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Old 11-17-2002, 07:55 AM   #16
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Thumbs down HPI Diff Shafts

I noticed the posts about HPI and thought I'd offer some whining of my own.

My problem is the lousy front Diff Shafts. Even the shiny "heavy duty" diff shafts break regularly. I'm not kidding, this has happenned 5 or 6 times in the 7 months I've been "playin with the dern thing".

I should point out that that we run in a recently sealed black top parking lot and run a simple oval. I have never hit a solid object and I have never had a problem with cartwheeling the car. (The body still looks reasaonbly new.) All my damage has come from "rubbing" other cars. I wouldn't feel so bad if everyone was having the problems (I run mostly against 2wd losi's, rc10's and rustlers) but thats not the case. There have been maybe 2 other occasions where someone else has lost a diff shaft.

In a simple comparison the HPI Diff Shaft is a whimp.

Has anyone found an alternate diff shaft product that doesn't break so easily??:
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Old 11-17-2002, 08:29 AM   #17
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if you want to do some serious bashing or jumping you cannot beat the durability of 1/8 scale buggy i have mugen mbx4xr and i raced a good bit this summer and i only broke parts on one or two occassions a hinge pin after a tough collision with concrete my fault 100% and a broken ball for a steering tierod bad landing on a big jump and i mean bad landing some things came apart but all could have been the fact i didnt use the proper locktite during assembly i have had nothing but good times with it so far and recommend it to everyone

you always get what you pay for
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Old 11-17-2002, 10:28 AM   #18
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Default HPI diff shafts

Let me ask you guys about your diff shaft problems.

Are you breaking diff shafts when they're brand new? (in a few hours) OR does it take a couple of weeks for this to happen?
Do you notice a groove in the outdrives where the dogbone/cvd pins ride.
Try using some kind of lubricant in the drive cups, most anything will do. I lube the drivecups on all of my cars/trucks and it has reduced the wear and damage to almost ZERO.
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Old 11-17-2002, 11:40 AM   #19
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Default your axles and FYI buggys

Well, I havent had BREAKAGE problems, but I have had warpage problems---my shiny cvds get all warpy and wobble a little, they are kinda soft I guess, I was going to try the aluminum ones, they are lighter(MORE ACCELERATION!!!!) and they are supposed to be stronger--Lubing is a good thing. Also if you rub someone elses tire or something and it "STOPS" the wheel momentarialy,then with your engine still trying to turn it, I would expect it to break!---In my case, I think the fantom 15 is just to much engine and it is twisting my center dog bones and breaking the outdrives and stuff--do you have a hopped up engine?

The solution is a little out of the MT class, I will get a buggy I think the ofna hyper 7 or rhe mugen--if you go to maxxtraxx.com, on there forums they have a very active 1/8 buggy forum--they enlightened me on the durability of these beasts!--they are incredible---and really they dont cost much more than the mt!---(and these are near the top of the line buggys) cheaper buggys can be bought for less than the mt racer in rtr form with a .21 engine and they are 1000 times more durable than the mt....Good luck!--I think I will just toot around on the mt for now untill I get a real beast!!!
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Old 11-17-2002, 04:59 PM   #20
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Thanks for the reply Popsracer,

My Diff Shaft life depends on how lucky I am. Today I didn't have any problems but I was never "rubbed". Yesterday with a brand new diff I didn't get two tanks of gas out of it before I bumped or was bumped, and the front diff broke. As far as my engine goes its an HPI 15 SS (about .78 horse per the specs) and I am using an HPI 2 speed, (12/15 & 52/49). The car is pretty quick and I'm happy with the set-up. I've not been putting lube on the diff as I really couldn't see that it did much, but I'll try anything to get more track time.

I guess a couple of other clarifications and thoughts. The car is an MT racer and has MIP shiny CVD's. The engagement between the CVD and Diff Shaft looks to be less than it should be. The slot depth on the diff is about 5/16", the pin which engages with the diff is just over 1/16" diameter. Under static conditions the pin is on the extreme edge of engagement with the diff. The outboard edge of the pin is about 1/32" inside the diff groove and I've always worried it would fall out. This hasn't happened, but it does put the diff under extreme stress.

Could the CVD's be too short??
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Old 11-17-2002, 05:16 PM   #21
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Zuper, if they wobble, they are bent. I managed to bend 2 shiny dogbones. You can go back to original dogbones. The updated ones from HPI are now much stronger. I never broke an axle though.

As for aluminum, stay away from them. They are actually weaker. The shiny CVD's are steel with a nickel plating.
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Old 11-17-2002, 05:54 PM   #22
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Default Your MT

mine is the same way as far as fitment---very shallow---and oddly enough when I have it set high for offroad, they fo in just a little!--but with the low street setting, they are very shallow---it would seem to be the other way around.. did you shim your diff correctly?--by the berrings?--this ammt of play, if you didn't could cause enough room for them to almost come out and maybe break them??--where are they breaking--the two little posts that fit in the out-drives? in the middle? or on the outside end? is it always in the same place ? Let us know...
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Old 11-17-2002, 08:08 PM   #23
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Default Re: HPI Diff Shafts

Quote:
Originally posted by Good Time
My problem is the lousy front Diff Shafts. Even the shiny "heavy duty" diff shafts break regularly. I'm not kidding, this has happenned 5 or 6 times in the 7 months I've been "playin with the dern thing".

In a simple comparison the HPI Diff Shaft is a whimp.

Has anyone found an alternate diff shaft product that doesn't break so easily??:
The so-called "heavy-duty" HPI diff outdrives are a joke. They are nothing more than the standard ones that have a chrome finish (and a poor one at that), instead of the standard black oxide. I went through a bunch of them before Troy posted on the now-defunct HPI Forum (Super Nitro section) that the slightly longer Rush outdrives were actually tougher. I tried them and lo! They worked just fine w/minimal wear.

It's just too bad that I no longer run any of my HPI stuff anymore...instead I expressly drive the NTC3 and the Mugen XR buggy these days. Speaking of which, Dan is correct...if you want to drive hard off-road, the NMT is the wrong vehicle. Get a 1/8 buggy...it's initially more expensive, yes, but compare that to the cost of constantly repairing that HPI truck. It's cheaper in the long run.
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Old 11-17-2002, 08:18 PM   #24
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Default Hpi diffs/outdrives

OldSkool is right, the Nitro Rush outdrives are better (longer too).
The shallow drive engagement sounds like a problem waiting to happen. Is the problem at both ends of the truck?
Dog bones may be better in this case.
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Old 11-17-2002, 09:38 PM   #25
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Zuper, never had problems with the diffs or diff shafts. I got one of the first batches of NMT's too but luckily installed the shims when it was just announced. The only reason I didn't strip anything was because after my .15FE, I ran a mild OS .12CV. I was just breaking regular suspension stuff.

I have known others that have stripped them even when properly shimmed but they are using 1+HP engines.
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Old 11-17-2002, 10:08 PM   #26
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Default VENTING---**Whining alert**

You know guys, I got on the Hpi forum as Speedjunkie, and wanted to get into the nitro stuff--the forum was busy and supportive. I know alot of people with rs42 s and i wanted somthing less limited and I got the mt--all the lhs carries was the Hpi and Associated kits. Well being a newbe and haveing minimal exposure, I bought HPI thinking that was all there was--hmmmm. Everyone talks up the name but I personaly have been very dissapointed. I love my MT, but lets face it I need a buggy--I wish I had only known---just goes to show what going with the flow will do . I just had to vent again
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Old 11-18-2002, 02:43 AM   #27
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You're not the only one. Myself and many others that used to have NMT's (and dumped a lot of money into it too) have either moved on to better stadium trucks (RC10GT or XXXNT) or 1/8th buggies.

HPI aren't as great as they used to be. Although the new Savage looks tempting...
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Old 11-18-2002, 09:24 AM   #28
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Yeah the savage looks pretty savage don't it?--I love that truck!--I've got three of them too. and they are ok...Yeah, I almost had you going!--Seriously, I would love one but I'm to scared---like I said you can make 'em pretty, you can post them everywhere, you can have great adds, you can hype it up--but if it wont stand up to the expectations that you stick into peoples minds, You will always loose in the end---I feel for them.
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Old 11-18-2002, 12:30 PM   #29
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The CVD/DIff Shaft engagement issue is only apparent on the front of the truck. I know they make different cvd's for the front and rear. Are the rear cvd's longer than the front ??

I believe if I can get some longer cvd's and maybe some Rush diff shafts I can put this one behind me. The Nitro Rush is 2 wheel drive, will the rear diff shafts from a Rush fit the front of an MT??

Thanks for the advice guys.
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Old 11-18-2002, 12:36 PM   #30
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Quote:
Originally posted by Dan
HPI aren't as great as they used to be. Although the new Savage looks tempting...
It does look nice, esp. if you want to race a monster-truck. But it's still too much like a modded T-Maxx (speaking of which, mine will be up for sale soon), but personally I am eyeing the Kyosho Mad Force, and will probably get one as soon as the bugs are ironed out and more aftermarket support becomes available.

3-speeds, .21-power, buggy diffs, out the box...yummmmmy...
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