Big Red's Custom Differential. Home

One Method to Strengthen a Chevy 10 Bolt Differential

Addiction. Webster's says: the state of being enslaved to a habit or practice or to something that is psychologically or physically habit-forming, as narcotics, to such an extent that its cessation causes severe trauma.

It all started innocently enough. I thought that I needed to personalize my vehicle. So, I got some Piaa windshield wipers from AutoAnything. I thought that fuel economy was important. I installed a stainless Cat back system. Then headers.

Everything started to cascade from there like an avalanche to more and more parts and speed equipment. I installed a Magnacharger TVS supercharger. Power and speed. I thought that I could stop at anytime. But, quite suddenly, I discovered that I was out of control. I had to have stronger fixes. I had to go to Summit Racing. I was sated for a while, but now it's: CUSTOM FABRICATION. Or, is it denial? I forgot what the analyst said.

In point of fact, the author's mental competence has been questioned several times. Who in their right mind would try to hot rod a vehicle that is subject to the onerous regulations of the California Air Resources Board. No matter how costly, and with insufficient funds, mind you. However, "Big Red" meets the CARB regulations, and there are CARB Executive Order stickers to prove it.

Anyway, this is a digression. The differential. It all started a long time ago. First the transmission blew up due to the increased power of the engine, and that was strengthened and upgraded. That just moved the weak link in power transmission further back to the differential. This is the story of strengthening my differential, or turning a Chevy 10 bolt to a 14 bolt differential. I know Darryl Atherton, who does custom fabrications. This was his idea to make a bullet-proof differential.

14 Bolt Installation

The Plan
Execution
Problems Encountered
The Final Results

I.The Plan

We started by getting a 14 bolt differential from a Chevy Silverado, and a 10 bolt differential for a 2003 Tahoe from the recycling center. The plan entails cutting off the axle housings from both differentials, and welding the Tahoe's axle housings onto the Silverado's 14 bolt center section. That gives a strong 14 bolt differential with the Tahoe's suspension and fitment.

II.Execution

It sounds simple. The 14 bolt center has to be machined for the joint with the 10 bolt's axle housings. Everything has to welded and aligned meticulously, and that had to be sub-contracted to an expert.

Cliff Fredricks, West Coast Frame, is that expert. He not only cut, welded, and aligned the 14 bolt center and the 10 bolt axle housings; but he also replaced axle housing's ends with welded on billet ends to capture the axle end bearings. That eliminates the usual "C" clip axle retention that is standard on the light duty Chevy differentials.

There are new 33 splined forged axles from Dutchman with the 6 bolt lugs for the Tahoe's wheels. A Detroit TrueTrac takes care of the posi-traction duties. And, finally lower 4:56 gears for the front and rear differentials.

III.Problems Encountered

The Edelbrock panhard rod had to have a section cut out and then strengthened with a welded in piece in order to clear the new Mag Hytec differential cover.

The Eibach coil springs lowered "Big Red" 1.5 inches, and that pushed the differential to the driver's side due to the travel arc of the stock length panhard rod. I carved a spacer out of 3 inch aluminum round stock, and made an adjustable panhard rod out of an aluminum hex rod and a right and left hand threaded rod ends. This moved the mounting point of the panhard rod outside the normal mount, but it clears the differential cover. Then the differential was measured and centered at normal ride height. The rod end jam nuts were tightened which will keep it centered.

The rear Eibach sway bar would not clear the Mag-Hytec differential cover when the Tahoe is raised by the frame and the rear suspension hangs down. We tried to move the sway bar mounts farther to the rear, but that did not completely clear it. Hellwig has a special rear sway bar that is made to clear the Mag Hytec cover, and that was installed with new rod end links. It is a solid sway bar and is much heavier than the Eibach bar. But, so does the 14 bolt weigh more than the 10 bolt. So much for trying to save weight for fuel economy.

There seemed to be vibrations at speeds above 85 MPH. I had the wheels rebalanced. I moved the front wheels to the rear and vice versa. I had the front end aligned again. All to no avail. I had the wheels rebalanced again. The only other thing changed was shortening the drive shaft. I took it back to Drive Line Service in West Sacramento. They found that it was out of balance.

At first, They blamed me for installing the U-Joints incorrectly. They rebalanced it, and I tried it. It did not work, but it moved the vibrations from 85 MPH to 100 plus MPH. I took it back and they replaced the drive shaft tube completely with a new DOM 3 inch steel tube and rebalanced it. It cured the vibrations. They disassembled the drive shaft, and it was sent to the powder coaters. Drive Line Service reassembled the U-joints, but there are still some vibrations at speed. Al Nichols got his digital angle finder, and dove under "Big Red". He determined that the differential Pinion Angle and the transfer case output shaft are not parallel. Drive Line Service did all of this work at no cost. Al Nichols and Jim Scoggan are true professionals.

I procured a pair of Spohn Perormance adjustable upper trailing arms to adjust the pinion angle. I had to drill out the 14 mm sleeves for the new, stronger than grade 8, Stainless Steel 5/8 bolts from Totally Stainless. About 75% of the bolts on "Big Red" are stainless ARP or Totally Stainless TS 17-4, and grade 8, or stronger.

I measured the angles at the pinion (6.65 degrees), the drive shaft (4.85 degrees), and the Output of the transfer case (3.85 degrees). After preliminary adjustments: pinion (3.80 degrees), the drive shaft (5.80 degrees), and the Output of the transfer case (3.85 degrees).

All the powder coating was done at Champion Powder Coating in Rancho Cordova, CA. They are a family run organization. Brian, and his brothers, with his Mom, Margaret; and Dad, Steve Walker run it with excellent attention to detail and good customer service.

The Computer, PCM, had to be updated with the differentials' gear changes. Those gear changes make the Power train Control Module's data input incorrect. This outwardly manifests itself as a speedometer reading that is way off. Fortunately, Mark Romans, with his HPTuners wizardry, updated the PCM to the correct gear ratios, and everything is back to normal. Normal being relative. Mark did the performance tune with the Tahoe on the dyno after the blower was installed. So, normal is not stock.

The spare tire does not fit with the bigger differential. I had to get a smaller diameter tire to fit in the same space. It should not be too much of a problem with different tire diameters on the back because the Detroit True Trac can compensate. It is not the best solution, but it is still a problem and it will be resolved at a future time.

IV.Final Results

While the gears are not completely broken in, it must be driven with a light foot. Even so, the Tahoe has tremendous acceleration. The top end must be lower because of the 4:56 gears, but it still has 110 MPH and still wants to rev further. It still has a way to go before red lining, but it is still being babied until break in is complete and the requisite fluid change in the differentials. Then track testing.