My step by step methods for correcting drivetrain mis-alignment.

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, and others.

Polar_Bus

Well-Known Member
Messages
754
Today was a good day in the end. It's amazing what you find when you go to re-assemble parts (meaning parts that just don't fit right). Spent the whole day today working on drivetrain alignment and dam most all the components were off, some a LOT.
By design the drivetrain is "fixed" meaning you can't adjust your spur / pinion backlash. This backlash is pretty critical to reliable power transfer to the transmission. Excessive teeth backlash and you will strip teeth or wear them out quickly. To tight will stress out your bearings and bind up your drivetrain and loss of top end speed. It's tough to explain how much backlash is "just right". Because most spur gears don't run perfectly concentric you will have a fluctuation in backlash as you run your gears around. I find the "tightest" spot and set my backlash at that point to "almost " zero backlash. What you don't want is to feel the gears bind. You want total smoothness all the way around. My Rovan's chassis does have the ability for a very small adjustment to set the gear backlash. The 2 mount bolts under the pull start housing are actually slotted to allow the engine to pivot a very small amount. This is how you can adjust your backlash. However it's NOT that simple. As you change the position of the engine, you alter all the mount positions of the connecting brackets that connect the engine to the transmission. My backlash from the factory did have a minor bind but not too bad, I want it perfect with zero bind. Once I found my tight spot I was able to set my backlash and lock down the engine. I wanted a beefier bracket that connected the clutch housing to the rear upper aluminum bracket. This is a weak link and could cause excessive flex IMO. I fabbed a custom bracket out of aluminum, and dam what a royal PIA to get the bracket just right. That bracket sets a precedent for all other components' proper alignment.


My primary alignment issue was the gear plate bracket would not line up with the rear upper diff bracket. The only solution was to remove about .040" off the surface of the clutch bell bracket where the gear plate bracket mounts. This would move the gear plate bracket inwards so I can get everything lined up. This is a very critical alignment as the trans input shaft bearing carrier, as well as the brake caliper all bolt together. After much fitting and filing material I got the gear bracket to fit nice, and the bolts that mount the trans shaft bearing carrier , and the brake caliper dropped right in and threaded in. Success !




The next issue was my brake caliper, first issue was it was way too tight fitting inside the gear bracket, simple fix was to open up the edges of the gear bracket with a file. My next issue was the caliper mount bracket pins were drilled crooked. The inboard brake pad (closest to the mount bracket) would not slide all the way down the pins. This was causing a lot of brake drag that I felt when rotating the tires. If you don't address this issue you will overheat your brakes and they will fail.


The solution was to drill the brake pad mount holes larger with a #30 drill. This added about .004" of clearance and the pads moved up and down smoothly. Keep in mind there is NOTHING wrong with having your brake pads "free floating". This will ensure there is NO drag on the brake rotor keeping friction heat to a minimum. While I have the brake caliper apart i'll share a little tip to gain some better , more "progressive" brake pad leverage. The typical brake cam has a simple slot milled through the shaft. This creates a very poor transfer of leverage to the inboard brake caliper. It's also like "all or nothing" as far as a progressive braking. I like to add a small radiused chamfer on the contact edge of the cam slot. This add better energy leverage passed to the brake pad. The pic shows the stock brake cam, and the black Sharpie ink is where you want to file a very small radius on the edge. Don't go crazy with the bevel because when you do this mod you also change the required sweep of the cam action, and you need to slightly add a bend to the cam arm bracket that attaches to your linkage. I'll cover that in my upcoming throttle linkage mod thread.




Here's an Autocad cross section screenshot of what i'm describing with the radius, the pic is pretty crappy :


Lastly was I needed to add a washer shim to the upper engine bracket on the LH side. You don't want to be "pulling" on any components when you tighten things up. The idea is to always allow brackets and mounts to remain unstressed as you tighten things together. Here's a pic of the final assembly, perfect compromise of gear mesh both tight and loose to compensate for the spur gear runout, and all the brackets fall into perfect alignment.


Last issue for today was the spur gear offset. From the factory my spur gear C clip was deformed and incorrectly installed on the shaft. It most likely would have popped off at the worst time and ended my day. This was a tough fix. If I pushed the spur gear as far as I could on the shaft I could get the C clip in the shaft slot BUT the OD of gear teeth was way too close for comfort for interfering with the clutch bell bracket. I was able to shim the spur gear outward using Fasteddy's hub shims (which fit the trans input shaft perfect ). Once I had comfortable gear clearance from the spur gear I had to machine material off the face of the spur gear so I can correctly install the C clip on the trans shaft. I removed about .040".

In this pic I actually have the spur gear pulled out just a bit, if I were to push the spur all the way and be able to engage the C clip the spur teath would be just about touching the center hub of the pinion bracket :







And that's it. The rear drivetrain is trued and not all twisted stressed from being slapped together from the factory. Again, just trying to add some knowledge tips for how you can tweak components to be better fitting which equals less rolling resistance, which ultimately means more HP put into the dirt ! (y)(y)



The final assembly :

 
Last edited:
Today was a good day in the end. It's amazing what you find when you go to re-assemble parts (meaning parts that just don't fit right). Spent the whole day today working on drivetrain alignment and dam most all the components were off, some a LOT.
By design the drivetrain is "fixed" meaning you can't adjust your spur / pinion backlash. This backlash is pretty critical to reliable power transfer to the transmission. Excessive teeth backlash and you will strip teeth or wear them out quickly. To tight will stress out your bearings and bind up your drivetrain and loss of top end speed. It's tough to explain how much backlash is "just right". Because most spur gears don't run perfectly concentric you will have a fluctuation in backlash as you run your gears around. I find the "tightest" spot and set my backlash at that point to "almost " zero backlash. What you don't want is to feel the gears bind. You want total smoothness all the way around. My Rovan's chassis does have the ability for a very small adjustment to set the gear backlash. The 2 mount bolts under the pull start housing are actually slotted to allow the engine to pivot a very small amount. This is how you can adjust your backlash. However it's NOT that simple. As you change the position of the engine, you alter all the mount positions of the connecting brackets that connect the engine to the transmission. My backlash from the factory did have a minor bind but not too bad, I want it perfect with zero bind. Once I found my tight spot I was able to set my backlash and lock down the engine. I wanted a beefier bracket that connected the clutch housing to the rear upper aluminum bracket. This is a weak link and could cause excessive flex IMO. I fabbed a custom bracket out of aluminum, and dam what a royal PIA to get the bracket just right. That bracket sets a precedent for all other components' proper alignment.


My primary alignment issue was the gear plate bracket would not line up with the rear upper diff bracket. The only solution was to remove about .040" off the surface of the clutch bell bracket where the gear plate bracket mounts. This would move the gear plate bracket inwards so I can get everything lined up. This is a very critical alignment as the trans input shaft bearing carrier, as well as the brake caliper all bolt together. After much fitting and filing material I got the gear bracket to fit nice, and the bolts that mount the trans shaft bearing carrier , and the brake caliper dropped right in and threaded in. Success !




The next issue was my brake caliper, first issue was it was way too tight fitting inside the gear bracket, simple fix was to open up the edges of the gear bracket with a file. My next issue was the caliper mount bracket pins were drilled crooked. The inboard brake pad (closest to the mount bracket) would not slide all the way down the pins. This was causing a lot of brake drag that I felt when rotating the tires. If you don't address this issue you will overheat your brakes and they will fail.


The solution was to drill the brake pad mount holes larger with a #30 drill. This added about .004" of clearance and the pads moved up and down smoothly. Keep in mind there is NOTHING wrong with having your brake pads "free floating". This will ensure there is NO drag on the brake rotor keeping friction heat to a minimum. While I have the brake caliper apart i'll share a little tip to gain some better , more "progressive" brake pad leverage. The typical brake cam has a simple slot milled through the shaft. This creates a very poor transfer of leverage to the inboard brake caliper. It's also like "all or nothing" as far as a progressive braking. I like to add a small radiused chamfer on the contact edge of the cam slot. This add better energy leverage passed to the brake pad. The pic shows the stock brake cam, and the black Sharpie ink is where you want to file a very small radius on the edge. Don't go crazy with the bevel because when you do this mod you also change the required sweep of the cam action, and you need to slightly add a bend to the cam arm bracket that attaches to your linkage. I'll cover that in my upcoming throttle linkage mod thread.




Here's an Autocad cross section screenshot of what i'm describing with the radius, the pic is pretty crappy :


Lastly was I needed to add a washer shim to the upper engine bracket on the LH side. You don't want to be "pulling" on any components when you tighten things up. The idea is to always allow brackets and mounts to remain unstressed as you tighten things together. Here's a pic of the final assembly, perfect compromise of gear mesh both tight and loose to compensate for the spur gear runout, and all the brackets fall into perfect alignment.


Last issue for today was the spur gear offset. From the factory my spur gear C clip was deformed and incorrectly installed on the shaft. It most likely would have popped off at the worst time and ended my day. This was a tough fix. If I pushed the spur gear as far as I could on the shaft I could get the C clip in the shaft slot BUT the OD of gear teeth was way too close for comfort for interfering with the clutch bell bracket. I was able to shim the spur gear outward using Fasteddy's hub shims (which fit the trans input shaft perfect ). Once I had comfortable gear clearance from the spur gear I had to machine material off the face of the spur gear so I can correctly install the C clip on the trans shaft. I removed about .040".

In this pic I actually have the spur gear pulled out just a bit, if I were to push the spur all the way and be able to engage the C clip the spur teath would be just about touching the center hub of the pinion bracket :







And that's it. The rear drivetrain is trued and not all twisted stressed from being slapped together from the factory. Again, just trying to add some knowledge tips for how you can tweak components to be better fitting which equals less rolling resistance, which ultimately means more HP put into the dirt ! (y)(y)



The final assembly :

Nice work ? I'm Gunna have to give my Baja A once over (more like 9 over cuz all the half asses stuff)
 
My fix for this problem cost me 200 dollars in parts .:mad::ROFLMAO::ROFLMAO::ROFLMAO::ROFLMAO:


I may have to perform a drivetrain alignment all over again as I bought a billet aluminum transmission carrier shaft bearing support. Stupid part is taking FOREVER to be shipped. It's coming from Hong Kong, I It was listed in California. typical lying offshore ebay sellers. My fault for not doing better research !
 
I may have to perform a drivetrain alignment all over again as I bought a billet aluminum transmission carrier shaft bearing support. Stupid part is taking FOREVER to be shipped. It's coming from Hong Kong, I It was listed in California. typical lying offshore ebay sellers. My fault for not doing better research !

For me it was either the Turtle racing Quick change diff. housing or the Turtle Racing Upper rear brace that through everything off on the Rovan. I changed both at the same time sooooooo .
 
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock    No Thanks