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HOT ROD Rescue: Custom CV-joint Driveshaft Helps Fix 1971 Challenger Drivetrain Vibration

Photos: Jon Dumas, Joe Kaiser, Frank Rehak

The bad vibrations on Bill Maher’s 1971 Dodge Challenger started after swapping in a TKO trans. Six different garages and replacing the entire drivetrain had failed to fix the problem.

The Combo

Years ago, Kevin Maher dated his wife in a classic Dodge Challenger. Ten years ago, Maher, now retired and living in Rosemary Beach, Florida, was looking to get back into cars now that finances and time finally allowed it. Purchasing a 1971 Dodge Challenger with a big-block, TorqueFlite trans, and 8¾-inch Chrysler rearend, he swapped out the automatic for a Tremec TKO 600 five-speed manual trans with a 0.64:1 overdrive using what was billed as a “complete bolt-in” aftermarket conversion kit.

The Problem

His 1971 Challenger plagued by severe vibration, owner Bill Maher says, “I don’t think I put more than 500 miles on the car in six years.”

After installing the trans, Maher says, “There was a constant vibration in all gears at any speed and rpm.” A six-year saga of futile attempted fixes accomplished nothing. “I had the trans in and out, gone through several times. I bought a whole new rearend: a brand-new Strange 60 with 3.91:1 gears and an Eaton Posi. I tried three different driveshafts—two of them were too short. I changed the flywheel and clutch. At least five reputable garages tried to solve the problem; the last one was a four-wheel-drive lift-kit ‘mudder’ specialist that supposedly knew how to find and solve weird driveshaft-angle problems.” Along the way, Maher changed the motor out for a brand-new, 522ci, 545hp, stroker big-block built by Carolina Motors. “[But] the drivetrain still vibrated. There was no support from the kit maker, who finally went out of business.”

The Diagnosis

With the problem still unresolved, a frustrated Maher says, “I figured it was time to get the car painted. It wasn’t really going anywhere!” Searching for a top-tier body shop, his quest led him to Cruise-In Restoration in Salisbury, North Carolina. As it happens, the up-and-coming facility also does complete ground-up car builds—and about everything in between. As owner Jon Dumas puts it, “We’re known for our paint work, but we can do just about everything. We do our research and make sure we know what we’re doing.”

Cruise-In Restoration is known for laser-straight paint jobs and turnkey restos, but owner Jon Dumas says, “We take on anything.”

Dumas testdrove the car, confirming Maher’s complaint. “There was a terrible vibration when on the highway, and when you stepped on it, it got pretty violent. It was terrible! You wouldn’t want to go on a long trip with it! The higher the rpm, the worse it felt.” Detailed inspection uncovered a bunch of drivetrain-related issues. Collectively, they all either contributed, or were the result of, the seemingly intractable vibration:

Initially, Dumas determined the existing driveshaft was too short and its angles were off. “This could have been caused by the kit’s poorly engineered crossmember. We saw the trans had a pile of flat washers between the trans mount and crossmember, apparently to try and correct the angles. This caused the oil pan to hit the steering drag link. The car’s ride height had been lowered slightly as well; it moved the rearend higher in the tunnel—this also changes the angles. The passenger-side polyurethane engine mount was broken, likely from the vibration and binding and the mount’s lack of compliance. The trans shifted harder than it should and was nearly impossible to shift into Reverse.”

Maher’s driveshaft was too short with excessive yoke stick-out from the trans.

John Dumas: “I could tell the driveshaft was too short. On a TKO, you want about 1.5-inch yoke stick-out past the bushing, and 3 inches inside the trans. Maher’s yoke was out about 2⅝ inches past the bushing.” Need to order a new ’shaft from scratch? With the vehicle resting on the tires, measure from the trans end seal to the center of the rearend pinion-flange U-joint.

Even worse than excessive yoke stick-out, the driveshaft’s front and rear angles were way off. Vainly trying to improve the driveshaft angle, someone had inserted a 1-inch stack of shims between the trans mount and crossmember (arrow).

It didn’t do much to improve the angles and actually caused the oil pan to bottom on the steering drag link.

The Fix: Driveshaft

A longer driveshaft was needed, but achieving the necessary angles with standard U-joints would require raising the trans, and for clearance that in turn mandates major floorpan surgery. Dumas brought in The Driveshaft Shop owner Frank Rehak to see if there was a better solution. Rehak explained the dilemma: “The velocity on a conventional U-joint varies. To prevent vibration, the U-joints on each end need to be in synch. You do this by controlling the difference in the angle. There can be no more than a 3-degree difference between the two U-joints, and they shouldn’t be offset more than ½ degree. Usually, the motor/tranny angle points down and the rearend up, but on this car the tranny end pointed up, creating a negative angle relative to the rearend, which was at zero degrees.”

As shown here, there are strict rules for driveshafts with conventional (non-constant velocity) U-joints on street-driven cars. The Driveshaft Shop’s Frank Rehak further explains how this should work in the real world: “Think of proper drivetrain layout as a slow waterfall. Water wants to flow downhill, and the ‘water’ should roll off the end of the trans at a gentle angle. The rearend [pinion shaft] should point slightly uphill.” These angles would be in relation to each other, not necessarily the ground.

There are several ways to check driveshaft angles. Traditionally the most common methods are a carpenter’s analog protractor, or even a digital angle finders. (Photo: Clarence Range)

Tremec now offers its “Toolkit apps” that turn your Apple or Android smartphone into an angle-finder. Whichever the device, you’ll need to measure the angles on the back of the trans, at the front of the rearend pinion flange, and on the shaft itself. (Photo: Jeff Smith)

Rehak came up with a novel solution: a trick aluminum driveshaft with a constant-velocity (CV) joint installed at the trans end. CV joints have gone mainstream on late-model Detroit performance cars like the Camaro, Challenger, and Mustang; Rehak says there’s no reason this newfangled tech won’t work in an older classic car. “We see this angle and clearance problem a lot today. Lots of people are installing bulky six-speed Tremec 6060 or Tremec T56 Magnum transmissions in old cars behind their swapped-in LS motors. They can’t get the trans high enough to achieve the right angle with conventional U-joints without cutting up the tunnel. With a CV-joint setup, the driveshaft angles can be 10 degrees off without any vibration problems. We do 15 to 20 CV-jointed ’shafts a week now. It may be cheaper than cutting up the floorpan.

The Driveshaft Shop built a trick lightweight aluminum driveshaft with a CV joint at the trans end, custom-fabbing the yoke, boot, and double-spline adapter to get it all to work. Shop owner Frank Rehak says, “The CV joint is at the front because that’s where the [angle] problem was. If the problem had been at the rear, it’s usually easier to change the pinion angle.”

“For the Challenger, we built a 3½-inch-od, 6061-T6 aluminum driveshaft with a front-mounted, German-made GKN CV joint. This is a well-engineered product that’s as strong as the 1350-series conventional U-joints on Pro Mod drag cars. We use a chrome-moly cage on the CV. They’re pretty much bulletproof.”

Late-model Detroit setups use a companion flange at the trans instead of the slip yoke usually needed on classic or aftermarket retrofit transmissions. No problem for Rehak: He fabbed a custom yoke that bolts to the front of the CV joint plus a double-spline 300M aircraft-steel adapter to connect the rear of the CV joint to the driveshaft.

The CV joint tolerates fairly severe driveshaft angles. Dumas was able to relocate the trans-mounting pad above the crossmember, curing the oil pan-to-steering drag link interference problem without cutting up the floorpan or resorting to a pile of shims. Later, the hard polyurethane mounts were replaced with softer, vibration-absorbing, OE-style rubber mounts.

With overdrive, driveshaft speeds have increased dramatically, so balancing is critical. “Rotational speeds of 7,000 rpm or even higher are not unheard of,” Rehak says. “Only three companies in the U.S. have a high-speed balancer. The Driveshaft Shop is one of them.”

The Fix: Mounts and Clearances

The Driveshaft Shop’s CV-jointed aluminum driveshaft eliminated 80 percent of the vibration without cutting up the floorpan.

With driveshaft angles no longer critical, thanks to the CV joint, Dumas reworked the trans crossmember to solve the oil pan/drag-link contact issue. Going for a testdrive with the new driveshaft installed, Dumas reported, “The vibration was 80-percent better, but there was still a little noise and shaking.” He installed more compliant (and vibration-absorbing) Anchor OE-style rubber mounts in place of the existing polyurethane mounts, including the one that was broken. Continual improvement was noted, but now Rehak was able to hear noise in the transmission itself.

The Fix: Bellhousing, Clutch, Trans

Dumas: “The clutch wasn’t engaging right. It wasn’t fully releasing and the flywheel got real hot.” Checking further revealed the hydraulic release bearing had excessive travel. There was also insufficient multidisc clutch element “sandwich” clearance. Fortunately, the clutch discs had worn normally and could be reused. The pilot bearing in the crank checked OK, too.

Dumas inspected the trans, bellhousing, and multidisc clutch. The flywheel and pressure-plate surfaces were scoured. Dumas attributes this to improper internal clutch clearances plus the wrong release bearing travel. He sent the clutch and flywheel to Clemmons Speed Shop for resurfacing and rebalancing.

The clutch manufacturer’s square shims for the multidisc clutch’s midplate-to-disc “sandwich” (shown) were too thin. Later, Dumas reshimmed to achieve 0.025-inch clearance using Seastrom Manufacturing ⁵⁄₁₆-inch-od, precision thin stainless steel round washers.

Dumas next took a closer look at the transmission. Its input shaft seemed loose with excessive endplay. Spinning the trans by hand, he could hear gear noise, so Dumas had Chancy Taylor at Selective Gearing go through it.

While those parts were out getting refurbished, Dumas checked the QuickTime bellhousing’s alignment relative to the engine crank centerline. It was out of tolerance, which puts excess side pressure on the pilot bearing, clutch plates, input shaft, and trans. Along with the clutch-engagement issues, it was responsible for hard-shifting into Reverse and the front trans bearing and shaft wear.

The bellhousing alignment was as much as 0.016-inch off-center due to an align-bored block.

Used by Maher to adapt the small-block Ford-pattern TKO trans to the Chrysler B/RB big-block V8, QuickTime bellhousings have a good accuracy reputation. The issue was Maher’s align-bored block; this straightens the main-bearing webs out, but moves the crank centerline up relative to the rear block-face bellhousing mounting dowel locations. Dumas used RobbMc Performance adjustable dowels to correct the misalignment. Easy to adjust, Dumas says that (unlike many competitors), RobbMc’s dowels are properly dimensioned for a Chrysler dowel-hole size.

Dumas says RobbMc bellhousing dowels fit Chrysler blocks better than competitive products. Use an open-end wrench to rotate them for proper alignment, then tighten the center setscrew to lock in the adjustment; no need to pound the pins in and out or recheck alignment if the bellhousing is removed. Three offset sizes are available: 0.007, 0.014, and 0.021 inch. RobbMc (inset)

Bellhousing alignment should be 0.005-inch TIR (total indicator runout) or less. Move the housing half the measured offset to achieve near-zero runout. Using the 0.007-inch RobbMc offset dowel set, Dumas corrected the 0.016-inch runout to near-zero horizontally and under 0.003 inch vertically.

Dumas installed Seastrom stainless steel shims between the multidisc clutch plates and discs to develop the correct element spacing. A Speedway setup tool made it easy to check the hydraulic release bearing clearance, which was then corrected with a Howe Racing release bearing spacer-shim kit.

Speedway’s hydraulic release bearing setup tool makes it easy to determine hydraulic release bearing travel. Hold the tool up to the bellhousing and push the rod in until it touches the pressure plate fingers. Flip the tool around, place it up to the trans face, and push the rod in until it contacts the release bearing. Then read the scale to determine your clearance.

Using the Speedway tool, Dumas found, “The clearance was 0.275 inch when it should have been 0.150–0.200 inch.” Two 0.050-inch shims from Howe Racing shim kit PN 82873 put the clearances within spec.

After shimming the bearing forward, the release bearing guide rod (arrow) was now too short to keep the bearing from spinning on the input shaft. Dumas made a new rod by cutting the head end off a ⁵⁄₁₆-18×4¼ ARP bolt to reduce its “grip” length (smooth area) to 3 inches. A ⁵⁄₁₆-18 jam nut tightens it against the retainer. Cut the thread end short if it bottoms inside the trans.

As for the trans itself, Selective Gear’s Chancy Taylor determined it needed a new 26-spline input shaft and front bearing up front. At the rear, the vibrating driveshaft had lunched the rear extension bushing. Officially, the only way to get a new bushing for a Tremec is to buy a $350 extension housing (yikes!). A little “secret” that saves big bucks is that a Ford C6/E4OD/4R100 auto trans rear bushing fits and the Pioneer replacement part is less than $7 from RockAuto.

Poor bellhousing alignment plus the badly set up hydraulic clutch damaged the transmission’s input shaft and input bearing; with less than 800 miles on it, the nearly new trans wouldn’t go into Reverse before Chancy Taylor at Selective Gears set it back to rights.

The Results

After fixing the driveshaft, clutch, trans, and engine mounts, all vibration is gone and the car can finally be driven as it was meant to be.

All vibration and gear noise were completely eliminated. The drivetrain now runs smoothly in all gears, at any speed or rpm. “I can’t believe it’s fixed!” exclaims an exultant Maher. “I’m really happy!”

Lessons Learned

Aftermarket parts don’t necessarily bolt in. There are always other factors that come into play.” — John Dumas, Cruise-In Restoration

Don’t expect complex parts to just bolt-on without any detailed checks and corrections. In this case, a marginally engineered swap kit was fatally compromised because the crank had moved up and the body moved down.

Maher was so impressed how Cruise-In finally fixed the problem he’s now letting Dumas fully restore the Challenger from the ground up.

Parts and Prices Does not include shipping; miscellaneous standard hardware, consumables, and sealant; or sales taxes. Labor is included only if cannot be performed by the average home mechanic. Priced 12/06/16 and subject to change. All dimensions in linear inches, except as noted. Brand Part Description Part No. Amt. Price From Cost Anchor Industries MOUNT, engine, rubber, black, 1970-1976 Chrysler A/B/E bodies w/ V8 2250 2 RockAuto $2.54 MOUNT, transmission, rubber, black, 1965–1980 Ford/Mercury cars w/ manual trans (fits Tremec) 2253 1 RockAuto $2.06 Automotive Racing Products (ARP) BOLT PKG., hex head, stainless steel, 170 kpsi, ⁵⁄16-18×4.250 UHL, 3.25″ grip, 1″ thread-length, ⅜” wrenching element, modified, 5/pkg., 1 used¹ 622-4250 1 Summit $25.97 NUT PKG., hex head, stainless steel, 140 kpsi, ⁵⁄16-18, 5/pkg., 1 used² 400-8652 1 Summit $3.97 Clemmons Speed LABOR & MACHINING, surface and balance flywheel/clutch assembly Labor — Clemmons $150.00 Driveshaft Shop DRIVESHAFT, aluminum, 6061-T6, 3.5 od, CV joint at transmission end Custom 1 Driveshaft $799.99 General Motors FLUID, synchromesh transmission, synthetic blend, 1qt (32oz) bottle 88900333³ 3 Summit $17.97 Howe Racing SHIM KIT, hydraulic release bearing, 0.050 thk (10/pkg., 2 used) 82873 1 Summit $10.97 Pioneer BUSHING, transmission extension, brass, 1966-1998 Ford C6/E4OD/4R100 (fits Tremec) 755014 1 RockAuto $6.60 RobbMc PIN KIT, engine clutch housing lineup, adjustable, 0.496 od (most Chrysler 6/8-cyl.), 0.007 offset 10174 1 RobbMc $29.00 Seastrom Manufacturing WASHER, flat, stainless steel, ⁵⁄16 hole, 0.390 id×0.750 od×0.005 thk, for multidisc clutch5 5710-322-5 10 Seastrom $37.92 WASHER, flat, stainless steel, ⁵⁄16 hole, 0.390 id×0.750 od×0.020 thk, for multidisc clutch5 5710-322-20 10 Seastrom $37.69 Selective LABOR, transmission teardown, inspection, and assembly Labor — Selective $450.00 Speedway GAUGE, hydraulic release bearing clearance setup 91381090 1 Speedway $49.99 Tremec BEARING ASSY., transmission main drive gear to case, TKO 2606064 1 Selective $75.00 GEAR, transmission main drive (input shaft), TKO, Ford 26-spline, 3.27:1 1st gear TCFM51986 1 Selective $199.72 SEAL, transmission extension rear oil, TKO, Ford 31-spline TCSJ1277 1 eBay $25.72 NOTES: ¹Use to make expedient hydraulic clutch release bearing pilot rod; cut off wrenching head, shorten grip to 3.00 inches. ²Use to tighten expedient bearing pilot rod against bearing retainer. ³Alternate PN ACDelco 10-4006. 4PN 1018, 0.014 offset; PN 1019, 0.021 offset. All are the same price per set. 5Use as needed to set multidisc clutch element “sandwich” clearance. 6Alternate PN 2606412. Total $2,285.05

NEED JUNK FIXED? If your car has a gremlin that just won’t quit, you could be chosen for Hot Rod to the Rescue. Email us at pitstop@HotRod.com and put “Rescue” in the subject line. Include a description of your problem, your location, a photo of the car, and a daytime phone number.

Contacts

ACDelco; Detroit, MI; 800.ACDelco; ACDelco.com

Anchor Industries Inc.; Cleveland, OH; 800.444.4616 or 440.473.1414; Anchor-Online.com

Automotive Racing Products (ARP); Ventura, CA; 800.826.3045 or 805.339.2200; ARP-Bolts.com

Clemmons Speed Shop; Winston-Salem, NC; 336.766.6919

Cruise-In Restoration; Salisbury, NC; 704.857.7186; CruseInRestoration.com

EBay Inc.; San Jose, CA; 866.540.3229 or 408.376.7400; eBay.com

GM Customer Care and Aftersales; Grand Blanc, MI; 810.606.2001; GM.com

Howe Racing Enterprises Inc.; Beaverton, MI; 888.484.3946 or 989.435.7080; HoweRacing.com

Pioneer Automotive Industries LLC; Meridian, MS; 800.821.2302 (customer service); 800.647.6272 or 601.483.5211 (tech); PioneerAutoInd.com

QuickTime, A Holley Performance Products Brand; Bowling Green, KY; 866.464.6553; Holley.com/brands/quicktime

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