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Aisin AX15 Bolt-On Transmission Swap Jeep

Posted in How To: Transmission Drivetrain on June 1, 2006 Comment (0)
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In the '80s, French auto and bicycle manufacturer Peugeot's pedal-powered gears were highly prized,but the company's automotive gear clusters were sometimes undermatched to their applications. Case in point is the Peugeot BA10/5 five-speed manual trans that came stock in many '87-'89 Wranglers, Cherokees, and Commanches, thanks to AMC's relationship with Renault. This LeTrans, found in as many as 158,000 Wrangler YJs alone, is marginal behind stock six-cylinder power and worthless with anything much bigger. The general consensus among 4x4 enthusiasts and trans shops is that the BA10 isn't worth the time or money to rebuild once it goes south.

Since the Peugeot five-speed is simply French swill, we investigated some replacement options. Affordability is first-gen Wrangler YJ's main appeal, so we at first 86'd the idea of adding a $2,300 trans/adapter package to a $3,000 vehicle (our guinea-pig '88 YJ with failing Reverse gear on its BA10). Besides, hard-core Jeepers who aren't total masochists are better off spending more up front, using a TJ or even a CJ as raw material to get a stouter stock geartrain.

Since we're focusing on YJ solutions, we ruled out automatic swaps due to housing lengths and cost of adapters. Details on readily adaptable manual trannies are contained in the comparo chart elsewhere in this article; we eliminated dinosaur gearboxes and ones that require expensive adapters from contention.

The Aisin-Warner AX15 emerged as the best all-around solution. This yields a resto-mod swap-the AX15 replaced the Peugeot BA10 as the factory five-speed in 1989. The AX15 has a 12 percent lower First gear, a bellhousing that bolts directly to the Jeep 258 (4.2L) and 4.0L sixes, and was factory mated to the NP231 transfer case. Incidentally, owners of '87 YJs and '84-'87 XJs should also consider upgrading their NP207 transfer case to the NP231, which became standard in the '88 model year: The NP207 has a 2.61:1 low-range ratio (compared to the 231's 2.72:1) and is difficult to adapt to non-factory trans/transfer-case combos.

The cheapest solution is to source an AX15 with bellhousing, shift tower, and all available related hardware at a junkyard. If possible, also get the attached NP231 since Peugeots had a 21-spline output shaft and the AX15 has a 23-spline shaft. Otherwise, the Peugeot-equipped 231's input gear will need to be swapped to 23-spline.

A more expensive but much more reliable and convenient solution is to order a rebuilt gearbox. We contacted Rockland Standard Gear (RSG), a factory-authorized rebuilder for New Process/New Venture, Tremec, ZF, and other OE geartrain manufacturers. A supplier to car dealerships and trans shops since 1981, RSG maintains an inventory of more than 5,000 ready-to-ship transfer cases (even indestructible NP205s). Rockland also rebuilds and customizes popular manual transmissions in addition to offering rebuild kits and replacement parts for them (including guts for the Peugeot BA10).

"Gorgeous" George Kreppein, Vice President of Rockland's Remanufacturing Division, has performed dozens of AX15 swaps himself since the early '90s. He stacked our deck by custom-assembling components to make this job a minimal-brainer. Some of the considerations and Kreppein's recommendations:

View Slideshow
Part Source Part Number Approx. Price
AX15 Transmission RSG AX15-03 $1,295
AX15 Bellhousing OE 53007105 $228
HD NP231 SYE, CV RSG 231JSYEK $1,195
Short-Throw Shifter B&{{{M}}} 45059 $171
Short Leather Shift Knob B&M 80744 $25
Crossmember Mount Advance Adapters 716007 $69
Clutch Kit with Bearing Luk 01-901 $249
Rear CV Driveshaft Coast Driveline (custom) $279

AX15 trans: Rockland assembled our gearbox to make it a direct bolt-in when mated to a used or OE-sourced bellhousing. A 10-spline, 11/16-inch input shaft makes our trans compatible with the OE clutch and pilot bushing. (Otherwise, a correct-diameter pilot might need to be sourced from approximately six different Jeep applications, or the OE one might need to be machined; OE AX15 tip diameter is 0.590 inch from '89-'96, 0.750 inch from '97-'99.) The AX output shaft is the same length as the BA10 but is a stronger 23-spline diameter (compared to the BA's 21-spline).

Bellhousing: The cheapest and easiest is to use an '89-'94 OE AX15 bellhousing, which shares the internal release-bearing setup with the BA10. (From '95-'99, the AX15 got an external fork and release-bearing setup. The advantage here is field-serviceability, but retrofitting requires linkage considerations. Also, some people adapt Jeep Iron Duke four-banger or '75 Land Cruiser external slave cylinders to the early AX15 bellhousings.) The rubber bellhousing grommet that stabilizes the hydraulic lines should be sourced from a dealer or replacement Jeep parts supplier to minimize potential hydraulic problems.

Clutch: The Rockland-prepped AX15's input shaft is the same diameter as the Peugeot BA10's, so the factory clutch and release bearing can be retained. (Replacement clutch kits sometimes include a new release bearing.) Craig Calkins at CRC Transmission recommended a Luk Pro Gold clutch kit with new release bearing. This setup provides greater-than-stock clamping force to accommodate this YJ's 33-inch tires without overpowering the hydraulic lines.

Shifter: To avoid clearance issues, a short shifter is recommended. Our solution was B&M's short-stick application for the AX15. Its quicker shifting (30 percent shorter throws) provides great seat-of-the-pants satisfaction following the swap. The 303S stainless shaft and choice of knobs add class and durability. Other options are to find a short tower from an AX15-equipped XJ or heat and bend a stock AX stick to clear the dash, seats, and console.

Floorpan: The stock tunnel plate and boots can be reused; torn boots should be replaced.

View Slideshow

Transfer case: Rockland offers an HD NP231, with optional slip-yoke eliminator (SYE). To combat big-tire stress, RSG builds the HD NP231 with six-pinion planetary gearsets (compared to the OE three-pinion setup), a heavier sprocket, and a wider chain. The OE CommandTrac 27-spline slip-yoke can be upgraded by Rockland's optional 50 percent stronger 32-spline fixed yoke to eliminate oil leaks and allow more driveshaft length (about 4 1/4 inches on a YJ and 6 1/4 inches on a TJ), curing lifted-Jeep vibration in the process. Available rear yoke options are for 1310/1330 U-joints or for a CV joint. We chose the CV since this particular '88 YJ had pronounced driveline vibration resulting from 4 1/2 inches of lift.

View Slideshow

Incidentally, RSG stresses that its direct-bolt-in HD231 is a much more affordable option than swapping in an NP241OR RockTrac (which Rockland also sells). Strength is comparable, and the RockTrac's 4:1 low-range comes at the expense of losing the speedo-the late-model electronic signal is incompatible with the earlier sending system.

Mounts: The AX15's mounting pattern is slightly different from the Peugeot's. Many "real" Jeepers can fabricate an offset plate to mate the existing mounts to the AX15. CRC Transmission chose the bolt-on route by slightly modifying an Advance Adapters plate intended for an NV3550 conversion-two notches were ground in the plate to clear trans bolts in the forward-facing side of the plate. This raises the trans about 3/4 inch and increases the driveshaft angle (another reason to choose a CV-style rear shaft and fixed rear transfer-case yoke) but keeps the overall conversion in the bolt-on realm. XJ and Commanche owners also have to modify the trans mount that mates to the exhaust flange and/or possibly swap in the later crossmember from AX15-equipped vehicles.

Driveshafts: The AX15 is the same length as the BA10, so the transfer case sits in approximately the same location. The existing front driveshaft can be retained; the RSG HD231's SYE creates additional room, so the rear shaft will either have to be lengthened or replaced if upgrading to this fixed-yoke transfer case. Once CRC had the RSG-assembled tranny/transfer case in place and the Jeep on the ground, they sent accurate measurements and the factory rear driveshaft to Coast Driveline. The custom Coast shaft combined the OE lower yoke with long-spline tube and CV upper joint. Vibration cured!

View Slideshow

Model OE Applications Gear Ratios (:1) Length (in) Weight (lbs) Input Splines Output Splines Notes
Peugeot BA10 '78-'89 XY, YJ 3.39, 2.33, 1.44,1.00, 0.79 16.75 94 10 21 Light duty, not worthrebuilding
AX15 '88-'99 YJ/TJ/XJ/MJ,'93 ZJ,Dakota/Durango 3.80, 2.33, 1.44,1.00, 0.79 16.75 94 10 23 Strong enough for a V-8,quieter than a NV3500
NV3500/3550 '00-'03 TJ 4.02, 2.32, 1.40,1.00, 0.73 12.37 97 10 (1 1/8 in. dia.) 23 Noisy at idle
NV4500 '93-present Chevy,'95-present Dodge 6.34, 3.44, 1.17,1.00, 0.73 12.37 195 10 (dia. varies) 23, 29, 30, 31 PTOs, heavy
NSG370 '05-present Liberty, Wrangler 4.50, 2.70, 1.70,1.30, 1.00, 0.80 NA 89 NA NA No removeablebellhousing
AX4/AX5 '94-present XJ,'87-'98 YJ/TJ 3.93, 2.33, 1.44,1.00, 0.83 w/AX5 10.25 79/94 14 21 OE with AMC 4-cylinder
Note: Gear ratios differ among applications; lowest First gear unit listed.

This job is straight-up R&R-no adapters or cut-n-paste fakery. Jeepers who can change their own clutches can likely handle the task. To avoid our having to wield a wrench in one hand and a camera in the other, CRC Performance Transmissions agreed to handle the in-and-out, which is easier with a professional transmission jack. During the job, CRC owner Craig Calkins shared these tips from his 25-plus years of working on 4x4 geartrains. (See the photos and captions for other observations.)
* Never grease the clutch/trans input-shaft splines.
* Deburr the trans housing where it mates to the bellhousing if necessary.
* If replacing the pilot bushing, always use the proper puller; don't lube a sealed-brass replacement; lightly lube a new bearing type pilot.
* Resurface or replace the flywheel as necessary. (Remanufactured flywheels are often cheaper than having the existing one resurfaced.) If the flywheel checks out (no high spots or hot spots), hand-sand the clutch surface with a sanding block to break the glaze.
* Replace the clutch assembly and release bearing in conjunction with the trans swap.
* Tighten pressure-plate bolts by hand. Uneven fingers means that something's wrong.
* Index the speedo gear correctly when transplanting it from the BA10 to AX15 to ensure the correct ratio.
* Shim the transfer-case linkage as necessary with washers to make it fit flush on AX15 housing.
* Use Loctite on skidplate bolts to discourage overtorquing and stripping out frame nuts.
Overall, this swap is an efficient solution to the Peugeot problem. Rockland took the guesswork out of the spline/gear and pilot-bushing variables, and CRC dialed in the details to demonstrate how a trans conversion can be executed to look OE with no fabrication or special mechanical skills required. The bottom line here is that Peugeot gears are great for 10-speed bikes, but they have no business in Jeeps.

Sources

Rockland Standard Gear
Sloatsburg, NY
877-774-4327
www.rsgear.com
Advance Adapters
Paso Robles, CA 93446
800-350-2223
www.advanceadapters.com

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