Gear vendors and drive train loading

[bshupe]

I am considering a gear vendors OD and I know there are many posts here about that. My question is am I putting my drive train under too much load running at highway speed with the engine at such low (1800) RPM with 37" tires.

The RPM calculator says that with the 37" take-offs my highway RPM is about 2800 and that seems about right. It says I will be at about 1800 with the OD unit and that just seems like its a little low for all the rolling weight I have and I dont want to start killing my trans etc. loading it up like that.

Any thoughts? Input from owners with the larger tires and an OD unit or an OD trans especially cherished.

 

[Keith_J]

You will be pushing a lot of air, that is more of a load than the weight of the vehicle. This will increase slip in the torque converter which manifests as heat in the transmission fluid. This is the problem with the Gear Vendor's OD unit. Bear in mind the stock engine torque curve too, you might not be able to swing such a low RPM meaning the combination will probably be shifting in and out of OD. And you won't see a great improvement in economy either because waste heat is wasted fuel.

The ideal solution is a 4L80 transmission. This is a bit more work but about the same cost. I plan to do it in the future, probably moving the engine forward so the transfer case stays in the same location. There is enough space with the only difficulty in changing belts out (must remove fan) with the engine forward.

With any serious highway use, replacing harmonic balancer every 10 years is a must. The stock unit uses a rubber ring as the damper-spring element. Rubber ages and hardens, reducing the lower frequency damping. This causes crank fatigue and failure. And also rear crank wobble which causes rear main seal failure. I cruise at GPS indicated 62 MPH (65 on the speedometer) because this higher RPM reduces intake noise. That is why 55 MPH sounds like the engine is tearing itself apart. Diesels have no throttle plate and the CUCVs don't have any intake snorkel or ducting to damp this noise. In stock tune, the engine is happy turning 3200 RPM as long as coolant temperature isn't too high. I get 14 MPG at that speed in my M1031.

 

[truck1]

The power band on the 6.2 is 1800-2200 RPM. My 1028 has a 4 " lift and surplus 37" radials. I have had a GV installed for 2 years. At 70 mph my TinyTach shows 2310 RPM, and my engine is happy. The GV allows you to manually at will shift into overdrive with a floor mounted switch. Or you can use auto mode and it engages at 45 MPH. The unit will dis-engage at about 20 automatically in either mode. They are a great solution to the low geared Cucv and allow use of the Turbo400 which is a proven tranny. Easy install.Pricey, but in my opinion worth it. I get 17-20 if I run at 65. My engine is not happy at 3200 RPM and I think damage will occur if running at that RPM for very long. You will not run at 1800 RPM at highway speeds with a GV OD engaged.

 

[Skinny]

I think the OP was not taking into consideration a very sloppy TH400 torque converter when doing RPM calculations. It's a non-lockup so you will probably add 300 ish rpm's to your equation.

 

[bshupe]

You will be pushing a lot of air, that is more of a load than the weight of the vehicle. This will increase slip in the torque converter which manifests as heat in the transmission fluid. This is the problem with the Gear Vendor's OD unit. Bear in mind the stock engine torque curve too, you might not be able to swing such a low RPM meaning the combination will probably be shifting in and out of OD. And you won't see a great improvement in economy either because waste heat is wasted fuel.

The ideal solution is a 4L80 transmission. This is a bit more work but about the same cost. I plan to do it in the future, probably moving the engine forward so the transfer case stays in the same location. There is enough space with the only difficulty in changing belts out (must remove fan) with the engine forward.

With any serious highway use, replacing harmonic balancer every 10 years is a must. The stock unit uses a rubber ring as the damper-spring element. Rubber ages and hardens, reducing the lower frequency damping. This causes crank fatigue and failure. And also rear crank wobble which causes rear main seal failure. I cruise at GPS indicated 62 MPH (65 on the speedometer) because this higher RPM reduces intake noise. That is why 55 MPH sounds like the engine is tearing itself apart. Diesels have no throttle plate and the CUCVs don't have any intake snorkel or ducting to damp this noise. In stock tune, the engine is happy turning 3200 RPM as long as coolant temperature isn't too high. I get 14 MPG at that speed in my M1031.

Thanks for the great info Keith! The balancer is defiantly on my list of things to do. I currently commute with this truck about 5 miles/day with an occasional run up the highway @ 55-60.

Im not so concerned about the air resistance since I dont have the contact box on board anymore. I also am only running a 1" body lift so no sky high aero issues to speak of.

A trans swap would be nice but Im not in the position to do any major rework of the engine location or crossmembers or t-case etc. Because the 1031 has the 205 t-case there are mating issues as well. I have spoken to my local tranny shop and he pretty strongly recommended against a big trans project and he would have gotten a pile of money out of the deal. I am inclined to build up the TH400 if it needs more capability including a good cooler installation.

 

[bshupe]

The power band on the 6.2 is 1800-2200 RPM. My 1028 has a 4 " lift and surplus 37" radials. I have had a GV installed for 2 years. At 70 mph my TinyTach shows 2310 RPM, and my engine is happy. The GV allows you to manually at will shift into overdrive with a floor mounted switch. Or you can use auto mode and it engages at 45 MPH. The unit will dis-engage at about 20 automatically in either mode. They are a great solution to the low geared Cucv and allow use of the Turbo400 which is a proven tranny. Easy install.Pricey, but in my opinion worth it. I get 17-20 if I run at 65. My engine is not happy at 3200 RPM and I think damage will occur if running at that RPM for very long. You will not run at 1800 RPM at highway speeds with a GV OD engaged.

2300 +/- sounds comfy to me. I knew the power band didnt start for a while, thanks for confirming that 1800 would be too low for cruising. I would like to get one of those tachs so I dont have to guess at these things. Temperature gauges would be an excellent addition as well. Im really not clear why they would not have put a temp gauge in from the factory.

Thanks again for the excellent input.

 

[cliffyp]

I have a 700r4 in my 1028. I totally disagree that 1800 is too low for cruising. Flat land cruising at 1800 rpm is wonderful, even mild hills. It's quiet and the 6.2 is putting out plenty of torque at this point. I think the sweet spot for cruising is 2000-2100. If I remember correctly, these J code 6.2's hit max torque at 2100 rpm. An overdrive is effectively a torque reducer, so as you go beyond 2100 and your torque output falls off the overdrive is reducing the final output to the tires farther.

As mentioned, the TH400 is not a lockup converter so you'll have plenty of slip. If you're calculating 1800rpm then you will probably actually end up turning the 6.2 around 2100 rpm. In my opinion you're perfect and you only need to address the heat dissipation for your transmission.

 

[bshupe]

I have a 700r4 in my 1028. I totally disagree that 1800 is too low for cruising. Flat land cruising at 1800 rpm is wonderful, even mild hills. It's quiet and the 6.2 is putting out plenty of torque at this point. I think the sweet spot for cruising is 2000-2100. If I remember correctly, these J code 6.2's hit max torque at 2100 rpm. An overdrive is effectively a torque reducer, so as you go beyond 2100 and your torque output falls off the overdrive is reducing the final output to the tires farther.

As mentioned, the TH400 is not a lockup converter so you'll have plenty of slip. If you're calculating 1800rpm then you will probably actually end up turning the 6.2 around 2100 rpm. In my opinion you're perfect and you only need to address the heat dissipation for your transmission.

Thanks for bringing up the heat issue again. I know/knew it was a factor but it sounds like I need to make the addition of a good trans cooler part of the GV project not a separate project in itself. I live in W. Washington and I have to drive about three hours to find anything that would qualify as flat land cruising. lol

Anyone have thoughts on getting a torque converter that has a modified slip rating?

 

[Keith_J]

Slip is a function of the stall speed design of the torque converter AND the load on the converter. Stall speed depends on the engine too. I doubt there are converters with lower stall speed out there.

With the stock system, you probably have 150-200 RPM of slip. With the overdrive, that could easily get to over 300 RPM. That is double the loss of energy, any efficiency gains from lower RPM will be more than offset by the increased slip. This is why lockup converters are now standard with overdrive transmissions. Remember, we had a 55 MPH national speed limit back then.

 

[Skinny]

Unless you absolutely need to get away from electronic controls, I think what you are describing would be a good candidate for a 4L80E swap instead of a GV overdrive. The nice thing about the GV unit is that you can manually control everything and retain the non electronic TH400. All of that has a price though.

The 4L80E is alot more modern of a setup than a TH400/GV setup. It has better gear ratios, lock up converter, can be tuned for shifts if it has an aftermarket controller, and will probably be pretty close if not cheaper than buying and installing a GV setup.

I understand why people use the GV unit but for the money it isn't exactly a no-brainer decision because you are still retaining a strong but useless TH400.

 

[MarcusOReallyus]

Thanks for bringing up the heat issue again. I know/knew it was a factor but it sounds like I need to make the addition of a good trans cooler part of the GV project not a separate project in itself.

Yep. Trans cooler is one of the easiest things you can do to protect your trans, and it's not horribly expensive.


If time constraints keep you from doing both at once, do the cooler first.

One suggestion: I've been doing a lot of reading on this - you want the external trans cooler installed BEFORE the radiator trans cooler. The hot fluid should run through the new external cooler FIRST (where it dumps most of the heat), and THEN through the radiator. Why? Two reasons:

1. Transmissions have an ideal temperature range. Like Goldilocks, you don't want it too hot, and you don't want it too cold. You want it just right. The radiator cooler is designed to maintain this temperature. External coolers can actually make the transmission run TOO cool. If your external cooler is dumping too much heat out, the radiator cooler will bring it back up to the correct temp. (Which helps cool your engine.)
2. By dumping the majority of the heat first, you avoid dumping it into your radiator, where it isn't doing your engine any favors.

 

[bshupe]

Excellent points all around.

The electronic trans does not fit into my overall plans for the truck from a complexity and reliability standpoint.

I think I would be inclined to spend a few bucks putting in additional cooling and even have the TH400 gone through if I felt like it needed to or if I was going to update the torque converter. My understanding on the torque converter is that you can get them custom to about anything you want, it is only a function of angle and clearance between the internal veins where the fluid transfers torque to make it what you want.

I suppose if I put a trans temp gauge in at the same time I would be able to see if it is running high or low and make adjustments to the cooler placement etc. to help regulate that.

That bring my needed gauge cluster to am uneven three I guess. Engine temp, oil pressure and trans temp.

 

[Skinny]

The lock up converter really is the big sell here, without it the auto trans is a power/fuel hog when you are trying to go for economy. Ever think of an NV4500 swap?

 

[cliffyp]

A built up 700r4 gives you a lower first gear, higher overdrive and no electronics.

 

[bshupe]

A built up 700r4 gives you a lower first gear, higher overdrive and no electronics.

I like that but I think we are already saying that the GV OD will be a high enough top gear given the torque converter slip and associated heat plus a higher OD might drop the RPMs out of the power band.

Your signature file says you have done this in your 1028. Your first hand experience is highly valuable, please do share more. Do you have a build thread about it? If not, can you please summarize here?

Thanks!

 

[cliffyp]

I don't have a specific build thread for my 700r4. Speddmon has a pretty in depth one http://www.steelsoldiers.com/showthread.php?t=99530

I did some research into 700r4 common problems and what to upgrade to address them. I put in aftermarket sun shell, steels, clutches, 2-4 band, corvette servo, larger boost valve and a shift kit. Total build was around $800. It's a very easy swap and the least expensive of the three options. The only catch, comes up in any thread about a 700r4, you've got to find a TV cable bracket.

I DD my 1028, 30 miles of state highway both ways. I cruise at 60 because its just a comfortable speed. Rpm's are a little under 2100, with stock tires. Long stretches of in town driving at 30 mph in 4th gear lock up I'm only turning 1100 rpm and that is enough to accelerate with traffic. It's not until my rpm's drop below 1000 that it feels like a dog and I want to downshift. If I need more acceleration (highway on ramp) I'll leave it in 3rd till about 45, then go into overdrive and lock up and that puts me at about 1550 rpm which is enough to continue accelerating with traffic.

I'm not the firsts vehicle off the line and I don't try and accelerate like a race car. I really enjoy the lower rpm's, the ride is so much quieter. I'm in South Texas so the only hills I see are the overpasses. The really low rpm's probably wouldn't work with hills but I don't think you'd have to delay to much. I've cruised at 1700-1800 rpm's many times and that doesn't feel underpowered in any way.

 

[bshupe]

I don't have a specific build thread for my 700r4. Speddmon has a pretty in depth one http://www.steelsoldiers.com/showthread.php?t=99530

I did some research into 700r4 common problems and what to upgrade to address them. I put in aftermarket sun shell, steels, clutches, 2-4 band, corvette servo, larger boost valve and a shift kit. Total build was around $800. It's a very easy swap and the least expensive of the three options. The only catch, comes up in any thread about a 700r4, you've got to find a TV cable bracket.

I DD my 1028, 30 miles of state highway both ways. I cruise at 60 because its just a comfortable speed. Rpm's are a little under 2100, with stock tires. Long stretches of in town driving at 30 mph in 4th gear lock up I'm only turning 1100 rpm and that is enough to accelerate with traffic. It's not until my rpm's drop below 1000 that it feels like a dog and I want to downshift. If I need more acceleration (highway on ramp) I'll leave it in 3rd till about 45, then go into overdrive and lock up and that puts me at about 1550 rpm which is enough to continue accelerating with traffic.

I'm not the firsts vehicle off the line and I don't try and accelerate like a race car. I really enjoy the lower rpm's, the ride is so much quieter. I'm in South Texas so the only hills I see are the overpasses. The really low rpm's probably wouldn't work with hills but I don't think you'd have to delay to much. I've cruised at 1700-1800 rpm's many times and that doesn't feel underpowered in any way.

Thanks for the expanded info and link, I will check that out. How did you procure the core and for how much?

Did you have to change out the tail shaft on the trans?

I think I read somewhere that you have to swap the tail shaft out on the 700r4 unless you get one that came from a 4x4. Did you have to do that?

 

[cliffyp]

I pulled the core from a '92 4x4 1500 at the junk yard, about $150. I think you could adapt a 2x4 to 4x4, but it's much easier to just start with the 4x4 version. The output spline count for the 700r4 is different than the TH400. Your choice is to either change the output shaft on the 700r4 or change the input shaft on the np208. Swapping the input shaft in the 208 is very quick and is much cheaper.

 

[bshupe]

I pulled the core from a '92 4x4 1500 at the junk yard, about $150. I think you could adapt a 2x4 to 4x4, but it's much easier to just start with the 4x4 version. The output spline count for the 700r4 is different than the TH400. Your choice is to either change the output shaft on the 700r4 or change the input shaft on the np208. Swapping the input shaft in the 208 is very quick and is much cheaper.

The 1031 has an NP205. Not sure if the input shaft is different than the 208.

If I was going to pull a trans out of a junk yard etc. it would basically go directly to the trans shop. It seems like it would be easy enough for them to change out the tail shaft while going through the trans but that may just be my ignorance of such things.

How does the lock up torque converter work if not electronically?

 

[cliffyp]

I don't know much about the 205.

As to converter lockup, when the solenoid inside the trans has 12v and ground, it locks up. You can manipulate either side of that equation to control when lockup occurs. On mine, power is always there and I interrupt ground. I have a three position switch on my dash. One position grounds, locking the converter regardless of gear (the trans won't lock in 1st). Second position cuts ground so no lock up. Third position is routed through a 4th gear pressure switch inside the trans. When it shifts into 4th the pressure switch closes proving a ground and lockup occurs. Normal driving I just leave it in this last position and I get auto lockup in overdrive. When towing or heavily loaded I manually lock it in the lower gears to eliminate converter slippage and heat build up.