Duramax/Allison Transmission Question

[Hastey]

All Allison transmissions in GM vehicles come from the factory with synthetic transmission fluid.

to further add to what Terry just said is that if you are now running anything but the DEXRON VI synthetic. I advise change it immediately. Also, carry a spare quart or two with you in case you have to add. You just don't walk into a quickie mart and pick that up.

I've had my Allison out of my truck. It's no fun at all. I had to hire a guy to help me. Even GM puts two mechanics on it at a 12 hour shop rate. 14 hours of labor to put a $9.00 front seal in. Oklahoma Panhandle sand will eat them out of there quick.

The cheapest I found a shop to do it was $1200 plus parts.

 

[porthole]

As long as we are on the D/A subject.
Long warm up idle times in cold weather are not good for the trans cooler lines.

Unless there has been a change, when cold the cooler circuit is also open, no t-stat to block the flow. That means cold thick trans fluid is still flowing (and at a good rate) through the lines to cooler and back.That is why you see so many cooler lines leak in the colder states.

The crimped hose ends on the cooler pipes can't handle s the pressure over the long haul. Replacing the 3 lines at over $100 each does not solve the issue.
There are aftermarket lines avaible that are superior the the factory items. If you have leaks, get the good replacements.

In 80000 miles I changed one line three times, one twice and the third I never did because it was too difficult.
Then I found out about the better stuff

 

[dave10a]

The dealer indicated I could take it out of this mode when we get to highway speed. I have had a question in my mind about what is the proper way to utilize this and what is best for my truck. Any comments and recommendations would be welcome.

Thanks,
Harry

When a someone makes a comment that you don't completely understand, one should always ask why

 

[porthole]

5]I am still new to the RVing life and have a question about towing our rig. We have a Chevy Silverado 3500 with Duramax Diesel and Allison transmission. My question is regarding the tow haul mode for the transmission. Should we leave the truck in tow haul mode the entire time we are towing? The dealer indicated I could take it out of this mode when we get to highway speed.

When a someone makes a comment that you don't completely understand, one should always ask why

Don't talk to anyone in the sales about your trans, including "service writers" at the desk. Your best bet is to talk to a tech that actually works on the vehicle and knows how the systems work.

The D/A combo are a terrific pair, well synced with computer controls. One of those controls is the T/H mode.
A few things are happening when you push that button. Line hydraulic pressures are increased so that the transmission clutches are able to keep pace with the load, up and downshift points are raised allowing the engine to do more work in the optimum torque range and most significant is that the torque converter is locked up from 2nd thru 6th.

Locking the converter means all the torque is going to the drive axle and not lost to torque converter slippage. The side benefit of locking is the fluid will run cooler since the heat build up is mitigated by not having the convertor slip.

In the non T/H mode the convertor still locks up, but not until 5th and 6th gear.

So what some folks are doing is getting up to speed but finding the truck is not shifting into 6th because of the programmed higher shift point. The converter is still locked, but switching off the T/H for a moment allows the truck to shift to 6th.

Your best bet when towing is to use the T/H mode. The trans will shift better with less slippage, the fluid will stay cooler, and that along with the less slippage means it will also last longer. Switch on and off if you desire to get into 6th gear.
And your engine/exhaust braking will work way superior with the convertor locked (think manual trans)

If you are not familiar with how the convertor works the easiest explanations is this.

Take two box fans and face them towards each other. Turn one fan on low, the other fan will start to spin, although just a bit slower because air is spilling off the fan blades.
Quickly switch up to high speed. The other fan will catch up, but because of the rapid increase of air flow even more air will spill off the blades and the 2nd fan will not ramp up at the same rate or speed.

Convertors work the the same using a fluid (that's why they are aka fluid drives). There are two "fans" inside a sealed housing, one attached to the crankshaft, one to the trans input shaft.
This liquid coupling and slippage is what allows you to stop at a red light and not have to disengage anything. The flow of fluid coming off the crank side is low enough to not work on the trans side. Step on the gas, spin the sucker up and the fluid starts to drive the trans.

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[Hastey]

In the non T/H mode the convertor still locks up, but not until 5th and 6th gear.


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I have the monitor screen in my cab for my Edge Performance Programmer. One of the things I monitor is the transmission and on my 5 speed and it shows the converter locking in 2nd gear on up. I'll forget to turn the T/H on after we take off and I can instantly tell that its off. It also shows me a % the torque converter is slipping while running.

 

[porthole]

I have the monitor screen in my cab for my Edge Performance Programmer. One of the things I monitor is the transmission and on my 5 speed and it shows the converter locking in 2nd gear on up. I'll forget to turn the T/H on after we take off and I can instantly tell that its off. It also shows me a % the torque converter is slipping while running.

Got it - so let me quantify my comments with this - I should have prefaced my comments with 2006 and above, as that was when the Allison got a major overhaul and extra gear (although if you really feel like, you can add the 6th to yours.

So with your 2nd gear on up, is that in T/H or not?

 

[Hastey]

Got it - so let me quantify my comments with this - I should have prefaced my comments with 2006 and above, as that was when the Allison got a major overhaul and extra gear (although if you really feel like, you can add the 6th to yours.

So with your 2nd gear on up, is that in T/H or not?

That is in t/h and I did not know I could add the 6th gear..................this is me thinking about spending money.....divorce.....weighing it all out.......money....wife kicking @$$.....I think I'll stick with the 5 speed.