Better Highway Gears

[robwymer]

I'm running a well-tuned 300 six, NP435, 4.10 Dana 60, and 30-inch rear tires in my 67 "stepside". Like many of us, I have been looking into ways to improve my truck's drive-ability at highway speeds. I've researched AOD, M5R2, T-5, and T-56 swaps, and of those the Mazda/Ford 5-speed M5R2 seems like the best option. I've also looked at overdrive units, but I don't want to spend TOO much and I really don't want another stick in the cab.

Then it hit me: why not just find an old 9" rear end with a 2.70 gear ratio? I should be able to find one without breaking the bank. They would probably have a different bolt pattern, but I'm looking to change my pattern anyway.

Right now my truck takes off perfectly in 2nd (3.34 X 4.10 = 13.7). That would make my granny low (6.69) much more usable, but still very much on the low side (6.69 X 2.70 = 18.1) which could come in handy if I ever load or tow with the truck. 2nd gear starts would likely require some clutch work (3.34 X 2.70 = 9.0). But I have taken off in 3rd with my 4.1 gears (1.74 X 4.1 = 7.1), so maybe 2nd gear starts would still be doable without a load.

With my current gears and 30" rear tires, this is what my shift pattern looks like:

2nd: little to no pedal required at launch to 13 mph @ 2000 rpm
3rd: 1100 rpm @ 13 to 24 mph @ 2000 rpm
4th: 1100 rpm @ 24 mph to 55 mph @ 2500 rpm

With a 2.70 rear end and 28" rear tires (would match the front) my pattern would look like:

1st: surely no pedal would be required, 9 mph @ 2000 rpm
2nd: 1000 rpm @ 9 mph to 19 mph @ 2000 rpm
3rd: 1100 rpm @ 19 mph to 36 mph @ 2000 rpm
4th: 1100 rpm @ 36 mph to 65 mph @ 2100 rpm

The M5R2 is still a tempting choice with the 3.75 1st gear and .80 5th, but I would be limited to a 3.55 in my Dana 60 which would bring 2200 rpm @ 65 mph. I could install an M5R2 and a 3.25-geared 9" rear, but we start talking dollars again.

Any thoughts?

[Bullitt390]

2.75 is more likely, no such thing as a 2.70 9" factory gear.

3.00 gears are extremely common.

2.72 was available in 1979. I have heard of 2.54 9" ratio.

Josh

[robwymer]

Thanks for the additional info Josh. 2.72 or 2.75 are close enough to 2.70 for me, and 2.54 sounds interesting, but could cause problems during upshifting (especially 1st to 2nd when hauling or towing). That said my 300 makes great low-rpm torque. Even though I haven't tried towing anything yet, the speed limit in my neighborhood is 15 mph and I can put it in 4th and idle around at 15 mph (about 700 rpm). I can even accelerate from there.

[Bullitt390]

Mostly just depends on what you want to do. Most of the 9" drop-outs for the 2.75-3.00 gears are going to be for 31 spline axles.

In regards to 1st gear useability I swapped in a 5:1 1st gear T19 and have 3.00 rear gears with 31" tires. 1st gear isn't too bad and it quite useable from stoplights and stop signs. And you aren't having to shift within nano-seconds of taking off.

Josh

[averagef250]

You really should never do a 1-2 or 2-1 shift in a 435. Non synchro 1st and such a big jump between countershaft speed from 1-2 makes it a really bad idea, just beats the tar outta the tranny.

I've run 35" tires with 3.54 gears and 435 with an EFI 300 six. The result is pretty gutless, not a good idea.

300's like to cruise around 2500 rpm. EFI can go lower, carb won't see any benefit.

[robwymer]

Oh yeah, non-synchro 1st gear. Forgot about that...Dang it! I was really looking to hang on to the NP435 because its a good tranny, but I really need some more usable gears. I was also hoping to get what I was looking for by just swapping one piece (the rear axle), but I guess I'll have to tackle this in steps - starting with the axle.

That opens the tranny discussion back up. Josh - the T-19 sounds interesting and has a sync'ed 1st gear, but I've read that T-19s may not be smooth shifters.

I've also read the M5R2 swap tutorial, and I'm not sure if I want to modify the cross-member and floorboard and fabricate a clutch linkage.

I wouldn't mind getting some additional feedback or thoughts, especially from folks who have swapped in the 5-speed.

[70_F100]

That opens the tranny discussion back up. Josh - the T-19 sounds interesting and has a sync'ed 1st gear, but I've read that T-19s may not be smooth shifters.

Not sure where you heard that, but I have to disagree.

I had a 78 Scout with a T19 (4.0 first gear) that I bought new and drove for over 200,000 miles without a single hiccup.

This summer, I put a similar T19 in my '70, and it's smooth as silk, too.

[averagef250]

The T19 shifts fine, it shifts the same as any other old clunky pickup 3/4 speed. The M5R2 shifts much smoother with shorter throws.

There are no floor modifications. The hydraulic clutch means installing a clutch master on your firewall and modifying the clutch linkage a little. Many have done this.

[robwymer]

I would like to get my truck in the 2000 rpm range from 60-65 mph, because I think it has the torque to do it with 28-29" tires. I don't know anything about stressing the NP435 by shifting from 1st to 2nd on takeoff. Its seems to me a the difference in gear ratio from 1st to 2nd is about the same as from 2nd to 3rd (both about 2:1). The drive ratio on 1st gear with 2.54 gears would be almost 17:1, while my 2nd gear is currently almost 14:1, so it seems like 1st COULD be useful. But the M5R2 still tempts me.

After a little road-testing, I can upshift from 1st (granny) to 2nd with the NP435, no problem. I have to come to a complete stop to shift into 1st, but that isn't a problem for me as I don't downshift into 1st when I stop. Currently downshifting past 3rd while stopping is pretty much pointless, but I could probably downshift into 2nd with a 2.75 or 2.54 rear end.

But the shorter throw of an M5R2 sounds really good, too. I would like more info, pictures, etc, of what was done to get the hydraulic clutch to work in our trucks, especially with a straight six or small block.

Decisions, decisions...

[Bullitt390]

My T19 shifts fine under normal circumstances, but it doesn't like 4000+ shifting. But as others have said, it's a long throw from each gear and not short like the Mazda or ZF5 or NV4500 etc...

Josh

[averagef250]

I would like to get my truck in the 2000 rpm range from 60-65 mph, because I think it has the torque to do it with 28-29" tires. I don't know anything about stressing the NP435 by shifting from 1st to 2nd on takeoff. Its seems to me a the difference in gear ratio from 1st to 2nd is about the same as from 2nd to 3rd (both about 2:1). The drive ratio on 1st gear with 2.54 gears would be almost 17:1, while my 2nd gear is currently almost 14:1, so it seems like 1st COULD be useful. But the M5R2 still tempts me.

After a little road-testing, I can upshift from 1st (granny) to 2nd with the NP435, no problem. I have to come to a complete stop to shift into 1st, but that isn't a problem for me as I don't downshift into 1st when I stop. Currently downshifting past 3rd while stopping is pretty much pointless, but I could probably downshift into 2nd with a 2.75 or 2.54 rear end.

But the shorter throw of an M5R2 sounds really good, too. I would like more info, pictures, etc, of what was done to get the hydraulic clutch to work in our trucks, especially with a straight six or small block.

Decisions, decisions...

This makes zero sense.

If your truck is geared halfway correctly you can't effectively take off in granny gear, it flat does not work. There's nowhere's close to the same difference between 1-2 and 2-3 in any granny transmission. The difference in ratio between 1 and 2 is very large, 2 and 3 is much closer.

M5R2, 3.00 gears and 31" tires is a good combination if you have an efi engine or diesel. Carb it's a waste, go with a 4:1 T19 as overdrive is pretty much useless

[gregamorton]

average does the effective low cruise rpm range change from a carb engine to the efi? I noticed in one of your reply's onetime that you said that the 300 run real nice at 2500rpm. I always thought the 300 would run best at 1600-2000 rpm pulling or just cruising. My theory on running a gas engine at low rpm for fuel mileage might be wrong on the carb engines.

[robwymer]

Thanks for the input Dustin. I settled on 2500 RPM as a desired shift point because I figured that would keep the 300 in it's power curve. You've certainly given me something to think about. The 3.54 gears would work well if it weren't for the NP435 gearing - at least with my application and what I want to do. It would also make my 14:1 2nd a 12:1 2nd, which would necessitate more clutch.

Maybe I should replace the transmission. But it's just that I hate to settle for less than what I'm looking for, so I will end up spending way too much time and "garage fund" money. Which means smart @$$ remarks from the "better" half.

[averagef250]

How do 3.54 gears use "more clutch"? 3.54's and 30" tires is a low geared son of a gun in my world. It should feel fine starting off in 2nd gear. If you were going to use a 5 speed or 4:1 T-19 3.54's wouldn't work. You'd need 3.00 gears.

[robwymer]

Dustin,
I'm currently running 4.11 in the Dana 60, and taking off in 2nd (3.34:1) feels pretty much perfect right now, with an overall 14:1 ratio. Switching to a 3.54 rear end would give an overall 12:1 ratio in 2nd gear, meaning a steeper take-off requiring more clutch.

However, I read in one of your previous posts in a related thread that the M5R2 has a 3.90 1st gear, when I thought it had a 3.75 1st gear. Strangely enough, this small ratio difference could make all the difference in my application. If 1st is 3.90, the overall ratio with a 3.54 rear would stay 14:1, which should work well with slightly smaller rear tires (I'm running 235/75/15 in front and 31X10.5/15 rears).

Is the M5R2 1st gear 3.90:1 or 3.75:1?