3 speed manual to 4 speed manual? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Blue_71 · 03-19-2003, 09:15 PM

what all do i need to do this? the parts i have are:
all clutch linkages and new clutch/pressure plate
high hump
column converted to 4 speed (did that when i put the 3 speed in the floor)
4 speed shifter

will my 3 speed driveshaft and cross member work? the cross members look identical to me, but i think the driveshaft is going to be too short

**CPNE** · 03-19-2003, 09:38 PM

The xmember should be find because it bolts to the bell housing. The 3 speed has a slip yolk whereas a truck 4 speed does not. You will have to change driveshafts. Beware, a 3/4 ton DS won't fit a 1/2 ton due to rear end differences. There are also different carrier bearings to consider as well. It's easier to go from 3 speed to auto than to 4 speed because of this.

If this is a car 4 speed, then it's a different story altogether.

Blue_71 · 03-19-2003, 09:44 PM

it's an SM465, i was looking and it looks like the yolk can be changed, but the 3 speed seemed longer, so i didnt think it owuld work... how hard is it to find a SM465/v8 half ton driveshaft front half?

**CPNE** · 03-19-2003, 09:53 PM

There are a lot of factors here, carrier bearing mount and location being a big consideration. If it were me, I'd see about having your existing front driveshaft modified rather than trying to locate the correct setup. Fast68 went thru this a year or so ago and never had any success locating the correct setup for what it's worth

Blue_71 · 03-19-2003, 09:58 PM

when i measured the 3 speed seemed 5 inches longer, any idea what it would cost to have a driveshaft lengthened that much? i'll call tomarow to get an excact quote.. it looks to me like i can take the yolk off the drivehsft, and then bolt the 4 speed to it with the little "u" clip things it connects with

03-19-2003, 09:38 PM	#2
CPNE Resident Curmudgeon Join Date: Dec 1999 Location: NH Posts: 6,664	The xmember should be find because it bolts to the bell housing. The 3 speed has a slip yolk whereas a truck 4 speed does not. You will have to change driveshafts. Beware, a 3/4 ton DS won't fit a 1/2 ton due to rear end differences. There are also different carrier bearings to consider as well. It's easier to go from 3 speed to auto than to 4 speed because of this. If this is a car 4 speed, then it's a different story altogether. __________________ Currently on or near the homestead: 67 Chevy SWB 2WD stepside 350/3 on tree (Pat's) 67 GMC SWB 2WD Fleet 402/auto (Brian's under construction) 67 Chevy 3/4 ton 2WD 402/auto (Business Hauler) 67 Chevy 1 ton dually 2WD 396/4 speed (Former business hauler, Needs TLC) 68 Chevy 1/2 ton Suburban 2WD 250 six/3 on tree (Brian's Needs TLC) 70 Chevy 3/4 ton 4WD 350/4 speed (Pat's - Disguised as a 68 GMC) 71 Chevy SWB stepside (Crushed by tree - parts donor) 72 Chevy 3/4 ton 4WD (Parts donor) 72 Chevy 3/4 ton 4WD Suburban (Parts Donor) 72 GMC 3/4 ton 4WD 292 six/4 speed (Mine - Disguised as a 67 GMC) 81 GMC 4WD Dually Dump Body 350/4 speed (Business Hauler) 82 Camaro Z/28 355/Super T-10 (Pat's toy) 93 Caprice 9C1 (Brian's Cop Car) 02 Toyota Camry (Reliable but a souless steel and plastic hulk) 2011 2SS RS Camaro M6 Factory Hurst Shifter Maybe I need to sell some of this crap Yet another Bozo with a sawz-all

03-19-2003, 09:53 PM	#4
CPNE Resident Curmudgeon Join Date: Dec 1999 Location: NH Posts: 6,664	There are a lot of factors here, carrier bearing mount and location being a big consideration. If it were me, I'd see about having your existing front driveshaft modified rather than trying to locate the correct setup. Fast68 went thru this a year or so ago and never had any success locating the correct setup for what it's worth __________________ Currently on or near the homestead: 67 Chevy SWB 2WD stepside 350/3 on tree (Pat's) 67 GMC SWB 2WD Fleet 402/auto (Brian's under construction) 67 Chevy 3/4 ton 2WD 402/auto (Business Hauler) 67 Chevy 1 ton dually 2WD 396/4 speed (Former business hauler, Needs TLC) 68 Chevy 1/2 ton Suburban 2WD 250 six/3 on tree (Brian's Needs TLC) 70 Chevy 3/4 ton 4WD 350/4 speed (Pat's - Disguised as a 68 GMC) 71 Chevy SWB stepside (Crushed by tree - parts donor) 72 Chevy 3/4 ton 4WD (Parts donor) 72 Chevy 3/4 ton 4WD Suburban (Parts Donor) 72 GMC 3/4 ton 4WD 292 six/4 speed (Mine - Disguised as a 67 GMC) 81 GMC 4WD Dually Dump Body 350/4 speed (Business Hauler) 82 Camaro Z/28 355/Super T-10 (Pat's toy) 93 Caprice 9C1 (Brian's Cop Car) 02 Toyota Camry (Reliable but a souless steel and plastic hulk) 2011 2SS RS Camaro M6 Factory Hurst Shifter Maybe I need to sell some of this crap Yet another Bozo with a sawz-all

03-19-2003, 09:58 PM	#5
Blue_71 Bloo Join Date: Feb 2001 Location: Barren County Kentucky Posts: 6,285	when i measured the 3 speed seemed 5 inches longer, any idea what it would cost to have a driveshaft lengthened that much? i'll call tomarow to get an excact quote.. it looks to me like i can take the yolk off the drivehsft, and then bolt the 4 speed to it with the little "u" clip things it connects with



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