really confused

[Lrpalo]

Ok so I have 4:56 gears front and rear in my truck. I have always assumed that gears have to match front to rear. But my buddy is rebuilding a 89 full size bronco with ttb. and he told me that the gears in his truck were 3.50 back 3.54 front and i thought this would make his drivetrain tear itself to pieces

 

[strvger]

they should be closer really. some have 4.10/4.11, some have 5.12/5.13. etc. with the difference he has, he'll probably be ok as long as he doesn't wheel it too hard, or try to use the 4 wheel drive on smooth roads for very long.
most of the difference in the gears front and rear have to do with the differences in drive shaft lengths. shorter one (front) may turn a little faster than the longer one (rear). that 0.1 difference in the gear sets is enough to compensate for that. where it will tend to break will be somewhere in the transfer case typically, as the difference will bind on the output shafts and then the gears in there.
just my $.02.

 

[feellnfroggy]

His drivetrain will def bind up if he uses it on a non slip surface such as pavement. However if he is building or it was built to be a mud truck he should be fine, I wouldnt use it for crawling. And if he is running two different size tires to match the gearing then he should be ok. But he really needs to match up those gear. I dont think ford put anything stock that far apart in size.

 

[jeffw920]

so why would the shorter front shaft turn at a different rate than the longer rear one

 

[fourwheelford]

It will bind like a mofo if he touches dry pavement, I guess you were able to do this on older 4wd models it helps the front end bite more, but like stated before thats a big difference.

 

[hondaxr650]

so why would the shorter front shaft turn at a different rate than the longer rear one

It won't.

 

[Sasquatch_Ryda]

It will bind like a mofo if he touches dry pavement, I guess you were able to do this on older 4wd models it helps the front end bite more, but like stated before thats a big difference.

It will be perfectly fine...that .04 is a tiny difference...Lots of trucks were like this as you could only get 3.54 gears for the Dana axle in the front of it and 3.50 gears for the Ford built axle in the back if it.

You could create worse problems with just lowering the air pressure in the just the front or rear tires, or having a tire that is a little bit different size than the rest.

 

[AllanD]

Ok so I have 4:56 gears front and rear in my truck. I have always assumed that gears have to match front to rear. But my buddy is rebuilding a 89 full size bronco with ttb. and he told me that the gears in his truck were 3.50 back 3.54 front and i thought this would make his drivetrain tear itself to pieces

Unless he has a factory 9" in the back? No.
normal combination for a 9" equipped (1981-85) could have had a 3.50 rear axle ratio mixed with a 3.54 ratio D44 front.

But TTB full size Bronco and F-150's made mid 85-up came with the 8.8" rear axle with 3.55 gears...

4.10 geared F150's came with 4.10 gears in the 8.8" in the back and 4.09 ratio in the D44 front axle.

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