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I’ve had the 59 f100 on the road for a couple of months now and I’m thinking about changing the diff gears to get better highway driving. I’m currently sitting at roughly 3000rpm at 60mph. 3.07:1 gears should get me down around 2200rpm at 60.
The truck has the original T98 4 speed and 3.92:1 Dana 44 diff. The truck originally had the 223 I6 but now it has a worked 272 y block.
Anyway just looking for some advice from anyone that has changed out gears to achieve better highway driving. I think lowest I can get is a Yukon gear set at 3.07:1, but not too sure how that would effect my acceleration low down. Also wondering with lower rear gears if the t98 1st gear becomes a usable gear?
I have no direct experience to offer but my opinions are based on decades of experience (from when these were just new or used trucks, and cars).
I think the huge difference in ratios between first and second will still leave you starting in second gear. I suspect that first gear remain what it's always been, a "tractor gear." I'm unsure but with a 3.07:1 differential, first gear might work for starting off with a heavy load.
I don't know that I've ever seen a Ford truck with a 3.07 from the factory but I'm sure it must have happened. I'd be inclined to go with a 3.25:1 unless your engine is built for bottom-end torque. That would leave you some room to adjust tire diameter to get you exactly where you like. It's also closer to 3.50:1 which used to be a good "catch-all" street/strip ratio in the days before overdrive. Speaking of overdrive, that's the modern answer. With the right overdrive transmission you could leave the differential alone and have all the benefits of a low drive gear and a usable first gear.
I agree, 3.25 would probably be better all around. 2200 rpm is really low end of the torque range which will cause more throttle to keep it moving. There is a sweet spot where the Y is more comfortable probably closer to 2800 rpm..
Thanks for the advice Lou. I suspected the 3.07 would be too low and I’d hate to spend the money and be disappointed. The 3.50 sounds like it might be just enough to take the edge off while driving at 60.
The perfect solution would be an overdrive for the T98, did they make an overdrive for these transmissions? Ideally I would love to put a 5 speed with overdrive but I’m in Australia and the 93 and earlier mustang T5 isn’t available here and I’m not aware of anything as a suitable replacement, plus that would be the moment the snowball started to roll and I've already spent enough money getting this truck on the road over the last 3 years.
Hiball-
Thanks for the input. Yeah I’d like to find that sweet spot at 60 and have a gear that helps with the sweet spot through out the rest of the gears. At the moment it revs a bit high in every gear with the speed limits around town.
I think there might've been an overdrive option, as I've seen an "Overdrive Cable" referenced is some of the parts catalogs. Also could be looking around for a gear vendors unit.
I have 3.00:1 in my 60. T98 behind a 292. I now start out in granny gear and it works like a regular 1st gear. Truck is much better at highway speeds. So I see no problem with your plan and I think you will like it. But you will no longer start out in 2nd.
I am not an expert on the subject, but I never found any overdrive for our trucks, just heard rumors they might have existed but were rare as hens teeth. Something that hard to find had to be way more expensive then changing a differential, so I went that route.
One thing to keep in mind is these trucks were geared low partially because they are a bit underpowered when loaded. 146HP is slightly higher than a modern 4 cyl gets. I noticed when I have Red loaded hills get challenging both up it losing speed, and down if not careful overheating the brakes.
I would love an overdrive box too! In my dream world, low would be 1:1 and high would provide 130% overdrive for unloaded flat cruising. Using synchronized Electonic on-the-fly switch on the dash that is switchable once at my desired speed or anytime to split gearing.
The cost of converting to an OD trans like a T5 is expensive. How much fuel will it save to pay for its self? You can buy a lot of fuel for that amount of money. Just lowering the rpm with a differential change would be the most economic way to go. If you don't do any heavy hauling another choice would be a 3 speed OD, but they are getting hard to find also. Thats the route I went. I went to lower rear gears 3.89 because of the hilly terrain where I live that they are putting a stop sign on every damn little street intersection and with the OD it cruises comfortably between 60-70 mph.
I am not an expert on the subject, but I never found any overdrive for our trucks, just heard rumors they might have existed but were rare as hens teeth. Something that hard to find had to be way more expensive then changing a differential, so I went that route.
One of my parts trucks came with an overdrive unit. It use to be my friend's dad's truck and he said it was a blast to drive. The cluster gear had broken teeth for first gear so I just went with a normal three speed. Since then I have found a new cluster gear and a couple other parts and the unit is on the to do list, which is quite long. At any rate they are out there. They were more common in cars I believe.
Thanks Walston that’s good to know it drives ok with that low gearing. is that a 9 inch in your truck?
I think I may have hit my first hurdle... I noticed when looking at gear sets that all the gears below 3.92:1 would say in the spec- suitable carrier break 3.73 and down. I have read the carrier break is 3.73/3.92, so I’m on the high side. So it seems that I’ll need a different carrier to fit the 3.07 ring gear and have it mesh correctly. I’ll probably just wait to find a cheap 9 inch.
Red- oh yeah an OD would solve all my problems. I think what happens next is going back to the drawing board. I do want to 4 link the rear and install coil overs and eventually install a ifs and box the frame then build a blown Y. So I might have to drive with the 3.92’s for now.
Hiball- yeah true, that is a lot of fuel. I do actually have a 3 speed with R10 OD from a 56 F100 but the box is a column shift manual. Not sure if there is a way to make the 3 speed a floor shift
spurredon- sounds like you might have to bump the OD rebuild up the list, haha.
I don't remember the exact cutoff but the 9" predominated in the F-100/F-150 until some in the late 90's. Among those used in trucks, most were 28 spline which will allow you to swap the carrier with another truck. You might have to swap the pinion yoke with your original unit if the dimensions (length or u-joint) are different enough to matter.
There are floor shifters for the 3 speed trans. I had a standard 3 speed with a floor shifter I found at a swap meet, pre computer days 1988-1990 took a lot of leg work. Same with finding the 3 speed OD trans just like yours. It took a little fabrication to adapt the shifter to the OD trans. The only draw back was the shifter sits further back and did work well with the bench seat. I had a Cadillac bench at that time so I had to replace it with bucket seats.
Off topic: I have a home made from scrap engine stand that I run my back up engine on that has small casters like yours. I play hell at my age rolling it in and out of the garage. I just bought new larger wheels and hope that helps. That will be next weeks project if all goes well.
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