Does anyone know what the torque limit is for 5th gear? I am referring to the amount it can hold before slipping when already engaged, not during a shift.

it will hold until it slips.....

LOL

hundred horse over stock is pushing your luck

The other day I was passing someone and was into it more than I ever had been w/the lp on. I drive this thing pretty conservatively. I was going around 75 when the engine started pulling through the gear. I let off immediately, and didn't set any codes, but knew what had happened. I know they cut the torque back to 520 in 5th w/the LLY because it is weaker than the other gears, but have never seen an actual torque number that it can endure. Probably isn't one published, and would have to be determined on a dyno. Just curious. After warranty expires, I'll put a Transgo kit in to raise line pressure.

marcdeluca
I wasn't aware of any tq cutback and don't believe there is. Sounds to me like you blew through the torque converter( overpowered it) instead of 5th. I question your trans bypass filter. Is it hooked inline to the return(cooler line) or is it hooked into the control main filter(spin-on). I would not tamper with anything to do with the spin-on.
mike

I thought there have been at least a couple threads on power limits in 1st and 5th. . . Anyone have any source information? Not that I would believe that anyway. . . It's been proven wrong before. . . . (4th gear/5th gear runs Kennedy? or there too many other factors). I'm really curious now, and you know what they say about curiosity. . .

Thanks,
Dennis

Mike, I currently don't have the bypass filter hooked up. I need to get a pressure regulator because I am feeding it from the line pressure fitting beside the spin-on. From all I have heard, 5th gear will slip before the TCC slips. I have a Snap-On scanner, and it gives a data line for TCC slippage. Sometime soon I'll take a friend to read it while I push the truck hard and see what it shows. I'm just going to be careful with the thing, having supplemental lp on it makes scary power!

I haven't tested 5th gear vs TCC for holding power, but in 4th, the TCC gives first.

The 1st and 5th torque derate is common knowledge published directly by GM somewhere.

My truck would slip the converter in 5th with the juice set to 125 hp on my LB7, 90 hp it was fine. That was on the street with at 6700# truck and 265 tires. You can either slip the trans or you can slip the converter(or both I suppose), if you see 0 converter slip you still may be screing stuff up ;)

the only clutches that were beat up on my trans apon dissasembly were c3's and c4's and that dosnt have anything to do with 5gear does it?

Banks and Edge couldn't get the Allison to slip in 1-4 gears with 900tq. I believe 5th gear is good for 680tq. Go to the Edge website, they have that information there.

That was the number I was looking for. Thanks for the info. Took me a bit to find the Edge website, but 680 is what they say.

Most Allison 1000's TC's seem to break free at a point just over 700RW, but like Edge but 680 is about it for any margin of safety...

My 2005 held good approaching 800RW, but I beleive that is because it hadn't been abused. It will easily blow away the trans in 5th gear at this level...

I guess it makes sense that they wouldn't make 5th gear to take brutal torque. With a stock motor, you would never be pulling anything fast enough to need it. Normally, it would be in 4th once you hit a hill. I still think it is a neat combo, this engine and trans.

Not to mention that GM recommends towing with 5th locked out. . . so if you tow in 5th and break it, I suppose GM could say . . . "Too Bad, you didn't take our recommendations."

I don't remember reading anywhere that I should tow with 5th gear locked out. Do it all the time with a stock motor and it just keeps going.

With a stock converter on any vehichle the the clutch should always be released when towing. The stock clutch and pressure will not hold up to a load.

mike

I am pretty sure it is in the owner's manual. . . I will have to go check it out again later. . .

Thanks,
Dennis

With a stock converter on any vehichle the the clutch should always be released when towing. The stock clutch and pressure will not hold up to a load.

mike
Mike, are you referring to the torque converter clutch or 5th gear? The TCC must be locked up most of the time to keep from cooking the fluid when towing. My '91 unlocks under heavy load, and it really gets hot. I had to put a manual lockup switch on it to keep it cool. What you said used to be true on the older overdrives because the converters weren't stout enough, but not anymore. Unless you pump the motor up, the alli converter is very good, from what I have heard.

Going into limp from overpowering it isn't disasterous. Just wanted to make that clear. You just don't want to do it too many times. Few Allisons actually break. They just limp easier as they get beat up.

BAIMPALA wrote: Not to mention that GM recommends towing with 5th locked out. . . so if you tow in 5th and break it, I suppose GM could say . . . "Too Bad, you didn't take our recommendations."


Then how are the 2001 and 2002 DMAX/Allison owners supposed to tow and lock-out 5th gear? The 2001-2002 trucks do not come with an Overdrive Lock-out switch (as your 2004 has). I always tow in 5th gear. The truck was designed to handle this.

I don't think there is any problem towing in 5th w/a stock engine. The combo is designed to not overstress the trans in 5th. The LB7 is 520 ft. lb.s, and the LLY cuts back to 520 in 5th. Adding additional power is the concern. My problem is that my engine doesn't know about the additional power it is producing w/propane, so I need to be careful.

Oops, I read the manual transmission part where it says don't use 5th gear. . . sorry.:o