boostd2valve

My Feedback: (36)

Hello..Just picked up a monster GT in a trade...4.6 model, has the .28 pro on it...anyway..It seems to run good, trans shifts into 2nd gear...Problem is, top speed is about 15-20 mph with the engine high reving...and thats after 2nd gear...and thats only after like 20ft and its maxxed out...any ideas where to start before i start taking it apart? thanks in advance

Voxmagna

Does the glow plug have a _washer on it? how is your idle setting does the truck pull in neutral/no gas applied*?

Maj_Overdrive

My Feedback: (11)

Sounds like you have a problem in the driveline somewhere. If the engine is revving high, but the truck isn't moving something is slipping and not letting the truck get up to full speed. Since you're shifting into 2nd you can eliminate the clutch and probably the transmission too. Although it would be fairly easy to pull it and check for any stipped gears, broken drive pins. Check all the grubs screws on the drive cups for the cvd's, make sure they're tight. Check to make sure all the cvd's have their pins in them, check your wheel hexes for the same and to make sure none of the hexes in the wheels are stipped. If that all checks out the problem is probably in the diffs, with a broken pin, stripped spider gear, etc.

boostd2valve

My Feedback: (36)

yeah..i didnt think it was a clutch problem, i didnt think it would let it shift if it was slipping on that end..and it didnt jerk at all so i didnt think any of the tranny gears wear missing teeth...i didnt check diffs or any of the shafts yet... but if the truck is running i cant hold it back when i give it gas....i was just seeing if there was any known problems..only problems i ever had on any of the Gt's i owned where shifting problems and they were minor...engine is set to factory specs thanks

Maj_Overdrive

My Feedback: (11)

Wait a sec, I think I may have figured it out. If you hold it in place and give it gas on a surface like dirt and all 4 wheels spin evenly then the problem is in the transmission. Specifically the one way bearing for 2nd gear. The truck would still sound like its shifting into 2nd as the rpms might drop for a second. But once in 2nd gear with the one way slipping the rpms will climb and the truck won't gain any speed. Its worth checking into, also easy to diagnose once the trans is apart. Just hold the gear the one way is in, hold the shaft and turn the gear on the shaft. It should turn one way and should hold on tight when you try to turn it the opposite way.

cummins driver

My Feedback: (31)

The 2nd gear on the MGT is actuated by a sprag that come out and grabs the 2nd gear. 1st gear has a one way bearing.

I would start by checking the slipper clutch. Also, i assume the gearing is factory ( 16/52 ) because if someone has installed something like a 13t bell, its going to be much slower. Just some things to check.

Maj_Overdrive

My Feedback: (11)

Forgive me, I haven't messed with nitro and 2 speeds in awhile, you're right about the one way being on 1st gear. The 2nd gear assemly is locked onto the shaft usually with a grub screw or pin. And if the 2nd gear assembly is able to slip on the shaft, it will still sound like it is shifting into 2nd gear. But it will slip soon after shifting while trying to put the power down, and the engine will quickly start screaming. The same thing will also occur if the teeth on 2nd gear are stripped, something to check into. The slipper clutch is not likely to be the culprit. If it was loose enough to slip in 2nd like the OP described the slippage would be very obvious in 1st gear as well.

The OP should fire the truck up, drop it in some dirt, hold the rear bumper and give it enough throttle to spin the tires. This will put a good load on the slipper, and if any wheels aren't spinning there's a problem in the cvd's, diffs, or hexes. If that all checks out its time to open up the transmission.

boostd2valve

My Feedback: (36)

sorry guys..Been on vaca all week!(lucky me lol) anyways..the gearing is 16/49..and the hexes are pefect...do some tinkering tomorrow and see what i come up with! thanks for all the input so far!

boostd2valve

My Feedback: (36)

well..changed slipper out..still did same thing...clutch bell clutch looks brand new...i ended up pulling trans out...the screws are tight and nothing is stripped, is there anything else to look for..it seems to have a forward only conversion..

Maj_Overdrive

My Feedback: (11)

Did you check to make sure the 2nd gear assembly is locked onto the shaft and not slipping? The 2speed assembly is on the intermediate shaft, 1st gear is the larger gear and has the 1 way bearing, 2nd gear is the smaller gear. In the center of 2nd gear theres the shift mechanism it has a grub screw that locks it onto the shaft, you'd have to take apart the assembly to make sure that part in the center is locked onto the shaft. THe forward only conversion is pretty simple, just a gear that engages the shaft with a pin. If something was wrong there the truck wouldn't move at all. Might want to check the manuals online to make sure everything looks right though.

Can you explain what its doing a bit more, step by step. If you hold the rear bumper and give it gas do all 4 tires spin? Roughly the same speed? Does it shift into 2nd gear at the right rpm? What happens after it shifts? Do the rpms climb quickly after shifting?

boostd2valve

My Feedback: (36)

engine high revs like something is slipping...if i nail it, it would pull wheels off ground...but after that it would high rev like a clutch has let go...then it will shift into 2nd pretty hard and then do the same thing...in 20 ft it would be screaming and about to blow up and only be going about 15-20mph...if i hold the bumper..it will spin all 4 wheels, i actually pulled the diffs out today just to check...no stripped gears, and nothing seems to rounded out...in the trans, the one way seems to be working proper..and the 2nd gear is tight on the shaft,

Maj_Overdrive

My Feedback: (11)

Well I was assuming the problem was revealing itself only in 2nd gear, but knowing that it is in 1st too opens up some possibilities I had dismissed. Still a very weird problem because everything would have to be just right (or wrong) for it to occur. From what you descibe it sounds like the slippage is occuring when the engine is in the power band, but grabbing enough to get the truck moving and even pull wheelies from a stop. Tighten the slipper down, so you can eliminate that. Next use some sandpaper or a sanding drum on a dremel and scuff up the inside of the clutch bell really good where the clutch shoes contact, just in case its got any glaze on it. I'd also rough up the clutch shoes too, I'd use sandpaper instead of the dremel if they are not aluminum shoes so you don't ruin them. You can also do this to the slipper too as glaze can form on it too which can cause more slippage than you want. I'd try doing this before replacing any parts, if it helps but doesn't cure the problem then you'll know what to replace.

While you are scuffing up the clutch bell and shoes, double check that the nut holding the flywheel to the engine's crank is nice and tight. Might want to take the flywheel off and make sure it has the correct collett or if its missing too.

The only other thing that could cause the symptons you describe is the one way bearing, but that would only slip in 1st gear, once in 2nd there wouldn't be anymore slip. There is also the possibility the truck is attempting to shift into 2nd, but it never fully engages or the sprag/pawl disengages downshifting back to 1st. Combine that with a bad one way and you could get the symptoms you descibe.