Slipping center or rear differential.  
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All Forums >> RC Cars, Buggies, Trucks, Tanks and more >> RC 1/8th Scale Buggies >> Slipping center or rear differential.
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Slipping center or rear differential. - 1/26/2004 2:57:22 PM   
RessurectionX


 

Posts: 99
Joined: 1/13/2004
From: Phelan, CA, USA
Status: offline 		I was out bashing my car around my house today when I noticed a whinning noise coming from it, and a loss of power. So I pick the car up and give it some gas and nothing. Then I set the front wheels back on the ground and give it some gas and it spins like it should then I set the rear wheels on the ground and under pressure the wheels down spin and something is slipping. So I have encountered my first problem from my pbs since i bought it. It is hard to track the nose down but it does sound like it is coming from the rear dif but could it be the center? Is it a possibility that something could have come loose and did not break or strip? Because I noticed this right after I landed upside down off of a jump. Is it a possibility that maybe I could have landed on one wheel and maybe something loosened. I want to get the the source of the problem before I take the car apart (Save me time). Is there a way i can tell if it is either the center or rear diff. Thanks.
       Post #: 1

RE: Slipping center or rear differential. - 1/26/2004 2:59:00 PM   
RessurectionX


 

Posts: 99
Joined: 1/13/2004
From: Phelan, CA, USA
Status: offline 		Also I noticed when I hold one back wheel down I can still spin the other freely with little resistance.

(in reply to RessurectionX)
       Post #: 2

RE: Slipping center or rear differential. - 1/26/2004 3:03:06 PM   
Sherak



Posts: 231
Joined: 1/5/2004
From: , UNITED KINGDOM
Status: offline 		Absolutely bizzare, I had exaclty the same problem with my PBS yesterday and was stumped to the problem, Anyho after a little investigation under the hood it was no big deal.

Basically the transmision cups in which the dog bones sit in are connected to the diffs gears and a grub screw keeps the cups from spinning independantly, one or two of the grub screws had come lose so when any pressure was applied the cups were slipping (not applying pwer to the back wheels) tighten up the grubs and you have power again.

(in reply to RessurectionX)
       Post #: 3

RE: Slipping center or rear differential. - 1/26/2004 3:17:12 PM   
RobH



Posts: 524
Joined: 12/8/2003
From: Drums, PA, USA
Status: offline
quote:

ORIGINAL: RessurectionX

Also I noticed when I hold one back wheel down I can still spin the other freely with little resistance.


That's just making the diff work.

I had my rear diff gears blow on me. I was at the track when it happened so I found out two quick ways to check. 1.) put the RC on the ground with your foot in front of it. If you give it gas and the rear tires don't spin on the ground, the rear diff is blown. 2.) hold the cvd or dogbone in place where it goes into the rear diff. As you spin the rear wheels by hand the CVD/dogbone should spin in your hand regaurdless how hard you try and hold it. If you can hold the CVD/dogbone in place while you turn the rear wheels in the same direction, the diff is blown.

I'm sure you can apply the same stuff to the font diff. The center diff would be a bit different. I think you would try to hold the main gear in place while you push the buggy forward and back. You shouldn't be able to hold that gear in place.

I hope this helps. I ended up changing my gears out for the Kyosho MP 7.5 gears. I don't know if that buggy take the same size as mine, but the Kyosho diff seems to be a very popular design to copy. I think even the Savage diff gears interchange with the MP 7.5 gears. At $7-$8 per set it's a pretty cheap upgrade too.

Oh yeah before I forget. If you take the gears out, they may not look that bad. In my case, just the edges of the gears were rounded and that was enough to cause malfunction.

Good Luck,
RobH

(in reply to RessurectionX)
       Post #: 4

RE: Slipping center or rear differential. - 1/26/2004 3:19:30 PM   
RessurectionX


 

Posts: 99
Joined: 1/13/2004
From: Phelan, CA, USA
Status: offline 		Thanks for your help Sherak but I dont exactly know what you mean. I know where the dog bone sits in the rear trans cup but I dont understand what you mean by grub screw. Maybe once i get the back case opened up I will understand more.

(in reply to Sherak)
       Post #: 5

RE: Slipping center or rear differential. - 1/26/2004 3:20:12 PM   
RessurectionX


 

Posts: 99
Joined: 1/13/2004
From: Phelan, CA, USA
Status: offline 		Or maybe I am not understanding at all.

(in reply to RessurectionX)
       Post #: 6

RE: Slipping center or rear differential. - 1/26/2004 3:26:25 PM   
RessurectionX


 

Posts: 99
Joined: 1/13/2004
From: Phelan, CA, USA
Status: offline 		RobH I tried your advise on holding the rear cvd and spinning the wheels and I can easily hold it without it spinning. It takes little pressure to hold it to. But is there a chance that what Sherak was saying could also be the problem or is it totaly blown. Oh well better get to work taking it apart.

(in reply to RobH)
       Post #: 7

RE: Slipping center or rear differential. - 1/26/2004 3:57:57 PM   
RessurectionX


 

Posts: 99
Joined: 1/13/2004
From: Phelan, CA, USA
Status: offline 		Well i got the rear of my car detached from the chassis and Sherak was right the set screw that sits in the dif was loose and was almost all the way backed out. I tightened it and I no longer have the problem. Glad it was a simple fix. But just to make sure the part you are talking about is part #87004 on page two of the instructions manual right? That is the part that was loose and was causing the slipping. Also what weight oil do you guys recommend using in the rear diff. A racer up at the lhs told me to pick up these three weights 3000, 7000 and 5000. He also gave me an order from back to front but I dont remember what he said exactly.

< Message edited by RessurectionX -- 1/26/2004 10:56:55 AM >

(in reply to Sherak)
       Post #: 8

RE: Slipping center or rear differential. - 1/26/2004 5:54:36 PM   
RobH



Posts: 524
Joined: 12/8/2003
From: Drums, PA, USA
Status: offline
quote:

ORIGINAL: RessurectionX

Well i got the rear of my car detached from the chassis and Sherak was right the set screw that sits in the dif was loose and was almost all the way backed out. I tightened it and I no longer have the problem. Glad it was a simple fix.


sweet. I don't have any expierence with that buggy.

Looking at the oils weights, I would guess the order is 5k/7k/3k (front / center / rear). It seems a lot of combinations go big/biggest/small. Some I heard are 5k/7k/1k, 3k/10k/1k. I personally am trying to stick to my basic RTR setup until I have enough track time to know what I'm doing. Right now, I'm running 5k/10k/1k.

-RobH

(in reply to RessurectionX)
       Post #: 9

RE: Slipping center or rear differential. - 1/26/2004 6:51:44 PM   
RessurectionX


 

Posts: 99
Joined: 1/13/2004
From: Phelan, CA, USA
Status: offline 		Yeah thanks anyway RobH. I know the two cars are not similar but it wouldnt have suprised me if it was stripped. Just glad to see it wasnt and it was a very easy fix.

(in reply to RobH)
       Post #: 10

RE: Slipping center or rear differential. - 1/26/2004 7:37:24 PM   
RessurectionX


 

Posts: 99
Joined: 1/13/2004
From: Phelan, CA, USA
Status: offline 		Looks like I spoke a little to soon. I was all fired up thinking just that little set screw was my problem and everything was going then I started my car stuck it on the ground and went to take off. I hear a very familiar sound. Something is slipping. So now I am really puzzled. I can no longer hold the dogbone with my fingers or even plyers but when I stick the car on the ground the rear wheels wont turn and it sounds like something is slipping. Hmm... Is it possible that the gears are stripped just enough to where i can hold the dogbone but when its on the ground they slip? Also this isnt the center dif. is it? I have no experience with 4 wheel drive cars so its hard for me to tell. But like I said before the front wheels are working like they should. Hopefully Sherak will respond to this and tell me if that part number I gave him was the grub screws he was talking about. But I am guessing it wasnt and was only part of the problem because he said one or two of the grub screws were loose. There is only one set screw in there. Please anybody else with any helpful information respond. Or can someone tell me what he means by a grub screw.

< Message edited by RessurectionX -- 1/26/2004 2:36:59 PM >

(in reply to RobH)
       Post #: 11

RE: Slipping center or rear differential. - 1/27/2004 1:25:54 AM   
RessurectionX


 

Posts: 99
Joined: 1/13/2004
From: Phelan, CA, USA
Status: offline 		Sorry guys for all the post but please bare with me. I took my rear dif apart and there is no sign of rounding what so ever. And that got me thinking of what was happening when i set the rear wheels on the ground and gave it gas. One thing that was happening and I didnt mention was the cvd going to the back wheels wasnt spinning, or was trying to spin. And correct me if I am wrong but if the rear dif was stripped then wouldnt the cvd going to the rear wheels spin, and the gears inside the dif that were stripped would be the cause of the rear wheels not spinning. If the center dif was stripped then I can see how it wouldnt spin the cvd. So am I right to say that the rear isnt stripped and its the center spider dif causing all the problems? Please reply.

< Message edited by RessurectionX -- 1/26/2004 8:19:49 PM >

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       Post #: 12

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