half circle so the block will sit on the axle and almost wrap around it. This is where I'll cut off the perch and roll the axle backwards an inch, weld the block on the top and use a piece of 3"x27", (or however long it winds up being), flat stock to make up the face, wrap under the axle and make up the rear of the block. Then the block will virtually be welded all the way around the axle. After I do the same to the other side, I'll weld a piece of 1 inch tube from the inside middle of one block, over the pumpkin, and to the inside middle of the other. Now for the ladder/traction bars...still designing these. I saw a pair of straight up and down ten inch blocks, they werent even welded to the perch and they sure looked precarious. This is what prompted me to try something different, but I'm not sure what the 10 inch long base under the spring is going to do to my ride...probably feel like riding on a stagecoach, but then I'm not building a cadillac! Thanks again for the time spent getting me the info I need.

 

Oops...if you have 14 deg. with a six inch lift, it stands to reason that I should need 21 and 3/8 deg. therefore, I should need to roll the axle about 1 3/4 inches...I think.

 

That big of a block seems a bit extreme to me- with that much leverage added to suspension, somethings bound to fail eventually- did you consider the shakle flip idea??? and you could drop your front mount also to gain some more lift.