70 MPH at lower RPM

franklin2 said:

Yes, you will never get rid of the slip from the c6. And like was said the more load you put on it, the more it will slip.

2000 rpm gives me the most power when towing a load, and I get that easily in 4th gear going down the highway. It also turns the fan fast enough for cooling. 5th gear for me is just a running around empty grocery getting gear. It's interesting since I locked my fan solid to see the rpm required to get proper cooling through the radiator.

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Yup, there is such a thing as gearing too tall.

When I first changed from 4.10 to 3.08, I basically sacrificed 1st gear for an extra top gear. With 4.10s I was out of 1st as soon as I entered an intersection so it seemed redundant. Another thing I noticed with 3.08s, is I gained the ability to kick down into 2nd way up to 50 MPH. It was a rough equivalent to 4.56 gears in top (non-OD) gear. So oddly enough, it actually made for a better gear spread once out of the hole.

These days with my E4OD, I can hold 2nd gear up to 55 MPH rather easily. Towing in overdrive doesn't work well, but having two cruising gears is nice because I can use overdrive when empty, or 3rd gear when loaded. Makes for a nice quiet ride at speed too.

I'm guessing you have 3.55s behind your ZF5?

I have 4.10's on mine, with 35 inch tires. I would rather have 33's I believe. But that is what was on the truck when I bought it. They are 35x12.5x16.5 so when they wear out I will probably have to get new wheels also.

Just a reference from my drive a minute ago

3.55 e4od stock tires

65mph=1600rpm

75mph=2000rpm

thanks for info, i'll have to take it out on another drive and verify my RPM again. Hope it's just shorter gears and not excessive slippage.

I replaced the stock converter in my van with a new low stall diesel one. The stall on the Ford OEM one is not well suited for the diesel rpm's and can hurt mileage, produce more heat, raise rpms and decrease power to the wheels.

Definitely not as efficient as a lockup, but easy to install and cheap compared to ab e4od swap.

grimmjeepers.com has a great gear calculator that you can compare tire sizes and gear ratios and it will give you all the info you want. you can even ad in the GV on there. only towing 5k behind you you can get away with 3.55 no problem. here in pa with our hills around me, and towing 8-10k, i just swapped to the 4.10's.

but i will never own a truck with a viscous drive trans. i drove one a few weeks ago and couldnt stand it. lol

Surprised nobody caught my screw up there. Way off on my rpms. 65 is 2600, 70 is closer to 2800. But I have taken her all the way to 3800 in 5th.... gps said 107

my 1987 f250 6.9 ZF5 with 3:55 gears runs 70mph at 2000rpm with 235/85/16s

Sorry for the long hiatus, the rear end i believe is 10.25 with 4.10 gears, I'm prepping for the ZF5 speed conversion, and Russ Type4 if you can repost some of your old install pics it would be appreciated. I have 2 ZF5s both 2 wheel drive but one has a driveline brake on it, and i still have to figure out what i need to slap the gearvendor I have currently connected to the T-19 4x4 set up. thanks in advance. by the way Type4 I sent an email about a chra question on the old ats turbo on the truck.

side topic, has anyone used long range gear (LRG) found him on instagram-he rebuilds transmissions. Do you guys have any shop suggestions or rebuild parts for the ZF5 and where to get them? thanks in advance

Ray-Ray said:

Sorry for the long hiatus, the rear end i believe is 10.25 with 4.10 gears, I'm prepping for the ZF5 speed conversion, and Russ Type4 if you can repost some of your old install pics it would be appreciated. I have 2 ZF5s both 2 wheel drive but one has a driveline brake on it, and i still have to figure out what i need to slap the gearvendor I have currently connected to the T-19 4x4 set up. thanks in advance. by the way Type4 I sent an email about a chra question on the old ats turbo on the truck.

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ZF5 with the driveline brake is going to be out of a superduty model truck and will be a 4x4 since the driveline brake mounts where the transfer case normally would and a 2wd ZF5 would have a very different tail housing without that mounting flange.

david85 said:

Nice truck, BTW! I always liked that style of front bumper.

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I second that...very nice looking truck...!!