Measuring your Saginaw 800 Gearbox - 3" or 3.25" box?
 
3" Gearbox measurement

3" Gearbox measurement

Customers often end up with a gearbox that they don't know the vehicle it came from.  Then, they want to know "can it be upgraded to a fast ratio?" One way to answer that question is to know what size gearbox it is.  

Saginaw 800s come in two sizes; 3" and 3.25". When talking about 1960s through 1980s GM automobile boxes, most B-bodies (full size GM cars) came with the 3.25" box. A-body and F-bodies came with the 3" gearbox. The 3" can be upgraded to the 12.7:1 fast ratio, the 3.25" cannot. (The 3" box can be a drop-in replacement for the 3.25" and that's how full sizes vehicles are upgraded to fast ratio.) 

To check your gearbox size, measure the round aluminum endcap (which faces the front of the car) as shown. 

3.25" gearbox measurement

3.25" gearbox measurement

There are other ways to tell what gearbox you have, but sometimes you still need to know the size. Other ways to identify your gearbox will be covered in a future post.

 

 

Marty Preuss
Rag Joint - removal and installation

A common mistake with rag joints (flexible couplings) is to think that loosening its "pinch" bolt is all that's required to remove the rag joint from the steering gearbox. Loosening the bolt is not enough, the bolt must be removed from the rag joint for it to slip off the input shaft. The same goes for installation - insert the bolt after the rag joint is positioned on the shaft.

 
 
Rag Joint and Pinch Bolt

Rag Joint and Pinch Bolt

Pinch bolt installed on rag joint

Pinch bolt installed on rag joint

 
Marty Preuss
Is my gearbox on center?

PowerSteering.com's practice is to ship gearboxes on center. And as the heart of your steering system, its center position is important during installation. However its not difficult to tell if a gearbox is on center. The majority of steering gearbox brands, power & manual, use gaps in the pitman shaft splines to tell you if it's at center; the input shaft provides a clue too.

Most pitman shafts are indexed with 4 large spline gaps. When the spline gaps line up with the axis of the steering box, its on center. If they aren't lined up, it's not on center.

Furthermore, when at center the flat on the input shaft will be at top-dead-center. If there is a rag joint attached, the rag joint's pinch bolt will be at top-dead-center. See the photos below for examples. The input shaft alone doesn't tell you if you're at center, i.e. if its a 4 turn lock-to-lock gearbox it will be at top-dead-center in 4 places. (These conditions do not all apply to reverse rotation or 4 x 4 GM gearboxes.) 

 
 

Centered Gearbox

Uncentered Gearbox

If you have a rag joint (flexible coupling) on your input shaft, the pinch bolt is at top-dead-center when the gearbox is at center, as seen below. 

 
 
Marty Preuss