How to replace Z Car ZMXB8 differential bearings
by William Goodwin
Ceramic Orange Seal Bearing Installation
We will be installing new bearings in all 3 differentials and also in the steering rack. First off you want to start with a nice clean car as not to carry any foreign materials like dirt and sand into the new bearings and or the differential gears. You will also need a 1.5mm, 2mm,and a 2.5mm allen wrench and also a 4mm nut driver, and a small phillips and also a flat screwdriver.
Starting with the front end you must first remove the front shocks and the shock tower by removing the 2-4mm nuts at the top of the shocks and 2-2mm screws on the lower arms at the bottom of the shocks then the 6-2mm screws that fasten the shock tower to he differential bulkhead.
Next we will work on separating the differential bulkhead from the chassis. To disassemble the front end you must first locate and remove the 2mm screw holding the bumper in place then the 4-2.5mm screws that hold the differentials bulkhead to the chassis as shown.
Next you will locate and remove the 2-2mm screws which connect the upper chassis brace to the differential bulkhead and the 2-4mm nuts which hold the front upper arms in the rear to the top of the steering assembly. Turn the car over and remove the 2-2mm screws that hold the front chassis brace to the chassis and remove the whole assembly (chassis brace, steering top plate, and differential top brace) all as one unit.
Now you can remove the differential bulkhead from the chassis.
Now you must remove the 2 long phillips head screws that hold the front lower arm pin holder, then the 2-2mm screws that fix the front of the differential bulkhead assembly. Now you may remove the front cover and access the front differential. At this time it will be good to change the pinion gear bearings also. First remove the front input shaft by loosening the 2mm set screw then you can first remove the shaft then the pinion gear. Now with a small screwdriver from the rear of the bearing you must slowly work your way around it pushing the old bearing from the case first one side then the other.
The steering rack is now easily accessible. Pull both sides up together and remove as a unit with all components still attached. Remove the 4 bearings by using a small screwdriver and reaching inside carefully working around the bearing till it comes out. Now install the 4 new bearings and slide the entire unit back in place.
When applicable you will disassemble and re-assemble all 3 differential units by following the same process. First you must remove the 4-2mm screws that fix the gear to the differential gear case. You will also find 1-2mm set screw in the side of the case which you must also remove to gain access to the output drive pin.
On the gear side you will remove the small crown gear and the output shaft drive pin then slide the output shaft out of the gear which will allow you to change the bearing. Next you must remove the 2 sets of spider gears and their shafts (pay attention to all shim locations) and the lower crown gear. Now you can slide the output drive pin out of the hole in the side of the case that you removed the set screw from.
Now you are able to remove the output shaft and slide the old bearing off of the case. It is recommended that you should have a new set of o-rings for your diff units to ensure a good seal on the output shafts. To install the new bearings just slide them onto their locations then fill and re-assemble the differential unit. Be sure to use blue loktite on the 4-2mm screws and also on the 2mm set screw.
To remove the center differential turn the chassis over, locate and remove the 4-2.5mm screws that fix the center differential to the chassis.
Remove the 4-2mm screws that attach the center bulkhead top plate and slide the 2 bulkheads off of the center differential.
Follow the same process to replace the bearings as instructed earlier in red text. Then re-assemble center diff unit by sliding bulkheads in place and locating brake disk in proper location and re-install in chassis with the 4 2.5mm thick screws and blue loktite.
The rear differential is almost the same as the front with a few exceptions. You must first remove the rear shocks by the 2-4mm nuts at the top and the 2-2mm screws at the bottom.
Then you will want to remove the front 2 pins that locate the rear arms to the chassis. You must also remove either the long screw that connects the chassis brace to the rear differential and wing stay or the 2-2mm screws that attach the chassis brace to the chassis (I prefer the 1 long bolt to the 2-2mm screws.)
Now turn the car over and remove the 4-2.5mm screws that fix the differential bulkhead to the chassis and remove the entire unit from the chassis. Next you will locate and remove the rear toe plate by way of the 2-2.5mm screws and then remove the remaining 2-2mm screws that hold the differential bulkhead cover in place.
At this time it will be good to change the pinion gear bearings also. First remove the front input shaft by loosening the 2mm set screw then you can first remove the shaft then the pinion gear. Now with a small screwdriver from the rear of the bearing you must slowly work your way around it pushing the old bearing from the case first one side then the other.
Follow the process for differential bearing replacement as stated in red text earlier. Then reassemble and re-install in chassis. Be careful to locate the brake disk properly and all shims during installation and use blue loktite on all screws.
You are now ready to enjoy your new bearings. Please allow a few tanks for them to break in fully. Thank you for your purchase of these fine premium quality bearings for your RC car from Boca Bearings.