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HPI diff changes

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shorty

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Hi all
If u already know about these changes then I'm sorry for telling any one again
I recently got some pre assembled diffs from hpi and when I took the new ones and my old ones apart to change my diff mods over I noticed the screws have changed I think it is because the old ones tend to back them self’s out. I noticed that mine are always lose when I go to services my diff
Here’s a pic
diffs.JPG
 
Are those the 4 screws that lock in the diff housing to seal up the bevel gears?

If so, it would seem that the new screws wouldn't work as good. B/c the screws thread into nylon and the new screws have the wrong thread type for doing that. The threads on the new ones look more like metal-to-metal screws.

I would be hesitant about screwing them into the nylon diff cup. I think they would simply rip out b/c the thread can't grab onto the nylon.

Later...
 
well they actually they hold lot better and dont tell me not to use these like it was something i come up with
i am just leting u know that HPI had changed the screws
 
the machine screws hold better agianst vibration and torsional stress, becuase there is actually more threads being made in the plastic than the self-tapping screws..even though the threads are smaller there is alot more of them. at least i think thats how it works lol
 
The fine threads do hold alot better than the coarse ones. the coarse ones actually backed out on me on more than 1 ocasion. now all i need to do is figure out what weight oil to run that won't leak out
 
Wow that is interesting the arrow's shorty made are quite the artist rendering. Newayz I would agree that the machine screws will hold a lot better this is why like (even though they are junk) when you get a set of screws from RCscrewz that they are are all fine thread.
 
The fine screws do indeed hold better. When I rebuilt my diffs and did the 4 spider mod I replaced the coarse screws with machine screws. They had been a little bit loose, backed out on their own, possibly contributing to the destruction of the diff. The machine screws have not backed out at all at my last inspection.
 
Not trying to argue w/ anyone, but this is a pretty good topic to philosophize.

Nice Q & A info, I would agree that the self-tapping thread could have a tendency to back out more, when compared to the machine screws.

However, it just seems that the machine screws, when inserted into the nylon, would just rip out. True, they have a tighter thread pattern than the self-tapping. This is why the machine screw will not back out.

But, what about the material they are tapping into? It is relatively soft, like wood, definitely not like metal. So in theory, you have more threads (which does help the back out problem), but you are also reducing the grip factor. Thus, you will probably strip the nylon with the machine screws. Look at the threads for screws that go into other soft material such as wood. They definitely don't use machine screws for putting together houses, decks, piers, speaker boxes, etc....

Look at the spaces that are b/t the threads. What do you think would be stronger, a piece of nylon that is this wide /...../ (self-tapping) or a piece of nylon that is only this wide /../ (machine) ?

The thin pieces of nylon that would be b/t the threads of the machine screw would be weaker, in comparison to the thicker pieces of nylon from the sef-tapping screw. By using a machine screw in soft material, you are basically putting a plug, or a nail in it. True, it solves the back out issue, but it seems that it would strip faster and also provide less support.

Another thing to consider is that the screws are going into the diff housing and it is a high stress area. So imagine this example. The thickness diagrams (above) represented a similar high stress area such as a dam holding back water. I would rather live below a dam that was this thick /...../ than this thick /../
 
It is much easier to strip a plastic part with the self tappers than with a machine screw. Give it a try and find out for yourself.

I have stripped out countless holes in plastic using the self tappers. Just when you go for that extra 1/4 turn to make sure it is tight, bam, stripped. However, the machine screws clamp down tight. I have yet to strip one out.
 
Yeah, I plan to switch mine out & see what happens. I haven't had a problem w/ the self-tapping backing out but I thought I would try the machine screws anyway. I actually have the diff taken apart right now b/c I have to replace the 13 tooth bevel gear.

293301.jpg


Plus I am going to try & make a gasket to seal the diff housing to the bottom skid plate to keep dirt & debris out of them.

Later...:mex:
 
Originally posted by Digital Liquid
Plus I am going to try & make a gasket to seal the diff housing to the bottom skid plate to keep dirt & debris out of them.
Click to expand...

You can use silicon for the sealing of the diff to the skid. I beleive that it is even recommend over on the HPI site under Q&A section. I have done it and works most excellent.
 
Alein, thanks for the tip, but I am going to try a piece of regular automotive gasket and cut it to the proper size. It will end up being similar to the gasket that is inside of the diff cup.

That way I can get into my diff housing freely & check anything out if I need to. With silicone, you have to clean it all off and re-apply it & wait for it to cure everytime you need to get into the diffs.

True, I don't go into the diffs too often, but I'm gonna try the paper gasket anyway.

Later....
 

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