Engine RPM - Allison Trans -Rear end gears.. HELP

[floridawheels]

OK so it seems I have bought the wrong truck. Hindsight is such a wonderful thing. I simply cannot afford to get a different truck at this point so I simply MUST find a way to make this one work. I have done quite a bit of homework and investigating but am running out of new/usable information so I am putting this out to the community for help.

2007 Hino 338.
Allison series 3000 auto trans - 5 speed.
5.57 rear gears.
275-70/22.5 Michelin XZA2 (38" tall)

Factory dash speedometer is off by 6mph so all stated speeds given here are from 2 dash mounted GPS units that have always been in agreement on speed.

The "Green zone" on the tach ends at 2200rpm. Redline starts at 2600rpm (Note: The below testing was done empty. 70mph was reached only long enough to get the RPM reading and then immediately backed off down to below redline)

70mph = 3000rpm
65mph = 2560rpm
55mph = 2150rpm
50mph = 1850rpm

I want (NEED) to be able to go 60 and stay in the 1700-1900rpm range. I am not interested in going any faster than 65 - 70mph max and want / NEED to cruise at 60. Rolling at 50mph on the interstate is not realistic but 55 is tops and at that RPM the fuel mileage is not tenable.

The Allison trans is currently programmed as a 5 speed. I have confirmed that the transmission is 100% compatible with a software update that will allow it to be a 6 speed. All it takes is a code available from Allison and about $200 in shop labor fees. In order to get this code from Allison I need a letter from the chassis manufacturer saying it is ok with them to do this. I just spent 2 days on the phone with Hino factory representatives. I went all the way up as far as to talk to one of the top 5 guys in charge of American Hino operations. The final answer from them is,"Sorry, but no letter". I don't want to discuss getting a letter or what to tell Hino in order to get them to give me a letter. It just is not going to happen. Further discussion about getting a letter is a waste of time at this point.

What I do want to talk about is how to drop the RPM WITHOUT loosing what little power I currently have. The truck has "acceptable" pulling power as it is but the cruise speed RPM is to high. I could change rear gears. I know 4.11 is available for this rear end but I am very concerned it will make the power no longer acceptable. Same goes for larger tires.

Questions:
1) Does anybody know of a shop in the US that is able to reprogram the trans? This is really THE proper answer to this issue and what should have been done from the factory. This would be BY FAR my preference to do.

2) Several years ago (About 1995) I had a 4x4 F350. I had purchased and installed an auxiliary transmission that was installed between the transmission and the transfer case. You could get it configured either as an over or under drive unit. It worked really well. I contacted that company to see if they made a unit for a business class (class 7) truck. Apparently they no longer make those units for any truck. Does anybody know of a divorced/secondary/external overdrive transmission that I might be able to use for this truck?

3) I seem to remember hearing about 2 speed rear ends. This may be as good or better than the auxiliary trans idea. Does anybody have any info on this option?

Any information is greatly appreciated. Thank you all in advance!

 

[paullud]

I would just look at swapping out the gears if you can't find a shop that will make the adjustment without the letter.

 

[davekc]

I have done the letter route many years ago with Freightliner. Not too sure on Hino but that 5 speed will kill you on fuel. Hopefully our resident Hino expert "Greasyshirt" will chime. Seems pretty knowledgeable on your setup. You could change the axle but you have to be careful doing that. I would get the correct information prior to that change with that engine and low horsepower.

 

[greasytshirt]

Go to (a different) Allison dealer. Tell them someone stole the computer off of your truck. Get a new TCM, already programmed with 6 gears? I guess this would work. This is not something I've dealt with in person, I've only heard of it secondhand.

The next easiest thing to do is to change the rear end gear. I'm gonna work some numbers.

Edit: No automatic six speed was available in 2007, so that might take a bit of explaining.

 

[greasytshirt]

Ok, let's see...

38" tire
0.75 overdrive ratio
5.57 rear gear

At 70mph, you should be turning 2500 rpm. Hmm.

Is your ABS light on?

 

[greasytshirt]

The 07 338 had two different rear axles. If you have a 5.57 rear in it now, that means you have a RS21-145. Available ratios are 3.90, 4.11, 5.29, and 5.57.

The 3000 Allison has the following ratios:
1st 3.49
2nd 1.86
3rd 1.41
4th 1.00
5th 0.75

In 5th gear,
50mph=1847 rpm
55mph = 2032
60=2216
65=2401
70=2586

If you moved up to a 41 inch tire (11r 22.5's are around this height)

50=1712
55=1883
60=2054
65=2225
70=2396

A three inch taller tire would drop rpm around 200 at 70mph.

5.29 rear, 38" tire

50=1754
55=1929
60=2105
65=2280
70=2456

4.11 gear, 38" tire

50=1363
55=1499
60=1635
65=1772
70=1908

As you said earlier, the truck is a little on the gutless side. They also like to rev. The spread between the 5.29 and 4.11 is large. You might be thinking that 4.11 looks perfect. I'd say that's going to get annoying having the truck drop into a lower gear every time you even think about hitting the accelerator.

 

[floridawheels]

Go to (a different) Allison dealer. Tell them someone stole the computer off of your truck. Get a new TCM, already programmed with 6 gears? I guess this would work. This is not something I've dealt with in person, I've only heard of it secondhand.

The next easiest thing to do is to change the rear end gear. I'm gonna work some numbers.

Edit: No automatic six speed was available in 2007, so that might take a bit of explaining.

Yeah....Already thought of that. No 6 speed in 2007 and if I go to a 2008 the engine was equipped with different emissions stuff and that might mess with the trans programming? Is the TCM plug the same? I think I would have to come up with a VIN in order to get the 08 TCM? Would the VIN need to be the same rear gears? (I think it probably would).

I have called several Allison dealers so far and all have said the same thing... need a letter...

See next post about rear gears...

 

[floridawheels]

The 07 338 had two different rear axles. If you have a 5.57 rear in it now, that means you have a RS21-145. Available ratios are 3.90, 4.11, 5.29, and 5.57.

<<Snip>>

As you said earlier, the truck is a little on the gutless side. They also like to rev. The spread between the 5.29 and 4.11 is large. You might be thinking that 4.11 looks perfect. I'd say that's going to get annoying having the truck drop into a lower gear every time you even think about hitting the accelerator.

Yeah, the power is already marginal. Yeah the 4.11 "LOOKS" great but... I think if gearing is the only and last resort then something in the high 4's would actually be the right choice but, of course nothing in that range seems to be available! Not to mention that a trans reprogram (with the letter) is less than $300 and the gears change can be up to $5,000 I'm getting really frustrated with the whole deal and severely regretting having bought the Hino in the first place.

I think if I went to the 4.11 I would have to stay on the throttle so much just to maintain speed that it would invalidate the fuel savings of making the switch. The 5.29 does not make enough of a change (Only about 100rpm) to come close to justify the expense either.

I am REALLY Hoping to find a shop to do the trans reprogram as this is really the only reasonable fix as the gears just do not seem to be viable.

NOTE: I just re-read your post. You said there were 2 different axles that year. What gears are available for the other axle? I might (with a LOT of luck) be able to find one in a salvage yard if the right gear is available. Of course I might win the lottery too.... sigh..

 

[greasytshirt]

Can you slap four 41" tires on there and see if it makes a big enough difference?

The RS23-160 rear has 5.63, 5.38, 4.10, and 3.91 gears. So, exactly the same problem.

If you can get the rear gearset out of a used truck, a gear r+r isn't hard (relatively speaking). Pull out both axles, unbolt the center section, pry the old gearset out and shove the new one in the hole. Simple! A transmission jack would be helpful, because that thing is heavy as hell.

 

[greasytshirt]

The 08-10 trucks are only different in that they all had air compressors, exhaust brakes, and dpf. Everything else is basically the same, iirc. when specifying a tcm, they're going to want the model and serial # of the trans, I think.

I googled "allison 3060 ecu reprogramming" and found this place. TKT Sales: Allison Transmission Parts Supplier. Electronic Control Units

 

[floridawheels]

Can you slap four 41" tires on there and see if it makes a big enough difference?

The RS23-160 rear has 5.63, 5.38, 4.10, and 3.91 gears. So, exactly the same problem.

If you can get the rear gearset out of a used truck, a gear r+r isn't hard (relatively speaking). Pull out both axles, unbolt the center section, pry the old gearset out and shove the new one in the hole. Simple! A transmission jack would be helpful, because that thing is heavy as hell.

I may be able to get my hands on some larger tires for a test run if nothing else. In fact I have been discussing that with a friend locally. He is concerned that if I put only larger tires on the back and leave the small ones on the front (For the duration of a 25 mile or so test run) that the driveline angle will be changed and that could be harmfull to the the driveline. I think the largest tires would be 12R24.5 those area about 7" taller than mine. That means a 3 1/2" ride height increase. If my math is correct those would be about the same as changing to 4.11 gears. That would give me a good idea of what to expect after a gear change if nothing else.

As for the "Other axle".. since the available gears for it would be the same,at least I can cross that off my list of things to worry about... LOL..

I think my buddy has located a 4.11 used chunk for about $650 delivered. On the back burner is a thought of getting it to try. Not a huge investment in parts if it does not work we can put the 5.57 back in. He was a truck mechanic and we would be doing the work at a diesel shop he has occasional access to so the labor would be mostly on us.

However.... the most interesting read for me this morning is your post immediately below this one..!

 

[floridawheels]

The 08-10 trucks are only different in that they all had air compressors, exhaust brakes, and dpf. Everything else is basically the same, iirc. when specifying a tcm, they're going to want the model and serial # of the trans, I think.

Well I do have air brakes. An exhaust brake would be nice to have. I wonder, can I get one from an 08-10 and install it in my system? Would I need any new ECU or TCU programming as a result of adding that? And of course I do not have or want DPF... LOL.

So, will a 08-10 TCU work for me?

I googled "allison 3060 ecu reprogramming" and found this place. TKT Sales: Allison Transmission Parts Supplier. Electronic Control Units

THIS..!!! My Google foo is weak master. I just called them but they are not open on the weekends. I'll be on the phone with them first thing Monday morning! Even if I have to buy a new/refurb TCU it would be worth it if they can/will program it for 6 speed.

I'll post up sometime Monday what they say...

 

[floridawheels]

Hey... it just hit me.... If I change the rear gears do I have to have anything done to the ECM or TCM?

 

[x06col]

Hey... it just hit me.... If I change the rear gears do I have to have anything done to the ECM or TCM?

You may want to just face it.........a turd is still a turd no matter what color you paint it, no matter what gear ratio you put in it it's still a turd. Now that you have some experience with equipment and know what you want for your load and driving habits......go get that truck. You will save yourself lots of time and money rather than trying to screw the pooch......they are not called stealerships for nothing.

 

[greasytshirt]

I may be able to get my hands on some larger tires for a test run if nothing else. In fact I have been discussing that with a friend locally. He is concerned that if I put only larger tires on the back and leave the small ones on the front (For the duration of a 25 mile or so test run) that the driveline angle will be changed and that could be harmfull to the the driveline.

The driveline angle will not change. It WILL turn the ABS light on, which is a problem not to be taken lightly. You'll need the same tire on each axle.

I think the largest tires would be 12R24.5 those area about 7" taller than mine. That means a 3 1/2" ride height increase. If my math is correct those would be about the same as changing to 4.11 gears. That would give me a good idea of what to expect after a gear change if nothing else.

Total tire diameter is what's important. One of those calculations above showed the difference in switching to a 41" tire. It would only be a 1.5" increase in ride height.

However.... the most interesting read for me this morning is your post immediately below this one..!

I know, right? Idk why Allison is so uptight about it.

 

[greasytshirt]

Hey... it just hit me.... If I change the rear gears do I have to have anything done to the ECM or TCM?

No, but the speedo cal will get thrown off. It is able to be recalibrated.

Since the speedometer is already off, I'm curious. What's the vin?

 

[floridawheels]

No, but the speedo cal will get thrown off. It is able to be recalibrated.

Since the speedometer is already off, I'm curious. What's the vin?

PM Sent with VIN.

Speaking of VIN.. Can you give me the breakdown of what the various numbers mean? That will help when I go looking for used parts.

 

[floridawheels]

The 08-10 trucks are only different in that they all had air compressors, exhaust brakes, and dpf. Everything else is basically the same, iirc. when specifying a tcm, they're going to want the model and serial # of the trans, I think.

I googled "allison 3060 ecu reprogramming" and found this place. TKT Sales: Allison Transmission Parts Supplier. Electronic Control Units

No go with these guys. Not able to do it and had no suggestions of who might be able. I'll keep looking. Got to be somebody able to do it.

Failing that, I guess I can investigate the possibility of getting a 08 TCM and seeing if it will work. That is assuming of course that the 08's all had 6 speeds? Next question is if the TCM looks for a serial # inside the transmission?

 

[greasytshirt]

That is assuming of course that the 08's all had 6 speeds? Next question is if the TCM looks for a serial # inside the transmission?

These two questions I don't have the answer to offhand.

Can you take a pic of the numbers on the TCM, the connector, etc and post them? I have a couple of TCMs hanging around (with known faults, they're just for testing purposes), and if one happened to match up, I might be inclined to send one down your way just to see what happens.

 

[floridawheels]

These two questions I don't have the answer to offhand.

Can you take a pic of the numbers on the TCM, the connector, etc and post them? I have a couple of TCMs hanging around (with known faults, they're just for testing purposes), and if one happened to match up, I might be inclined to send one down your way just to see what happens.

Sorry for the delay in responding, I was on the road and my passwords were at home!

I'll be happy to take the requested pics and will post them as quickly as I can. Might take a day or so though.

I did some preliminary MPG testing.

65mph ~2300rpm 300 miles in Florida on interstate. 7.2

53mph ~1900rpm 250 miles same sections of road, almost identical conditions 8.7mpg

At that RPM I am well inside the powerband and the engine is not lugging at all.

That is 1.5mpg difference! I do not know of any other modification I can make that will even come close to that sort of improvement. However,I simply can not drive at 53mph all day every day. It is just not feasible to do so unless your staying in mostly urban areas where you don't get on the highway for a few hundred miles at a time.


With the loads (weight) I am hauling I really do not want to give up any of the rear gearing I have by making a ring/pinion or tire size change. I really think trans programming is the way to go and am continuing to investigate this avenue.