old granney 4spd chevy behind a 6bt?

[Deere Jon]

I am planning a conversion into an 82 Chevy 3/4 ton 4x4. The truck has the old granny 4spd manual trans, bullet proof but lacks an overdrive. The truck has a 3. 73 rear end, will I be happy with this setup or not? The truck currently has a blown 6. 2 and I don't know how many rpms the engine ran going down the road at 70 mph. Thanks Jon

 

[clinebarger]

depends on how tall your tires are. i think you whould be happier with a NV4500/5600

 

[TKingsbury]

My truck with stock gearing (3. 54), tires, and pump adjustments will do almost 70 mph wide open in 4th gear. I don't think you'd like it.

Travis. .

 

[mjendrejcak]

you could probaly get a rough guess on RPMs use the calc at this site



http://www.4lo.com/calc/gearratio.htm

 

[DKarvwnaris]

I am planning a conversion into an 82 Chevy 3/4 ton 4x4. The truck has the old granny 4spd manual trans, bullet proof but lacks an overdrive. The truck has a 3. 73 rear end, will I be happy with this setup or not? The truck currently has a blown 6. 2 and I don't know how many rpms the engine ran going down the road at 70 mph. Thanks Jon

One of the reasons the bread trucks with these transmissiona are so slow is the gearing of the rear ends. Most are 3. 42 ratio and its still not very pleasant to get on to the interstates with. Typical tire size on the bread trucks are 235/85/16r's.

If you're planning a 4bt conversion, you could regear to 3. 42's or even better, 3. 08's. The only other solution would be 32" or 33" tires and live with the high rpm's. Fuel mileage will suffer though.

If you're planning a 6bt repower, you had best rethink your opinion of the "old granny 4spd manual trans" being bulletproof. The input shafts on these transmissions are much smaller than the nv-4500's they will break and even twist off if you push a 5. 9 very hard or turn it up. (its only as strong as its weakest link). The other inferior component you're going to have with a 5. 9 conversion running the GM transmission is the clutch/ flywheel. It is considerably smaller than the Dodge flywheel and clutch assembly which equates to less friction to transfer the power to the transmission. A dodge clutch has enough problems holding up to the 5. 9 at full power with a load behind it, 4bt bread trucks even have issues with the GM clutches lasting. The only advantage to the GM clutch is it's cheap to replace, so long as the flywheel doesn't get scorched or glazed over. The GM flywheel is over $700. 00 last I priced one. One of the reasons I am set on the Dodge bellhousing adapters and transmissions.

 

[Deere Jon]

Thanks men for the honnest repies. I will pas on the 4spd.

 

[JLEONARD]

Well they used to put that transmission behind the old 292 6cyl gasser (assuming it's the same transmission from the late 60's). That was a very low rpm engine similar to the Cummins in that of aspect.

I ran one for a lot of years that was pretty hopped up and it never hurt the transmission.

No idea what the rear end ratio was though.

Jay

 

[DKarvwnaris]

Well they used to put that transmission behind the old 292 6cyl gasser (assuming it's the same transmission from the late 60's). That was a very low rpm engine similar to the Cummins in that of aspect.

I ran one for a lot of years that was pretty hopped up and it never hurt the transmission.

No idea what the rear end ratio was though.

Jay

Most of the vehicles with that engine and transmission were running 3. 08, 3. 42, and possibly a 4wd optioned 3. 73 rear end for towing/ camping specials. I remember a 2. 73 ish gearing option in a few of the mid 70's 2wd GM trucks. The torque of a gas 6 cylinder is still not much compared to the mass of the b series cranks and flywheels, its just not the same to really compare them.

These transmissions are very strong and durable, but that is also within their designed and rated applications. I ran one for over 200,000 miles in my old farm truck that my grandfather once owned, the case was never opened up and the truck was treated more like a tractor than a pickup truck. The granny low was a real stump puller in it, but it could not get up to interstate speeds with its old straight six engine in it, which turned about 500 rpms above the average governed b series if I remember right. (That truck had 3. 42 gears in it)

Even as a young farm boy, I knew the truck did not like 65 mph, it was groaning to hold at 60 as it was. We all drive faster than that nowadays, that's just the reality of the curreny rat race life we live.

 

[JUeckert]

jon. other than having the handi cap of higher rpms at highway speeds,i wouldnt worry about the durability of the 4spd holding up behind a[ stock 6bt]. i have the same setup that you are describeing,but my 6. 2 has a banks turbo on it. the entire drivetrain has over 375k on it,10k on the new engine. those were some very hard working miles,with a lot of abuse. i know of many 4spd trannys in 1 tons with modded 454 engines,they are holding very well. round my parts,its a very common transmission to use in 4wd mud trucks,some of these boys run some very high power 454 [expensive] engines. lastly,there is also a local heavy equipment mechanic i have used over the years,he has a 83 model chevy service truck with a 4spd and 3. 42 gears,he has been running a 6bt in it since the late 80's,no probs. a 4500 transmission would be a more pratical choice.