Will this engine/tranny combo work ok? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Brad · 05-05-2003, 02:42 AM

I'm getting ready to do the LWB-SWB swap and when I do, I think I'm going to swap out my 3 speed for a 4 speed NP435 and go back to 3.07 in the rearend. I've included my final drive calculations and gear reduction for the swap and want to know what you all think.

Here are the gear ratios for the SM-318 3-speed, the SM-420 and NP-435-GA 4-speed transmissions.
Trans 1st 2nd 3rd 4th Rev
SM-318 2.94:1 1.68:1 1.00:1 ~-~ 2.94:1
SM-420 7.06:1 3.58:1 1.71:1 1.00:1 6.78:1
NP-435-GA 4.56:1 2.28:1 1.31:1 1.00:1 5.64:1

- (my percentages don't seem to match up in this post, but you get the idea)

SM318 --- 10.97 6.27 3.73
\ / \ /
57% 59%

NP435 ---- 14.00 7.00 4.02 3.07
\ / \ / \ /
50% 57% 76%

Also, see this related post:
Will NP435 work with 1 piece driveshaft

crazy longhorn · 05-05-2003, 08:34 AM

14 to 1 is a tad low, but it should work for you. My longhorn multiplies out at 13.4 in 1st (3.28 1st x 4.10 rear gears). In stop/ go traffic, first only needs to roll 10 ft ....then grab 2nd! IMO, around 12 to 1 multiplication in 1st is about right. You wont need to worry about slipping the clutch on takeoff tho.....

As far as the shaft, Im not familiar with the NP435 trans. If it has a slipyolk at the back of the trans, you should be able to go 1 pc on the shaft on the shortbed truck....shaft lenght needs to be keeped @ 6 ' or under C to C on the caps. if no slip yolk, you might talk with driveline service about building a slip/slide(like the rear shaft in a 4wd). Good luck,crazyL

Brad · 05-05-2003, 12:36 PM

No, it doesn't have the slipyoke - I guess that's really what I was wondering about. I still have my 2 piece shaft, and I'm wondering if that would work. Does anyone have a pic of this slipyoke thingy off a 4x4??? Would it basically just be a slipyoke that bolts to U-joints?

Now that you mention it, that 14 to 1 would be low, but great for burnouts with the six,

Thanks, this is what I'm looking for - things that I might otherwise overlook.

crazy longhorn · 05-05-2003, 01:08 PM

Yes, the front end of the d shaft will be splined, & have a slip yolk ,that works on the shaft as opposed to in the trans. The u joint then just bolts to the back of the trans. Sorry, I dont have a pic tho...... crazyL

05-05-2003, 02:42 AM	#1
Brad Out of the carpool lane. Join Date: Jan 2000 Location: Clark Co, WA Posts: 5,672	Will this engine/tranny combo work ok? I'm getting ready to do the LWB-SWB swap and when I do, I think I'm going to swap out my 3 speed for a 4 speed NP435 and go back to 3.07 in the rearend. I've included my final drive calculations and gear reduction for the swap and want to know what you all think. Here are the gear ratios for the SM-318 3-speed, the SM-420 and NP-435-GA 4-speed transmissions. Trans 1st 2nd 3rd 4th Rev SM-318 2.94:1 1.68:1 1.00:1 ~-~ 2.94:1 SM-420 7.06:1 3.58:1 1.71:1 1.00:1 6.78:1 NP-435-GA 4.56:1 2.28:1 1.31:1 1.00:1 5.64:1 - (my percentages don't seem to match up in this post, but you get the idea) SM318 --- 10.97 6.27 3.73 \ / \ / 57% 59% NP435 ---- 14.00 7.00 4.02 3.07 \ / \ / \ / 50% 57% 76% Also, see this related post: Will NP435 work with 1 piece driveshaft __________________ 1968 C-10 SWB, 5.7 Vortec/700R4/3.73 posi, Torch Red 1968 Camaro, 250/Powerglide, all original (No, I'm not gonna drop a 350 in it!...Jeez!) 2000 Honda VFR in the faster yellow! 2008 Husqvarna TE-610 1967 C-10 SWB 'Six Appeal'-Gone but not forgotten... Last edited by Brad; 05-05-2003 at 02:45 AM.

05-05-2003, 08:34 AM	#2
crazy longhorn Fabricate till you "puke" Join Date: Jun 2002 Location: Ill Posts: 9,402	14 to 1 is a tad low, but it should work for you. My longhorn multiplies out at 13.4 in 1st (3.28 1st x 4.10 rear gears). In stop/ go traffic, first only needs to roll 10 ft ....then grab 2nd! IMO, around 12 to 1 multiplication in 1st is about right. You wont need to worry about slipping the clutch on takeoff tho..... As far as the shaft, Im not familiar with the NP435 trans. If it has a slipyolk at the back of the trans, you should be able to go 1 pc on the shaft on the shortbed truck....shaft lenght needs to be keeped @ 6 ' or under C to C on the caps. if no slip yolk, you might talk with driveline service about building a slip/slide(like the rear shaft in a 4wd). Good luck,crazyL __________________ 69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears.... Last edited by crazy longhorn; 05-05-2003 at 08:52 AM.

05-05-2003, 12:36 PM	#3
Brad Out of the carpool lane. Join Date: Jan 2000 Location: Clark Co, WA Posts: 5,672	No, it doesn't have the slipyoke - I guess that's really what I was wondering about. I still have my 2 piece shaft, and I'm wondering if that would work. Does anyone have a pic of this slipyoke thingy off a 4x4??? Would it basically just be a slipyoke that bolts to U-joints? Now that you mention it, that 14 to 1 would be low, but great for burnouts with the six, Thanks, this is what I'm looking for - things that I might otherwise overlook. __________________ 1968 C-10 SWB, 5.7 Vortec/700R4/3.73 posi, Torch Red 1968 Camaro, 250/Powerglide, all original (No, I'm not gonna drop a 350 in it!...Jeez!) 2000 Honda VFR in the faster yellow! 2008 Husqvarna TE-610 1967 C-10 SWB 'Six Appeal'-Gone but not forgotten...

05-05-2003, 01:08 PM	#4
crazy longhorn Fabricate till you "puke" Join Date: Jun 2002 Location: Ill Posts: 9,402	Yes, the front end of the d shaft will be splined, & have a slip yolk ,that works on the shaft as opposed to in the trans. The u joint then just bolts to the back of the trans. Sorry, I dont have a pic tho...... crazyL __________________ 69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears....



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