How to Rebuild, Shim, Strengthen and Race Lube an HPI Savage X Differential
by admin @ 10:14 pm. Filed under Gear Ratio Tips, RC Events in South Carolina, HPI Savage X, HPI HellFire
Stop the presses since writing this up, I have learned a great deal about shimming savage differentials. I learned, for one, that the procedure described below is INcorrect. The small shims shown do absolutely nothing for the issue at hand, which is to #1) tighten up the play inside the diff cup and #2) tighten up the play with the crown gear and the pinion gear.
I highly recommend that you check out this article for the proper procedure on how to shim savage differentials: Here is the link to the article
Just keep that in mind when you read this
How to Rebuild, Shim, Strengthen and Race Lube a Savage X Differential - Using an Aluminum Differential Housing, axle Shims, O rings, and the Differential Lube of your choice
If you don't want to end up like I did last weekend, busted up with a stripped out spider gears in the rear end differential, you might want to strengthen up your differential. Here's How I did it…
Here's My Savage X after 10 minutes on a nice mud track - the stock, plastic differential coupled with a bad gear mesh did a real number on the rear end and left me with no truck to race
This is the culprit that brought down my Savage:
The first thing I did when I got home was to get on the computer and start ordering parts. I was determined that this would not happen again. If it does happen again, I'mgoing to an Ofna Rear End, which is apparently very very strong.
Here is a list of the parts that you will need:
1) HPI Savage 4-Gear Differential Gear Set (you'll need one cup for front, one for rear)
2) Nova 7075 Aluminum Alloy Differential Cup for Savage
3) Mugen 5,000wt Silicone Differential Lube (for Rear differential)
4) Mugen 7,000wt Silicone Differential Lube (for Front differential)
5) Mugen 50,000wt Silicone Differential Lube (for coating the outside of the differential assembly)
6) BRP Axle Shim .250x.309x.014″ (get 2 sets)
7) HPI O-Ring 5×8x1.5mm Savage 21 (6) (get 2 sets)
8) HPI O-Ring 6×9.5×2mm Black Savage 21 (8) (for the cups where the dogbone goes in, for cushion)
9) Great Planes Pro Threadlocker
10) For Differential Gaskets, I just used the old gasket, putting a thin layer of Permatex Silicone Gasket Maker there. If you need to replace your differential gaskets, Ofna makes a compatible set - Diff Gaskets
Below are some pictures of the assembly. Also, here are 2 videos showing you the point of all this:
1) The fact that the stock plastic differential flexes under load and
2) What is meant by "shimming" the differential (I know it doesn't work right now, fixing it)
Here's that stock plastic differential cup:
A few Notes on assembly:
On the Savage X, the differential is very easy to remove. All you have to do is remove 6 screws, the lower hinge pins, and pull off the differential cover. After you have the diff out, spray it down and clean it up some with some carburetor cleaner. Take it apart, noting how it goes back together!
Once you have it apart, clean up the inside, again, using carburetor cleaner or whatever works for you. Remove all cleaner residue before you go to put this back together, it might break down your diff lube if you don't.
Take the diff access set looking screw out of the side of your stock plastic diff cup, it's on the side of the cup. Transfer that screw to the new alloy aluminum diff cup AFTER you put the shims and the inside retainer pin on the shaft. Replace the inside o ring with a new one. Remove the old bearing from the stock plastic diff cup and transfer it to the new aluminum diff cup.
Put the entire gear assembly together DRY a few times, noting any play in the shafts going into the differential. You want a few thousandths of an inch play there. You want a Little play, but want to avoid too much. You are trying to get those spider gears inside to mesh as good as possible. Shim up any play with the tiny axle shims you bought.
When the play is all shimmed up right, put in your hex screw (set screw looking screw) into the side of the new aluminum diff housing. Pour your differential lube into the cup and remember that the bevel gear will displace some of that lube leave some room at the top.
Put the whole assembly together, locktight the 4 screws, and cinch it down. Note: you can't use the stock 4 screws, you will be using 4 diff cup screws that come with the aluminum diff cup.
Coat the outside of the assembly with 50,000 weight Lock Lube to catch dust. Also, put some 50k lube around and near the bearings to catch any dust and dirt that would want to enter into the assembly. You will be servicing this differential after every gallon of fuel. Put the entire assembly back into the housing, throw your 6 screws and 2 hinge pins back in and get ready to LIGHT UP THE TIRES because you're going to be transferring all of that torque to the wheels WAY more effectively now.
FYI, RTR, out of the box, there is virtually NO lube in the differentials
by admin @ 10:14 pm. Filed under Gear Ratio Tips, RC Events in South Carolina, HPI Savage X, HPI HellFire
Stop the presses since writing this up, I have learned a great deal about shimming savage differentials. I learned, for one, that the procedure described below is INcorrect. The small shims shown do absolutely nothing for the issue at hand, which is to #1) tighten up the play inside the diff cup and #2) tighten up the play with the crown gear and the pinion gear.
I highly recommend that you check out this article for the proper procedure on how to shim savage differentials: Here is the link to the article
Just keep that in mind when you read this
How to Rebuild, Shim, Strengthen and Race Lube a Savage X Differential - Using an Aluminum Differential Housing, axle Shims, O rings, and the Differential Lube of your choice
If you don't want to end up like I did last weekend, busted up with a stripped out spider gears in the rear end differential, you might want to strengthen up your differential. Here's How I did it…
Here's My Savage X after 10 minutes on a nice mud track - the stock, plastic differential coupled with a bad gear mesh did a real number on the rear end and left me with no truck to race
This is the culprit that brought down my Savage:
The first thing I did when I got home was to get on the computer and start ordering parts. I was determined that this would not happen again. If it does happen again, I'mgoing to an Ofna Rear End, which is apparently very very strong.
Here is a list of the parts that you will need:
1) HPI Savage 4-Gear Differential Gear Set (you'll need one cup for front, one for rear)
2) Nova 7075 Aluminum Alloy Differential Cup for Savage
3) Mugen 5,000wt Silicone Differential Lube (for Rear differential)
4) Mugen 7,000wt Silicone Differential Lube (for Front differential)
5) Mugen 50,000wt Silicone Differential Lube (for coating the outside of the differential assembly)
6) BRP Axle Shim .250x.309x.014″ (get 2 sets)
7) HPI O-Ring 5×8x1.5mm Savage 21 (6) (get 2 sets)
8) HPI O-Ring 6×9.5×2mm Black Savage 21 (8) (for the cups where the dogbone goes in, for cushion)
9) Great Planes Pro Threadlocker
10) For Differential Gaskets, I just used the old gasket, putting a thin layer of Permatex Silicone Gasket Maker there. If you need to replace your differential gaskets, Ofna makes a compatible set - Diff Gaskets
Below are some pictures of the assembly. Also, here are 2 videos showing you the point of all this:
1) The fact that the stock plastic differential flexes under load and
2) What is meant by "shimming" the differential (I know it doesn't work right now, fixing it)
Here's that stock plastic differential cup:
A few Notes on assembly:
On the Savage X, the differential is very easy to remove. All you have to do is remove 6 screws, the lower hinge pins, and pull off the differential cover. After you have the diff out, spray it down and clean it up some with some carburetor cleaner. Take it apart, noting how it goes back together!
Once you have it apart, clean up the inside, again, using carburetor cleaner or whatever works for you. Remove all cleaner residue before you go to put this back together, it might break down your diff lube if you don't.
Take the diff access set looking screw out of the side of your stock plastic diff cup, it's on the side of the cup. Transfer that screw to the new alloy aluminum diff cup AFTER you put the shims and the inside retainer pin on the shaft. Replace the inside o ring with a new one. Remove the old bearing from the stock plastic diff cup and transfer it to the new aluminum diff cup.
Put the entire gear assembly together DRY a few times, noting any play in the shafts going into the differential. You want a few thousandths of an inch play there. You want a Little play, but want to avoid too much. You are trying to get those spider gears inside to mesh as good as possible. Shim up any play with the tiny axle shims you bought.
When the play is all shimmed up right, put in your hex screw (set screw looking screw) into the side of the new aluminum diff housing. Pour your differential lube into the cup and remember that the bevel gear will displace some of that lube leave some room at the top.
Put the whole assembly together, locktight the 4 screws, and cinch it down. Note: you can't use the stock 4 screws, you will be using 4 diff cup screws that come with the aluminum diff cup.
Coat the outside of the assembly with 50,000 weight Lock Lube to catch dust. Also, put some 50k lube around and near the bearings to catch any dust and dirt that would want to enter into the assembly. You will be servicing this differential after every gallon of fuel. Put the entire assembly back into the housing, throw your 6 screws and 2 hinge pins back in and get ready to LIGHT UP THE TIRES because you're going to be transferring all of that torque to the wheels WAY more effectively now.
FYI, RTR, out of the box, there is virtually NO lube in the differentials
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