4 speed w/granny gear...lets talk...

[bobs409]

I got my 71 C20 on the road today and this transmission sure leaves alot to be desired.

I knew 1st gear was all but useless but 2nd is way too low as well. Pull out in 2nd and by the time you get movement, you have to shift to 3rd which then feels too high of a gear. And to go from 3rd to 4th? Wow, another large jump. It's fine if your going down hill but heaven forbid your going up hill during that 3-4 shift. Your choice is to rev the engine up the hill in 3rd or hit 4th and bog your way up. Sure seems odd to me. The gear ratio's seem way out of whack. Certainly not going to be the best for fuel mileage. lol

My truck has a 4:10 Eaton rear by the way. I have a rebuilt 1984 305 from a Camaro in it now which runs good.

I just want to see what others think of these transmissions.

[tcb-1]

unless your in the business of stump pulling or rock crawling, they are useless imho. However they are bulletproof!

4.10's are quite low for the M-20/SM465. My truck has 3.07's and it's not too bad, but oh do I pray for a wide ratio M-21 or M-22 someday...

[69GMCLonghorn]

bobs409, welcome to the world of driving a real truck, my friend! Back in the day, that was all they had; wide ratio or automatic. I've driven these trucks with the granny gear transmissions for years. It does take an adjustment, but it's really not that bad. The GOOD thing about putting one of these behind a V-8 is that you CAN lug 'em quite a bit, and wrap 'em out when you want to. I can run 3rd from about 8 MPH to around 65 if I really tach it out. I can run 4th from 20 to ??? Just drive it more and you will get the hang of it and realize that it's really not all that bad.

Also, don't get your hopes up with swapping out gears in that rear end. All they have is 4.10 or 4.56.

If you want a really great setup, save your pennies and add a Gear Vendors! You get 7 forward gears (you can't split 1st). You get O/D and a whole bunch of middle gears. But the whole shootin' match will set you back around $3500.

[1969 GMC]

I agree, since it is a wide ratio truck trans it is sometimes undesirable. I dd'ed my GMC for a year and a half before the rockwell exploded, and it came to be second nature. However, I did stumble across a big New Process 542GL for dirt cheap, so I picked it up. It is from a Chevy school bus chassis, so it will bolt to any chevy engine. It is basically the same as the SM465, with the addition of an extra gear, first is still granny low, and 5th is still direct...should be a little better to drive on the road. The only downside is, this tranny is HUGE!. It also has a 13" clutch. Oh, and it is 2wd...so I am also going to swap in a divorced t-case. Shift pattern is in my avatar.

here are some pics...http://s14.photobucket.com/albums/a3...ik/NP542%20GL/

for reference...
SM465 ratios:
1st- 6.55
2nd- 3.58
3rd- 1.57
4th- 1.0

NP542GL:
1st- 7.33
2nd- 3.96
3rd- 2.19
4th- 1.76
5th- 1.0

[lilred67]

i have a sm465 in my '67 with 3.07 gears. there is a jump between 3 & 4 but not that bad if you twist it up in 2nd. with the higher gear ratio i can get more mph in second before i go to third and it's not that noticible to me but i have driving it that way for 15+yrs. they are tough tranny's, it will be hard to tear one up........but it has been done!!

[Ace in the hole]

I have the sm465 in my truck and kind of like it. It's not all that bad once you get used to it. Are there better geared tranys out there? Yes, but this one will likely out last them all.

[Shyguy]

I have had 3 trucks with the 4 speed granny transmission and liked driving them all. Of course I use my trucks to work with. The first one I had was a '72 GMC that I used to pull boats up to 26 ft and travel trailers about the same length in Northern California. I had that one for I guess 20 years or so.

The two I have now are a '67 swb stepper and a '71 lwb stepper. The '67 has a l6 and the '71 has a 350 V-8. For the way I drive and use the trucks the transmissions work out great.

Now my son says he would not have a truck with the old granny 4 speed and likes the three speed or automatics better. I guess at present he has 3 running trucks.

I think it just depends on what you use the truck for and the kind of driving you do.

Danny

[Average Joe]

I too am new to the granny 4 speed. I have the sm465 in my '67 suburban. I really disliked it in the beginning but its growing on me. The truck has a 283 so it really likes to wind out in 2nd before I grab 3rd. I'm going to be towing a 3000 pound trailer over the Cascades memorial day weekend so I guess we'll see how high she'll wind in 3rd.

[bobs409]

Thanks guys. I don't know about towing anything with this. Maybe if it's all down hill or if I stay in 2nd!

I guess I'll have to get some more "seat time". Maybe it will grow on me.

I used to work at a garage back in the late 80's and we had a 79 Chevy wrecker I drove that had the 4 speed trans. I know for a fact it wasn't like this one. 1st was still a useless stump puller but the other gears seemed more appropriately spaced. With a car on the back, I'd easily pull out in 2nd, not have to race it up to hit 3rd and no big jump to 4th. That trans I liked alot. Must have been a different ratio set up?


Anyway, the truck is fun to drive with the manual steering and that 4 speed. LOL

[chevellelover]

I have the granny 4 speed in mine and if i want to get any power in 3rd or 4th i have to wind it up real high but i usually have to kinda bog up hill in 4th I havent found a way around it. But if you are getting after it 3rd usually nice a nice pull because it is so long.

[bobs409]

Major update: Turns out the vacuum advance was not working so the engine was not putting the power out it should have.

Now that it's been replaced and timing set correctly, the truck has alot of power and getting up the hills isn't so bad now. What a difference!!!

I sure am loving it now. Manual steering & 4 speed, I know I'm driving a REAL truck. lol

So, now I need to know how to get about 20 MPG around town with it?


Thanks guys,


Bob

[69GMCLonghorn]

Tow it with a Prius?

[dan42]

Originally Posted by 69GMCLonghorn

Tow it with a Prius?

That's about it. I enjoy driving mine with the 465 in it as well. It reminds you that you're driving an old truck.

[hicktownhotrodder]

what i love about my 465 with 4.57 rear ratio is that i never have to shift once im in the high hole. around any corner i want

[WorkinLonghorn]

Some of these trucks were ordered with the New Process 435 4speed. It was perfect for camper carrying trucks since the granny low was just 4.56-1.
Then second is 2.28, third is 1.31,and 4th 1-1. In some literature it is called "CR" or CLose Ratio. I've had both and preffer the close ratio one. If I was pulling a 31 foot Airstream up a hill and had to stop for traffic, I (and my clutch) would rather have the 465 granny with it's 6.55 low.

[69GMCLonghorn]

I have an NP435 in mine but it does not have the 4.56 granny gear. It has a 1st gear that is actually slightly lower than the 465 (6.68). I do know that certain model 435's (mainly newer ones) did have a 4.56 or 4.90 first gear and actually it makes it a much more usable gear. I had one in a Ford Diesel many years ago. The tranny was the only thing that DIDN'T fall apart on the truck!

[powell72]

My wife likes her SM465 so much she refuses to let me talk about swapping it out.

[Mike C]

You solved your problem before I finished the post! I was going to say your torque output is the problem. All of the idiosyncrisies of the granny gear trans virtually disappear when you have a motor with a strong torque ouput at low RPM.

I used to have a 236 degree at .050 cam in my Jimmy and it made for a lousy drive. With the 206@.050 cam in it now, it is a joy to drive. If your engine is built to make peak power at around 4200-4500 rpm, the SM465, or SM420 for that matter, is nice. Build a 350, 383, or even better, a big block for it and the trans gets even better.

[LostMy65]

I can't remember what rearend I had in my 65, but I could put it in third, get the rpms up for the race, drop the clutch and run it all the way up to 70 without shifting any gears.

[BIGBLU 72]

im glad you got it figured out! I LOVE SM465's! have one in my Jimmy w around 2.73s after tire height so with the granny gear i pull anything (including stumps) with little to no problem!

[Vintage Windmills]

I'm assuming the 67 GMC 4 spd has to be the SM420? Looks like it has the following ratios:

SM465 SM420
1st- 6.55 7.06
2nd- 3.58 3.58
3rd- 1.57 1.72
4th- 1.0 1.0

Thoughts on the SM 420 behind the 305 V6 in the GMC I'm getting? Plan to restore it and use it to lug a few trailers around but no serious mileage at all. With the torque of the big block V6 it should work pretty good with wide ratio?

[bosco200]

You gotta love that granny low, trust me when you get into a situation where theres a kid in a 98 f150 and hes saying your truck doesnt have any balls.....trust me it all pays of in the end.

[LostMy65]

Originally Posted by Vintage Windmills

I'm assuming the 67 GMC 4 spd has to be the SM420? Looks like it has the following ratios:

SM465 SM420
1st- 6.55 7.06
2nd- 3.58 3.58
3rd- 1.57 1.72
4th- 1.0 1.0

I haven't drove both, so I wonder how much difference that jump from 3rd to 4th feels between the SM465 and SM420
It looks as though the SM420 has a wider gap between 3rd and 4th.

[bosco200]

Lol found the vid of that truck pull...sorry bout the quality....

250 inline 4 speed granny low 4.57 rear end gives an a** whoopin

YouTube - 1972 C20 vs Some ford

[BAGNDRAGIT]

i love my 465, course its backed by a 400hp+ 327

i havent used first gear since the day after i bought the truck.