This is a post for my brother, who has a '84 Bronco. He has a 4-speed tranny, and when he's in 4th at about 75mph, his tach reads almost 4000RPM's! He has the 351W motor and stock gears in the axles. Are all Bronco's like this? It will only be a matter of time before the engine goes if he has to run a long trip at decent speeds, I think. He already blew a head gasket (we just finished replacing) on the way to NY--4 hour trip at 75mph. Any ideas? Seems like the whole t-case is geared waaaay down...he does have a VERY low 1st gear. Help!!

 

Could someone have had larger tires on this Bronco before your brother owned it? What size tires are on it now?

 

He has 31's on it now. But shouldn't a V8 only turn @2500RPM max for highway driving? What's a safe RPM for long trips?

 

What kind of trasfercase is it? Full time or part time? Are you sure the transfer case is in 2wd or high (not high lock for full time case.) Your tranny has a 4th gear of 1.1 and if the gears are still stock 3.55. You should not be pulling 4K with 31" tires. Check the transfer case. Then make sure of the axle gears.

 

I am more inclined to think the tach is wrong. You are not going to run a 351 at 4000 rpm for any distance without having some kind of other problems. The first that comes to mind would be the motor would overheat. There would be a tremendous amount of high rev motor noise. Gas mileage would be none existant. Even with 5:13 gears your rpm wouldn't be that high. Got to be the tach.

 

Yeah, I was inclined to believe that it was the tach, because he just replaced the 3rd member and it has something like 3.50 gearing. I just wasn't sure if Ford made a t-case that was geared super-low throughout all gears. And YES, we know it's not in low range

 

My F-250 turns about that- it has 4.10 gears from the factory. I ran it up to Maine once, 75-80 the whole way, with no probs or mass destruction. Maybe I just built the engine right- it's a 300-6! Just be glad you don't have my old Bronco- 4.56 gears, maxed out @about 50 mph.

Jared