Dyno Testing an Allison 740

[Doug1968]

Fellows,

I recently purchased a used Allison 740 transmission. I am having it dyno tested by my local Allison Service Center. Has anyone been through this test process?

I am curious to hear how many have been through this test. I will drop the transmission off drained of oil with no lines attached and the flex plate removed.

They will hook up the transmission, circulate oil from there test bench and run the transmission to check for output. They will load the output shaft, check the shift points and check for leaks.

Cost is $250

After this test I will have a good feel for how the transmission will operate.

Has anyone been through this process?

Doug

[Chopper Scott]

I've never been through that process but I have to admit that it sounds like money well spent! Add up the time to redo such an installation, the tranny fluid that you undoubtedly don't want to reuse and possibly a tow back home if it fails down the road...... pretty cheap insurance. I'm sure we'll all be interested in your results.

[JackConrad]

When we had our 740 rebuilt, they put it on a dyno afterwards to make sure it was working correctly and no leaks.  In our case it was included in the price.  I did not actually see them dyno it, but I did see the dyno. Jack

[Melbo]

Please take note that a dyno test is just that and does not promise a trouble free trans --- The torque converter in my ZF failed after it was dyno tested.

It has since been rebuilt and now is just fine.

Not to scare you but just a heads up from experience.

Melbo

[luvrbus]

Allison will give you a good test on the torque converter they will do a stall test 3 or 4 times then they will tell you the ratio for the stall and tell you if you have a single stage,3-element or a polyphase converter.
I am hoping you have the 3 element type converter that is the model that makes for a smooth shift on the 740 no jerking on down  or up shifts

good luck

[kyle4501]

Like any test, a dyno only provides a snapshot of what it is doing during the test. It ain't no crystal ball, but rather another piece of the puzzle. 

While it may not be able to promise a trouble free transmission, it will let you know what the shift points are. I'll bet they can see if the clutches are slipping too. You will also know if it clunks or thunks inappropriately.

I'm going to have mine dyno tested so that I can verify the shift points match my engine's power band. I will also know how it performed before I installed it. If the test shows problems, I'll be able to get them resolved before I install it in the bus. 

[Doug1968]

Clifford,

The tag on this transmission is marked, HT 740 - 9C20

When I google that number I get specifications on a transmission with a 3 element converter?

Is it possible to tell which converter it has by this number?

Oh, by the way, I will need to buy that flex plate if you still have it.

Doug

[5B Steve]

  What you might also do is a oil analysis. Alot of people say it's for engines only, however their is a test

for transmissions also.

  Steve 5B.......