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2005 Chevy Tahoe Drivetrain and Axle Upgrade - Rosco P. Drivetrain

Posted in Project Vehicles on August 7, 2015
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Blowing apart a perfectly good, running, and driving rig with plans to make that rig a lot better can start to seem like a bad idea after the truck has been on jackstands for weeks (if not months). We bet you are getting tired of seeing images of the large white former police car in our driveway. Lord knows we are tired of seeing it there. The good news is we’ve whittled away the project enough to have driven it a few hundred miles now. Getting it running and driving was important for our morale, but also to establish what worked and what didn’t.

We are very happy with the Tahoe, although it’s not done. Our educated guestimate of spring rates (with help from Rob Bonney Fabrication) seems to be close to being on point. The suspension works as planned but still needs a bit of tweaking made possible with the help of a few parts from Synergy Manufacturing. The tie-rod end at the pitman arm is at a very severe angle. It is not safe and needs to be fixed. We’ll tackle that with help from Rob Bonney Fabrication and Sam’s Offroad. With driveshafts and a slip yoke-eliminator for our NP241C from Tom Wood’s Custom Drive Shafts, we got that GM power to the axles and wheels. Last, we get the NP241C shifting with parts from JB Custom Fabrication. We also have to modify the Tahoe’s exhaust Y-pipe a touch to clear the front driveshaft.

The SUV is driving, but we still want to build a front bumper and rock sliders, add a winch, regear the axles, and add lockers and maybe a rear sway bar. Once that’s done we’ll outfit the truck for family adventures. Somehow the build just keeps on going, but we are getting close to enjoying the fruits of our labors.

We told you about how we rebuilt the NP241C that would soon find its new home under our Tahoe in Part 4 of Rosco P. Drivetrain. After talking to Tom Wood’s Custom Drive Shafts we were ready to tear back into the aluminum box. That’s because we didn’t realize that Tom Wood’s offers a slip-yoke eliminator kit for NP241Cs. Tom Wood’s cuts down a factory NP241 shaft and machines the end so a CV flange will fit and supplies an aluminum seal retainer that replaces the factory tailhousing.
The kit eliminates the wear-prone slip yoke from the rear output of the transfer case and allows the use of a longer collapsible driveshaft with a double cardan joint on the transfer case end. The longer shaft means less severe angles and a driveshaft that will last longer than the factory part. Installing the slip-yoke eliminator was as easy as the T-case rebuild and should have been done when we did that project, but we like doing everything twice. Now we can also bolt in a nice steel collapsible rear driveshaft from Tom Wood’s Custom Drive Shafts.
When we got the AAM 9 1/4 Ram front axle, the factory driveshaft was still attached. Lucky for us the Ram’s CV mated to the front output on our NP241C. The only issue was that at full bump our recycled shaft was 1inch too long. A driveshaft that is a too short might be OK, but one that is even a little too long can damage your transfer case. Tom Wood’s Custom Drive Shafts shortened (and rebalanced) our front driveshaft after verifying that all the joints and yokes were good to use.
With the front driveshaft shortened and installed, the position of the Ram pinion caused the driveshaft to want to share space with one of the catalytic converters. One relief cut above the cat and a new 2 1/4-inch crossover pipe welded in using our Miller welder, and we had enough room for the driveshaft.
As a result of trying to reuse parts we already had on hand, the tie-rod end at the pitman arm (bottom) was just about maxed out at ride height. Any suspension droop or flex would bind and eventually cause failure. On a Ram 2500 this tie-rod end goes into the pitman arm from the top. Our design had the tie-rod end bolting to the pitman arm from the bottom. We found a similar tie-rod end, Moog ES3417T (top), intended for a 1999-2004 2WD Ford F-250, F-350, or Excursion. The taper is the same as our factory 2012 ram tie-rod end with a 14mm 1.5 retaining nut and 1-inch 16 tpi shank. The only difference is the new tie-rod end has a bend that places the ball joint in the correct direction to work with our modified steering system.
We ordered up a new pitman arm from Sam’s Offroad made of 1-inch mild steel and available with tapered holes or as a blank. We ordered a blank and had Rob Bonney from Rob Bonney Fab and his well-equipped Index mill machine a taper that passes through the pitman arm at about 10 degrees.
Bonney also machined a flat surface for the castle nut to sit on when tight. With the new tie-rod end and the machined taper in the pitman arm, the steering should be happy when flexed or at full bump. We measured the throw of the AAM’s knuckles at the tie-rod end mounting point and then figured a point on the new pitman arm that moved about 1/2 inch farther (1/4 inch per side). Our throw at the knuckles was 6 3/4 inches, so the tie-rod end at the pitman arm should move 7 1/4 inches lock to lock. This allows the axle stops to determine the steering throw and not the weaker steering box sector shaft.
With 12 inches of travel, getting the Tahoe all flexed out might put undue stress on the steering, the front driveshaft, and even the axle side mounts for the coilovers. To reduce the burden that these parts would see we called up Synergy Manufacturing for a set of the company’s 14-inch Quad Wrapped, Ultra Strength limiting straps and limiting strap clevises. These straps are heavy-duty and should last for years under our Tahoe and prevent damage to the rest of the suspension system.
With the NP241C assembled for (hopefully) the last time and the driveshafts in place, we addressed how to shift the transfer case from the driver seat. We tracked down this nifty cable shifter made in the USA by JB Custom Fabrication. These shifters are available for a wide variety of transfer cases, including our NP241C, twin-sticked transfer cases, and doublers. Several different lengths of shifter cables are available. We drilled a hole in the floor of the Tahoe and routed the cable through a Daystar Fire Wall Boot (PN KU20040BK). Then we built a mount out of some steel plate.
The 2WD 4L60E tailshaft speed sensor wiring in our Tahoe won’t plug into the NP241C’s speed sensor because the plug is different. We scavenged this plug at the junkyard and spliced it into our truck’s wiring harness. So far we have put about a thousand miles on the truck, and with the original Tahoe front wheel sensors bolted to the 2012 Ram AAM wheel bearings and the above two wiring modifications we have had no computer issues.
We finally took the big Tahoe out on a local trail just enough to stretch her legs. We found the Tahoe drove there fine, but the transmission didn’t want to shift in 4-lo so we’ll have to dig into that. For now we’ll keep on spinning wrenches and taking pictures for Part 6 of Rosco P Drivetrain.

Sources

Miller Electric
Appleton, WI 54912
920-735-4141
www.millerwelds.com
Daystar
Phoenix, AZ 85043
800-595-7659
www.daystarweb.com
Sam's Offroad Equipment
Tulsa, OK 74107
800-446-5503
www.samsoffroad.com
Synergy Manufacturing
San Luis Obispo, CA 93401
805-242-0397
www.synergymfg.com
Tom Wood's Custom Drive Shafts
877/497-4238
www.4xshaft.com
Rob Bonney Fabrication
602-370-7955
facebook.com/pages/Rob-Bonney-Fabrication/193559750764429

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