3 speed Tandem

[Red Horse]

A friend asked me about a "3 speed axle".  My  response..."no clue" other than I remember when Eaton or  Rockwell offered a 3-speed tandem.

 ring a bell with anyone?  and how did they work?  My memory says they were two 2-speeds but how could you get a third ratio out of that?

[j hancock]

Ahhh, Eaton 3 speed axles for tandem suspension. 

For low range operation, both axles were in low.  high speed, both axles in high.  Intermediate speed was accomplished by having one axle in low and the other in high. 

The interaxle differential took care of the rest!  You know where this is going....

A lot of interaxle differentials got torn up and died.  Soon it was highly recommended to use either high or low for both axles.  The intermediate speed was best left for sitting around the campfire and talking about the good old days!

[Vladislav]

1 hour ago, j hancock said:

A lot of interaxle differentials got torn up and died.

Difficult to imagine the things would go another way with that setup.

But the fact that someone resolved to offer such solution to the market seems interesting. I always enjoy finding examples of extraordinar engeunity.

[j hancock]

3 speeds needed more maintenance and the gear lube HAD to be changed on a strict schedule.  It was something to try and gave trucks more gears and tighter splits.  With the development of Eaton 13 speed transmissions and others, 3 speed axles were set aside.

A manufacturer has to keep thinking and developing new ideas or they will get left behind.

[Red Horse]

7 hours ago, j hancock said:

Ahhh, Eaton 3 speed axles for tandem suspension. 

For low range operation, both axles were in low.  high speed, both axles in high.  Intermediate speed was accomplished by having one axle in low and the other in high. 

The interaxle differential took care of the rest!  You know where this is going....

A lot of interaxle differentials got torn up and died.  Soon it was highly recommended to use either high or low for both axles.  The intermediate speed was best left for sitting around the campfire and talking about the good old days!

Thx Jim- I thought it was something like that but wasn't quite sure.-I would imagine the two ratios were pretty close too.

[h67st]

It sounds like the inter axle would die early using that third speed. My dad had an Astro in the early 70's with the diff lock switch on the dash; they always said never leave that locked on dry roads or bad things would happen.

[Red Horse]

16 minutes ago, h67st said:

It sounds like the inter axle would die early using that third speed. My dad had an Astro in the early 70's with the diff lock switch on the dash; they always said never leave that locked on dry roads or bad things would happen.

And MOST importantly-never engage when you had a wheel spinning!

[theakerstwo]

The three speed had a different power divider that was not like the single speed rears.It did not have much problems if the grease was changed often.C H trans. had many of them plus they were common here in the 60s and 70s.Also some may have seen this but alot of truckers that had a single speed eaton tandem would install a two speed in the rear housing and use it for a short time to get a 200 RPM split by dropping it into low.This would eat the power divider if used very long time.