Sprint77 modded rear dom broke my Truck!

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str8jailbird

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Yep, LOL, just like it reads. Got the new pipe today in the mail, installed no probs. Ran for about half a tank and *WHAM*. High revs, no movement. Ended up snapping a front CVD into multiple pieces at the wheel end, and snapped the new rear diff cup Rob just sent me to replace the last one. The low end and all around power gain with the rear dom mated to the 28.5 kit is AMAZING. Maybe too much so. Well, had a spare CVD and dremeled a stock diff cup. 2nd half of the tank no problem. I think it's gonna eat diff cups on the rear though and the CVD's will not last with the torque the engine now puts out.
 
I heard of people upgrading to better parts like the drive shafts, dog bones, and joint cups. Is there a list somewhere showing which parts to get or what will swap out directly....anything from MCD or HPI?
 
My diff cups are holding up pretty good at the moment (now I just cursed myself). Must be 2 tanks of hard bashing and nothing but body damage. what gears you running, i got the 27/33 mcd's in at the mo, haven't tried 25/35 with my 77dom yet.


LK there's a list of pre run things to do like green loctite the dogbone pins, get an hpi airfilter, upgrade kit, centre the dogbones with fuel tubing or 1/2 a decidamp earplug and some other bits and bobs. there's a few threads which highlight the weaknesses and fixes and the best part is 95% are pretty cheap to do.
 
mooman007uk said:
My diff cups are holding up pretty good at the moment (now I just cursed myself). Must be 2 tanks of hard bashing and nothing but body damage. what gears you running, i got the 27/33 mcd's in at the mo, haven't tried 25/35 with my 77dom yet.
LK there's a list of pre run things to do like green loctite the dogbone pins, get an hpi airfilter, upgrade kit, centre the dogbones with fuel tubing or 1/2 a decidamp earplug and some other bits and bobs. there's a few threads which highlight the weaknesses and fixes and the best part is 95% are pretty cheap to do.
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I am running the stock 25/35. MCD gear for the "pinion" , stock 35 then 2 25 ramtech steel for the remaining 2. That darned CVD was in pieces. It looks like it just exploded at the end where the ball joint goes into the axle. Hey Moo, my "homemade" diff cup didn't break, not even a crack (damn now I did it). I checked my 5B's diff cups to see if maybe I could swap. The shaft is a lot larger, and the length too long. I figured if a modded one were used it may work but for how long? You'd need a lathe or a CNC to mill the shaft diameter smaller. I would like to see if the MCD's or FG's might work.
 
I concur......I just received my Sprint77 modded DOM and it tore my little truck up......yeah, I was still using the stock servos thru 8 tanks with zero problems.......I do have my Pico installed and the 3PM 2.4GHz failsafe set.....but the th/br servo started acting up and with the torque the 28.5 kit delivers was somewhat a funny adventure.....braap braap braaaaaap brap braaaap.....smoking all 4 MT tires and spinning out....Thanks Sprint, beautiful work and super fast shipping....now where's my rollcage or do I have to wear a safe like Moo?....and yes Kryp I just finished installing the 645 and 5745 !!! Maybe we can get a deal on parts if we buy together jailbird:D
 
Piranha2 said:
I concur......I just received my Sprint77 modded DOM and it tore my little truck up......yeah, I was still using the stock servos thru 8 tanks with zero problems.......I do have my Pico installed and the 3PM 2.4GHz failsafe set.....but the th/br servo started acting up and with the torque the 28.5 kit delivers was somewhat a funny adventure.....braap braap braaaaaap brap braaaap.....smoking all 4 MT tires and spinning out....Thanks Sprint, beautiful work and super fast shipping....now where's my rollcage or do I have to wear a safe like Moo?....and yes Kryp I just finished installing the 645 and 5745 !!! Maybe we can get a deal on parts if we buy together jailbird:D
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I'm All in brother!, lol. I forgot the difference from when I first installed the rear dom on my 5B SS. I should have known better especially with the 28.5 on my Ramp. Hey Moo, I already considered that. If you heat the diff cups up and let them slowly cool then it makes the steel "bend" easier right? Vs heating it up real hot and quenching the heated steel in oil say. That would make it stronger but brittle? I have considered trying this, maybe I'll ahve to order a set of the stock diff cups from Rob and give it a try.


Rob, a note on the drive shafts. The CVD's are crapping out on me not the stock driveshafts. So far they are holding up nicely. I really wish my uncle was still working, he was a machinist and I know he would have no problem milling diff cups for me. Too bad he doesn't have that kind of stuff at home. I would actually try to buy titanium stock for diff cups to be milled from and have a bulletproof differential. There are a few machine shops around and my younger brother used to work at a few of them, maybe he can help. Anyone know what the grade steel would be needed to mill diff cups that are a lot stronger? Yep., I am to that point.
 
Sprint 77 said:
I think it is a matter of getting the ones we got hardened but not to had. Rob your the engineer what rockwall should we shoot for 52?
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"DUH NAH NAH NAH" (superhero music) SUPER SPRINT TO THE RESCUE! So do we need to temper or harden??? Temper maybe, just need to know what temp, how long, is it color tempering etc. Not too much, not too little. I just don't know where it should be to be the best of both worlds, strong but not brittle, flexible but not permanently bend.
 
Like to see some pic of the failed Diff cups. Maybe some rings on them as done with early Baja 5 B problem may be a more emediete solution.


Post them up start a thead for Diff cup solutions.
 
Sprint 77 said:
Like to see some pic of the failed Diff cups. Maybe some rings on them as done with early Baja 5 B problem may be a more emediete solution.
Post them up start a thead for Diff cup solutions.
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Sprint, it's not the actual cup like Moo said. It's the shaft where the pin goes through. Hey Moo, will tempering work? Redhot and room cool these diff cup shafts? Maybe make them a little flexible instead of so darn brittle?
 
yup I just drilled out one of my stock outdrives for a larger pin. I put the whole upgrade package in and sheared one off at the pin hole in less than half a tank with the mt tires 9/64 drill bit for reference is a perfect fit and the largest dremmel bit shaft is the same size as these pins if needing replacements
 
mooman007uk said:
I think tempering might work...I'd try just heating to yellow (500f) then a slow cool down, not knowing the type of steel makes it hit and miss, I think heating it to cherry may make it too ductile
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Yeah, that's what my brother said when I asked him. I did a little checking and the temp ranges vary from 300-500 and from 700-1400. for some reason the 500-700 range is not used. I can't remember why, crystalization or something.
 
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