JP91

I need help asap folks. I have a 3 speed with od and it has to go. I need a five speed and I know there's a few I can get. ZF 5 speed, M5OD and one other I can't remember. I have a 85 300-6 and i need to know what I can get. Please help me folks

wdg&whg

What's wrong with the 3spd od?

JP91

Needs another gear. I took the 3.08 s out and put 4.10s in. It's turning at least 3500 or more running 45 down the highway

alwayshear

Umm, it doesn't quite work like that. You currently have 3 gears and overdriven gear. If you switched to a 4 speed with overdrive it wouldn't help unless the overdrive gear was significantly lower than the overdrive gear in your current transmission. To get your rpms down you're going to need a taller tire or re-gear the rear down or an aftermarket overdrive unit. 4.10s are cool down low but if you need this truck to go on the highway 3.55s might serve you better. There are gear calculators out there that can help you pick the best gear for your setup.

Oh, just for information, there are transmissions that have two overdriven gears, the BW T56 comes to mind, but I don't think that is what you were asking about.

Take a look at this:
http://www.gearvendors.com/f2wd4s.html

Notice the chart that shows the gearing of a 4 speed and a 5 speed. Disregarding the "Over" rows, both transmissions have an OD gear of .071. Both transmissions would result in the exact same highway rpm in a given vehicle, all else being equal (i.e. rear gears, motor, ECT....) The 5 speed would take off quicker but the top end would be the same.

JP91

Wow thanks for all that. But let me ask this if I was to get 33s could I get the granny low 4 speed and not turn high rpms without changing out the 4.10s?

pwhughey3

no i have 33's, 3.55's, and the NP435, in my truck and it still runs over 3000 rpms on the hwy...

JP91

Ok. I'm runnin 35s right now and that's as big a I can go. The gears I put in the front end won't allow any bigger. I guess with me havin 2 more inches on you isnt gonna help me keep rpms down. I guess my only choices are to keep my overdrive or the zf5 speed right?

Jessef100

my truck has 4.10 gears in it with a granny 4 speed manual and its a beast but to drive it over 50 mph the motor is screaming. same problem jp91 is havin so what u guys are saying is to help with higher top speed and loewr rpm's u should change the gears and not the tranny?

JP91

I did the 4.10s because 3.55s I don't like and 3.73s would have been ok. But I wanted to know when I hook to something it's either gonna drag it or pull it. So I put in 4.10s

nice shot

You shoudl take this into consideration as I recently did. Do you drive on the freeway/country roads or 4x4 more often? If you drive on the freeway more, switch back to the 3.55's. You could always upgrade your transfer case to something with a great low range and it will pull almost anything. I know in my old jeep I went with 4.10's on 35in tires. I could easily cruise at 70 on the freeway. When I needed to go offroad, I simply put my tcase in 4L and went rockcrawling with something like a 4.xx gear ratio (see:np245)

Just a thoguht bro.