Automatic transmission problem...

[jamesroney]

OK, so everybody knows I hate automatics...but @nvrstuk convinced me that they are the future, and I am a dinosaur. I think @lars and @Yeller were also auto proponents.

So to postpone extinction, I built my crawler and left my NV4500 in the shed. Can those of you that crawl with an automatic PLEASE tell me how to drive it?

I have a fuel injected engine putting out a nominal 75 lb-ft of torque at idle. Then I have:

Torque converter nominal stall, 1.8 ratio.
Transmission first gear, 2.80
Doubler, 2.72
Transfer case, 4.0
Rear axle, 5.38

Crawl ratio = 164.
Effective torque multiplication = 295.
Wheel torque at idle at stall = 22,125 lb-ft.

I can't stop this thing. In neutral, with brakes fully applied, I can lock up all 4 wheels. But in gear, my engine torque idles thru the brakes. Dropping from reverse to neutral to first results in some pretty significant suspension jacking.

I was playing in the rocks, and I came down over an obstacle onto my rocker. My spotter told me to stop, reverse a little, as he moved a rock into the hole. Reverse was easy, I climbed right backwards, but of course the brakes wouldn't hold. So roll forward, but again...it won't stop. So shift to neutral again. So I find myself cycling into neutral a lot. Going from Low to Reverse requires paying attention. Reverse to low...pretty easy. It was actually easier to wheel it with the transfer case in high.

So here's my technical question for you automatic guru's. Where is the right place in the valve body to install a valve to force neutral? I don't want to shift it. I just want to defeat it momentarily.

 

[66broncoCT]

What is your idle rpm? With 5.38 gears it is going to push against your brakes more then 3.50 gears but it should still stop. Do you know what rpm your torque converter stall is? I’m not sure what kind of crawling you’re doing but do you need to be all the way down in low range with the double and the transfer case? Would take some of the torque multiplication away if you were in a higher range. I’m sure you’ve thought of all this just offering suggestions.
I’m not sure if there is a way to temporarily force neutral in the transmission sorry. You could do a full manual valve body and run it in second instead of first

 

[jamesroney]

What is your idle rpm? With 5.38 gears it is going to push against your brakes more then 3.50 gears but it should still stop. Do you know what rpm your torque converter stall is? I’m not sure what kind of crawling you’re doing but do you need to be all the way down in low range with the double and the transfer case? Would take some of the torque multiplication away if you were in a higher range. I’m sure you’ve thought of all this just offering suggestions.
I’m not sure if there is a way to temporarily force neutral in the transmission sorry. You could do a full manual valve body and run it in second instead of first

Thanks!
Factory 1300 stall, and 650 idle RPM. (although the IAC does kick in if I turn on the AC.)

I ended up running on the doubler with the transmission in "L" with the t-case in HI for most of the trail, but in the technical sections, I put the T case in L, and the doubler in High. But then I was crawling faster than my group.

 

[Yeller]

Well..... I have no idea on the valve body, I've never known anyone to do a mod like that. I'm sure its possible, but I have no experience.

1st off, an auto needs far less gear than a manual. I know eveyone wants that 200:1 crawl ratio, I prefer 40-50:1. for 1 it stops, the other is when you need that tiny bit of wheel speed, instantly it is there. The secret is driving with both feet. no gas when doing technical down hill and a tiny bit of throttle, 1000-1200rpm is usually more than enough, when climbing and control speed with the brake. it is just a different driving style that works. Try running the tcase in high range, I think you'll be surprised, and when you need that bump it is right there instead of hammering it to get some rpm and winding up all of the gearing and not getting there. I've found with an auto getting past 50:1 has very rapidly diminishing returns and actually becomes a hinderance, can't stop it and when you need a bit of momentum, it is not available. Even the last unlimited, rear engine, rear steer, portal axled buggy I built was only 66:1 in first gear and ran a manual valve body for shooting walls and ledges. My personal buggy is only 42:1 and Bronco is as well, you have to drive like its an automatic and not a manual. These are all reasons I like the 3.0 Atlas with a 4 or more gears and 3.8 with a C4. IMO more gear is just wasted.

I'll use the new Heep rubicon for instance, I hate the 4:1 case, it is just too deep unless your running 37's with 4.10 axle gearing. I feel the standard X/sport model 2.72 is much easier to drive and make do what you want, it does take a tiny bit more driver skill, but it is a small curve that takes a bit of thought and practice.

You are deep enough I'd run a manual valve body. I've gotten a few guys that have the 4.3 and 5.0 atlas's to do that and they are sooooo much happier.

 

[Yeller]

better built vehicles will always crawl faster than the lessor built vehicles

I always tell everyone, outside of my inner cycle of wheelers, I typically will drive faster than you will in all scenarios. I'm comfortable, know my equipment and read terrain so I'm just faster, not bragging, just repeating observed experience. I tell them I will gladly wait, also gives me time to get back to spot for them LOL.

 

[gnpenning]

In some situations going down hill kick the front end out of gear.

Are you sure your converter is at the rated RPM?

Curious, what brake system you are running and tire size.

 

[Yeller]

In some situations going down hill kick the front end out of gear.

Are you sure your converter is at the rated RPM?

Curious, what brake system you are running and tire size.

not to badger something that works for you, but with this amount of gear it gets wweeeeiiiiird really fast in rear only even on flat level ground. Then there is the potential to wedge a non driven tire and wind up on your lid, driving over it. still can't stop but front only is more effective, not driving over a dead tire and you can steer. I always encourage to never kick the front out going down, only the rear. We do that often in competition, drive off font only, it keeps the rear from pushing so you have more control, but we are usually driving off of stuff that most would call a cliff, not a hill

 

[lars]

As for me, I now have a 4R70W with a shiny new 3.0 Atlas behind it. But no way to shift the transmission, no exhaust aft of the headers, yet-to-be-reflashed Explorer PCM and a bunch more missing but. Was hoping to get it running before foot surgery but failed. Now looking at October-November before I can pick it up again. I had manuals only in my hobby vehicles for the last 50 years, most recently an NV4500 in the Bronco for the last 20. So I’m reading along, as clueless as anyone, hoping to learn.

 

[lars]

What transmission did you wind up installing, James?

 

[jamesroney]

As for me, I now have a 4R70W with a shiny new 3.0 Atlas behind it. But no way to shift the transmission, no exhaust aft of the headers, yet-to-be-reflashed Explorer PCM and a bunch more missing but. Was hoping to get it running before foot surgery but failed. Now looking at October-November before I can pick it up again. I had manuals only in my hobby vehicles for the last 50 years, most recently an NV4500 in the Bronco for the last 20. So I’m reading along, as clueless as anyone, hoping to learn.

Exhaust? Funny that you should mention it. Exhaust was my project for today. I wish someone would sell exhaust as good as I make myself. Every time I build one, I swear I’ll never do it again. I can get performance exhaust for my ‘Cuda, my Mustang, my Tiger, and my pickup truck…but nobody wants to sell anything *cheap* for a Bronco. It’s weird.

 

[jamesroney]

What transmission did you wind up installing, James?

I have the same ratios as an AOD. Kinda like a 4R70W with AODe planetary in it. (Cause I didn’t want to be “too low”)

 

[jamesroney]

In some situations going down hill kick the front end out of gear.

Are you sure your converter is at the rated RPM?

Curious, what brake system you are running and tire size.

Great questions!

Converter is factory. It's hard to determine how much torque an engine produces at idle. Nobody wants to post those numbers on the internet. But I figured 50-75 lb-ft was not unreasonable.

Brakes? Well, whatever the fine folks at Dynatrac were providing with their 5 lug Pro Rock Dana 60 back in the 2000's. Look to me like GM calipers from a K10 against Early Bronco rotors. Rears look like El Dorado calipers on F150 rotors.

Tire size shouldn't matter, but I'm sporting 35's.

 

[toddz69]

I have the same problem as you do with my configuration, which is similar but different - 700R4, 4 spd Atlas with 2.72 doubler and 3.8 main gears and 4.11 gears (soon to be 4.56). In what I call "stupid low", I think I can hold the brakes now but the suspension jacks up like crazy and I don't like to do it. I'm not a hardcore crawler so I've mainly used that gearing combo for exhibitions and occasionally some super steep downhills. I run my 2.72 doubler and the t-case in Hi for probably 90% of the time when I feel I need low range. If I was doing it again, I'd not get a 4 speed and just do a 3.0 Atlas - as @lars and @Yeller suggest.

Todd Z.

 

[gnpenning]

not to badger something that works for you, but with this amount of gear it gets wweeeeiiiiird really fast in rear only even on flat level ground. Then there is the potential to wedge a non driven tire and wind up on your lid, driving over it. still can't stop but front only is more effective, not driving over a dead tire and you can steer. I always encourage to never kick the front out going down, only the rear. We do that often in competition, drive off font only, it keeps the rear from pushing so you have more control, but we are usually driving off of stuff that most would call a cliff, not a hill

That is why I said SOME situations at the very beginning. Going up or down kicking out the front or the rear has advantages in the right situations and every vehicle may give you a somewhat different response. Definitely not a one size fits all.

 

[Speedrdr]

I’m confused with part of this delving off into the weeds about the brakes and/or TC not holding at idle speed. If the TC is a 1,300 stall and idle of 650 rpm, looks like the TC would not ‘lock up’ until it got another 650 rpm.

Mind y’all, I have driven and still drive auto transmissions but know ZERO about them and would welcome enlightenment.

Randy

 

[Broncobowsher]

The torque converter math is all wrong. You are not getting 1.8:1 multiplication unless loaded. It is not a fixed gear/number. Loaded at full throttle, yes. At idle, no. The fluid dynamics gets deep, drag ( the initial driving force changes at the cube to the speed delta). The stator then redirects the reactive flow to add additional input drive to the impeller.

I'm guessing you have manual brakes. I played this same game with a 4r70w with 3.15 transfer and 4.88s. initial fix was to program the transmission to hold 2nd gear at idle.

Real fix was to hydroboost.

 

[Yeller]

I’m confused with part of this delving off into the weeds about the brakes and/or TC not holding at idle speed. If the TC is a 1,300 stall and idle of 650 rpm, looks like the TC would not ‘lock up’ until it got another 650 rpm.

Mind y’all, I have driven and still drive auto transmissions but know ZERO about them and would welcome enlightenment.

Randy

Randy, you get to the point with enough gear ratio that the light drag you feel at idle that typically allows you to gently roll into a parking curb transfers enough torque you can’t hold the vehicle back by the brakes. You have to get to 2-3 times the stock gear gearing to work. For reference a stock EB is 20:1 in first gear, James is 8x that much. Starts becoming very apparent at about 50:1. Your average 2wd pickup is 8-10:1 in first gear. Like most things when fluid dynamics is involved the curve is not linear, there comes a point in short order it is straight up.

 

[Speedrdr]

Randy, you get to the point with enough gear ratio that the light drag you feel at idle that typically allows you to gently roll into a parking curb transfers enough torque you can’t hold the vehicle back by the brakes. You have to get to 2-3 times the stock gear gearing to work. For reference a stock EB is 20:1 in first gear, James is 8x that much. Starts becoming very apparent at about 50:1. Your average 2wd pickup is 8-10:1 in first gear. Like most things when fluid dynamics is involved the curve is not linear, there comes a point in short order it is straight up.

Steve,
Thanks for an explanation that I am able to understand. I guess going to a higher stall TC would not work either. I think I’ll just stay with my 3-on-a-tree. lol

Randy

 

[Yeller]

@Speedrdr Higher stall helps but causes other things to be problematic.

As a side note, This is the kind of stuff we do in competition

 

[Speedrdr]

@Speedrdr Higher stall helps but causes other things to be problematic.

As a side note, This is the kind of stuff we do in competition

Holy cow, Steve! That’s hard core wheeling right there. I think I’ll stick to the mud holes and woods trails…BUT that does seem like a good time and much fun.

Randy