I wanted to find out what the rest of you thought about the 72ish transmissions with granny gear. I just recently read about them and i was wodering how having only three real gears effects your top speed around town.

 

I have no problem crusing @ 70-75 with my 4 speed, still has a lot of throttle left to go too. I have a tach on the way, so I don't know the RPM's, but it certainly doesn't feel very high.

Mileage is still around 12 with a 428 under hood, so I'm happy with it.

Keith

 

The three gears is no problem....You go through 1 and 2 pretty quick and then cruise in 3....I live in Colorado and I easily accelerate from 65 up to 75 going uphill.....65 for me is about 3000 rpm (390 Engine/New Process 435 Trans/NP 205 T-fer case) What's really fun with the 4x4 is shifting in to L and 4L.....boy! What a crawler!

 

4 speeds with granny low were built for engines with a wide power band - generally 1500 RPM to 3500 RPM. If you look at all the ratios in the trans you will see it covers all speeds normally driven.

On the ones I have used, first was just to start the load, second to about 25 MPH, third to 45 or 50, and high for cruising. It sucks a bit in that if you can not pull a hill in high you have to drop below 50 MPH, and hitting second in the mountains keeps you below 25 MPH. But that is the nature of the beast.

The old cast iron engines seemed to last a lot longer if you kept them below 3000 RPM, so we would use the rear end ratio and tire size to turn the engine around 2600 RPM at our cruizing speed.

 

I ran a 390 with .060 overbore, 10:1 flat tops, and a 260/270 rv cam, with the relatively stock 2bbl carb and intake(gasket match ported heads and intake manifold, along with mild reworking of carb jets and metering rods for side-hilling) and I never pulled a gear i the mountains. I lived in Jasper, Alberta for 8 yrs, and had that truck maxed out for towing and hauling a few times and all 4th required was a bit more fuel to keep it at speed up the hills. If your engine is stock, you may suffer. With everything I did, I was running an average of 18 mpg highway(empty) and around 13-15 loaded, in town was ok at around 10-12 depending on my heavy foot. Mileage would have been better with an intake and off-road carb added to it.

 

I never use granny gear on my '72 unless I'm pulling something, and thats just to save some clutch wear. If I punch 1st gear I just get tire spin anyhow, and its wound tight in about 2 seconds. Sometimes I wish I had an auto tranny so I could just hold it to the floor and let it do its thing. Those 4 speeds arent the greatest for "speed shifting".

 

I have a 76 f-100 that had a 302 3 speed and when I droped in a old 72 360 FE and granny low 4 speed in 16 years ago it made a great work truck. with the 302 if I was tring to pull a heavy load to get it moving required slipping the cluch a lot. and often it was snip a tire or bog. The 360 is well worn but drop it in granny and somethings going to move.