Notorious How to know if you have enough shims?

[thepiper]

So I got my diff shims in (exterior diff shims). I have taken apart everything, removed the stock shim, which is thicker than the shims I got. How do I know how many shims to install? Even with just stock shim, I don't feel any clicking between the gears.

 

[SrC]

If the diffs 4 screws are all snug and tight and there is no end play left to right with the stock shim, leave as is. You truly need to remove the whole bulkhead to see any visible backlash by looking at the input gear and ring gear. Extreme slop can be heard. An audible ticking sound. Only visible way is by looking thru the bottom opening of the bulkhead (removed from the chassis). I would reuse the original shim. The fact that it was in place means it is probably correct as is. But after a few hard bashes, the gears will break in, the bearing carriers will settle in place and an additional shim may be in order. And maybe not. Just have to check them.

 

[3d-rc.myshopify.com]

Like @SrC said has to be visibly checked. I have had a few diff housing require shims on opposite ring side and a couple need shims on both sides. Some need the pinion shimmed as well. But you have to see to tell. It's good to check shimming after a couple packs and then again every 5or so after. If you don't blow a ring gear by then it will last a while

 

[SrC]

I agree with @Lovestricken , I have had to shim both ends as well. I had a real hard time with a few diffs. I needed just the right shims both left and right. That can happen. It threw me off for awhile trying to figure that one out. Without the bulkhead removed, you are doing it blind. If you shortcut this, it is really hit or miss.

 

[thepiper]

I agree with @Lovestricken , I have had to shim both ends as well. I had a real hard time with a few diffs. I needed just the right shims both left and right. That can happen. It threw me off for awhile trying to figure that one out. Without the bulkhead removed, you are doing it blind. If you shortcut this, it is really hit or miss.

I added one shim to front and rear. I didn't feel any greater resistance. If it sounds like straining in any way, I'll remove the front one, as that is likely the diff with the least wear.

 

[SrC]

You will hear a heavy growl if they are too tight. But the best way is to remove pinion and check drive train for excessive binding by hand for a final check. The assembled diff should free spin somewhat easily unattached to the rear drive shaft. They do loosen up after a good break in.
There is a learning curve... by doing it over and over you develope a knack for it. Watching many videos help. From different people doing it is good. You learn different aspects of it from different people. There are differing techniques. You have to find what works best and efficiently for you. But in the end there is only one correct way done right. How you get there is up to you.

 

[thepiper]

You will hear a heavy growl if they are too tight. But the best way is to remove pinion and check drive train for excessive binding by hand for a final check. The assembled diff should free spin somewhat easily unattached to the rear drive shaft. They do loosen up after a good break in.
There is a learning curve... by doing it over and over you develope a knack for it. Watching many videos help. From different people doing it is good. You learn different aspects of it from different people.

I did remove the pinion, and turned the diffs by grabbing the drive shaft. I put some Lucas grease in it, a bit more than was in there from factory. I'll likely open it up after a run and wipe off any excess that isn't making contact with the gears

 

[SrC]

Don't worry about the extra grease. But if you want to its ok. I watched a video of someone, a YT'er I will let remain anonymous here, who swore stuffing the whole bulkhead with grease was the right way to do it. That's a different story which is NO good.. But, Extra grease at the bottom where it touches the chassis is good because it keeps water and dirt from entering. They sell gaskets to seal off the lower bulkhead to the chassis also. Many guys use them. Its good too. I don't. Just some grease.. I like my own grease and and remove the original.
I think the factory is a bit light with the grease anyway. I find its stinks too like its just animal fat grease or something.

I want my diff to smell like car grease not cooking lard fat.

 

[thepiper]

Don't worry about the extra grease. But if you want to its ok. I watched a video of someone, a YT'er I will let remain anonymous here, who swore stuffing the whole bulkhead with grease was the right way to do it. That's a different story which is NO good.. But, Extra grease at the bottom where it touches the chassis is good because it keeps water and dirt from entering.

I also pushed some around the besrijg area, including where the bearings sit in the bulkhead. I figure it will prevent water from enter for a little while. I was seeing some slight rusting on a portion of the bearings, on the outer ring. But every bearing, it was a certain portion, right where the case comes away to allow for removal.

 

[3d-rc.myshopify.com]

Good explanation but remember every model is slightly different. Arrma shims the outside of the bearings and shim the pinion before you shim the out drive.

 

[SrC]

I also pushed some around the besrijg area, including where the bearings sit in the bulkhead. I figure it will prevent water from enter for a little while. I was seeing some slight rusting on a portion of the bearings, on the outer ring. But every bearing, it was a certain portion, right where the case comes away to allow for removal.

I do the same. Good idea.

 

[thepiper]

Good explanation but remember every model is slightly different. Arrma shims the outside of the bearings and shim the pinion before you shim the out drive.

Why the pinion first? Most advise I've gotten here concerns shimming diff. How does shimming outside the bearing impact things? Bearing wear?

 

[3d-rc.myshopify.com]

Why the pinion first? Most advise I've gotten here concerns shimming diff. How does shimming outside the bearing impact things? Bearing wear?

Most people honestly think they know what they are doing because someone told them or they watched a video... shim the pinion first so it is as far into the case as you can before it hits the diff itself. I will link a video about that....
Think of it this way you shim the side to side until it is the most perfect mesh ever. But that pinion is only 2/3 engaged with the crown gear. How good is that shimming really. Feels great but it's no where as good as it could be. So you do the pinion then the sides. Also say you do the pinion shim, then the side to side shim. Now its perfect right??...... wrong ? you can usually add couple more. When you think you are done. I grab a couple more .01 shims and add 1 to each side. They cancel each other out but tighten that case up a lot. It is a lot of trial and error. Sometimes just 1 extra is needed and some times 1 extra is too much. I set a new diff just the smallest bit on the snug side. I assemble and resemble a diff at least 5 times before I am happy enough with it. When you get it right you will feel it in the case when you spin it.
As far as the shimming on the bearings. That's to stop the actually gear mesh from falling apart or moving in to tight. I will throw a few videos up here and study them well.

 

[Willl]

Where in the US can you purchase 13x19mm shims for the pinion?

 

[3d-rc.myshopify.com]

These are what I use. Both different thicknesses. I recommend a couple packs of each per truck.

 

[Willl]

Thank you Sir

 

[thepiper]

Most people honestly think they know what they are doing because someone told them or they watched a video... shim the pinion first so it is as far into the case as you can before it hits the diff itself. I will link a video about that....
Think of it this way you shim the side to side until it is the most perfect mesh ever. But that pinion is only 2/3 engaged with the crown gear. How good is that shimming really. Feels great but it's no where as good as it could be. So you do the pinion then the sides. Also say you do the pinion shim, then the side to side shim. Now its perfect right??...... wrong ? you can usually add couple more. When you think you are done. I grab a couple more .01 shims and add 1 to each side. They cancel each other out but tighten that case up a lot. It is a lot of trial and error. Sometimes just 1 extra is needed and some times 1 extra is too much. I set a new diff just the smallest bit on the snug side. I assemble and resemble a diff at least 5 times before I am happy enough with it. When you get it right you will feel it in the case when you spin it.
As far as the shimming on the bearings. That's to stop the actually gear mesh from falling apart or moving in to tight. I will throw a few videos up here and study them well.

I see what you're getting at, but if your gear alignment is 1/3 not contacting, you have a poor design diff. 0.1mm here and there will not really alter how perfect the contact area is, and if is visibly off, observable with the eyes, you are likely dealing with 0.5mm or more, requiring a lot of shimming on the pinion and ring gear.

As for tightening things up, you want tight to remove play. Too tight will start increasing friction in bearings, and cause faster wear.

 

[SrC]

These RC diffs are not precision like scale car diffs. Sometimes we can only get them "good enough" to where they will "function good enough". And that's purely subjective and applies on a diff by diff basis. Diff bulkheads are very much part of this equation. There is inconsistency in mfr. You have to work best with what you have in front of you. Many go the HR and Vitavon alloy bulkhead route with more consistent results. At a $substantial$ cost however. (They still must be shimmed "good enough"). So that's a personal financial call. I wouldn't buy them just because they look trick. $Ouch$. But they are tempting. And some feel they are absolutely required for a good diff setup and use them out the gate. I am on the fence regarding this.?‍

Edit: I notice that no matter what you do, there is always going to be a high spot and low spot between the Pinion and ring gears as it rotates. More evident the closer your mesh becomes. So at some point you have to stop with bringing the mesh closer. There is a trade off. More so with plastic diff cups IMHO.

 

[SrC]

I also pushed some around the besrijg area, including where the bearings sit in the bulkhead. I figure it will prevent water from enter for a little while. I was seeing some slight rusting on a portion of the bearings, on the outer ring. But every bearing, it was a certain portion, right where the case comes away to allow for removal.

I lightly smear all the outer races and the inner races of every bearing in my rigs. Helps prevent galling as the bearings wear over time. Then they wont seize up and bricked bearing removal is easy. Had bearings seize up before on axles and diff output cups etc. I also lightly smear some grease on the axles before sliding on the wheel hexes. They can seize up also.

 

[thepiper]

I lightly smear all the outer races and the inner races of every bearing in my rigs. Helps prevent galling as the bearings wear over time. Then they wont seize up and bricked bearing removal is easy. Had bearings seize up before on axles and diff output cups etc.

So even wheel hub axles? How does the grease stay on? Can you show any pics of how you apply the grease?