M1007 - CUCV Suburban Clone Build Thread

[Keith_J]

Keith, the 4L80E coast in over drive. If 1, 2 or 3 are manually selected it will bring the engine rpm up. But, with no throttle valve or exhaust brake. The diesel just revs but doesn’t really contribute to slowing my 7-8K pound truck on the steep grades. 1st selected would have the engine up to around 3,000 rpm and us rolling near 30 mph. Near as my research has shown. That is how the 6.5/4L80E behave.

I guess I need to look into that with my current turbo install. Variable nozzle actuator can be set at closed throttle position sensor to restrict exhaust flow area. Ideally, exhaust back pressure should be equal to intake to keep turbine thrust bearing load at a minimum. With minimum throttle, EGT is low and I've yet to run this simulation. Of course I'm extrapolating turbine map since Garrett only publishes fixed geometry data for a 0.38 A/R turbine. Wide open is an A/R of 1.2.

 

[Barrman]

You hit on the main reason I haven’t even search for exhaust brake information yet. Intuitively it seems turbo damage is a very real possibility. That is why Jake brakes are preferable in my opinion.

 

[Barrman]

I did some more research about engine braking with the 4L80E. Then I read through my Compushift 90 page manual and found an option for locking the torque converter in any gear. That made me curious so I called them up. I bought their transmission control module 5 years ago mostly based on the phone call I had with them when calling for information. I got the same guy this time and he reconfirmed my choice of going for the best customer service option.

I told him my experience and my wanting to lock the torque converter clutch in lower gears when off throttle to give better engine braking. He said that was a bad idea and it sounded like I might have a transmission failure. I asked him to explain.

The 4L80 is designed to coast or freewheel when overdrive is selected and the throttle is below 5 percent.

3rd gear selected manually offers very little engine braking by design. But, the converter clutch could be locked manually in 3rd. However, the band for the 3rd gear isn't made to do much engine braking and will destroy itself if used that way with a load.

2nd gear selected manually is supposed to offer full engine braking. As is 1st when selected manually.

He told me to put the transmission in 2nd, accelerate normally from a stop until it shifts into 2nd on its own and then get off the throttle. If I have engine braking at that time then all is well. If the engine goes to idle my 2nd gear over run band is burned up. Try it again with 1st manually selected from a stop and see if the engine goes to idle when at around 10 mph and throttle released.

Mine went to idle in 2nd and engine braked in 1st.

What allows engine braking in 1st and 2nd are two different methods. If the 1st gear method fails the first sign is normally no reverse gear since the same part does both.

My reverse and 1st gear engine braking worked and I had free wheeling in 2nd. So, my band was burned up and could have been burned up since I bought the used transmission out of China Grove 6 years ago since I had never done that test before.

I started researching that overrun band and found everyone has this issue. It is a badly designed part that fails with common regularity. There is a $800 "heavy duty" fix kit out there that even has a disclaimer about how it might be better, chances are it will eventually fail as well.

Transmission fluid looks, feels and smells good. So, I am going to leave it as is while I look at options and save money.

The other part of going down hill, the brakes, was addressed by adding Hawk hi performance brake pads. I can't find cross drilled and slotted rotors for the 8 lug 10 bolt axle. Once I got the Hawk pads bedded in they work great. I drove the Cowdog today for the first time in a week and got reminded of how much better they are in normal driving by getting thrown forward after applying what muscle memory says was normal brake force for a light. They stop the truck in a hurry. Which, should allow less brake applied time going down mountain which should mean less heat. Plus, I trust their glue holding the pads together better at temperature than the O'Reily ones.

So, I think I have going down hill covered. There is still the uphill part of our trip to address. I got concerned anytime I was at more than 210° engine coolant, 200° engine oil or 200° transmission temp. Reading through the TM's for the HMMWV, Chevy publications and stuff online. It seems I am just a big scaredy cat.

Chevy trucks had 230° as redline for engine coolant. The HMMWV doesn't even turn on the cooling fan until 225° and also considers 230° redline. I never hit 220°.

Engine oil is also considered just fine below 220°. Especially, synthetic like I have in there for the turbo.

GM considers 275° hot for the 4L80E. Me hitting 222° is not an issue it seems. Just out of normal for me.

Power going up hill was never a problem. I never lacked power at any altitude or climb angle on the road. I did learn to keep it above 2200 rpm for the best boost/EGT/power combination. The Snow water meth injection never let EGT get above 900° if it was on. About half way through our trip I lowered the injection low boost "on" from 5 to 3 psi. That made a tremendous difference in performance, temperatures and water usage. 1 gallon used the first 2,000 miles and then once I changed the settings I used 8 gallons the next 1,000 miles. They were fun miles though.

 

[Sharecropper]

Great write-up. Thanks for posting.

 

[Mullaney]

I did some more research about engine braking with the 4L80E. Then I read through my Compushift 90 page manual and found an option for locking the torque converter in any gear. That made me curious so I called them up. I bought their transmission control module 5 years ago mostly based on the phone call I had with them when calling for information. I got the same guy this time and he reconfirmed my choice of going for the best customer service option.

I told him my experience and my wanting to lock the torque converter clutch in lower gears when off throttle to give better engine braking. He said that was a bad idea and it sounded like I might have a transmission failure. I asked him to explain.

The 4L80 is designed to coast or freewheel when overdrive is selected and the throttle is below 5 percent.

3rd gear selected manually offers very little engine braking by design. But, the converter clutch could be locked manually in 3rd. However, the band for the 3rd gear isn't made to do much engine braking and will destroy itself if used that way with a load.

2nd gear selected manually is supposed to offer full engine braking. As is 1st when selected manually.

He told me to put the transmission in 2nd, accelerate normally from a stop until it shifts into 2nd on its own and then get off the throttle. If I have engine braking at that time then all is well. If the engine goes to idle my 2nd gear over run band is burned up. Try it again with 1st manually selected from a stop and see if the engine goes to idle when at around 10 mph and throttle released.

Mine went to idle in 2nd and engine braked in 1st.

What allows engine braking in 1st and 2nd are two different methods. If the 1st gear method fails the first sign is normally no reverse gear since the same part does both.

My reverse and 1st gear engine braking worked and I had free wheeling in 2nd. So, my band was burned up and could have been burned up since I bought the used transmission out of China Grove 6 years ago since I had never done that test before.

I started researching that overrun band and found everyone has this issue. It is a badly designed part that fails with common regularity. There is a $800 "heavy duty" fix kit out there that even has a disclaimer about how it might be better, chances are it will eventually fail as well.

Transmission fluid looks, feels and smells good. So, I am going to leave it as is while I look at options and save money.

The other part of going down hill, the brakes, was addressed by adding Hawk hi performance brake pads. I can't find cross drilled and slotted rotors for the 8 lug 10 bolt axle. Once I got the Hawk pads bedded in they work great. I drove the Cowdog today for the first time in a week and got reminded of how much better they are in normal driving by getting thrown forward after applying what muscle memory says was normal brake force for a light. They stop the truck in a hurry. Which, should allow less brake applied time going down mountain which should mean less heat. Plus, I trust their glue holding the pads together better at temperature than the O'Reily ones.

So, I think I have going down hill covered. There is still the uphill part of our trip to address. I got concerned anytime I was at more than 210° engine coolant, 200° engine oil or 200° transmission temp. Reading through the TM's for the HMMWV, Chevy publications and stuff online. It seems I am just a big scaredy cat.

Chevy trucks had 230° as redline for engine coolant. The HMMWV doesn't even turn on the cooling fan until 225° and also considers 230° redline. I never hit 220°.

Engine oil is also considered just fine below 220°. Especially, synthetic like I have in there for the turbo.

GM considers 275° hot for the 4L80E. Me hitting 222° is not an issue it seems. Just out of normal for me.

Power going up hill was never a problem. I never lacked power at any altitude or climb angle on the road. I did learn to keep it above 2200 rpm for the best boost/EGT/power combination. The Snow water meth injection never let EGT get above 900° if it was on. About half way through our trip I lowered the injection low boost "on" from 5 to 3 psi. That made a tremendous difference in performance, temperatures and water usage. 1 gallon used the first 2,000 miles and then once I changed the settings I used 8 gallons the next 1,000 miles. They were fun miles though.

.
I have to agree with @Sharecropper ...
Heck of a good write-up @Barrman !

It they have anything at all that will solve the problem - just based on being able to talk to the guy you talked to 5 years ago - I would be willing to spend more money there!

 

[Barrman]

He almost got me for the TCC switch and wiring harness but I wanted to do the test to see if it would even work. He gave me the part number in case I decided I wanted it later.

 

[Another Ahab]

I did some more research about engine braking with the 4L80E.

They were fun miles though.

Fun is the goal.

Thanks for the post, Barman!

 

[Barrman]

The Cowdog pulled the 6BT M715 we have been working on for Sermis the last decade or more out of my class last Friday. Then, Saturday I drove it to his place 90 miles away. This is the heaviest load I have ever had on my trailer and the Cowdog. His engine is about 600 pounds more than the 6.2 in my M715. His tires are also heavier than mine. Since my M715 is right at 8,000 pounds according to the local scrap yard scale. I would estimate his at 8,700 or more with the 14bolt/D60 CUCV axles and all.

The 12.50 Michelin tires wouldn't clear my trailer fenders either. I made a short video of the truck on the trailer before I left:

My expensive but the more I use it more worth the cost Weigh Safe weight distribution hitch has a scale built into it. We rolled the M715 up the trailer until we had 900 pounds tongue weight and tied it down there. Then we added the spring arms and adjusted the hitch according to what the app said to do.

It pulled great control and suspension wise. Since his windshield was bolted in the up position to the top frame. I had a wind brake come along for the ride. 28-30% throttle would give me 52-53 mph on flat ground in 3rd gear unlocked. Which was about 2250-2300 rpm. Trying to run 60 required more than 50% throttle. It wasn't a race so I just eased along at 53 nice and happy.

Climbing a hill about half way there I hear an exhaust leak. I turned down the radio and listened on the next hill. Yep, it was an exhaust leak. There was a historical marker a few miles ahead I knew had a nice clean concrete pad in front of it so I just coasted along until I got there, pulled over, shut down and got my tools out. I figured it was the 6.2 drivers manifold to Banks cross over pipe flange leaking at the donut gasket. The exact same thing happened to me last August pulling a M101 to get the 12K trailer axles and tires my car hauler is now wearing. Except, 2 of the 3 nuts were just plain gone! I tightened the remaining nut down and drove on. I figured out that there was no noise below 3 psi of boost so I coasted up the hills and charged down them. It was still a fun drive that way.

Sermis and I spent more than an hour wrestling his 40" tires back on once we got the truck off the trailer. Driving home with just the empty trailer I was able to run 62 or so and not get above 3 psi of boost except for a few times.

Now that my horizons have been expanded about what is "hot" and what is just "normal" for the 6.5 and 4L80E. I have to write that the truck pulled great with me never wanting power and only getting above 210° indicated during the first part of my trip when I was trying to run 60 mph up hill in 90° weather. I am confident I could have run 60 or more if I was so motivated and kept it below the new to me red lines.

 

[Barrman]

I forgot to write about the brake upgrades yesterday. After my trip to the mountains I installed some performance front brake pads. Hawk Performance HPS to be exact. They are expensive:

https://www.amazon.com/dp/B000CO6634?psc=1&ref=ppx_yo2ov_dt_b_product_details

But, they work amazingly well. I already commented a few post up how they do with an empty truck. Pulling the heavy M715 was the first big test of them too. It took me a while to catch on what was actually happening. My trailer brake controller has a g meter for lack of a better term inside of it. When it gets the brake light signal as I push the brakes, it turns on the trailer brakes a little and then senses how much help I am needing by how much it is getting bounced around. I haven't moved the intensity setting of that unit since I pulled my M715 back in March. What was happening Saturday was it would come on at a very low setting and either stay there or basically turn off. The new front brake pads were stopping the truck so well and so smooth it didn't see the need to help much. Pulling my M715 it was at 50% power or more on most stops.

I wanted to get that written before I forgot for a few months.

 

[Another Ahab]

I forgot to write about the brake upgrades yesterday. Hawk Performance HPS to be exact. They are expensive:

But, they work amazingly well. I already commented a few post up how they do with an empty truck.

"Getitng what you pay for" isn't ALWAYS true, but with tools and parts it is lots of time a good rule of thumb, you know?

 

[Barrman]

Life cones at you fast. I think that is a line for a commercial or something. But it sure is true. I went looking for this thread and was amazed it has been 3 months since I posted to it. I have more reasons to confirm that I am an idiot.

When I built the truck I didn’t have a crack free coolant over flow tank and couldn’t find a new GM one online. So, I put a generic O’Reilly’s 1 gallon tank on. It cracked like the first day I got the truck to temperature. I didn’t worry about it and my coolant seemed ok. Always needing a quart every month or so which I could never trace to where it was leaving from. One day I happened to see a drip from the passenger fender and followed it to the over flow tank.

Not wanting something that cracks on there ever again I bought an aluminum 2 liter over flow tank off Amazon. Around my small town running empty it was perfect. I could top off the radiator, drive for a week or a month and the radiator was still topped off the next time I checked. Problem solved.

Until I trailered my M715 to the Rally and back last March. I was down on coolant and couldn’t figure out where it went. This continued into our trip to the Rockies in June. We stopped for food in the little town of FairPlay at 9,954 elevation. Walking back out to the truck it was pucking coolant all over the place. I had just topped the radiator off that morning and hadn’t been over 214° climbing into that town. Well within my newly understood normal range. The same thing happened a few days later at another mountain pass town where I shut it off. I just topped it off again when cold and kept driving. But, I was worried.

Fixing the ac, researching the transmission engine braking, researching and upgrading the brakes were first. Then I got around to coolant. I stumbled across this website that had a formula for how big the overflow tank needs to be;

https://blog.cantonracingproducts.com/blog/calculating-expansion-tank-size-requirements

My truck was projectile vomiting because it had a 1/2 gallon over flow tank when it needed at the minimum a gallon to 1.5 gallons. As I wrote above, I am just an idiot sometimes. Thankfully, people are making actual square body Chevy overflow tanks new again. The space between the Cold line and the Hot line is almost an entire gallon. All is well in my world now.

Oh, I couldn’t use a CUCV overflow tank of which I have several spares because of the battery mount on the drivers side and the turbo air filter on the passenger side.

Hopefully, someone can learn from my mistakes.

 

[Sharecropper]

Life cones at you fast. I think that is a line for a commercial or something. But it sure is true. I went looking for this thread and was amazed it has been 3 months since I posted to it. I have more reasons to confirm that I am an idiot.

When I built the truck I didn’t have a crack free coolant over flow tank and couldn’t find a new GM one online. So, I put a generic O’Reilly’s 1 gallon tank on. It cracked like the first day I got the truck to temperature. I didn’t worry about it and my coolant seemed ok. Always needing a quart every month or so which I could never trace to where it was leaving from. One day I happened to see a drip from the passenger fender and followed it to the over flow tank.

Not wanting something that cracks on there ever again I bought an aluminum 2 liter over flow tank off Amazon. Around my small town running empty it was perfect. I could top off the radiator, drive for a week or a month and the radiator was still topped off the next time I checked. Problem solved.

Until I trailered my M715 to the Rally and back last March. I was down on coolant and couldn’t figure out where it went. This continued into our trip to the Rockies in June. We stopped for food in the little town of FairPlay at 9,954 elevation. Walking back out to the truck it was pucking coolant all over the place. I had just topped the radiator off that morning and hadn’t been over 214° climbing into that town. Well within my newly understood normal range. The same thing happened a few days later at another mountain pass town where I shut it off. I just topped it off again when cold and kept driving. But, I was worried.

Fixing the ac, researching the transmission engine braking, researching and upgrading the brakes were first. Then I got around to coolant. I stumbled across this website that had a formula for how big the overflow tank needs to be;

https://blog.cantonracingproducts.com/blog/calculating-expansion-tank-size-requirements

My truck was projectile vomiting because it had a 1/2 gallon over flow tank when it needed at the minimum a gallon to 1.5 gallons. As I wrote above, I am just an idiot sometimes. Thankfully, people are making actual square body Chevy overflow tanks new again. The space between the Cold line and the Hot line is almost an entire gallon. All is well in my world now.

Oh, I couldn’t use a CUCV overflow tank of which I have several spares because of the battery mount on the drivers side and the turbo air filter on the passenger side.

Hopefully, someone can learn from my mistakes.

Thanks for posting. It seems I may be an idiot too. With all the time, energy, and money I have been pouring into my P400 / 765R4 / NP241 drivetrain build, I haven't even considered the size and quality of the coolant overflow system. I even purchased a new high-dollar radiator and new poly bushings, but the coolant recovery went right over my head. I'll make sure this system will be upgraded when I finally get around to swapping out the drivetrains.

 

[Barrman]

Glad I’m not the only one overlooking it.

 

[87cr250r]

Coolant recovery is surprisingly unimportant. When the system is at its hottest, the system will be full. We know this from off-road motorcycles. Of course, who wants to waste coolant finding a that perfect level.

 

[Another Ahab]

Life cones at you fast. I think that is a line for a commercial or something. But it sure is true. I went looking for this thread and was amazed it has been 3 months since I posted to it. I have more reasons to confirm that I am an idiot.

You are no idiot, Barman. You're just like the rest of us, we all ealrn as we go.

Of course, there is the posibilility that that makes EVERYBODY an idiot...so we're ALL family!!!

 

[91burb]

I think they had a few bad batches. 3 of my trucks have 10 year old 60G’s in them and work perfect. I’m on my 3rd set now in 5 years with the Cowdog.

Has anybody mounted the rifle mounts in a suburban in the pick up location? Next to the seatbelt I have a 91 v2500 Suburban that the paint is toast on, was probably going to paint it up with the 383 carc and make this my new hunting rig

 

[Barrman]

I don’t know where the truck rifle mounts go. The m1009 rifle mounts will fit the suburban though I didn’t use them because the rear speakers are in the way. I kept the speakers.

 

[91burb]

I don’t know where the truck rifle mounts go. The m1009 rifle mounts will fit the suburban though I didn’t use them because the rear speakers are in the way. I kept the speakers.

 

[91burb]

I’m sure either one could be made to work. I was just curious if anybody had done it yet

 

[Barrman]

The pictured fore stock mount shouldn’t be a problem. However, since the Suburban floor is different than the truck floor. The butt stock mount might take some imagination.