BASIC DRIVESHAFT ALIGNMENT

Ideally, the transmission output shaft should point directly at the differential pinion shaft. This causes the driveshaft to make a straight path, reducing the amount the u-joints move (and wear).

However, because the ride height changes with differing loads, and because the leaf spring suspension allows the pinion angle to change under engine load, the driveline angles will not always be ideal. In other words, the driveshaft alignment will be a "compromise."

Typically, the best compromise for driveline alignment in the S-10 trucks and Blazers is to have the transmission output shaft point about 1" to 2" above the differential pinion shaft.  This can be accomplished by installing adjustment shims between transmission, and the transmission mount. The reason to have it point slightly above the pinion shaft is so when the truck is carrying a load, the driveshaft angles will not get worse.

The pinion angle should be about 1/2° to 2° low when the vehicle is parked on level ground. During normal driving, due to spring wrap-up, the pinion angle will come up and be parallel to the transmission output shaft.

S-10 short bed/short cab trucks lowered two-inches in the rear have a driveshaft mis-alignment of:

1. 1° to 2° between the transmission output shaft and the driveshaft.
   
2. 1° to 2° between the driveshaft and the pinion shaft.

Mis-alignment beyond 3° causes noticeable vibration and excessive wear on the u-joints.

One problem caused by vibration is that it will cause the truck to fall apart quicker -- with the dash rattling, and interior parts coming loose. The differential pinion seal and the transmission seal will also wear out and leak. The transmission tailhousing bushing will also wear out more quickly if the driveline is vibrating.

The driveshaft alignment kit will reduce the mis-alignments mentioned above to less than 2° -- greatly reducing vibration and wear.

Advantages to improved driveline angles are:

1. Reduced driveline vibration
   
2. Less wear on driveline parts
   
3. Better power transfer to the rear wheels
   
4. Improved fuel mileage

TRANSMISSION OUTPUT SHAFT ALIGNMENT

The truck shown above is a short bed/short cab which was lowered three inches with lowering springs.

After lowering a truck, the first step in getting the driveshaft aligned properly is to raise the back of the transmission so the output shaft points directly to the differential pinion shaft.

The transmission shown above was raised 3/4" with an aluminum spacer. Ideally, the transmission should be raised slightly higher, however, if the transmission were raised any higher, the transmission would contact the floor of the truck and rattle on bumpy roads, unless the floor of the truck is modified (hammered) to improve clearance.

The bolts that attach the transmission mount to the transmission are longer than stock to accommodate the thickness of the spacer, and are included in the driveshaft alignment kit.

PINION ALIGNMENT SHIMS

The Stealth Conversions pinion alignment shims should be installed directly to the leaf spring with socket head cap screws supplied with the alignment kit.

When installing the shim onto the leaf spring pack, hold the spring pack together with a pair of Vise Grips® or C-clamps before removing the original bolt.

If lowering blocks are used, the alignment shim should be installed on top of the lowering block (see next page). Stealth Conversions Lowering blocks are designed to allow bolting alignment shims on top of the lowering blocks.

Bolt Comparison

Pinion Alignment Shim Installation Tips

The stock bolt (shown on top) that holds the leaf-spring pack together is 3/8" diameter by 2" long with a 3/8"-24 thread. It has a head diameter of 9/16", and a head height of 5/16".

When installing axle alignment shims to adjust driveline angles, the original bolt may be too corroded to remove without breaking — or a longer bolt may be necessary.

The 2°, 3° and 4° axle alignment shims from Stealth Conversions are about 1/4"  to 3/8" thick at the center, and may require changing the original leaf spring bolt with a longer bolt. The Stealth Conversions Alignment shims come with a pair of 2-1/4" long socket head screws and hex nuts.

If the socket head bolt is too long and interferes with the lower shock plate, cut the bolt with a hack saw, or a grinder.

Lowering Blocks and Pinion Alignment Shims

Lowering Blocks and Pinion Alignment Shims

On trucks lowered with lowering blocks, we recommend billet lowering blocks from Stealth Conversions.

The Stealth Conversions lowering blocks are unique in that the top of the block is threaded. This allows the pinion alignment shim to attach to the lowering block, while leaving the full height of the cap screw for the rear-axle locating hole.

Stealth Conversions also has heavy-duty U-bolts for S-10 trucks with lowering blocks. The U-bolts use 9/16" diameter threads instead of the 1/2" diameter U-bolts that come with "universal" lowering kits. In addition, the Stealth Conversions U-bolts are made for the 2-3/4" diameter axle tubes used on S-10 trucks, instead of the "universal" U-bolts made for 3" diameter axle tubes.