Gears? my 351 screams over 50mph!

[paramagic]

I have a stock 66 with a 351W and NP435, and it absolutely howls if I go over 50mph! Anyone else had this? Will a gear swap solve this, and how expensive can that get? Thanks EB guru's!

 

[Jeepster]

What size tires, and what gears you running in the axle?

 

[74bronc]

"Screams" meaning makes alot of noise, makes funny noises or the RPM's just runnin high? I don't have a tach, but my RPM's at 65MPH are well over 3K. I have a 351W, C-4, 4:11's and 33" Tires. It used to bother me, but now I just tune it out. If something is going to explode, I would hate for it to happen at that RPM, but it really isn't that high. The other thing that sucks is the gas mileage!

 

[paramagic]

I'm running 31" BFG's and the gears are whatever was stock, 3.50? I can't measure right now 'cause I'm out of town for a few days.

 

[green73brc]

Stupid question but is it going through all the gears? Do you know what the RPM is?

 

[stevew]

If it had a 6 cyl it has 4:11's possibily 4:56's . 31's will run the rpm's up pretty quick . If you have those gears consider 33's or 35's .

 

[Jeepster]

[quote author=stevew link=board=5;threadid=18006;start=0#msg137731 date=1054316152]
If it had a 6 cyl it has 4:11's possibily 4:56's . 31's will run the rpm's up pretty quick . If you have those gears consider 33's or 35's .
[/quote]

gee.....what a shame : ;D
must suck to be told you gotta up size. ;D

 

[Broncobowsher]

Change the cooling fan. When I went from not enough air electric to an engine driven flex fan, it turned into a screaming engine.

Take the fan off and go for a lap around the block. Put the bolts back in so you have a waterpump, just leave the fan off. just remember the only moving air is from the vehicle moving, don't let it idle.

 

[TOMKLU]

Is your transfer case stuck in LOW?

 

[BwoncoHowie]

After driving a car with overdrive and 2.73s all week long (1800 rpms at 65 mph), then I get in the 73 with c-4 and 3.50s along with a 7-blade fan. Then I guess it does seem like it's taching a little high with 31's, 2500 rpms @ 55mph. I get over it though ;D

 

[tcjones76]

My 302/C4 w/30's and 3.50's tachs at about 2700 rpm at 65 mph. Not too bad, don't need to go any faster!

 

[SteveL]

we had the same problem on our 66. It runs good now with 3.50's, 33's, 4spd, nd a 351w.. I just swapped the 72 to 3.73 and it runs nice. gets up to about 80 on the highway.

 

[brokenhorse]

With my I6,30s and 411s She is at about 3300 at 63mph :-

 

[paramagic]

Thanks guys, I'll figure out exactly what gears I'm running when I get home next week. How much of a difference will going from 31" to 33" tires make on the rpm's? Sounds like a simpler fix than a gear swap..?

 

[smorton]

DON'T change your gears! That is a big waste of money because you don't gain anything for 4-wheeling. If it is a 66 it should have 4.11 gears in it because that is what they used on the 6 cylander motors.

I have 35's with 4.11's in my 66 with a 351 w also. I run about 2800 rpm's at 70 mph. The biggest improvement you can make for the noise is to swap in a clutch fan. The fan will not run at the speed of the motor because of the clutch therefore it makes less noise AND it cools better because fans become less efficient after they reach 2000+ rpms

The front of my vehicle was a little crunched so I chopped out the center of the radiator core support (It didn't fit the bigger radiator anyway) and welded square tubing across at the top and bottom with spacers in between. Basicly this moved the radiator more toward the front grill (you have to remove the hood latch hardware) and gave me enough room for a heavy duty 18" - 7 blade clutch fan.

It is soooooo..... much quiter and cools a lot better because of the bigger fan too. I also get a little better throttle response too. It is one of the best improvements I have made on my rig yet as far as drivability on highway/around town.