Help with gear transmission advice

[Frank M. Hardcastle II]

I am new to this board and have searched other posts for advice. I just purchased a 1984 GMC 3500 4dr. dually with 48,000 verified miles. It came with a huge camper and other electronic devices I'm unfamiliar with. I have removed the camper but have trouble with the transmission and gearing. I can't find anyone including the dealer to tell me anything about the transmission and rear end. It has a 6.2L with a Banks Turbo. The transmission is a 4 speed manual. It has a compound low in the upper left position with 1st gear in the lower left, 2nd upper right and 3rd lower right. I have been searching the internet and think it may be something referred to as a SM465. I have no way of confirming this as I can't find anyone to decipher the VIN. I have been told that the rear end will have a small tag of some sort attached to a bolt that will have some sort of encripted number identifying the gear ratio. I can't find it. While driving this truck back from South Dakota where I bought it I felt like I was going to blow up the engine at 65 MPH. The tachometer showed about 3200 RPM's. At 70 MPH it is about 3500 RPM's. I shift out of 1st into 2nd at 15 MPH. Out of 2nd into 3rd at 25 MPH. Can anyone help me with this delima. I have been told that if I change the rear gear ratio I will benifit by about 500 RPM's. I've also been told that I need to change the transmission to a NV4500 5 speed. these are not inexspensive modifications for me and will take some time. From what I read here my RPM's at cruising speed need to be near the 1800 mark.

[moody]

Post your Vin . Someone may be able to tell you what it was built with.

[schoitmike]

I just posted about the same thing but my new rig has an auto tranny, im afraid to drive it over 55mph because the engine is screaming. It is very likely we have 4:10 gearing, and 3500rpm seems real high for a diesel, most I know red line at 2800, these may be diffferent but I dont know.
your truck sounds like a truck I almost got, If you ever think of selling in the futre let me know.
Did your truck have an owners manual? there may be some engine data there, if so will you post it, Ive been searching the net for days and no tech info.
thanks and good luck,
mike.

[DmaxMaverick]

Both of you have direct (1:1, no OD) for high gear. Unless you are running really small tires, your rear gear ratio could be 4.56:1, especially if they are CUCV's. Check the rear gear ratio yourself, and don't trust any markings or RPO's you find. The gears may have been changed at some time.

If you have an open diff or loose limited slip, raise one wheel and rotate it exactly 1 rotation. Count the turns of the drive shaft (tranny out of gear or P, E-brake off). The driveshaft will turn exactly 1/2 the actual ratio. A 4.10 will a little more than 2 turns, and a 4.56 will turn 2-1/4 turns. If you have a locker or tight limited slip, you will have to raise both wheels (they will turn at the same rate, in the same direction), and the shaft turns will exactly match the ratio.

Another option is to remove the rear end cover and count the gear teeth on the ring an pinion. Divide the ring gear teeth by the pinion teeth for the ratio.

[HammerWerf]

Frank,

From you description, The tranny may be the SM-465. I have on in my 84 C20. Good tranny, generally sounds like it is chewing on rocks when in neutral and the clutch engaged. Chevy put that tranny in everything up to the C-60's. Visual from under truck, 2 PTO plates, and a total length of about 12 inches.

Given that you have a c-30, rear gear most likely will be a 4:10 . Like DmaxMav said, you could have a 4:56 back there, I think it was an option in those trucks. Rear axle is probably a Dana-70. Cover has 10 bolts and is a full floater.

HammerWerf

[thejunkman2005]

Ok, I might be wrong here. But chevy used the SM465 tranny for everything from big to small for years! The 1/2 ton trucks got them, and few C60s got them also. It's the grand daddy of all standard transmissions, and will take more than you can imagine to break it. It does not have OD, but otherwise has great gear ratios. Top of the line tranny right there.

Now, for rear gear ratio.. That's a little trickier.

Now, in the early years, chevy put a tag on the glovebox with the gear ratio, right there, rear simple to read, no prob. Just open the glove box, and look for a sticker with all the trucks options.

Now, in the later years chevy changed that tag over to codes that you can no longer decipher with ease.

If you have the second style tag you have another option for checking gear ratio.

Jack up one rear tire, mark the tire with soapstone on the bottom, then mark the driveshaft directly towards you. Turn the tire one complete turn counting how many times the driveshaft goes around. Then simply multiply that times 2, and you have your gear ratio.. Simple enough?
Standard
If the driveshaft goes around 1 and 3/4 times, you probably have 3.73s
if the driveshaft goes around 2 times, you have 4.10s
if the driveshaft goes around 2 and 1/4 times, you have 4.56s.

I do this all the time, as I'm trying to find a good set of 3.73s for my future dump truck which will be powered by a 6.2 diesel.

Most 1ton trucks will run 4.10s, or 4.56s. My buddies 1ton 3+3 dually 454 auto runs 3.73s! Which is pretty amazing for that big of a truck.

Good luck,
Len

[thejunkman2005]

Oh yeah, and swapping to an NV4500 is a VERY expensive venture. Expect the price tag to run 2k unless you have a lot of friends in good places.

And for the rear axle. If you have wide width duallies, you'll have a D70, super strong, and really nice.

If you have a Narrow width dually, you'll have a Corp 14b. Which is also a super strong rear axle. If you don't have duallies at all, you'd still have the corp 14b.

Len

[Frank M. Hardcastle II]

Post your Vin . Someone may be able to tell you what it was built with.

Moody,
"Post your Vin . Someone may be able to tell you what it was built with."

Great Idea. There seems to be a wealth of knowledge here that is absent at my local GMC dealer.

Thanks Moody.

1GTHC33J9ES525960

[Frank M. Hardcastle II]

schoitmike,
"I

[Frank M. Hardcastle II]

DmaxMaverick,
"Both of you have direct (1:1, no OD) for high gear. Unless you are running really small tires, your rear gear ratio could be 4.56:1, especially if they are CUCV's. "

What is a CUCV?

"Check the rear gear ratio yourself, and don't trust any markings or RPO's you find."

What is an RPO?

"If you have an open diff or loose limited slip, raise one wheel and rotate it exactly 1 rotation. Count the turns of the drive shaft (tranny out of gear or P, E-brake off). The driveshaft will turn exactly 1/2 the actual ratio. A 4.10 will a little more than 2 turns, and a 4.56 will turn 2-1/4 turns. If you have a locker or tight limited slip, you will have to raise both wheels (they will turn at the same rate, in the same direction), and the shaft turns will exactly match the ratio. Another option is to remove the rear end cover and count the gear teeth on the ring and pinion. Divide the ring gear teeth by the pinion teeth for the ratio."

Thanks, I have never had that explained before. I

[Frank M. Hardcastle II]

HammerWerf,
"From you description, The tranny may be the SM-465. I have on in my 84 C20. Good tranny, generally sounds like it is chewing on rocks when in neutral and the clutch engaged."

Thanks HammerWerf, now I know that it

[Frank M. Hardcastle II]

Thejunkman2005,
"great gear ratios. "

Do you think I could benefit by going to a 3:42 rear end?

"Top of the line tranny right there. Now, for rear gear ratio.. That's a little trickier. Now, in the early years, chevy put a tag on the glovebox with the gear ratio, right there, rear simple to read, no prob. Just open the glove box, and look for a sticker with all the trucks options."

I checked there and could not find anything with that information on it. I also checked the drivers door and radiator housing. Drivers door was tire pressures and GVWR nothing on the radiator housing.

"Jack up one rear tire, mark the tire with soapstone on the bottom, then mark the driveshaft directly towards you. Turn the tire one complete turn counting how many times the driveshaft goes around. Then simply multiply that times 2, and you have your gear ratio.. Simple enough?
Standard
If the driveshaft goes around 1 and 3/4 times, you probably have 3.73s
if the driveshaft goes around 2 times, you have 4.10s
if the driveshaft goes around 2 and 1/4 times, you have 4.56s.
I do this all the time, as I'm trying to find a good set of 3.73s for my future dump truck which will be powered by a 6.2 diesel. Most 1ton trucks will run 4.10s, or 4.56s. My buddies 1ton 3+3 dually 454 auto runs 3.73s! Which is pretty amazing for that big of a truck."

Do you think that a 3:42 or 3:73 will work well with my 4 speed w/o OD?

"If you have wide width duallies, you'll have a D70, super strong, and really nice."

I have the wide dually with the regular truck bed
Thanks Len
Frank

[DmaxMaverick]

[quote=Frank M. Hardcastle II]DmaxMaverick,
"Both of you have direct (1:1, no OD) for high gear. Unless you are running really small tires, your rear gear ratio could be 4.56:1, especially if they are CUCV's. "

What is a CUCV?

"Check the rear gear ratio yourself, and don't trust any markings or RPO's you find."

What is an RPO?

"If you have an open diff or loose limited slip, raise one wheel and rotate it exactly 1 rotation. Count the turns of the drive shaft (tranny out of gear or P, E-brake off). The driveshaft will turn exactly 1/2 the actual ratio. A 4.10 will a little more than 2 turns, and a 4.56 will turn 2-1/4 turns. If you have a locker or tight limited slip, you will have to raise both wheels (they will turn at the same rate, in the same direction), and the shaft turns will exactly match the ratio. Another option is to remove the rear end cover and count the gear teeth on the ring and pinion. Divide the ring gear teeth by the pinion teeth for the ratio."

Thanks, I have never had that explained before. I

[HammerWerf]

Frank,

To answer you question about the redline. On these engines, it is around 3500 - 3600 rpm. Detroit Diesel likes to build high speed engines. Cummins redlines around 2800 rpm. Not sure about the Ford, but I don't think it is nearly as high as the GM.

DmaxMav is right, these engines will run at the governer all day.

HammerWerf

[Frank M. Hardcastle II]

Frank,

To answer you question about the redline. On these engines, it is around 3500 - 3600 rpm. Detroit Diesel likes to build high speed engines. Cummins redlines around 2800 rpm. Not sure about the Ford, but I don't think it is nearly as high as the GM.

DmaxMav is right, these engines will run at the governer all day.

HammerWerf

3500-3600. Looks like I've been at redline on more than one occassion.
Governor? Do all 6.2L's have governors? I haven't hit it yet. If it does have one I'll feel much better about the RPM's I've seen. Perhaps too much damage hasn't occurred.

[arveetek]

3500-3600. Looks like I've been at redline on more than one occassion.
Governor? Do all 6.2L's have governors? I haven't hit it yet. If it does have one I'll feel much better about the RPM's I've seen. Perhaps too much damage hasn't occurred.

Yes, all 6.2L's have governors. You can't damage the engine by running down the highway too fast. The only way to damage the engine from high rpm is by trying to hold the truck back by means of engine braking when coming down a mountain, but that would be hard to do.

You can hit the governor in these engines, but it sounds like you're about to push the pistons out of the heads! But it doesn't hurt anything, it just sounds bad. Next time you drive the truck, just push the throttle all the way down when in third gear, and it'll rev up and all of a sudden stop accelerating and hold a steady high rpm. Then you can shift into 4th. It's a funny feeling.

When my engine was still n/a, I used to run up to the governor in each gear before shifting when towing large loads. Now with the turbo and other mods, it has enough torque that it likes to shift much sooner.

Casey

[HammerWerf]

Frank,

My expirence of " hitting the Govenor " was that it defueled the engine, and the engine acted as a brake. I went from smoke & howl to decelerating rapidly in a moment.

the 3500 rpm is the factory set speed for the engine. There is a video on this site showing a gentleman in the Netherlands sled pulling with a Massy-Fergeson tractor that has a 6.2l turbocharged twin injector pump for an engine. He runs the engine up to about 5000 rpm in the pulls. really something to watch, especially when you see a full size volvo(?) front loader not be able to pull the sled as far.

HammerWerf

[Frank M. Hardcastle II]

Frank,

My expirence of " hitting the Govenor " was that it defueled the engine, and the engine acted as a brake. I went from smoke & howl to decelerating rapidly in a moment.

the 3500 rpm is the factory set speed for the engine. There is a video on this site showing a gentleman in the Netherlands sled pulling with a Massy-Fergeson tractor that has a 6.2l turbocharged twin injector pump for an engine. He runs the engine up to about 5000 rpm in the pulls. really something to watch, especially when you see a full size volvo(?) front loader not be able to pull the sled as far.

HammerWerf Is this engine really indestructable? I'm begining to think I may need to start a collection of 6.2L's and Banks Turbo Chargers. I'll need one for my K1200LTC motorcycle, one for my wife's Toyota Camry and one for the family G20 van. Hey, if Boss Hoss can put a 500 ci V-8 on a motorcycle why can't I put a diesel on one? The information avaible from the posters of this board is great. I didn't think I could find a group as helpful as BMWLT.net but after getting all this advice so quickly I find I was mistaken. You guys are great.
Thanks

[HammerWerf]

indestructable? No.

A number of issues to be aware of.

Prior to using the search function, Go to bottom of page and expand the range of dates it will search through.

Keep the cooling system clean. Overheating is an enemy of any engine. Head gasket is vulnerable to overheating.

The engine Dampener (harmonic balancer) needs to be monitored when the miles start getting high ( say >95,000). The rubber shear ring can harden, soften, bulge, or anything else it feels like. Cranks have been broken after this gets out of phase.

The main web area ( crankshaft's home). This area is a known weak zone. Some blocks are more delicate than others. Cracks can penetrate into the coolant jacket. Several fixes are being tried at the moment. Jury still out on the fixes. AM General (Hummer) ownes the engine now, and has instituted multiple changes to improve the block.

Cylinders 7 & 8 can be galled when failure involves high exhaust gas temperature. Heat management is very important in these engines.

Look for a posting by ronniejoe. He has a 3 part article, in his signature line, that describes the failure and rebuild of the motor in his suburban.
The articles that are available to the members are always full of info that helps keep thing running

HammerWerf

[Frank M. Hardcastle II]

Well I found some numbers but don't know what they mean.
On the differential casing.

082
70HD
C37453

Anyone have any idea what that means?

[HammerWerf]

Frank,
The 082 indicated the axle was manufactured in 1982

the 70HD is the axle is the Dana model 70 heavy duty. Really good axle.

The other numbers you found I don't recognize right off hand.

HammerWerf

[HammerWerf]

Frank,

The other numbers I did not recognize, I think is the "Bill of Material" number. This number is important as the way of identifying the parts that will fit that axle. Apparently, not all parts fit all axles.

HammerWerf

[Frank M. Hardcastle II]

Frank,

The other numbers I did not recognize, I think is the "Bill of Material" number. This number is important as the way of identifying the parts that will fit that axle. Apparently, not all parts fit all axles.

HammerWerf

Thanks Guys! I found the gear ratio. I feel like such an idiot. I've looked at all the descriptive stickers I could find. Drivers door, glove box, under the hood on the wheel well and radiator support(?) at least 3 times now. I must be going blind or something. Found it on the drivers wheel well under the hood. 4.56. I found a ratio calculator on the net that shows at 3200 r.p.m.'s I would be traveling about 65 m.p.h. with a 4.56 rear end ratio. Well thats what my speedometer shows. Now I know. Next question is how much farther do I want to go? I don't want to lose too much power but sure would like to be in that 1800 r.p.m. area for maximum fuel mileage. I was thinking about 3.73 or 3.42. A local gear shop said they could change out the gear for $650 if I only moved up one step (4.11?). The caculator I found indicates only a 7 m.p.h. increase at the same 3200 r.p.m. I'd really like to increase my top speed to 90+ m.p.h. but don't know how this will impact my SM465 4 speed Muncie with Granny Low. I'd still like to be able to take off from a stop without using granny low every time.

[DmaxMaverick]

The ONLY way you are going to be able to get your RPM's below 2K at 65 is:

Increase gear ratio to 3.42/3.73 with an OD 5 or 6 speed or the gear change with oversize tires. A 5 speed OD will lose the granny low.

Increase gear ratio to 4.11 with OD tranny and oversize tires.

You can play with the combinations, and adding an aux. OD gearbox will increase your chances of getting into the RPM range you want. Also, oversize tires, while they do increase your final drive ratio, have more parasitic loss than gears, requiring more power/fuel to turn them.

[arveetek]

I don't want to lose too much power but sure would like to be in that 1800 r.p.m. area for maximum fuel mileage. I was thinking about 3.73 or 3.42. A local gear shop said they could change out the gear for $650 if I only moved up one step (4.11?). The caculator I found indicates only a 7 m.p.h. increase at the same 3200 r.p.m. I'd really like to increase my top speed to 90+ m.p.h. but don't know how this will impact my SM465 4 speed Muncie with Granny Low. I'd still like to be able to take off from a stop without using granny low every time.

My suggestion would be to go the 4.11 gears and install an overdrive transmission. That would give you better cruising rpm and still keep the power level there. I'm really happy with my 4.10 gears, 30" tires, and overdrive tranny. It's a good combination for power and highway driving.

Casey