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JB Conversions LoMax 4:1 Gears
for the Dana 300

By Jack Brinks

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While you’re standing at the press, reverse the input gear process above. Press the input shaft back into the stock bearing making sure the original shims stay in place by using grease to retain them. Install the new LoMax input gear onto the splines of the input shaft and secure with the new retaining snap ring provided in the kit.

Now measure the gap below the retaining ring with a feeler gauge. It should be no more that 0.003”. If more, it will be necessary to add shims to correct. Spec is 0.000” to 0.003”. Next, install the special double-lipped seal into the input housing.

To install the new shift rails into the front output bearing retainer housing, mount the housing in a padded clamp or vise to avoid damage to the aluminum surfaces. First, pry out the old shift rail seals and use a small hammer to tap in the new seals until they are flush with the face of the housing.

JB Conversions LoMax

Install the 2 new heavier detent springs (if you choose to do so – read Road Testing comments first!) in the bores on top of the housing. Place a detent ball on top of the spring in the left bore, and insert the slotted end of the new shift rail, with the slot vertical, (the rail with the large area removed for gear clearance) into the bore on the back side of the housing. Push the rail in until it contacts the ball and, while using a small punch to push down on the ball, continue to push the rail forward until exactly 4 11/16” is left sticking out of the housing. Remember not to rotate the rail while doing this. Follow this by inserting the shift interlock pills into the side bores as far as they will go. Check to make sure they will not obstruct installation of the second shift rail.

JB Conversions LoMax

Place the second detent ball on top of the remaining detent spring, and with the second shift rail positioned with the slot vertical and the detent slots towards the inside, push down on the ball as before end push or tap the second rail until exactly 5 5/16” remain out of the housing. Again, do not rotate the rails during installation.

Now, with a punch or similar object, rotate the second rail 90 degrees counter-clockwise. You will feel the detent ball pop into place. Then, rotate the first rail 90 degrees clockwise and tap it slightly towards the rear. You should feel the detent ball pop into place.

JB Conversions LoMax

Tap the first rail rearward one more notch until it is even with the other rail. I used RTV to seal the shift interlock bores in the side of the housing, or you can use insert plugs if you bought a rebuild kit. I also know some folks who use pipeplugs threaded into the aluminum housing. The choice is yours. Set the housing aside for later.

JB Conversions LoMax

Now, back to the press. Place one of the two 27 tooth LoMax gears inside the case and insert the rear output shaft through it, making certain you install the stock thrust washer on the shaft above the gear. Support the shaft inside the case as shown in the photo and press the bearing (#25880) onto the shaft until it contacts the thrust washer. Make sure the gear can turn freely.

Put the remaining 27 tooth LoMax gear inside the case with the front output shaft passing through it, place the bearing (#86649) under the gear and press it on until it contacts the ridge on the shaft. Make certain you support the bearing inner race so you don’t damage the cage. Note: this is very difficult to do! Get some help here holding everything while you do this or, if you’re very careful, do what I did and use a punch and small hammer to carefully tap this bearing onto the shaft. It took awhile, but since you can’t see the bearing during the pressing operation, I felt better using the punch.

Install the new slider ring, 18-tooth LoMax gear and bearing (another #86649) onto the front output shaft and press it until the bearing hits the ridge of the shaft. Again, be careful not to press on the cage of the bearing - just the inner race. Make sure the gear will turn freely after installation.

Put the last slider ring over the clutch teeth of the rear output shaft and install the front input gear assembly into the front of the case, using RTV to seal it to the case. Install the 6 Allen bolts, pulling the input assembly down evenly. Torque these down to 10 Ft Lbs.

JB Conversions LoMax

Bolt the rear output housing to the case after installing the original bearing shims. Torque to 35 Ft Lbs. Then install the bearing (#15117), install the new seal and then the output driveshaft yoke, torque it to 100 Ft Lbs and verify end play of 0.002” to 0.005”. If you use your old bearings, this measurement will probably be correct, assuming it was right in the first place. If it is incorrect, you will need to remove the housing and re-shim accordingly.

JB Conversions LoMax

Install the bearing race (#M86610) into the rear bore (supporting the rear of the front output shaft) of the case. Then install the retainer plate and original shims. Don’t seal it now, as we’ll need to check end play later and may have to re-shim it.

Place the shift forks in the case, big one first. Install the front output housing, inserting the shift rails through the forks as you go. Put some oil on the forks/rails to help facilitate this process. Bolt the housing in place, and torque it to 35 Ft Lbs, using RTV to seal it to the case. Install the 2 set screws for the shift forks. Use a thread locking compound, such as Loctite, to secure these screws and torque to 14 Ft Lbs. Now, you can verify front output shaft end play using a dial indicator. It should be between 0.003” to 0.006”. If you used your old bearings, you’ll probably be OK, again assuming everything was OK to begin with! With new bearings, you may need to re-shim the retainer plate to gain the desired end play. When you get it right, don’t forget to seal the retainer plate to the housing using RTV and torque it to 35 Ft Lbs. Install the new front output shaft seal and yoke and torque the nut to 100 Ft Lbs.

JB Conversions LoMax JB Conversions LoMax JB Conversions LoMax

Use wheel bearing grease or Vaseline to install the needle bearings in the new LoMax idler gear. Don’t be afraid to use as much as needed to hold the needles in place. It’ll mix with the gear lube and not hurt a thing. Remember to install the 3 spacers, with the thick one in the middle, and make sure you install all the needles. Place the cross shaft into the back of the case and, using grease or Vaseline coat one of the thrust washers to hold it in place as shown in the photo. Again using grease, place the other thrust washer on the opposite side of the case, using your finger to keep it lined up as you roll the idler gear into place. Line up the flat on the rear of the cross shaft with the retainer and push the cross shaft through the thrust washers and idler gear, making certain that all needle bearings stay in place. If you used enough grease, this should be fairly easy. Then, install the retainer and bolt to lock the cross shaft in place, torquing it to 23 Ft Lbs.

JB Conversions LoMax JB Conversions LoMax

Install the inspection cover, using the supplied gasket and RTV to seal it, and install the speedometer gear assembly into the rear output housing in the same orientation as originally. Torque both inspection cover and speedo assembly bolts to 15 Ft Lbs.

That’s it! With the exception of re-installing the transfer case and filling it with the gear lube of your choice, you’re done! Externally, it doesn’t look any different, but you’ve just successfully installed your new LoMax 4:1 gears!

Now, first the road test and then the real fun; the off-road test!

JB Conversions LoMax JB Conversions LoMax



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