Kraton Center diff mount

Bigjoe

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For those of you who replaced the plastic diff mount with the modified red aluminum mount, have you noticed afterwards the binding that occurs when spinning the diff?

It seemed like a great little mod so I decided to give it a go but upon tightening up the modded support the diff became difficult to spin. So I compared it to the plastic one and the aluminum piece is 3.5mm thicker but places the bearing in the same location, if that makes any sense. Ultimately it's about 1.7mm narrower between where the bearings sit.

You can also see from the side that the modded one sits at an angle when tightened down. It can't register flat against the tray. The tighter you crank the screws the more load is placed on the bearings, not good for them at all. Plus the top mount screw holes don't line up without some significant elongation.

Sucks because I really like the idea but it won't work for me. So much more load on the drivetrain and it'll kill the bearings. The only two fixes I see would be to fill the mounting holes with jb weld and redrill a couple offset or machining the bearing pocket deeper ( Vanning?).

I know HR makes one but I thought I read there were issues with that piece as well.
 

Trickelitrick

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For those of you who replaced the plastic diff mount with the modified red aluminum mount, have you noticed afterwards the binding that occurs when spinning the diff?

It seemed like a great little mod so I decided to give it a go but upon tightening up the modded support the diff became difficult to spin. So I compared it to the plastic one and the aluminum piece is 3.5mm thicker but places the bearing in the same location, if that makes any sense. Ultimately it's about 1.7mm narrower between where the bearings sit.

You can also see from the side that the modded one sits at an angle when tightened down. It can't register flat against the tray. The tighter you crank the screws the more load is placed on the bearings, not good for them at all. Plus the top mount screw holes don't line up without some significant elongation.

Sucks because I really like the idea but it won't work for me. So much more load on the drivetrain and it'll kill the bearings. The only two fixes I see would be to fill the mounting holes with jb weld and redrill a couple offset or machining the bearing pocket deeper ( Vanning?).

I know HR makes one but I thought I read there were issues with that piece as well.
Had the same issue blew my bearing twice in a row lol so now im using the plastic...BUT it is a good idea to have someone make an alu mount with the same dimensions as the plastic piece
 

Vanning

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I have not noticed anything binding as of now, but I did previously blow a bearing using that setup . I'm willing to check anything when I get home today. I can compare it to what you are witnessing. I have a HR motor mount and found that I can't use it with the HR opposite side diff hanger. There was way too much play. Now I have the HR motor mount and the modified motor mount red diff hanger. I recall noticing that I got lucky with the fit. However.... I had to modify the after market HR mount. I spent lots of time setting up that entire assembly. This is all why I continued to make it work.


I had to modify the top plate a little... I had to slightly elongate the holes, I leave that all loose, install the five screws from under the chassis and snug them. then tighten down the top plate 4 screws. The center diff spins free between the 2 hangers. I don't think that has much to do with what you are saying but I want to just mention that.

You could be right about the stock motor mount used with the opposite side modified motor mount. I did blow a bearing doing that.. however, I blew out 2 other bearings in the center drive line pretty fast also. The outer pinion bearings. I'm replacing them with Boca ceramic hybrids Also.

I'll look later tonight to see if I can find out anything. But I have spent time looking at the fitment of the center diff. I have had 4 different combinations and did take note of different tolerances.


Had the same issue blew my bearing twice in a row lol so now im using the plastic...BUT it is a good idea to have someone make an alu mount with the same dimensions as the plastic piece

I think the HR one is the same as the stock plastic one. I'll have to double check.
 
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Bigjoe

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I have not noticed anything binding as of now, but I did previously blow a bearing using that setup . I'm willing to check anything when I get home today. I can compare it to what you are witnessing. I have a HR motor mount and found that I can't use it with the HR opposite side diff hanger. There was way too much play. Now I have the HR motor mount and the modified motor mount red diff hanger. I recall noticing that I got lucky with the fit. However.... I had to modify the after market HR mount. I spent lots of time setting up that entire assembly. This is all why I continued to make it work.


I had to modify the top plate a little... I had to slightly elongate the holes, I leave that all loose, install the five screws from under the chassis and snug them. then tighten down the top plate 4 screws. The center diff spins free between the 2 hangers. I don't think that has much to do with what you are saying but I want to just mention that.

You could be right about the stock motor mount used with the opposite side modified motor mount. I did blow a bearing doing that.. however, I blew out 2 other bearings in the center drive line pretty fast also. The outer pinion bearings. I'm replacing them with Boca ceramic hybrids Also.

I'll look later tonight to see if I can find out anything. But I have spent time looking at the fitment of the center diff. I have had 4 different combinations and did take note of different tolerances.




I think the HR one is the same as the stock plastic one. I'll have to double check.


What was loose on the HR diff hanger for you? I might just pick up one if the dims are the same as the plastic piece. It would sure beat that flexy, stripped screw hole stock plastic.

On a side note, I'm going to try to mod the HR mount like you did. More fun than sending it back. Ought to interesting with a drill press. If it comes out a tenth of yours I'll be happy. Haha.
 

Vanning

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What was loose on the HR diff hanger for you? I might just pick up one if the dims are the same as the plastic piece. It would sure beat that flexy, stripped screw hole stock plastic.

On a side note, I'm going to try to mod the HR mount like you did. More fun than sending it back. Ought to interesting with a drill press. If it comes out a tenth of yours I'll be happy. Haha.

A drill press with an x - y vice mounted to it will work as long as there is no slack in the drill chuck area of the press. . I have 2 things done to the mount.... I didn't share everything. If you get the red motor mount finished, send me a message and I'll tell you how to finish it up 100%. I have 2 good runs on mine... no problems.

To answer your first question. If I used the HR motor mount, and the metal HR hanger on the other side of the diff. I would have needed shims behind the bearings to take up lots of play or find maybe one thicker bearing or both. Large amounts of play.... I could slide the center diff back and forth an excessive amount. Totally unexceptable but could be dealt with. I opted to just try the diff hanger that we all made from the motor mount. In my senerio, it fits perfectly with the HR motor mount. it took away all the slack I had using both HR pieces.

What you are saying... there isn't enough play using the stock motor mount and our modified motor mount hanger... it's putting a side load on the bearings. You also have to remember. We are using that red mount in the reversed direction..... Is it made dead center, or is the bearing slot off center ? I looked at that till I went blind... if it is a little off, it's very slight. I recently put that to bed and decided it was. However, now you make me want to check it again and I will. If it is off center.... I'll have to use the HR part and shims. From what I remember... our modified motor/diff hanger allows the diff to sit square and it isn't cocked sideways ... but it could be too tight against the bearings.

Great post
 
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dpricenator

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Well, here I am reading this am praying this is what happened to me this weekend. I finally got everything back together. I had to use the stock servo mount, since US CUSTOMS still has mine.

I ran a couple 4s Packs through the car, and everything seemed like it was working fine. A couple small jumps and some good technical runs around some cones, so I wan one and off the gas quickly with a bunch of turns in there. Then I switched over to 6s to see the beast really open up. Not 10 minutes in to the 6S run, the center diff bearing is no longer in the mount. Being a little frustrated after all the work I did, I just put the car in the trunk and went home. I'll have to give it a closer look before I know if it was the bearing or not. I did elongate the holes on the top piece that holds the roll cage, so I knew it was not an exact fit. I may go back to the plastic one. Do we think/know the Hot Racing diff hanger is a quality part and worth using?
 

Bigjoe

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A drill press with an x - y vice mounted to it will work as long as there is no slack in the drill chuck area of the press. . I have 2 things done to the mount.... I didn't share everything. If you get the red motor mount finished, send me a message and I'll tell you how to finish it up 100%. I have 2 good runs on mine... no problems.

To answer your first question. If I used the HR motor mount, and the metal HR hanger on the other side of the diff. I would have needed shims behind the bearings to take up lots of play or find maybe one thicker bearing or both. Large amounts of play.... I could slide the center diff back and forth an excessive amount. Totally unexceptable but could be dealt with. I opted to just try the diff hanger that we all made from the motor mount. In my senerio, it fits perfectly with the HR motor mount. it took away all the slack I had using both HR pieces.

What you are saying... there isn't enough play using the stock motor mount and our modified motor mount hanger... it's putting a side load on the bearings. You also have to remember. We are using that red mount in the reversed direction..... Is it made dead center, or is the bearing slot off center ? I looked at that till I went blind... if it is a little off, it's very slight. I recently put that to bed and decided it was. However, now you make me want to check it again and I will. If it is off center.... I'll have to use the HR part and shims. From what I remember... our modified motor/diff hanger allows the diff to sit square and it isn't cocked sideways ... but it could be too tight against the bearings.

Great post

If the HR center mount is dimensionally the same as the plastic one: 6.5mm thick, centered screw holes, and a 5mm pocket for the bearing then that's what will work for my chassis. I have perfect clearance with the plastic piece. If it's spread slightly I have just a slight bit of fore and aft movement that just hits zero as I close it and pop the top on. With the red mod the thickness is 10mm with the same centered screw holes and 5 mm bearing pocket. That's what killing it for me, the 1.75mm closer bearing location.

As far as the red mount, if I was a betting man I would put money on it that it's centered. Purely eyeing it vs the plastic piece against both sides though. It couldn't be more than a couple thousandths either way. Could be worth measuring for the fun of it.
 

Vanning

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If this makes any sense.... the 2 HR black parts together don't work and need shims. The 2 red Arrma parts together are too tight. The HR motor mount and red Arrma mod part works. The red Arrma motor mount and the HR black hanger works. Then there is the stock setup that obviously works.

Basically......
If black is combined with red... it works. All these combos work to a degree, However...some peoples part may not be perfectly made and cause binding.
 

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dpricenator

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OK, Gonna have to go back to the stock diff hanger until there are more of the Hot Racing Aluminum versions in stock. I really hope I did not blow the diff or hurt my new diff carrier. Hoping it's just the bearing.
 

Vanning

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OK, Gonna have to go back to the stock diff hanger until there are more of the Hot Racing Aluminum versions in stock. I really hope I did not blow the diff or hurt my new diff carrier. Hoping it's just the bearing.
There was probably just slightly too much side force in the bearing. Then once it got hot

and loaded with grit it blew.
 
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Kauaiguy

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There was probably just slightly too much side force in the bearing. Then once it got hot

and loaded with grit it blew.
Mine fits fine, wonder how come there not all the same?Although it didn't have room for the rock too!
 

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Thats funny how all these tolerances vary. Makes you beat your head against the wall trying to find the perfect combo.

This is what I'm working with. I bolted the HR motor mount and red mount on the chassis with the center diff and it still binds. It's much better than with the two reds but still about .5mm narrower than the diff. I also tried the HR motor mount with the plastic mount and it is loose like Vanning said, about .75mm of fore and aft slop. The plastic does secure the bearing pretty good so it probably would be acceptable even with the HR motor mount not securing the bearing too well.

Too bad because the whole point of this is to get rid of the plastic.
 

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Vanning

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I have a HR motor mount, HR center diff housing, 2 Boca ceramic bearings and I went with the Red modded diff hanger. My diff spins freely and I can feel very slight back and forth movement. I did feel I got lucky when it all worked.

You have to mount everything in the chassis with no motor or drive shafts. Then see how it all spins.

If I recall...Kauaiguy may have blown a bearing with the stock setup. Stock motor mount and plastic hanger. That would rule out a few thoughts if he did.

I'm wondering if the HR metal differential case locates the bearing a little more inward allowing more clearance ? Or, your binding is from something else. One of your parts may be slightly off and if it's the 2 red ones...it's going to magnify the worst because they do seem to be the snuggest fit.

View attachment 6365 View attachment 6366

Thats funny how all these tolerances vary. Makes you beat your head against the wall trying to find the perfect combo.

This is what I'm working with. I bolted the HR motor mount and red mount on the chassis with the center diff and it still binds. It's much better than with the two reds but still about .5mm narrower than the diff. I also tried the HR motor mount with the plastic mount and it is loose like Vanning said, about .75mm of fore and aft slop. The plastic does secure the bearing pretty good so it probably would be acceptable even with the HR motor mount not securing the bearing too well.

Too bad because the whole point of this is to get rid of the plastic.

Do the bearings account for 10mm ? I come up with 10.57mm of room for the bearings to fit,using your measurements. 31.76 -21.19 = 10.57. If I recall...the bearings I just got were 5mm wide.

Try making sure your upper plate has enough hole clearance and isn't forcing the tops of the mounts together...I know that's a long shot but that's just a thought. I really think you just have a mount that isn't square on the bottom. Maybe you can square it up better.

View attachment 6365 View attachment 6366

Thats funny how all these tolerances vary. Makes you beat your head against the wall trying to find the perfect combo.

This is what I'm working with. I bolted the HR motor mount and red mount on the chassis with the center diff and it still binds. It's much better than with the two reds but still about .5mm narrower than the diff. I also tried the HR motor mount with the plastic mount and it is loose like Vanning said, about .75mm of fore and aft slop. The plastic does secure the bearing pretty good so it probably would be acceptable even with the HR motor mount not securing the bearing too well.

Too bad because the whole point of this is to get rid of the plastic.

With the 2 HR parts, .75 of fore and aft is no good....the spur would be all over the place. That probably could be shimmed and be golden. .35 a side I actually was going to go that route but the red hanger worked with my HR motor mount. I actually could cut the perfect size shims to take all the fore and aft out of the 2 HR mounts.

View attachment 6359
Mine fits fine, wonder how come there not all the same?Although it didn't have room for the rock too!

Some of them are probably much more square against the chassis.
 
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Bigjoe

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I have a HR motor mount, HR center diff housing, 2 Boca ceramic bearings and I went with the Red modded diff hanger. My diff spins freely and I can feel very slight back and forth movement. I did feel I got lucky when it all worked.

You have to mount everything in the chassis with no motor or drive shafts. Then see how it all spins.

If I recall...Kauaiguy may have blown a bearing with the stock setup. Stock motor mount and plastic hanger. That would rule out a few thoughts if he did.

I'm wondering if the HR metal differential case locates the bearing a little more inward allowing more clearance ? Or, your binding is from something else. One of your parts may be slightly off and if it's the 2 red ones...it's going to magnify the worst because they do seem to be the snuggest fit.



Do the bearings account for 10mm ? I come up with 10.57mm of room for the bearings to fit,using your measurements. 31.76 -21.19 = 10.57. If I recall...the bearings I just got were 5mm wide.

Try making sure your upper plate has enough hole clearance and isn't forcing the tops of the mounts together...I know that's a long shot but that's just a thought. I really think you just have a mount that isn't square on the bottom. Maybe you can square it up better.



With the 2 HR parts, .75 of fore and aft is no good....the spur would be all over the place. That probably could be shimmed and be golden. .35 a side I actually was going to go that route but the red hanger worked with my HR motor mount. I actually could cut the perfect size shims to take all the fore and aft out of the 2 HR mounts.



Some of them are probably much more square against the chassis.


Yes, the bearings are 5mm each, 10mm total. Should have mentioned that. It would have made the measurements make more sense.

So far I haven't messed with the top plate other than just eyeing up the hole locations with the mounts. If all was ok with the two reds then I would have elongated the set of holes over the red mod as well as removed the outer locating edge to keep it from pulling the mounts together.

The two mounts are machined pretty well. I measured the distance between them at the base and top and there's about .10 mm difference. It would be tempting to taper the base of the red mod to bring it in but angling the bearing like that can't be to good. There is a lot of slop in these cheap bearings so it might work. Or maybe they'll just explode with the rpms they see, lol.
 

Vanning

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I can get the holes to just about line up....if I look down from the top, it's just about dead on. I had to slightly adjust 2 holes to clear the button head screws . Your chassis could be slightly bent like a taco....just a thought.
 
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