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Diff Problems

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DOGPILE

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Hello again.

Finished running in the new Picco .26 engine and i must say it is an awsome piece of technology, the way it lifts the front of the truck off the ground on command is ace but my problem is not with the engine it is with the rear diff.

During the run in process i blew the rear diff so i went out and bought 2 new sets of diff gears from HPI and fitted 1 of them into the rear of the truck. After about 30 seconds of running the rear diff gears have rounded off again so i installed the Spider Diff Mod thinking the extra set of gears would add more strength to the diff but i have just found out that the Spider mod made no difference to the strength of the diff, in other words it lasted about 30 seconds on no more than half throttle.

My question is: What can i do to stop my truck from eating diff gears so fast or why is it eating them so fast. (thats 2 questions in one).

I have a 14 t CB and a 49 T Fly, stock Savage .21 parts although they are new ones, also i have fitted the ribbed tuned SS pipe.

Please help cus i am running out of threadlock for the screws.
 
Did you make sure to elimate any play in the diff when you did the spider mod? What oil weight are you using?
 
You have too much torque going to the diffs. With a 14T CB and a picco .26, the power going to the diffs is just too much for them to handle. You should consider putting on a higher CB like a 16T, 17T, or even 18T along w/ a 49T Spur Gear. You should still be able to pull the front end up on command. I only have the stock .25 engine & can pull the front end up on command w/ a 16T CB. By going to a lower gear ratio, you will alleviate some of the torque going to the diffs.

You might want to also go to a possibly go to a thicker diff oil/grease. When you did the spider mod, what weight of oil did you use?
 
I used a 10k diff grease cus its all i could get at the time. I did take into acount the extra power this engine would produce and posted the problem on here to get your opinions before i did any upgrading. I followed all the advice given and am still having trouble. I think i will go from a 14t CB to a 16 and see if it makes a difference to the diff distructing engine, otherwise i look like running the slowest front wheel drive truck in the world.
 
i used a high grade bearing grease the oil keep leaking out and there running smoth with the bearing grease
 
Originally posted by Digital Liquid
You have too much torque going to the diffs.
Click to expand...

I say hogwash to that line right there. There has to be an underlying issue here that dogpile is not addressing at all. I am running a 15/52 setup with my picco and I have been doing so for a full gallon and both of my diffs are just fine. Dogpile did you check to see if the diff cups or main diff gears are not chipped or warped. A lot of times what happened for me was the diff cup itself was warped or the pin that holds the two small spider gears worked itself in to the thick part of the diff casing itself. This could be your issue. You have not corrected the problem in the first place so it will remain. Have you checked to make sure that the diff cups and the shaft that they ride on are straight and not bent at all??
 
I agree with newnitrofan.Their has to be something else going on here.Definitely check the diff housings and make sure the pins haven't gouged into the sides of the housing.Check the bearing and make sure the drive cups aren't bent.Also check to make sure the screws that hold the ring gear in place haven't stripped out.I ran my 8port on the stock S21 diffs for about 5 gallons before they went.After they went I replaced the housings and did the 4 spider mod and haven't had a problem since.
 
When I got my truck the rear diff had worked it's way sideways in the housing but was still working ok. I just can't buy there is too much power there to keep tweaking diff gears. If that was the case teh front one would be going too. Something else is wrong. It might be worth it to just get some new diff cups as they are like $6.00 and you get two and it also comes with two gaskets.
 
hope you find the explination to all this so you can get your monster running right! like someone else said, maybe there is something loose inside the diffs. you never know.
savager
 
Thanks for the help people. I will check the condition of the diff housing when i strip it down again, also i have bought a 17t CB (Cheers Digital Liquid) just to try and ease the pressure off the diffs. I have a spare set of shafts and gears for another spider mod but dont want to trash those before i empty a tank so i will go over the diff with a fine tooth comb. Thanks again.
 
Sounds like you've got too much play in the diff which is allowing the gears to skip when power is applied. I just went through this myself after doing the 4 spider mod only to discover less than a gallon later that the excess play was about to kill my diff. It did claim my new cup as the screws started backing out of it and warped the holes rendering it unusable. I noticed that the center of my 43t ring gear had wore some allowing the output to move excessive inside of it and let the pinion skip when applying power. I happened to have some new ones so I installed it however I'll have to come up with a shim of some sort before too long or I'll destroy it especially with my mach 26 providing the motivation now.
 
Sorry to go off topic here but puffnstuff how is that mach26 treating you man. I am interested to hear how this motor is compared to a picco26 per sey.
 
DP, here is another suggestion. When you reassemble everything make sure you have the right screws in the proper place. Some of the screws are longer than others and each one has there own specific place on the truck.

If the screws get mixed up and you put a long screw in the bottom when bolting on the aluminum bottom skid, it can possibly go all the way through and push up against the drive cup. This would end up locking your drive cup in place and you would end up shearing diff gears.

It would be a good idea to spin each part as you put it back together to make sure that there isn't any binding or mis-alignment of teeth. Before you crank the engine & run it, push the truck around on the ground to also test for any binding issues.

Let us know what you find out.

Later....
 
Originally posted by newnitrofan
Sorry to go off topic here but puffnstuff how is that mach26 treating you man. I am interested to hear how this motor is compared to a picco26 per sey.
Click to expand...

Well so far I've got 8 tanks through her and she's a screamer, much more lively than the s25. I started out running 15/52 but today I dropped her to 13/52 and she's still faster than my s25 was at 15/49. My temps are hovering around the 250-270 range and it's hot outside at around 85F so I can't complain. I had to get the xtm 24.7 backplate to mount the rotostart but I bought the one that comes with the backplate/one way/shaft all in the same package from hobby people and it was 21.99 versus 18.99 for the one way by itself. If I had somewhere to do a speed run I'd gear her up just for the fun of it and give it a go. Over at savage-central a fella named tbill has 4 savages with multiple engines and he gives a detailed comparison between them all just in case you're were wondering.
 

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