Lets start off with the back ground story on the truck. Names Shawn by the way. I married a 90 f-150 body to the frame of an 85 f-250 that had a 7.3 idi installed in it. Its been four long months but the body swap and everything is complete and looking damn good. The last issue that I have is the top speed in this beast is about 43 miles an hour, and she is screaming doing that. I have already checked the 4x4, its not stuck in four low or anything like that. When that was all checked, I went to the rear end and pulled the cover off to find that it has 4:10 gears in it. I have a 4 speed truck that used to be someones mud toy so they didn't need hwy speed I reckon. I do know that my rear end is the 10.25, I believe its a dana 70 due to some stamping on the axel. Now I am looking for a ring and pinion set but I keep finding this semi float rear end set as well as the regular dana 60 not the 70. So my question is, how can I tell if its the semi float or full floating rear end? While on the subject of rear ends, when I put it in first gear, it seems like there is some drag in the yoke before it goes in to the rear end. It jars real bad and then finally takes off? Common or maybe there is something wrong? Any advice will help. TXH

 

Full float has the big hub that sticks through the center hole in the rim, the axle shaft is removable by 8 bolts on the hub. Semi-float does not have the protruding hub. The bearing is pressed onto the axle shaft and into the housing tube. Dana 60 was available in both styles, Sterlings were all full float. Re-gearing a 4x4 gets expensive, you might want to think about a donor truck with a set of 3.55 axles and/or an overdrive transmission swap.

 

No they weren't, there were a fair number of F250LD trucks made with 10.25 SF axles, I got one.

 

Good to know... I've never seen one!

 

Not to be picky but in 4th with 4.10 ratio doing 43mph is only reving around 1900rpm, thats not really screaming, but if your tcase (asuming np205) is stuck in 4 lo you'd be up around the 34-3500 rpm range, this is with stock tire size and that would defently be screaming!

My c6 with 3.55 doing 70 was at 3200rpm, so something does seams wrong with your setup (C6 with 3.55 is like a 4 speed with 4.10 due to tq losses)

This is confusing, lets clairify this a bit, a sterling 10.25 will NOT have a fill plug on the diff cover, it will be on the other side of the center section and will have removable drums without taking the hubs off. A Dana 70 will have a fill plug on the cover and a BOM on the axle tube and the hubs have to come off to remove the drums.

Also if its a dana axle, the ring gear will have DANA stamped into it near where you found the ratio.
Being a 85 chassie and 250 you may have a dana 60 also.

Asuming u-joints arn't shot and the driveshaft can be turned a lot (like a rev or two before hitting any resistance), it more then likely worn out LS clutches or broken spider/side gear teath.

 

OP.... 4.10 gears are common and stock in many trucks. 43 MPH sounds low though, what size tire, and what do you consider "screaming"?

My recommendation, find one of the many 3.55 ratio 10.25 sterlings used in 87-97 F250s and swap it in.

 

X3, something else is wrong. I've had plenty of trucks with 4:10s and 70 is my cruising speed, they all did fine at those speeds.

 

my 88 with 4.10 gears and a C-6 trans redlines at 80mph.
so 43 mph sounds like the transfer case is in low gear still.

 

FWIW my C6/4.10 truck tops out idk about 75/80 with 37" tires.

My TC(13-56 2.7 low) broke a while back and was stuck in low, I couldn't get over say 30. The shift fork broke inside, it felt like it was shifting out of low, but wasn't.

 

So its been a minute since I have checked this forum. Sounds to me like I may have something else wrong. But if I put the transfer case in 4 low, its like snap your neck kinda low. The one thing I have noticed, there is no difference in the rev between 4 hi and 2 hi. Is it possible that its stuck in 4 hi or will the transfer case ratio not be any different between 2 hi and 4 hi?

 

I gotta question for BruteFord. You said to find a sterling from an 87-97 f-250, will they bolt up to an 85 frame. I do know that I took a ring carrier and the pinion gear out of an 87 f-250 and the carriers were different. I also know that the rear end that I took the carrier out of, was not a DANA and mine is. The ring gear bolt centers were 1/4 small than my DANA carrier. And I appreciate everyones help.

 

The ratio for 2hi and 4hi is the same, both hi, 1:1.

Yes a 10.25 from a IIRC 86-97 F250HD or F350 will bolt right up. I'd have to research but the U-joint might be different, even so conversion joints are available.

 

To expand, I said F250 before cause for the most part F250s got 3.55s and F350s got 4.10s.

You never did say what tire size nor what you consider screaming?

Nor what axle you currently have, how sure are you that it's 4.10s, how did you check?

 

the gear ratio is the same between 2 hi and 4 hi. the only difference between the two is in 4 hi the front driveshaft is engaged.

 

My F350 with 4.10 will top out around 80 in 3rd, i.e direct drive. There are millions of us driving on the highway with 4.10s.

It appears to be in low range. How have you determined it is in high range? I suggest trying to turn the front drive shaft. With the hubs unlocked, the shaft should turn; otherwise, it is in 4 low or high (I am betting Low).