Need highway gearing - The 1947 - Present Chevrolet & GMC Truck Message Board Network

CCCC · 03-11-2007, 06:25 PM

My 1970 C30 Flat Bed with 350 ci and NP 4 speed manual trans runs out great, but the rear gear ratio is high (probably 4:11) and the engine is turning about 3000 rpm at 60 mph. I need to get into a highway ratio and would rather not revise the rear end gears because sometimes I need the low for pulling.

Does anyone know of a good and relatively simple fix – a bolt-in overdrive or speed change unit (manual control is OK) or a 5 or 6 speed trans replacement? Simplest and strongest is best.

All info and ideas will be appreciated.

Paul

dan42 · 03-11-2007, 06:27 PM

There was a thread talking about that yesterday - not sure what it was called but it had some ideas - page back a day or two throught the threads.

regal8r · 03-11-2007, 06:28 PM

if youre doing alot of highway driving, get a 700r4...unless u NEED your 4spd...

BCOWANWHEELS · 03-11-2007, 10:23 PM

the gear vendors overdrive unit bolts to the rear of the sm 465 tranny and will do the trick but its $$$$$$$
bob

**WorkinLonghorn** · 03-11-2007, 10:48 PM

I have about the same situation and have been looking around for a NV4500 5 spd which is at least as strong as the 435 and has a .73 overdrive and has a lower 1st gear. You would be at 2190 RPM at 60 MPH (based on your info above) and have great low pulling power.

snj8198 · 03-11-2007, 11:33 PM

I run an NV4500 in my '71. Excellent trans, i strongly recommend it. I run it hard behind my 496 so it's strong, has a 5.61 1st gear which is not as low as the SM465's 6.55 but atleast it is sycronized. There is an earlier Chevy and Dodge version that ran a 6.34 first gear also. With 33's and 4.11's I run about 2200 RPM at 60mph. I better check that for sure but that sounds pretty close.

CCCC · 03-12-2007, 01:45 PM

Thanks WorkinLonhorn and snj8198. I have not experienced the NV4500 but will start looking right now. Would rather avoid the cost and hassle of an added unit. 2200 rpm at 60 mph might be just about right in this rig and the pulling power would remain. Can you estimate what a guy should pay for a good condition NV4500? And, a good source? Thanks again.
Paul

03-11-2007, 06:25 PM	#1
CCCC Registered User Join Date: Mar 2007 Location: San Pedro River, SE Arizona Posts: 734	Need highway gearing My 1970 C30 Flat Bed with 350 ci and NP 4 speed manual trans runs out great, but the rear gear ratio is high (probably 4:11) and the engine is turning about 3000 rpm at 60 mph. I need to get into a highway ratio and would rather not revise the rear end gears because sometimes I need the low for pulling. Does anyone know of a good and relatively simple fix – a bolt-in overdrive or speed change unit (manual control is OK) or a 5 or 6 speed trans replacement? Simplest and strongest is best. All info and ideas will be appreciated. Paul __________________ CCCC 67 Sting Ray Coupe 327 4sp; 68 K10 Suburban 327 4sp; 69 K20 Lifted 383 4sp; 69 C80 Fire Truck 478 V6 5sp/2sp; 69 C20 Longhorn 327 4sp; 70 C30 Wrecker 350 4sp; 70 C30 Flat Bed 350 4sp; 71 C20 LWB 350 4sp; 72 K5 Blazer 350 4sp; 72 C30 Flat Bed Gooseneck Hauler with sleeper 350/TH400; 72 C20 Longhorn 402 4sp; 52 Mack LTL Supercharged Cummins 5sp x 3sp; 01 Dodge 5.9 HO Cummins 6spd; 02 Safari Trek 2430 8.1 Vortec on Workhorse Chassis; 03 Silverado 2500 HD 4wd Duramax/Allison Moved but still in the family 70 C20 Custom Camper 350/TH350; 72 K5 Blazer CST Highlander 350/TH350 Recently sent to new homes 72 C30 MoHome 402 4sp; 72 K5 Blazer Conv 350 4sp; 75 GMC 6000 Aerial 350 w Allison; 72 GMC 3500 Utility 350 4sp; 70 GMC 3500, 350 4sp

03-11-2007, 06:27 PM	#2
dan42 Registered User Join Date: Feb 2007 Location: Cali Central Coast Posts: 5,191	Re: Need highway gearing There was a thread talking about that yesterday - not sure what it was called but it had some ideas - page back a day or two throught the threads. __________________ '67 SWB Fleetside ZZ4/350/Tremec 5-speed/4link/Scott's IFS - and fun as heck! SOLD Click here to support the board Philippians 4: 6-7

03-11-2007, 06:28 PM	#3
regal8r Registered User Join Date: Oct 2006 Location: Lincoln, Nebraska Posts: 112	Re: Need highway gearing if youre doing alot of highway driving, get a 700r4...unless u NEED your 4spd...

03-11-2007, 10:23 PM	#4
BCOWANWHEELS Registered User Join Date: Nov 2006 Location: KINGSPORT,TN. Posts: 3,035	Re: Need highway gearing the gear vendors overdrive unit bolts to the rear of the sm 465 tranny and will do the trick but its $$$$$$$ bob

03-11-2007, 10:48 PM	#5
WorkinLonghorn Senior Member Join Date: Dec 2006 Location: Studio City, Calif. Posts: 2,865	Re: Need highway gearing I have about the same situation and have been looking around for a NV4500 5 spd which is at least as strong as the 435 and has a .73 overdrive and has a lower 1st gear. You would be at 2190 RPM at 60 MPH (based on your info above) and have great low pulling power. __________________ '69 GMC C2500 Custom Camper, 8 1/2' bed, New GM 350, NP 435 Close Ratio 4spd. Trans., 3.73 Dana-60 open.Camper and Trailer wiring, PS, PB, AC, tach , three gas tanks, 2nd owner, Work-Truck supreme. Best $300 I ever spent.

03-11-2007, 11:33 PM	#6
snj8198 Registered User Join Date: Feb 2007 Location: Star Valley, WY Posts: 2,038	Re: Need highway gearing I run an NV4500 in my '71. Excellent trans, i strongly recommend it. I run it hard behind my 496 so it's strong, has a 5.61 1st gear which is not as low as the SM465's 6.55 but atleast it is sycronized. There is an earlier Chevy and Dodge version that ran a 6.34 first gear also. With 33's and 4.11's I run about 2200 RPM at 60mph. I better check that for sure but that sounds pretty close.

03-12-2007, 01:45 PM	#7
CCCC Registered User Join Date: Mar 2007 Location: San Pedro River, SE Arizona Posts: 734	Re: Need highway gearing Thanks WorkinLonhorn and snj8198. I have not experienced the NV4500 but will start looking right now. Would rather avoid the cost and hassle of an added unit. 2200 rpm at 60 mph might be just about right in this rig and the pulling power would remain. Can you estimate what a guy should pay for a good condition NV4500? And, a good source? Thanks again. Paul __________________ CCCC 67 Sting Ray Coupe 327 4sp; 68 K10 Suburban 327 4sp; 69 K20 Lifted 383 4sp; 69 C80 Fire Truck 478 V6 5sp/2sp; 69 C20 Longhorn 327 4sp; 70 C30 Wrecker 350 4sp; 70 C30 Flat Bed 350 4sp; 71 C20 LWB 350 4sp; 72 K5 Blazer 350 4sp; 72 C30 Flat Bed Gooseneck Hauler with sleeper 350/TH400; 72 C20 Longhorn 402 4sp; 52 Mack LTL Supercharged Cummins 5sp x 3sp; 01 Dodge 5.9 HO Cummins 6spd; 02 Safari Trek 2430 8.1 Vortec on Workhorse Chassis; 03 Silverado 2500 HD 4wd Duramax/Allison Moved but still in the family 70 C20 Custom Camper 350/TH350; 72 K5 Blazer CST Highlander 350/TH350 Recently sent to new homes 72 C30 MoHome 402 4sp; 72 K5 Blazer Conv 350 4sp; 75 GMC 6000 Aerial 350 w Allison; 72 GMC 3500 Utility 350 4sp; 70 GMC 3500, 350 4sp

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