3.08 upgrade?

[HBF84]

Bullnose Enthusiasts! I would be grateful for some advice...

I have a 1984 2x4 short bed with a 4.9 liter engine, the 4 speed manual transmission with overdrive, and a 3.08 rear end. Can I change the ring and pinion to a 3.55, 3.73LD, 3.73HD, or 4.10 using the same housing? Or to upgrade, do I need to find a whole new differential/axle assembly at a wrecking yard?

The goal is to upgrade to increase towing capacity as much as possible. I won't be towing too often but when I do, I would like to be able to tow as much as possible in lieu of buying a new truck! Why buy a new truck when you can rock the bullnose down main street?!?

 

[Nothing Special]

Not sure what "LD" or "HD" is in that context, but yes, you can regear any axle to those ratios. It's not easy (I've done it once, it took me about 5 weeks). And if you have someone else do it (which I strongly recommend unless you KNOW you want to do it yourself) it ain't cheap. Figure around $1000. So often it's cheaper to find a new axle that has the gearing you want. But then you'll have a junk yard axle of unknown quality, so you pays your money and takes your choice.

If you do regear you'll need to know what axle you have (or at least the shop that does it will need to know). You can probably reuse your original differential (although some axles do require a different diff if you go past a certain point, called a "carrier break", that's often around 3.73, but will depend on what axle you have).

Or while you're regearing is a good chance to put a traction-aiding diff in if you want to do that. It's the same labor to regear, replace a diff, or do both at the same time. So if you;re going to do it, the same time is the right time so you only need to pay for the extra parts. There are a lot of options that I think are a lot better than a factory limited slip, so if you do decide you want something other than what you have, do a little research before just getting a limited slip because you've heard they're better.

[Danny G]

Not sure what "LD" or "HD" is in that context, but yes, you can regear any axle to those ratios. It's not easy (I've done it once, it took me about 5 weeks). And if you have someone else do it (which I strongly recommend unless you KNOW you want to do it yourself) it ain't cheap. Figure around $1000. So often it's cheaper to find a new axle that has the gearing you want. But then you'll have a junk yard axle of unknown quality, so you pays your money and takes your choice.

If you do regear you'll need to know what axle you have (or at least the shop that does it will need to know). You can probably reuse your original differential (although some axles do require a different diff if you go past a certain point, called a "carrier break", that's often around 3.73, but will depend on what axle you have).

Or while you're regearing is a good chance to put a traction-aiding diff in if you want to do that. It's the same labor to regear, replace a diff, or do both at the same time. So if you;re going to do it, the same time is the right time so you only need to pay for the extra parts. There are a lot of options that I think are a lot better than a factory limited slip, so if you do decide you want something other than what you have, do a little research before just getting a limited slip because you've heard they're better.

Where you the one that was explaining diffs to me before? If so need to find those links, great info.

[Danny G]

Bullnose Enthusiasts! I would be grateful for some advice...

I have a 1984 2x4 short bed with a 4.9 liter engine, the 4 speed manual transmission with overdrive, and a 3.08 rear end. Can I change the ring and pinion to a 3.55, 3.73LD, 3.73HD, or 4.10 using the same housing? Or to upgrade, do I need to find a whole new differential/axle assembly at a wrecking yard?

The goal is to upgrade to increase towing capacity as much as possible. I won't be towing too often but when I do, I would like to be able to tow as much as possible in lieu of buying a new truck! Why buy a new truck when you can rock the bullnose down main street?!?

Whatever gear size you go with, there was a thread also with a calculator that you could put your gearing into and your wheel size and get your optimum rear gear/rpm figured out for the tire size your want to use.

[Nothing Special]

Where you the one that was explaining diffs to me before? If so need to find those links, great info.

Yep, I was at least one doing that. Here's the link to my thread on diffs on a different board. I'm glad you found it helpful!

 

[Gary Lewis]

Whatever gear size you go with, there was a thread also with a calculator that you could put your gearing into and your wheel size and get your optimum rear gear/rpm figured out for the tire size your want to use.

Not a thread but a page: Documentation/Driveline/Calculators. It should let you figure out what RPM you'll be turning with any transmission, tire size, and rear gear combination.

But let's talk about transmissions. None of the 4-speed OD transmissions were very heavy duty. So if you want to tow very much you should consider changing out the transmission as that will be your weak link.

Unfortunately the Bullnose era was when the manufacturers were just seeing that they needed OD transmissions. And they started introducing them in the light-duty trucks, only. Then later in the decade the heavy-duty trucks started to get them.

So, if you want to tow heavy loads you should consider a heavier duty transmission. But the ones that come out on these trucks, like the T-18/19 and the NP-435, do not have an overdrive so you'll hurt your MPG. But the ZF5 from a later truck can allow you to tow heavy loads and it has an overdrive. However, it is a truck transmission and it needs to be shifted S.L.O.W.L.Y.

You have a lot to think about.

[Rembrant]

I have a 1984 2x4 short bed with a 4.9 liter engine, the 4 speed manual transmission with overdrive, and a 3.08 rear end. Can I change the ring and pinion to a 3.55, 3.73LD, 3.73HD, or 4.10 using the same housing? Or to upgrade, do I need to find a whole new differential/axle assembly at a wrecking yard?

The gear ratio options you mentioned are available as are many others, assuming you have an 8.8 diff, which would have been standard in a 1984 2x4 short bed. I believe there are also 3.27 and 3.31 ratios available, and then many more above the ones you noted.

If you do regear you'll need to know what axle you have (or at least the shop that does it will need to know). You can probably reuse your original differential (although some axles do require a different diff if you go past a certain point, called a "carrier break", that's often around 3.73, but will depend on what axle you have).

I seem to recall reading somewhere along the way that the 8.8 diff did not have a carrier break, but somebody can correct me if I'm wrong.

 

[Nothing Special]

.... So, if you want to tow heavy loads you should consider a heavier duty transmission. But the ones that come out on these trucks, like the T-18/19 and the NP-435, do not have an overdrive so you'll hurt your MPG. But the ZF5 from a later truck can allow you to tow heavy loads and it has an overdrive. However, it is a truck transmission and it needs to be shifted S.L.O.W.L.Y....

Gary, How does the ZF5 shifting compare to a T-18 or NP-435? Those are the two reasonable truck transmissions I have experience with. They don't shift like car transmissions, but I never found them too bad (other than not going into the non-synchro 1st until you stop).

But the absolute worst transmission I've ever had the displeasure to drive was the ZF-6 in my '08 F-250. Several times in the less than one year I owned that truck I had to coast to a stop on the side of a highway because I couldn't get it into any gear while I was moving. And it wasn't just me. Everyone who drove that truck said it was the worst shifting trans they'd experienced. The only "good" thing about it was that it was so bad that after being at the dealer for over 30 days of attempting to fix it Ford bought the truck back from me on a lemon-law claim (I didn't like a lot of things about the truck, so I was happy to be able to upgrade to an older truck without losing my shirt on resale of a truck I had bought new).

I want to go back to a manual trans sometime, and I'm wondering if the ZF-5 is enough better than the ZF-6 to consider. But my front-runner right now is an NV-4500.

But back to HBF84, while swapping in an older heavy-duty 4 speed does mean you'll lose overdrive, that's not necessarily a bad thing for you. I don't know what your current overdrive ratio is, but if it's 0.7:1 (which is fairly typical), that's a lot like changing your 3.08 axle gears to 4.4. So just changing the trans might be all you need to do.

 

[Gary Lewis]

.... So, if you want to tow heavy loads you should consider a heavier duty transmission. But the ones that come out on these trucks, like the T-18/19 and the NP-435, do not have an overdrive so you'll hurt your MPG. But the ZF5 from a later truck can allow you to tow heavy loads and it has an overdrive. However, it is a truck transmission and it needs to be shifted S.L.O.W.L.Y....

Gary, How does the ZF5 shifting compare to a T-18 or NP-435? Those are the two reasonable truck transmissions I have experience with. They don't shift like car transmissions, but I never found them too bad (other than not going into the non-synchro 1st until you stop).

But the absolute worst transmission I've ever had the displeasure to drive was the ZF-6 in my '08 F-250. Several times in the less than one year I owned that truck I had to coast to a stop on the side of a highway because I couldn't get it into any gear while I was moving. And it wasn't just me. Everyone who drove that truck said it was the worst shifting trans they'd experienced. The only "good" thing about it was that it was so bad that after being at the dealer for over 30 days of attempting to fix it Ford bought the truck back from me on a lemon-law claim (I didn't like a lot of things about the truck, so I was happy to be able to upgrade to an older truck without losing my shirt on resale of a truck I had bought new).

I want to go back to a manual trans sometime, and I'm wondering if the ZF-5 is enough better than the ZF-6 to consider. But my front-runner right now is an NV-4500.

But back to HBF84, while swapping in an older heavy-duty 4 speed does mean you'll lose overdrive, that's not necessarily a bad thing for you. I don't know what your current overdrive ratio is, but if it's 0.7:1 (which is fairly typical), that's a lot like changing your 3.08 axle gears to 4.4. So just changing the trans might be all you need to do.

Bob - The three manuals I've owned and driven in these trucks, the NP435, T-19, & ZF5, have all driven pretty much the same - like truck transmissions. By that I mean they don't want to be hurried in the shifting. And, bear in mind that all three were well worn. But I have a newly-rebuilt ZF5 about to go into Big Blue, so should have that experience to tell some time this year.

The only issue I thought I had with the ZF5 was bad synchros. The 3rd gear ones were worn so you had to be really slow with it. But that's the case with Big Blue's old T-19 as well.

Also, with the ZF5 it would some times not go into reverse until you moved the truck. But that turned out to be a broken gear.

Otherwise the ZF5 was fine, albeit a bit noisier than the other two.

[Nothing Special]

Bob - The three manuals I've owned and driven in these trucks, the NP435, T-19, & ZF5, have all driven pretty much the same - like truck transmissions....

"Like truck transmissions" doesn't scare me. But when a friend (who drove a Dodge with the HEAVY NV5600) drove my '08 and had to crawl off a higher speed section road in 1st gear because he couldn't get it to upshift, that makes me leary of a manufacturer! (That friend had wanted to drive my truck because he couldn't believe it was as bad as I said. After driving it he said I was being to kind to it, it was way worse than I was saying.)