I have a 1970 F100 with a 4 speed manual tranny and a 351 Cleveland monster in it, but the tranny has the granny first on it so I have to start off in second. I was wondering if there is a way I could regear the tranny so I can start off in first and lower the RPMs in 4th when I'm on the freeway? I don't really want to replace the whole tranny, just because I'm on a shoestring budget (wife says it's not a family car, but I won't get rid of it). Thanks, Rich
Yep, like one said, probably easiest to switch to a higher rear gear. Either that, or find a different tranny. Preferably a 5 speed....One problem with many of the granny gear 4 speeds, first gear is not synchronized. IE: warner T-18, which is probably the most common in the older fords. Some had the NP-435's...But even those I think were not synched in first. The T-19 does have a synched first.. But even if you had that, first is probably so low as to make it silly for starting off. You're shifting to 2nd before you barely get going, unless you really want to rap it out. You probably have a pretty low rear gear. Either a 3.73 or a 4.10 I bet... The cheapest and most practical change is to swap the rear gear to a higher number. Like a
3.54, 3.33, 3.08, etc...But you have to remember, the higher the gear, yes the lower the rpm on the highway, but also you lose torque. So you don't want to get carried away with it. I have the same problem with my 68 F-250 with a 300 six. It's a T-18 and a 4.10 rear. I turn about
3061 rpm at 70 mph. I actually limit myself to about 2800 rpm usually...So I don't usually go over 60-65 mph. I do about 2650 at 60 mph. Going to a 3.54 rear, I would turn about 2643 rpm at 70 mph. With a 3.33 gear, which I can get for the dana 60, I would do about 2486 rpm at 70 mph. I wouldn't want to go any higher than that with a f-250. But a f-100, I might consider down to the 3.08 or so range, if it's mainly a street truck. In my case, the best solution is to keep the 4.10 rear for good torque, and get a 5 speed with OD. But they ain't cheap. A ZF which I would need for the f-250, is going for a pretty good chunk of change. I would also have to fit up for the hydraulic clutch. Maybe trim the drivehaft too...Lots more work than just changing the rear gear. I could go with a AOD, but they suck power, which I'm not overly crazy about with only a 300 six. But they do have a .67 OD, which is nice. With my 4.10 rear and a AOD, I would turn about 2051 at 70 mph not counting any slippage. :) Supposably, the AOD doesn't slip in OD. Supposed to be locked. MK
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