Wes P
Junior Member
- Joined
- Dec 5, 2019
- Posts
- 28
- Reaction score
- 17
- Location
- Texas
- First Name
- Wes
- Truck Year
- 1985
- Truck Model
- C20
- Engine Size
- 406
Greetings!
Some notes from my Gear Vendors experience:
A Gear Vendors OD installation in a C20 (or, presumably, any regular cab, long bed, 2wd, automatic, unmodified suspension) does NOT shorten the drive shaft enough to allow conversion to a one-piece drive shaft.
The GV kit comes with an involute spline slip yoke. The inherent run-out of this slip yoke is too much for a long/heavy drive shaft. A slip yoke with a longer spline engagement would be needed to sufficiently reduce run-out for a long one-piece drive shaft. Unfortunately, the GV tail shaft design does not support this.
The best solution I found to prevent vibration at highway speed is to eliminate the run-out at the GV tail shaft: Eliminate the supplied slip yoke. Use a bolt-on yoke for the GV tail shaft AND a 2-piece drive shaft OR a CV driveshaft.
On my C20, I went back to a factory-style 2-piece drive shaft. I moved the carrier bearing perch rearward about 6" and down 1/2". I shimmed the rear axle (Pinion) DOWN 1.5 degrees for a total of 3.5 degrees Pinion UP angle. The measurement from the Pinion yoke to the Carrier Bearing was then 39" and from the Carrier Bearing to the bolt-on yoke at the GV unit was 17.875". The Pinion and Front Shaft angles were then matched at 3.5 degrees UP/DOWN, respectively, for U-joint angle cancellation for the rear and center U-joints. The motor drive line is about 5 degrees DOWN. The front U-joint working angle is therefore 5-3.5 = 1.5 degrees. 0.5-1.5 degree U-joint working angles, in most cases, do not require cancellation.
Some photos below.
Cheers!
Wes
PS.
- In the end, I used the original bolt-on yoke from the TH400 for the GV.
- I did not cut or weld to relocate the carrier bearing perch. I only drilled the rivets and added bolts. I also kept the TH400 tail shaft housing and the original drive shaft. If I want to use the GV on another project down the road, it can be removed from the truck without a fuss. I recommend this to everyone.
- Be very careful and use a back stop when drilling the aft rivets of the carrier bearing perch. The fuel lines are directly behind them!
- The coaxial RCA electrical connections on the GV controller are a poor design choice. Crush the RCA connectors and secure the connections or they will come loose.
- "Car" GV units use ATF fluid. Do not use ATF in the deep-sump "Truck" GV units. Use Lucas 75-90 synthetic gear oil. Gear oil in the Truck unit shifts hard. I thought ATF would shift softer. In fact, ATF in the "Truck" unit shifts with unnecessary violence.
- For vehicles with longer travel suspension but short drive shafts (i.e. 4x4): Use CV drive shafts. Your drive shaft may be short enough for a one-piece, but the GV unit is designed for only +/- 5/8" yoke slip.
Some notes from my Gear Vendors experience:
A Gear Vendors OD installation in a C20 (or, presumably, any regular cab, long bed, 2wd, automatic, unmodified suspension) does NOT shorten the drive shaft enough to allow conversion to a one-piece drive shaft.
The GV kit comes with an involute spline slip yoke. The inherent run-out of this slip yoke is too much for a long/heavy drive shaft. A slip yoke with a longer spline engagement would be needed to sufficiently reduce run-out for a long one-piece drive shaft. Unfortunately, the GV tail shaft design does not support this.
The best solution I found to prevent vibration at highway speed is to eliminate the run-out at the GV tail shaft: Eliminate the supplied slip yoke. Use a bolt-on yoke for the GV tail shaft AND a 2-piece drive shaft OR a CV driveshaft.
On my C20, I went back to a factory-style 2-piece drive shaft. I moved the carrier bearing perch rearward about 6" and down 1/2". I shimmed the rear axle (Pinion) DOWN 1.5 degrees for a total of 3.5 degrees Pinion UP angle. The measurement from the Pinion yoke to the Carrier Bearing was then 39" and from the Carrier Bearing to the bolt-on yoke at the GV unit was 17.875". The Pinion and Front Shaft angles were then matched at 3.5 degrees UP/DOWN, respectively, for U-joint angle cancellation for the rear and center U-joints. The motor drive line is about 5 degrees DOWN. The front U-joint working angle is therefore 5-3.5 = 1.5 degrees. 0.5-1.5 degree U-joint working angles, in most cases, do not require cancellation.
Some photos below.
Cheers!
Wes
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PS.
- In the end, I used the original bolt-on yoke from the TH400 for the GV.
- I did not cut or weld to relocate the carrier bearing perch. I only drilled the rivets and added bolts. I also kept the TH400 tail shaft housing and the original drive shaft. If I want to use the GV on another project down the road, it can be removed from the truck without a fuss. I recommend this to everyone.
- Be very careful and use a back stop when drilling the aft rivets of the carrier bearing perch. The fuel lines are directly behind them!
- The coaxial RCA electrical connections on the GV controller are a poor design choice. Crush the RCA connectors and secure the connections or they will come loose.
- "Car" GV units use ATF fluid. Do not use ATF in the deep-sump "Truck" GV units. Use Lucas 75-90 synthetic gear oil. Gear oil in the Truck unit shifts hard. I thought ATF would shift softer. In fact, ATF in the "Truck" unit shifts with unnecessary violence.
- For vehicles with longer travel suspension but short drive shafts (i.e. 4x4): Use CV drive shafts. Your drive shaft may be short enough for a one-piece, but the GV unit is designed for only +/- 5/8" yoke slip.
