Sleeper Im looking at the same thing. On my Thunder Tiger ST-1 I mounted the sensor with hot glue on the fuel tank and the put the silver decal on the center diff. I think Im going to do the same on the hellfire.

Sounds like a plan, I'll have another look and see where it will sit well. I had it in my head that it had to be pointed at the flywheel so didn't even consider the centre diff as an option.

Cheers Keith

Tom

As long as the sensor stripe is on the drive train somewhere you will be ok. Obviously if its mounted on the diff you wont get the true engine RPM's though, just the drive shaft RPMS or the MPH if you do the roll out.

so in theory, if i mount it pointing at a wheel I will get the vehicle Speed in MPH?

I say that because if I point it at the fly wheel or drivetrain, I am only getting the speed that they are spinning at before any gearing is taken in to account. If i point the sensor at a wheel then I should get the actual speed of the car.

hey guys,

i just got a good deal on an HFss and a almost complete rollers and i was wonder what u guys thought....i have almost read this entire thread. just wanted to get some up dated ideas with the hellfire...it seems like a great truck....thanks in advance

The roll out is explained in the Spektrum manual. Here is a link with some info on it too. http://monster.traxxas.com/showthread.php?t=499627

Rtalyor what kind of ideas are you looking for?

well im not sure really i have read most of this thread page by page and my mind is mush lol...i am a long time basher and i am just getting into racing and i wanted to set the HF up for the track. and see how i did before i go and dump a ton of cash on a new race truggy. so i guess just the simple stuff to start with and what i should look for before i go out and break something because i should have checked it before hand....you guys seem to know alot about this truck so who better to ask then the guys that have them....thanks in advance

The SS is a reasonably strong truggy. Its just very heavy old style and wont compete with the newer style trugs. But it would be ok to start with.
For starting racing i would get a decent steering servo, decent tyres, failsafe and radio. Do you need an engine, pipe, starter box?
Make sure you shim the diffs or the pinion could go bye byes very quickly. You can upgrade to hot bodies spiral diffs or the cen gst diffs. Both are way way stronger than the stock.
Maybe get some spare grub screws for transmission, hinge pins etc.
A good set of wrenches is essential as the HF screws can strip easy.
Usual locktite screws.
Honestly i wouldnt spend to much on the HF as you will probably upgrade to a better trug in the near future. If you get a decent engine, servos etc you can keep those for the future?
Let us no how you go.

A better set of tires such as bow ties or crime fighters is a must if you are going to be racing.

Personally, I'm in love with the Hellfire, it may be like an "old" truggy, but I kinda like it like that. Reminds me of "old muscle vs new muscle" these days, old was slower, less agile, etc, but it's still a classic. I'm pretty sure I'll never end up selling my Hellfire like I sold my Savage, E-Maxx, and Rustler. Kinda a rare commodity these days too.

I'm still trying to figure out how you replace\shim differentials in the front and rear, as I've never done it before, but Ihaven't popped those open yet, I can't find specific "upgraded"Hellfire ones, which is odd since Ihear they broke all the time, generally a aftermarket parts maker would take notice

If you do a google search on how to shim a savage diff you will find a bunch of links, some with pretty good pictures showing how to do it.,

Ah Isee, it's just putting spacers basically to make "less play" with the differentials so they don't chew up if they skip or whatever. Do you think Ishould upgrade to say... GSTdifferentials, or do you think the stock ones shimmed (though this truck was previously owned and Idon't know how much he drove it) would be reliable enough?

Thats right, u put shims on to make the pinion and crown gear snug without being crunchy. You wont no until you open it up and see if the pinion is worn. I would open them up and use the stock diffs if they are still ok. Depends how powerful the engine is you use if they will last or not.
I replaced mine about 6 months ago with the gst diffs and havent had a problem since and thats running modded os 28s. Before that i had continous issues.

Okay, so basically on the Hellfire Ijust pop off the 6 screws on the front and rear, and I can get the gears out like that?With a GST differential, do you just take out the entire differential by the 6 screws, or is it more to put them in?I've never done differential work, nor have Iopened it so I have no clue, if I was going to do it now would be the time since the car is currently apart with the upper chassis off, waiting for upgraded aluminum parts to come in.

Hold both axles so that they can't move and then try to rock the pinion gear gently back and forth. Takes some experience, but there should be very little slack. Different people have different methods or techniques concerning shimmimg. I just know that I was blowing ring and pinion gears until I shimmed them crunchy. Diffs with new gears can be broken in (out of the vehicle) using a drill.

Ok...but how exactly do Iget the gears out?Do Ijust take off the 6 screws on the back and front end of the truck to access the front and rear diffs?Can I take them out from there? Just trying to find out how much Ihave to dismantle..I'd prefer to just order the GST diffs, but Im not gonna order them until Iknow how to put them in :P

Thats correct, 6 screws and pull the whole diff out. Remove the 3 small screw in the diff cups and there is the pinion and crown. You should open up the crown diff and change/top up the diff oil if required. Most use around 5 or 7 weight in the front and 3 or 5 in the back. Shim the crown and pinion if required. Read up on it. It is easy but takes experience to get it just right.
The gst internal diffs are almost a direct swap. The gear ratio? does change using the gst diffs. You will need to drop the clutch bell down to a 12 tooth or similar. A 12T will be like a 14/15T on the old diffs i think.

I finished breaking in my massive mods stage 6 os 28. Goes quiiiick!

Due to the HFSS brake outdrive cup easy worn out ! []

Anyone know which other brand is more durable and fit for HF ?

Thanks

Wow, I'm impressed, that puts the Hellfire in a whole other league compared to E-maxx, rustler, and Savage maintence for me...very easy to replace diffs then . I'll be replaceing them soon then with GSTs since they just slide in so that whenI install the Spec 3, I won't have any issues. Thanks a lot

use hot bodies brake outdrive cups- way stronger I had to machine them down a near the base, seemed to bind a little when the top plate was tightened down

You can get a whole center diff complete for $20 off ebay from a HB D8T- also the HB D8t 101 mm drive shaft assembly work also in the rear, much lighter. I use them on the front also with the Xray xtra long outdrive cups.

If anyone gives a crap I have been running vspec .21 with a HB D8T 13 clutch and 50T spur- Even with the extra weight of this truck it is an excellent combo for racing

Good info from you as usual.

I tried my old 086 pipe on my drag mod os 28/hellfire today and OMG so bloody fast ! Ive only had the mod os for a week and had only tried a 2060 and a jp3 on it until today. The 086 sure does make it scream. Wish i had a cam to take a vid.
Iam sure the stock diffs wouldnt handle the power but the cen diffs i have are definately a good purchase.

Igot one rear cen gst differential for 25$, I'm guessing the "rear gst diff" also works in the front of the Hellfire as well? Ibidded on another one so hopefully, it seems like the "rear differential"works in both front and rear. This is the one Ibought...

cgi.ebay.com/CEN-Genesis-Nemesis-GST-7-7-Rear-Differential-Diff_W0QQitemZ390148596322QQcmdZViewItemQQptZRadio _Control_Vehicles is that correct? It seems to be the complete diff that just pops in the Hellfire with all the gears inside it. Or do you have to take the gears out of the GST differential, and put them into the Hellfire's differential housing?

I guess Idon't have to upgrade the center differential?And could you possibly link me the 12t clutch bell you went with, and also why it's required to change it just because I'm changeing diffs? Thanks!

That is the correct diff. Front/rear all the same. You have to take out the pinion and complete crown diff and put into the HF plastic diff cases. You will need to shim them. It would be a good idea to open up the crown dif and replace the oil with whatever oil weight you want to run. I had to put the crown diff in the oven at approx 150 F to loosen the locktite on the screws to get it open. Otherwise the screws could strip easy.
You can use the cen outdrives it comes with 2. (i think?). They are stronger than the HF.
The centre diff is ok.
Just get a 12 clutch bell or 13 t from a lhs or ebay. I prefer a vented clutch bell.
The pinion/crown on the cen diffs have a differnt amount of teeth compared to the stock HF diffs. This then changes the gearing ratio. If you are running a 15 t now on the new diffs it will be like running a 18 t clutch bell which will strain the engine. If you put a 12 t on it will be similar to you running a 14/15 t on the stock gearing.

AhI see, Ithought that basically pulled out the HF diff houseing, and just put the cen gst diff houesing with gears in place...Ididn't know you had to take it apart. Are there two parts in one diff?Your saying crown and then pinon...aren't these both inside the one diff? Then Ijust put the out drives on the old hellfire houseing as well?I'm guessing I'm thinking this is harder than it is :P.

Have you changed out the center diff or no need?Also how do Iinstall the clutch bell?DoI have to take the engine off?And basically to get the thread lock off, Ijust throw the diffs they send me and put them in the oven @ 150 for like 5-10 minutes to loosen the thread lock? Also where could Ipick up some shims?

One more thing, looking at the back of the hellfire, and front, it seems it's not just 6 screws, but more so 10 or so. Ihave to take off the front and rear bumper\skid, then take out the 6 screws which will also drop the a-arms since two of them hold in the bushing that keep the a-arm up, and then the tiny little t-bone that goes around the front and back which is held in by 2 tiny screws...is this right?

And I see how to get out the clutch bell, I do have to take the engine out. I found a steel vented 12t clutch bell for the Revo, would this work? cgi.ebay.com/Traxxas-Revo-12t-vented-steel-clutch-bell-SRVO412_W0QQitemZ360222934263QQcmdZViewItemQQptZRa dio_Control_Parts_Accessories