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Discussion Starter · #1 ·
hi guys
my truck has a sm420 with 2.73 gears
tires are 205/75 in 15 it is about 27.5 inch tall
i get good gas mileage with this set up , actually its pretty for cruising even on highway
i presice again for cruising..not going fast ahahah

i have a small trailer about 1200lbs

last time i towed it and going up hill...was pretty slow..

also engine was getting hot going up hill ( engine is running lean )

but my question
do you think 2.73 is a good enough to tow ?
will it hurt anything ?
if i was to install 3.08 gears will it be worth it ?

thanks
 

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What truck/engine?

I have had a dozen 420's and more 465's then I can count. Few of those had 3.08 gearing and I had a few instances pulling around 1000lbs. But I am from lower "flat" Michigan.

That low gear will let you pull dang near anything even with a mere 200hp. But the 2/3 jump towing up a hill may be fun. Did you drop a 420 in a Cadilliac to pull a horse trailer like Chris LeDoux?


Don't outdrive your brakes.
 

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Discussion Starter · #3 ·
no its an old c10
and i have an old compact trailer shasta 13ft :):):):)
last time going uphill was......slow...
but good in gas...






What truck/engine?

I have had a dozen 420's and more 465's then I can count. Few of those had 3.08 gearing and I had a few instances pulling around 1000lbs. But I am from lower "flat" Michigan.

That low gear will let you pull dang near anything even with a mere 200hp. But the 2/3 jump towing up a hill may be fun. Did you drop a 420 in a Cadilliac to pull a horse trailer like Chris LeDoux?


Don't outdrive your brakes.
 

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After years of towing completly without or with inaccurate trailer brakes I tend to drive slow and coast alot using the gearing to slow down(yes I know your not supposed to do that).
A 465 and 420 can take you engine breaking using the transmission.

As for acceleration I see no issue. You may want a 383, 5.3 or 6.0 in front of that 420 for more torque (and better driveablity) when tackling hills.

I know a sm465 bolts right up using parts from oriley. I have the parts list at the house.

Unsure about a 420. Its close I just dont have one in front of me to see if the input is longer or something.
 

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also engine was getting hot going up hill ( engine is running lean )

While you may be happy with your gas mileage, if you lug the engine often enough it will cost more than you are saving on gas. I'd look more for something in a 3:23 range to make a difference. Better yet, get a used 5 speed to put in it . I can't imagine you are carrying anything very heavy with 205 tires and a small 1500 lb trailer. Do you really need that low first gear?
 

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I made the joke about the Cowboy Cadilliac because those had 2.7x gearing and even with a 472 or 500 big block would get mileage in the 20's on the highway.

The things were heavy pigs and even with 500ft/lbs of torque were slow as heck acceleration wise. This was mainly due to the gearing. But due to the gearing the engines also were generally run at lower rpm and could reach 300k mileage when other engines of that time were lucky to reach 150k.

I know with a sm465 I can beat the heck out of the thing. Do things like slap it into 3rd at 70mph to pass someone or stuff a 500 ft/lb engine in front of it with no transmission modification. The thing will run with bad bearings, bad seals, low oil, and once back at the house can be rebuilt in a weekend without specially tools.
The 420 is the 465's father and is the nv4500's grandfather. The 3 transmissions share very similar parts and are tough. I consider the 4500 less reliable then the 465 due to the overdrive issues.

I did bolt a sm465 into a rusted 76 Cadilliac back in 98. It was not pretty though. There was a saw all involved with the floor, manual clutch linkage, and the driveshaft extended with a rusted pipe. I was young, broke, and the car was cheap.

The thing was slow. But once I got over 45mph I could just cruise in 3rd using that big blocks torque to pull the car without needing to shift much. Could drop it down to 30mph in 3rd lugging that girl back up to 70 before shifting. Once I got up to highway speeds the thing would cruise. Steering and brakes were on par with a typical land yacht. But the engine was happy going 85mph with the 2.7x gearing.

On the other end of the gearing scale. I had a 84 13,000 lb c30with a 8x12 flatbed. The thing had a smog 350, sm465, and a FF 14 bolt with 4.56 gearing turning 235 tires. I used it for towing and tearing apart forklift trucks for parts/scrap. The things bed was high enough a fork truck could be loaded right off a semi dock in many cases and I cut them up right on the bed to get the electric motors, controlers, etc.

That 350 was only able to move with around 9,000 lbs (somewhat safely) because of that 4.56 gearing. I avoided the highway generally and drove it at 60. I eventually dropped a 383 into the thing around 350hp and was having fun (unloaded at a mere 6,000 with the speedometer needle buried most of the time on the highway getting mileage around lets say 6mpg. Eventually something had to go and in my case it was the rear main at what I would guess was 5000. The engine just locked, shut off, and the clutch slipped before I pulled it over. I bought some 80/90 and poured it in. Drove it to a rest area then drove the thing to the folks house where due to limited space to store the truck at the time I cut it up for parts. I have a video of driving it with the rods threating to come out the side of the block.

Over 10 years later
I bought my recent 89 3500(squarebody) with tbi 350, sm465, 4.56 14 bolt with 245 tires with the hopes of doing the same things I did with the 84.




For what your doing I would look for a 5 lug 10 bolt with a 3.42 gearing from a 90's 1500. Thats popular enough you should be able to swap axles rather easily/cheap(you may need to fab some brackets).
If this is truck is a old 6 bolt 1/2 ton then an adapter can be used to keep the 6 bolt look or you can run 5 bolt hubs on the front and then run 5bolt rims all around.

Your going to loose a little mileage. But I have ran 3.42 gearing with a 465 and its not that bad. The torque diffrence will be noticable on hills and when you need to pass. You should still be able to slap it into 3rd on the highway and bring it up to 75 to get around a semi before going back into 4th and cruise at 70.
 

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Good story.......and I like Cadillac 500s. Got two 500s and a 472 in the shop and I'm collecting parts to build a couple of them. Had a 33 Ford sedan with an old 365 Cad and 2 4 barrels years ago. Put a 500 in a regal. Smoked the tires but it wouldn't go anywhere. This time I'm doing it right with ported heads, shaft mount rockers and a roller cam. Hoping to get a 32 Ford to put one in. The stock engines were pretty well done by about 4200 rpms due to the rocker arm system and cam plus that low profile intake. Looking to make 500 hp and have a Tremec Magnum in a box to mount behind it. They do however make great truck engines in stock form.
 

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Discussion Starter · #8 ·
I made the joke about the Cowboy Cadilliac because those had 2.7x gearing and even with a 472 or 500 big block would get mileage in the 20's on the highway.

The things were heavy pigs and even with 500ft/lbs of torque were slow as heck acceleration wise. This was mainly due to the gearing. But due to the gearing the engines also were generally run at lower rpm and could reach 300k mileage when other engines of that time were lucky to reach 150k.

I know with a sm465 I can beat the heck out of the thing. Do things like slap it into 3rd at 70mph to pass someone or stuff a 500 ft/lb engine in front of it with no transmission modification. The thing will run with bad bearings, bad seals, low oil, and once back at the house can be rebuilt in a weekend without specially tools.
The 420 is the 465's father and is the nv4500's grandfather. The 3 transmissions share very similar parts and are tough. I consider the 4500 less reliable then the 465 due to the overdrive issues.

I did bolt a sm465 into a rusted 76 Cadilliac back in 98. It was not pretty though. There was a saw all involved with the floor, manual clutch linkage, and the driveshaft extended with a rusted pipe. I was young, broke, and the car was cheap.

The thing was slow. But once I got over 45mph I could just cruise in 3rd using that big blocks torque to pull the car without needing to shift much. Could drop it down to 30mph in 3rd lugging that girl back up to 70 before shifting. Once I got up to highway speeds the thing would cruise. Steering and brakes were on par with a typical land yacht. But the engine was happy going 85mph with the 2.7x gearing.

On the other end of the gearing scale. I had a 84 13,000 lb c30with a 8x12 flatbed. The thing had a smog 350, sm465, and a FF 14 bolt with 4.56 gearing turning 235 tires. I used it for towing and tearing apart forklift trucks for parts/scrap. The things bed was high enough a fork truck could be loaded right off a semi dock in many cases and I cut them up right on the bed to get the electric motors, controlers, etc.

That 350 was only able to move with around 9,000 lbs (somewhat safely) because of that 4.56 gearing. I avoided the highway generally and drove it at 60. I eventually dropped a 383 into the thing around 350hp and was having fun (unloaded at a mere 6,000 with the speedometer needle buried most of the time on the highway getting mileage around lets say 6mpg. Eventually something had to go and in my case it was the rear main at what I would guess was 5000. The engine just locked, shut off, and the clutch slipped before I pulled it over. I bought some 80/90 and poured it in. Drove it to a rest area then drove the thing to the folks house where due to limited space to store the truck at the time I cut it up for parts. I have a video of driving it with the rods threating to come out the side of the block.

Over 10 years later
I bought my recent 89 3500(squarebody) with tbi 350, sm465, 4.56 14 bolt with 245 tires with the hopes of doing the same things I did with the 84.




For what your doing I would look for a 5 lug 10 bolt with a 3.42 gearing from a 90's 1500. Thats popular enough you should be able to swap axles rather easily/cheap(you may need to fab some brackets).
If this is truck is a old 6 bolt 1/2 ton then an adapter can be used to keep the 6 bolt look or you can run 5 bolt hubs on the front and then run 5bolt rims all around.

Your going to loose a little mileage. But I have ran 3.42 gearing with a 465 and its not that bad. The torque diffrence will be noticable on hills and when you need to pass. You should still be able to slap it into 3rd on the highway and bring it up to 75 to get around a semi before going back into 4th and cruise at 70.









i find some 3.42 . im gonna throw them in and will see
 
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