The Stovebolt Site Forums The Parking Lot Big Bolts 1972 c50 sbc 350 m465 single speed rear.....

I'm wanting to reach at least 60mph... at the moment can only do 50 and that's got her spun out but when I have load doing 50mph causes over heating any suggestions on rear ends for hauling loads at at least 60mph because hauling loads at 40mph sucks.... thanks mike

welcome to the site! I am not familiar with the newer trucks, I'm sure someone will come along that is though. First question will be what lug bolt pattern is on it?

10 bolt lug on rear and front but front hub thing only bolts up to five of the 10....

It is a medium duty truck gmvw 26000lbs 14'×8' flat steel dump bed with wood walls converting to grain/dump truck

Correction Gmvw is 24000 lbs and tires are 8.25-20 all the way around

A 72 model was built to run 60 easily. Clean out your radiator and drive her 60 all day long. Your engine was built to cruise in the 3000 range. Not the 2000 RPM range like modern engines.

I did not know they made a C-50 rated at 26,000 GVW, I thought they only went to 24K...

What rear do you have and what's the ratio?

What size tires (front and rear)?

Mike B

correction gmvw is 24000lbs and tires are 8.25-20 all the way around... the rear is a single speed not sure what ratio is... how do u find that out?

Gm 3826111 is printed on the rear end below drive shaft connection does that have anything to do with ratio

Did a Google search for those number and a rear end for sale popped up and says ratio is 6.14

Chock the truck, release the parking brake, put the truck in neutral, jack up the drivers side rear wheels, put matching chalk marks at the driveshaft yoke and housing, also mark the brake drum to the backing plate. Then rotate the wheel and count how many times the drive shaft turns in one revolution of the wheel. Then multiply that number by 2, so if drive shaft turns 3 turns plus about 10% (36*). Multiply 3.10 by 2 = 6.20...the closest rear ratio to 6.20 is the 6.17, so that's what you have...a 6.17 single speed.

Much easier to do than to explain...lol

Mike B

OK got ya I know what u r talking about i actually have done that before but on a 4runner of my buddys totally forgot about that trick

So one rotation of tire gave me 3.6-3.75 turns on drive shaft what would that be

So 7.20 or close to that is my ratio got any info on what I can do to hit 60mph loaded at ummm 2k ish rpm so mpg improves and drive time cuz 40mph max speed loaded ain't cuttin it

3.6 x 2 = 7.20

3.75 x 2 = 7.50

The rear ratio that fits is the Chevrolet 15,000 pound, 7.20 ratio.

If you can find a 6.50/8.85 vacuum shift 2-speed you will gain about 10% or 5-6 mph. This pumpkin should be a direct swap other than the drive shaft may be to long.

Or you can look for a 6.17 single speed and swap pumpkins and gain about 15% or 7-8 mph, but you will loose pulling power when loaded.

As a side note, how often will you be loaded, are you putting this truck back to work?

Mike B

Yeah gonna be loaded most of time and yes trying to get it back to work ...in the past 3 weeks I been tearing it all down to replace clutch and once I dropped Trans and saw how oily everything was I decided to go ahead and pull engine and put new gaskets on it so I got it in pieces now but jus finished cleaning the antique grease off and painted the engine and trans so jus trying to spiff up the inner important parts the outside is a Lil rough around edges but hey is a work truck and the inside is what counts right

How loaded will it be most of the time (GVW)?

Mike B

Well max capacity is 24000lbs and truck non loaded weighs roughly 9000lbs so I'd say 5 tons would be max load carried could do more but not wanting to push it

I don't have a 1972 Truck Data Book, but my 1971 book shows C-50 with the following GVW ratings;

15,000 gvw has 7.50 x 20 8 ply (front and rear) as "Standard".

19,500 gvw has 8.25 x 20 10 ply front, 8.25 x 20 12 ply rear; 8750 pound rear springs.

22,000 gvw has 8.25 x 20 10 ply front, 8.25 x 20 12 ply rear; 7,000 pound front axle with 3.500 pound springs; 10,400 pound rear springs; HD Frame for GVW.

24,000 gvw has 9.00 x 20 10 ply front, 9.00 x 20 12 ply rear; 7,000 pound front axle with 3.500 pound springs; 17,000 pound rear axle; 10,400 pound rear springs; HD Frame for GVW.

Note, the 17,000 pound rear was Cast Wheels only, so your 10 lug rear is only rated at 15,000 which lowers your max gvw to 22,000 if you meet all the other criteria.

Is this an Air Brake truck?

Mike B

Tires are 8.25-20 thread ply:8 sidewall ply:6 load range E and that is all 6 wheels... no air brakes but haven't had much trouble stopping since I changed master cylinder was leaking behind pedal on floor board but has good brakes they are drum all the way around and on transmission brake

Gvw: 16000-24000lbs
Front:5000-7000lbs
Rear:11000-17000lbs
That is on plate inside driver door

With the 8.25 x 20's your not rated at 24,000. Do you know if your truck has the HD front axle and HD rear springs? I'm pretty sure you have the 15,000 pound Chevrolet Rear since you said it has 10 lug rear and 5 lug front.

Count the number of leaves on the front springs (7?) and measure the width (2.5" or 3").

Count the number of leaves on the rear main pack (should be 10 or 11) and measure the spring width (should be 2.5" or 3").

Also measure the frame from top to bottom right behind the cab at it's tallest area and give me that info as well.

With that info I should be able to help zero in on your real GVW rating.

Mike B

Front 7leafs Rear 14leafs and one spaced above stack on rear 2.5" front and rear width

Frame height behind cab is 9"

I need more info to ID the front axle...do you have 14" or 15" brake drums on the front? The 14" came on the 5000 pound axle and the 15" came on the 7000 pound axle.

Recount the rear springs, the Main pack should have 10 or 11 leaves unless someone added leaves...

Measuer the frame exactly, the Std frame is 9-1/8" and the HD is 9-1/4".

Mike B

OK front axle has 959022gm printed if that helps I.d and 15" drums.... frame is 9 3/16" exactly had to get a tape was using a small rusty square before....and rear leafs go like this from bottom to top. Short one longer one, short again long longer longer longer longer longer longer longer longer longer, spacer then like a backup leaf so total 14 leafs hope that helps but only way I could explain it with out pics

The Standard issue front axle rated at 5000 pounds had 14 x 2.5 brake drums, the optional 7000 axle has 15 x 3 drums.

The third leaf down from the top of the Main Spring pack will have turned down ends that hook the hanger pins. The bottom leaf has an eye and is pined to the front hanger, this is used to locate the springs and is called a radius rod or torque arm.

The Main Springs are just the springs that go through the frame hangers. The Aux Springs are on top of the Main and they contact frame brackets when the truck is loaded. So, I'm betting you have 10 Main and 4 Aux Springs...

How wide are the springs??? 2.5" or 3" ???

Also, look at the axle casting number again, you're missing a number I think...should start with a 2 or 3 and be seven digits.

Mike B

i scrubbed with alcohol and nylon brisol brush is its all down to clean metal now and there is still only 959022gm31 the 31 at end was covered but its clean now and only 6 digits before gm... springs are 2.5" wide... and brake drums are 15"x3"

OK, so 51x3 front brakes with 2-1/2" springs tells me you have the 7000 front axle.

We already figured you have the 15,000 Chevrolet Rear axle so your max GVW is 22,000 pounds.

"22,000 gvw has 8.25 x 20 10 ply front, 8.25 x 20 12 ply rear; 7,000 pound front axle with 3.500 pound springs; 10,400 pound rear springs; HD Frame for GVW."

Seems to me there sould be a plate on the truck stating the max GVW is 22,000 pounds, otherwise how would the DOT guy know what the truck is rated at?

Mike B

OK thanks for all that info idk if I ever would have known that so 22000lbs is maxed out I'll be sure to write that down sum where... why would dot need to see plate I have insurance and stuff for it already insured as farm truck and I jus told them the rating on the plate as it is they told me I could either put a F plate or H plate depending on what I'm hauling and from the difference in price of F and H plates I got F plate haha

Ok so I'm back and had sum more questions regarding the single speed and 2-speed rears for speed issues.... got the motor rebuilt and everything working as it should only problem I have now is only being able to drive 50mph loaded at 3000rpm

I have the 7.20 single speed and 4 speed trans and really all I want to do is be able to hit 60mph at 3000rpm or below anyone have ideas on this I read the two speeds give more low end and no top end would this be true with my 7.20 ratio cuz I feel like my ratio is really low geared

the 2-speed in my 58 2-ton has 6.4 and 8.75 ratios. I have 9r-22.5 tires and an SM420 (predecessor to your SM465) I am spinning ~3600 to go 60 down the freeway and 4200 to go 70. Not sure what the newer 2-speed ratios are or what tires you are running but the 2-speed may get you a little more speed per RPM.

Hmm so u have actually ran ur engine to 4000rpm to hit 70 I feel like she would be be literally anialating the fuel at that rpm lol and would over heat am I jus trying baby my engine haha cuz I try not to run it over 3000 rpm and had sum overheating issues fully loaded doing 50mph at 3k rpm

Mind u I was doing 50mph at 3k rpm for about 15 miles

So have got more time to play with projects and have found more resources for the 2 speed rear end swap out idea I had but jus don't know exactly what i want for the speed/power deal cuz what I'm shooting for is to be able to do at least 60mph highway top end while still being able to move 20,000lbs up hill low end wise and I thought a 2 speed rear would help me out with that maybe cuz right now I have a single speed 7.20 gearing with 8.25-20 tires.... And one question I have if I swapped tires to 9-20 tires would that give me anymore speed top end?

We used bob tails to deliver gasoline until the mid 70's. The engines reached their rated HP at 4200 to 4400 RPM. They were happy at that speed as long as we had a good cooling system. But they guzzle gas. That is the nature of the beast. We didn't expect over 5 miles to the gallon. My first semi was a V8 gas burner. I never let it get under 3800 and it was the happiest at 4200. Grossing 72,000 I got less than 2 miles per gallon. My line haul trucks now have 10.6 liter Cummins that cruise at 1500 RPM and get a little over 6 miles to the gallon grossing 84,000. Don't expect to approach modern performance and modern fuel economy with 45 year old engineering.

Measure the OD of both tires, if the 9 inchers are, say 10% larger, then they will get you 10% more speed at the same RPM, IF your engine can pull it.

Ed

yes, 4200 RPM to hit 70mph. I get between 8 and 9mpg, depends on the kind of driving I am doing. I think 60 sucks less than 70! (weighs almost 9K empty). I pulled my 35' travel trailer a to a vintage trailer rally in September (fairly flat, just up I-5) and got 7.9 mpg. I kept it around 60 with the trailer on. (trailer weighs a little over 6K).

If you put a 2-speed rear in it, it gives you more gears but no more top end. You would have to go with an overdrive, different rear end ratio, or taller tires to get more speed. The latter 2 may make you unhappy pulling any weight as you may have fun getting it rolling and then not be able to find the right gear pulling a hill, even a slight one!

As stated before, clean your cooling system out real well (have your radiator rodded out, or replace it) and you should be fine running 60 MPH.

Well my truck will not run 60 no matter what rpm it's revs out at 53ish the rear end will not let it go any faster then 53 unless I'm going down hill with clutch in loaded that why im.wondrring if I swapped the tires to 9-20s if that would put my top end at 60 with my rear end. 53mph at 3200rpm is all my rear end will allow me to do unless gravity is on my side