How To Identify Your Gearbox

This is a guide to help you identify Saginaw gearboxes and variations of each gearbox.

There are 5 different Saginaw gearboxes that we sell and service.

We can do rebuilds on many other styles of gearboxes, but for anything other than these listed you must send your gearbox into us for rebuild.
 


SAGINAW 800/808 GEARBOXES

This is the most common gearbox found in GM cars and small truck from the 1960’s into the 2000’s.

The difference between the 800 and the 808 is the size of the piston. The 800 has a 70mm piston and the 808 has an 80mm piston. This is easy to measure from the outside of the gearbox. If you measure the end cap, the 800 is roughly 3” and the 808 is just under 3.5”.

Saginaw 800 gearbox measurement   Saginaw 808 gearbox measurement

It came in both a 3-hole “L” and 4-hole “H” mounting pattern. The 3-hole is the same pattern, just missing one hole and will fit directly into any vehicle that had a 4-hole pattern. They are much more common and easier to find cores, so we typically sell the 3-hole version. If you must have a 4-hole pattern it can be special ordered.

Saginaw 800/808 s-bolt pattern    Saginaw 800/808 4-bolt pattern

Pre-1980 gears will have 5/8 and 11/16” SAE inverted flare fittings while 1980+ gears will have 16 and 18mm O-ring fittings. Again, the older SAE gearboxes are very hard to find, so the majority of the boxes we sell are metric. If you are installing into a pre-1980 vehicle that has inverted flare fittings, we can install a seat kit that will allow you to thread your existing hoses. Yes, the SAE thread pitch will thread into the metric threads!

 Saginaw 800/808 O-ring  Saginaw 800/808 Inverted Flare 

Along with the change of fitting style in 1980, the input shaft also changed from 13/16-36 (pre-1980) to ¾-30 after 1980. You can simply change the rag joint to accommodate a smaller input shaft. When counting the splines, it is important to know that the 30 and 36 counts include any missing splines that are removed where a flat on the shaft is.

Saginaw 800/808 input shaft dimensions

 

SAGINAW 708 GEARBOXES

This box was found in GM trucks and SUV’s up to 1986. It is easy to identify because it mounts on the outside of the frame and the mounting tabs are on the opposite side of the gear. Notice how the mounting holes are on the top side of the gearbox.

Saginaw 708 Gearbox

The one variable with the 708 gearbox is that it came with two different sector shafts. A threaded shaft (found in 2WD vehicles) and a notched shaft (found in 4WD vehicles).

Saginaw 708 sector shafts

Pre-1980 gears will have 5/8 and 11/16” SAE inverted flare fittings while 1980+ gears will have 16 and 18mm O-ring fittings. Again, the older SAE gearboxes are very hard to find, so the majority of the boxes we sell are metric. If you are installing into a pre-1980 vehicle that has inverted flare fittings, we can install a seat kit that will allow you to thread your existing hoses. Yes, the SAE thread pitch will thread into the metric threads!

 Saginaw 800/808 O-ring  Saginaw 800/808 Inverted Flare 

  

SAGINAW GMT GEARBOXES

This gearbox is found in GM trucks and SUV’s from 1987 on. It uses a 3 bolt “triangle” pattern. This box has many variations!

 Saginaw GMT gearbox   

Piston Bore Size

There is a casting number on the housing of the gearbox (Either 83 or 84). 83 is a “small bore” (GMT400). 84 is a “big bore” (GMT800). Most of the time: 1500 2X4, 1500 4X4 and 2500 2X4 use the small bore, and 2500 4X4, 3500 2X4 OR 4X4 use the big bore, but there are some exceptions.

 Saginaw GMT gearbox with piston bore size 83  Saginaw GMT gearbox with piston bore size 84 

Blind Spline

Most vehicles use a sector shaft with 3 Blind Splines, but some (usually Diesels) have 4 Blind Splines. You will need to know which you have.

 Saginaw GMT 3 blind splines  Saginaw GMTt 4 blind splines 

End Cap Number

Some models of vehicles have different internal stops to limit steering travel. There is a number on the end cap that will let us know what stops you need.

Saginaw GMT end cap number

Input Shaft

It is also a good idea to verify your input shaft type. 1987-2000 should have a ¾-30 splined input shaft and 2001 to present use a DD input shaft. Some models around the 2001 switch over may not follow these guidelines.

Saginaw GMT 3/4-30 input shaft  Saginaw GMT DD input shaft

If you have all this information you can go through the pick boxes on our website and order the gearbox you need.

 

SAGINAW FORD GEARBOXES

This box was used on limited Ford vehicles (Mustang and Cougar) from 1971-1973. It uses a 3-bolt triangle pattern very similar to the Saginaw GMT gearbox, but has 7/16-14 mounting bolt threads.

Saginaw Ford gearbox

Since this is a pre-1980 gearbox it will have 5/8 and 11/16” SAE inverted flare fittings and use a 13/16-36 input shaft.

We can build this gearbox with either a 12:1, 14:1 or 16:1VR, but most customers end up going with the 12:1 and a 35# valve.

 

SAGINAW BRONCO GEARBOXES

This box is found in 1966-1977 Ford Broncos. It came originally with a 21:1 ratio. We offer it with a 14:1 and a firmer valve for the perfect feel.

Saginaw Bronco gearbox