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Hi all...need some help here cause I don't really know anything about this stuff. Im building a 79. I want to pull a camper averaging 8K lbs now and then. Other than that just normal driving. I put F250 leafs in the back. I have a standard C6 and a 460 that I put a straight up timing set on. I have a 9" rear-end with 3.50 gears. I'll be running 33s. Trying to determine if I need to change my gears out or if the 3.50s will be ok? Anyone have any experience with this type of setup? Thanks in advance.
350's would be perfect for just cruising around. but if you're serious about towing you may be a little underwhelmed. some of it will be dependent on how many hills you're towing in. as long as you can get into 3rd gear and hold it you'll probably get by but that's questionable.
Isn't a 9" 4.10 and lower a different carrier ? maybe I'm thinking of the 8 3/4 but I know some are so you may have more issues.
I don't think you have to get another carrier with the lower gears, but I do think sometimes you will have to clearance the pinion support boss for the ring gear.. I think when you get up into the really low gears, you have to make some changes. I went back with the 3.50s in my 77 F150 for the cruising, but I also have an NP435 so I've got the low first. If the gears are already in there, put it together and drive it and see how it fairs. Can always change it out later.
I have this exact set up, except with a 351M. Every once in a while I pull a 16' cargo trailer with my toys weighing in at about 5,000 lbs combined. My truck pulled pretty good up to 55 mph. Anything past that she struggles. I imagine your 460 will do a little better pulling. But with 4.10 gears, it would be a lot better.
My '78 F350 has 4.10s ( Dana 70) and 32" tires. 70 is right at 3,000. I installed a GV O/D and the rpm dropped to 2,500 and I lost mileage because the engine was laboring with the 15,000 lbs it was trying to pull. Soooo , the stock 460 is being replaced with a high torque 521 ( 600+ft lbs) low RPM monster so the engine will not labor at the lower c rpm in O/D . It will be next year before I can go for a 3-400 mile trip and evaluate the change.
Leave it as is. If you are only towing on occasion it isn't worth the money to change the gears and then more money after that as fuel consumption will increase due to the higher RPM you'll be turning on the highway without the camper which will be 95% of the time.
With only towing 8K occasionally I think you'll be fine with the 3.50s, especially with the torque of a 460. It might struggle in big hills, those 33s are gonna make it feel like higher gears, 3.23s or around there. You got a 9" rear so if you bought a pre-built center it'd only take a couple hours to swap out. Some 3.90s or 4.10s would wake it up, something like 4.30s or 4.56s would be fun when you weren't towing , but they'd kill your top end speed.
Swapping to a later model tranny at some point might be worth considering. They usually have a lower first gear for better off the line pulling and better top end and fuel economy with O/D.
I have a 1976 F-250 with a 460 and C6. It has the 3.07 rear end gears.
3.07 rear axle gears
The original owner used it for years to pull a camper trailer in northern CA.
Hence, my suggestion is to try it with what you have and see how it works. You may not need to change anything. You can always make changes later if needed.
I meant to chime in yesterday with some questions. Such as, is this a short bed or long bed 150? Just thinking that 8,000 lbs is a lot of trailer for an F150. More so still with a short bed. F250 springs aside, it's a lot more than spring rate that makes for a safe tow.
Maybe you know all that stuff already, about axles, brakes, frame strength, wheelbase and all that other stuff and have been towing for years. But it didn't sound like it so I wanted to bring up other aspects of this for discussion.
He would most likely be using a WDH so the springs are not that big a deal.
I believe all states say anything over 2500 lb has to have trailer brakes and break away switch.
So if the trucks electric brake controller is adjusted right the brakes should also not be that big an issue.
Now long bed / short bed think can come into play as the long bed would most likely be more stable just like a 250 or 350 truck would be.
But if all we have is a F100 / F150 then that is what we use with the above equipment, WDH & brakes, and go slow he will be ok.
BTW I flat towed a backho behind a Toyota L/C thru some hills from CT to NY.
That had a shorter wheel base than a short bed PU and it only had a 230 straight six and drum brakes all around.
Dave ----
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, but they'd kill your top end speed.
