bronco seems to have real high rpms at 50mph.

[benelibutton]

I know this is normal. It had real small tires on it. I just put 31s on today but havent driven it yet. Is there anything else I can do to help a little bit more without doing a full tranny swap. What if I just changed the axles. I dont know much about this . If I changed to the smaller 28 spline ( assuming I dont have that already) would it change the gearing just a little bit. Anything well help. 1970 bronco. . Pretty stock

 

[quikdrummer]

I know this is normal. It had real small tires on it. I just put 31s on today but havent driven it yet. Is there anything else I can do to help a little bit more without doing a full tranny swap. What if I just changed the axles. I dont know much about this . If I changed to the smaller 28 spline ( assuming I dont have that already) would it change the gearing just a little bit. Anything well help. 1970 bronco. . Pretty stock

axle splines wont have any affect on how fast anything in the axle spins

any idea what the axle ring and pinion gear ratio are?

 

[benelibutton]

Nope prob stock for a 70. Really someone gave me bad info then. So I should change the ring and pinion

 

[AZ73]

Tranny or differential are your only choices

 

[quikdrummer]

Nope prob stock for a 70. Really someone gave me bad info then. So I should change the ring and pinion

well thats a pretty big expensive job. how high is the engine revving at 50? and what transmission is in it?

axle spline count is more to do with strength

 

[Revelation]

Check and make sure it is not in 4 low, seen that happen to many a Bronco owners.

 

[Fireball05]

Check and make sure it is not in 4 low, seen that happen to many a Bronco owners.

50mph in 4lo?!?! Pretty sure that isn't possible, is it? Happy to say I've never tried.

I've got 30" tires, 4.11 gears and the 3 speed. It runs 65mph but sings pretty loudly. If you've got 31s, I doubt you have a rear end or tranny that would have higher (lower?) gearing than mine, so you should be OK.

Do you know what your rear end is? 3.50s or 4.11s? Or maybe something even higher from a P.O. who was into heavy off roading? If you've got 3.50s it should drive pretty fine on the street at 60+mph.

 

[Revelation]

50mph in 4lo?!?! Pretty sure that isn't possible, is it? Happy to say I've never tried.

Yes I have been in one that reached 50 and was in Low range, She was screaming, but was doing it. At first it was thought that someone had pu 488;s in it.

 

[benelibutton]

Its not that bad . Im just used to driving a newer f350. Its prob fine. Its not in four low. I just put the new tires on today and havent driven it yet . I think it should do a little better. Heres the tires I had on before I lifted it prob 28 s or something

 

[Broncobowsher]

The mechanical fan sounds like you are really reving the engine when you are not.
Go to the tech section on the left of this page, go to the axle section, follow the "check your gear ratio" article. Piece of string and tape are all you need.
Do you have a tach? if not then get one. You have no idea what it is reving to just by sound.
What transmission do you have? If automatic are you sure it is shifting through all the gears? Pull it into 1st get some speed, shift into 2nd manual and it should have a pronounced shift. Add more speed and go into drive, there should be a pronounced shift again. At this point you have confirmed you are in top gear.

Yes, 50 MPH is possible in low range. With 4.88 gears and tera low gear (3.15) in the transfer case and only 33" tires 50 MPH is 5000 RPM in overdrive based on the 20 MPH at 2000 MPH I often did. With normal gears and stock low range 50 MPH could be done without overdrive. But it would be really screaming but doable.

 

[benelibutton]

I well do this when I get over to it tomorrom. Its got a 3 speed on the floor. Not automatic. Mechanically its good when I step on the gas rpms go up like they should and come down as they should.

 

[sprdv1]

Its not that bad . Im just used to driving a newer f350. Its prob fine. Its not in four low. I just put the new tires on today and havent driven it yet . I think it should do a little better. Heres the tires I had on before I lifted it prob 28 s or something

Nice lookin Rig...

 

[Timmy390]

I know this is normal. It had real small tires on it. I just put 31s on today but havent driven it yet. Is there anything else I can do to help a little bit more without doing a full tranny swap. What if I just changed the axles. I dont know much about this . If I changed to the smaller 28 spline ( assuming I dont have that already) would it change the gearing just a little bit. Anything well help. 1970 bronco. . Pretty stock

What do you consider high RPM's? I'm bumping 2850-2900RPM at 65ish and it's loud due to the Cherry Bombs. That RPM is right in the power band for the 302. 4.11's and 32's and it has power at that speed/RPM.

Tim

 

[WheelHorse]

F-350 at 70mph is probably turning what...1800 rpms in a diesel?

Put a tach in your old Bronco and report back.

 

[matts460]

My Bronco has 4.57's with 31's cruise 60mph sounds good, RPM around 3000 has great power (obvously) really not much differnt than the 4.11 i had. But im used to short gears in my other toys. LOL My Dad ran 4.56 gears in his 56 Bel-air with a 4 speed and 305ci motor. Tires were probly 25inches tall. We drove it to Colorado and all over Missouri over the years it ran great!

 

[bknbronco]

when i had stock tires with my 3 speed and 4.10 gears i couldnt even use first gear cause it was too low. You had to pretty much start in 2nd. If you started in first you were shifting to 2nd in like 10 feet. Now that i put bigger tires on (33's) i can finally use first and can cruse do the ffreeway at 70 no problem.

I also agree with what was said about the fan. Mine used to sound like a airplane taking off and i hated it. I switched to a clutch fan and now my truck is silent. Them stock flex fans are WAY WAY to noisy! Try driving it down the raod a bit and back with the fan belt pulled off. That gives you a idea of the noise a fan creates and how much it slows down throttle response. Dont go too far cause youll over heat without a belt going to the water pump, but even doing that in the garage and reving it up youll notice some huge differences.

Skip the tac! Learn to drive with out it! I go by feel and vibration. When you think its reving high step on it and hold it! Get that sucker to really rev up then you wont feel so bad when your just cruising and you know what its really sounds like to rev the piss out of it!

 

[OX1]

I know this is normal. It had real small tires on it. I just put 31s on today but havent driven it yet. Is there anything else I can do to help a little bit more without doing a full tranny swap. What if I just changed the axles. I dont know much about this . If I changed to the smaller 28 spline ( assuming I dont have that already) would it change the gearing just a little bit. Anything well help. 1970 bronco. . Pretty stock

I have 33's with stock gears which gives you an effective overdrive of at least 15% (over stock). I made up for it in first gear by puting in a T-18.

 

[benelibutton]

Thanks. I well put a tach in and test the new tires and go from there. I know its not in four because I can see the front driveline when I take the tunnel cover off.

 

[bknbronco]

Thanks. I well put a tach in and test the new tires and go from there. I know its not in four because I can see the front driveline when I take the tunnel cover off.

Well good news is that you have to take that cover off to see the driveline! The last bronco i test drove had so much rust you could seee the road through the tub and the gas tank consisted of a plastic gas can between the seats!

 

[BroncKrawler]

1970 still had the T-shift correct? The shift pattern from top to bottom is 4Lo 2Lo Neutral 2Hi 4Hi. Could still possibly be in 2Lo, I use that all the time around my property in my '68. Just something to check since the front shaft isn't spinning doesn't totally rule out low range.