Powertrain questions

[Taisho]

I can't figure out why my M715 only goes 25 mph.
Front axle- stock Dana 60.
Rear axle- stock Dana 70.
Engine- Rebuilt 454.
Tranny- Rebuilt SM465.
Transfer- stock NP200.
I've checked and double checked that the transfer is in High gear.

[kwai]

did you shift into 3rd gear? Just a thought.

slipping clutch? Have you checked RPM vs speed?

[Taisho]

Thanks Kwai. Yes, shifts into 3rd gear no problem. I did not suspect or detect any clutch slippage, but I'll double check the adjustment. As far as rpm's I'll install a tach.

[Barrman]

Is the engine struggling to get that fast or revving freely? My first thought was you are in low range on the transfer case.

[Taisho]

I can get to 25 mph very quickly. I dont detect any clutch slipping. Again I will check to ensure in in high gear.

[kwai]

how are you checking that the t-case is in high range?

[Taisho]

I've disconnected the linkages. Put truck up on 4 jack stands. Started engine, this way I could determine 2 wheel drive and 4 wheel drive. I made sure it was 2 wheel drive. Same for High - low. Wheels spun faster in high and slower in low. I shifted to low then drive short and I could determine it was in fact low. So I moved to high gear. Still 25 mph. I know it is 25, because of the speed trap sign, speedo and sign indicated 25.

[brute4c]

The following assumes that the motor is turning 3500 rpms and the clutch is not slipping...so if you verify those items are true...

With the trans in neutral, you could spin a tire and see if you can count the turns of the driveshaft coming out of the front of the tcase as opposed to the turns from the rear axle to the tcase...if they are really close to equal, you are in high range and the problem is not in the tcase...

If they are not really close to equal, either the tcase it not in high range OR there is something fishy in the tcase.

If the tcase falls into the first scenario, and the problem is not in it, then I would assume the problem is in the transmission somehow or the axles....I would have a hard time believing someone custom made axle gears in the 12:1 ratio range to be able to be that slow...so it would seem somehow then it would be in the trans...

[Taisho]

If my clutch was slipping wouldn't I smell that? Today I will continue to troubleshoot this.

[glenn]

If my clutch was slipping wouldn't I smell that? Today I will continue to troubleshoot this.

Usually but not always.