4 Spider diff on its way out

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rossb

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I was cleaning my truck up and lubricating everything and when I went to spin the rear diff I could feel the spider gears in the rear diff binding up.

The gears feel smooth when I lift all four wheels off the ground and spin the tires (all tires and transmission spinning, spiders not spinning).

If I leave the rear wheels on the ground, lift the front, and spin one front tire (with the other front tire spinning in the opposite direction) the front diff feels silky smooth.

If I leave the front wheels on the ground, lift the rear, and spin one rear tire (with the other rear tire spinning in the opposite direction) I can feel the spider gears binding up. It feels "notchy". This is something new.

I have 2 gallons through the stock motor. The 4 spider mod is far from bullet proof. Looks like I will have to rebuild the rear diff pretty soon.
 
2 gallons is a pretty long time for a diff regardless of how it's built.

You may also get it apart and realize it just needs a shim to tighten it back up. I guess it would depend on if the gears look ok or not.

I had the same kind of issue on my maxx. Took the diff all apart (the diff is completely aftermarket) and everything looked ok, but my gear lash was a bit on the loose side. I installed a .5mm teflon washer and it smoothed it right out.
 
Might be the housing too. I did the 4 spider mod after about 1/2 gallon. Housing was fine on the front.
On the back housing, the pins had already wore into the housing. Looks like they could come up with
something besides the plastic cases. All of em have their weak points. :cheers:
 
they should make diffs so the cross pins are supported by aluminum or steel bars that slide into the diff housing...so instead of one small end of the cross pin digging into the plastic case..the cross pin is inside of a metal bar with a hole in the middle of it for the cross pin..and the metal bar slides into the diff case were the pin normally does. i can't explain it so it makes sense, but i feel that would help alot on the problems of diffs being worn out by pins. doing that would be alot cheaper than going aluminum cases.
 
I called HPI and this would actually be covered under warranty. The problem is I would have to pull the diff and send it back for inspection so my truck would be down for a while. I would probably also have to remove the extra spiders. We are still in the middle of the bashing season so this is not a good option for me. I am about to order more fuel from Tower Hobbies so I think I am just going to order a new stock diff cup ($5 for two cups), two sets of HPI bevel gears ($5 each) and rebuild the rear diff for a total of $15 with an extra diff cup left over. Maybe in the off-season I’ll convert to aluminum diff cups.
 
I don't use HPI bevels. I went for Hot Bodies Lightening steel bevels and I have had no problems. I also use 5000wt Kyosho diff gear grease front and back.

Hot Bodies part # C8101-1 Hard Steel Diff Gear Set (Lightning Series) $5.50
 
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I use them because my LHS suggested them. They have been installing the HPI bevels in the past and had many problems with them so they started installing the Hot Bodies bevels with no complaints so far. So I grabbed them from the LHS and installed them myself using all the HB gears along with the same cross pins that everyone else uses when the install the HPI bevels and I have not had any problems.
 
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That's pretty cool. It was hard for me to believe that with all these vihicles and brands that there wouldn't be some parts that are interchangable.

Just to get it straight, you don't have to do anything special to the cases or anything to get these gears to fit?

Sorry to be a pest, but I like to use things that work and work well. But if I have to spend an hour of grinding or modifying, then it really isn't worth it.

BTW, cool sig.
 
nope, no modifying needed to the cases. They just dropped right in. I compared the larger bevels to the stock bevels and they were the same but the HB ones were probably made stronger.
 
I ran one aggressive tank through the truck today and when I took it in my garage to clean it up I noticed that the rear diff was silky smooth again. I let it cool and then ran a second aggressive tank through it and the rear diff is still silky smooth. I'm not sure what happened but I am going to leave it alone for now and see what happens.
 
After running the truck today I noticed that my rear diff was binding up again. I took the rear diff out and the first thing I noticed was that the 3000W oil I put in the rear looked like black mud. Some of the fluid must have leaked out because the level was lower than when I filled it. I pulled all 6 gears out of the diff and they all looked absolutely perfect. The cross pins also looked perfect. I took a close look at the diff cup and I noticed some wear in the area where the ends of the pins sit. It looks like the pins were pushing against the cup and "dented" it a bit. I cleaned up the pins, gears, and cross pins and installed them in a new diff cup with 3000W diff oil. I reassembled everything and it feels silky smooth again. Here is a picture of the damaged cup.

diff_cup.jpg
 
NJRC said:
I use them because my LHS suggested them. They have been installing the HPI bevels in the past and had many problems with them so they started installing the Hot Bodies bevels with no complaints so far. So I grabbed them from the LHS and installed them myself using all the HB gears along with the same cross pins that everyone else uses when the install the HPI bevels and I have not had any problems.
Click to expand...

HPI bevel gears are crappy, so your LHS is absolutely correct. I have stripped 2 sets of HPI gears already on my sprider mod. Am planning on sending it back to HPI, but for the cost and trouble of sending it back + down time, I will probably just switch to your recommendation and buy the HB bevel gears.
:depress:
 

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