3 on the tree

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trucknorris78

Junior Member
Joined
Jun 26, 2024
Posts
14
Reaction score
15
Location
Salix
First Name
Barry
Truck Year
1978
Truck Model
C1500
Engine Size
427
You don't use granny gear unless you're working the truck. Otherwise it's just a 3 speed, a strong 3 speed that will handle the engine, and would be minimal swapping since you already have the three pedals, etc.
I am looking at one now, actually. It is pre 1988 from a 4x2. Looks like 10 spline. Have to do some research about bell housing, yoke and clutch compatibility. I have an 11" clutch from the old one.
 

JBswth

Full Access Member
Joined
Jan 24, 2022
Posts
201
Reaction score
161
Location
Vallejo, California
First Name
James
Truck Year
1973
Truck Model
C25
Engine Size
292 cubic inches
This is mostly to see what opinions are out there. I am doing a frame up resto on a 78 GMC c15. I already have a 427 pushing 555hp. I want to keep the 3 on the tree because, I'm weird, I guess. Dearborn, M13 seems to be the only valid option. I do not yet know what rear gears I am going to run yet but, I am going to fab a 4-link rear. I am not racing the truck but, I am definitely going to play.
I'm going to pay for asking this but, what do you all think?
I think you need the Tremac. Yes, it is rare on a GM vehicle, but that's what my 73 C25 has, and is what was put in back of 454s that had a 3 speed. Rare, but they do exist. It is the torque, more than horsepower, that can break gears. Stay away from the little pencil sharpener size units that are in back of 6 cyl and 283.

J. B.
 

JBswth

Full Access Member
Joined
Jan 24, 2022
Posts
201
Reaction score
161
Location
Vallejo, California
First Name
James
Truck Year
1973
Truck Model
C25
Engine Size
292 cubic inches
You don't use granny gear unless you're working the truck. Otherwise it's just a 3 speed, a strong 3 speed that will handle the engine, and would be minimal swapping since you already have the three pedals, etc.
Powerglides are fine for small blocks and MILD big blocks that are not much more than 400 cubes, but I wouldn't put one in back of a souped big block.

J. B.
 

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