I put a 2" leveling kit in my F250. It had an "uphill" rake that I didnt like so I replaced the factory 2" blocks with a Fabtech 4" block kit. I love the look but now it has a low end vibration, mostly when you start out. Dont notice it much when I am up to speed.

Could the driveshaft angle be messed up with the new rear blocks? How do I go about fixing this?

thanks for any help

Jerry

 

Anybody help?

 

If you have a 2-piece driveshaft (just about sure you have one), you will need to lower it by installing spacers.

I would try a 1" spacer for a start. If you load the truck heavily, the correct spacer might be closer to 1/2". This drive-away shudder is common when one installs a lift kit. Many kits come with the proper spacers.

Lou Braun

 

Thanks Lou...I dont haul much at all...once in a great while Iwill put my wheeler in there but other than that, its an empty box.

One dumb question... where do the spacers go?

 

The shims are installed to lower the carrier bearing assembly downwards a bit. The carrier bearing is the assembly that joins the two rear drive shafts - look under the truck at the back end of the cab.

That bearing is bolted to the truck. Shims (I guess washers would also work) get added between the bearing and its mount. With an '03 you will probably have to fight some rust to loosen those bolts. That would be the hardest part of the job.

Lou Braun

 

So I was out at the local Ford Dealership and one of the mechanics noticed my lift. I told him about the vibration and he said that I needed to shim the rear blocks to correct the pinion angle.

That made no sense to me. The springs sit on top of the axle, right? so lifting the springs wouldnt change anything at the rear pumpkin. The angle problem should be at where the center bearing mounts to the truck as it has be lifted 2 extra inches. right?

I really need to figure this out before next weekend so I can tackle this problem.

Putting spacers between the center bearing carrier and the frame is the way to correct this vibration, right?

If I am right, how do I go about figuring how much of a spacer to use? and how critical is it to be exact?

thanks for any, and all, help.....

 

Kind of against the clock on this one fellas....please help....thanks

 

Never personally done it but shimming the carrier bearing is a viable plan, I think most aim around an inch or so.

 

Try shimming 1/4" to 1/2" for each inch you lifted, so maybe 1/2 to 1". Another possibility is the slip joint needing greased? Just a thought.

 

Thank you... the Ford guy was wrong then? It just didnt make sense to shim the rear block when carrier bearing was raised...... thanks again...think I will use some Grade 8 thru hard flat washers..( I work at fastenal)

thanks again..I really appreciate it... Rep sent

 

Ok guys....first of all, let me apologize for my ignorance. I have been all over the map with this pinion angle stuff. And I do apologize. Hopefully, this is the last question I ask.

I have decided to add shims instead of spacing down the carrier bearing. I have done SOME research and saw that the axle shims come in degrees. I replaced the stock 2" blocks with 4" Fabtech blocks so I am 2" out of "pinion angle".

What degree shim do I need to put in?

Thanks again..without FTE I would not even attempt doing this stuff....

 

If you could post a pic of the driveshaft angle (looking at it from the side) it would help diagnose your problem.

You will probably have to put a carrier bearing shim kit in it, but the pinion angle may be out of whack too.

Every truck is different. You can have two identical trucks with the same lift parts and it will sometimes take differing amounts of shims in the carrier bearing to correct them both. Sometimes you can shim as little as 1/8" either direction from optimum and get shudder. Diesels, especially Shortbeds with lifts, are the most problematic to correct. V-10's can be a pain too.

You can check the driveshaft and pinion angle with a magnetic protractor, available cheap from Harbor Freight or Sears. The driveshaft should be within 2 degrees of the pinion (driveshaft should be at a steeper angle, pinion should point down slightly in relation to driveshaft), if the pinion is at a greater angle (points upward in relation to driveshaft) you will have to correct the pinion angle or the shudder will never go away.

As previously stated, some trucks can be problematic to correct. My '03 6.0 Shortbed truck with 8" of lift took a custom CV driveshaft, a custom 2 5/8" aluminum carrier bearing spacer (with a 6 degree angle milled into it to match the angle of the driveshaft), AND I had to fabricate traction bars to control the spring wrap when I stood in the throttle hard off idle, especially towing.

Conversely, my '02 7.3 Shortbed truck with the same lift, same 38" tire, and same 4.30 gears, took 2" of carrier bearing shim, and it cured it, no custom driveshaft, no traction bars.

This can sometimes be a serious pain to correct, but it is worth it.

 

When you drop the axle away from the spring 2 more inches with a flat block, the angle where the driveshaft meets the differential is changed at that U-joint. If the Fabtech 4 inch blocks were tapered slightly, that angle would be unchanged. (or changed very little depending on how perfectly engineered the tapered blocks were, you get the picture)

With the factory driveline engineering, the driveshaft runs into that differential probably pretty darn straight, with very little angle. When you dropped that axle 2 more inches, unless you rotated that differential/axle slightly (with a tapered block...) you have introduced an angle.

 

The 2" blocks that came out were not tapered. The 4" Fabtech blocks that we put in, were tapered.

If I shim/space the carrier bearing housing, wont that change the angle of the front piece of the driveshaft?

This whole thing has got me very confused....

I am sure there is no easy answer but: Do I shim the third member or put spacers in the carrier bearing mount?

thanks again....

 

If the Fabtech blocks are tapered, then that pretty much eliminates the possibility of the vibration coming from the rear U-joint and is almost certainly coming from the center carrier bearing.

Yes dropping the center carrier an inch or so will change the angle of the front most U-joint, but it is a known thing and very common for the carrier bearing to be the cause of the take-off vibration. The output shaft U-joint, not so much. I wouldn't worry about that.

Drop the carrier bearing with a spacer and you should be good.