Rear Axle Ratio

[1969_Mach1 333]

I currently have a 3.89:1 rear axle gear in my 1969 Mach 1.  Now that I am older I'd like something a little lower since the motor revs pretty high just cruising at 45 to 50 mph.  Trans is a close ratio toploader 4-speed, motor is a 351W, original 14" wheels with tires that are 26" tall.  I'm thinking either a 3.70:1 or a 3.50:1 rear axle gear.  First gear in this trans is only 2.32:1 so I am not certain how well it will work with a 3.50:1 rear axle ratio.  Anybody have experience with this type of trans and rear axle gear combination?

[dream car 12]

I'm very happy with my 3:50 rear axle, close ratio toploader With 351W. Driving around neighborhood sometime I don't even use 4th gear. Going from 3:89 to 3:70 is not going to make a lot difference for a lot of works. That just my opinion.

[1969_Mach1 333]

Thanks, I've been wondering how that combination would work.  I've been tinkering with the gear ratio calculators and yeah, 3.89 to 3.70 is only about 130 rpm lower at 50 mph.

[RPM 1,190]

I know a couple of owners who are happy with 3.25s and toploaders. 

[ClubSport 29]

Switched from 3.25 to 3.5 when swapped my 8" to a 9" and the 3.25 was more convenient with my WR Top Loader

[1969_Mach1 333]

I'm starting to think a 3.50:1 might be the best choice with a close ratio trans.

16 hours ago, dream car said:

I'm very happy with my 3:50 rear axle, close ratio toploader With 351W. Driving around neighborhood sometime I don't even use 4th gear. Going from 3:89 to 3:70 is not going to make a lot difference for a lot of works. That just my opinion.

Does your car feel lazy at all in first gear?  First gear in a close ratio toploader isn't very low, it's only 2.32:1.  Unlike the wide ratio at 2.78:1.

[LoneWolf2U 136]

I ran the 3.5 rear end in my 70 Mach1 pushed by a stout 351Cj and close ratio toploader.

No problems getting it to move off the line, In hind sight a 3.25 may have been better for freeway travels.

Anything taller in rear would have made putting the power to the ground a challenge, Spinning is not winning but does make a cool smoke show.

[dream car 12]

7 hours ago, 1969_Mach1 said:

I'm starting to think a 3.50:1 might be the best choice with a close ratio trans.

Does your car feel lazy at all in first gear?  First gear in a close ratio toploader isn't very low, it's only 2.32:1.  Unlike the wide ratio at 2.78:1.

  In my younger year , I would probably preferred the lowest gear possible. So I can smoke the tires , and ludicrous mode on  take off.  Now I don't even drive on the freeway fear of rock chips. My 3:50 don't feel lazy in first gear, its a factory standard ratio for the GT-350 4 speed. Unless you are still young at hart, that would be different situations.

[1969_Mach1 333]

 

2 hours ago, dream car said:

  In my younger year , I would probably preferred the lowest gear possible. So I can smoke the tires , and ludicrous mode on  take off.  Now I don't even drive on the freeway fear of rock chips. My 3:50 don't feel lazy in first gear, its a factory standard ratio for the GT-350 4 speed. Unless you are still young at hart, that would be different situations.

Young at heart, not as much anymore.

[Dave R. 85]

Can't be much help as my 3.50 gear and CR toploader are twisted by a 428CJ. Lots of fun and fuel.   Dave R.

[1969_Mach1 333]

16 hours ago, Dave R. said:

Can't be much help as my 3.50 gear and CR toploader are twisted by a 428CJ. Lots of fun and fuel.   Dave R.

I only have a 351W, not nearly as much low end torque as your 428CJ.  The only combination I've had experience with on a 351W Mustang and 3.50 rear axle gear also had an FMX auto trans.  With the FMX's lower first gear ratio and torque convertor it was a good combination for street.  Not lazy at all and could still cruise 55 mph.  This was so long ago the highway speed limit was still 55.

[Dave R. 85]

Sounds like a fun combo also.   Dave R.

[1969vert 55]

I have a 3.0 with my top loader was a 2.79 8" before.

just a cruiser..

Might be ISO a 2.79 gear for a 9" ..used..

[1969_Mach1 333]

On 8/26/2020 at 12:24 PM, Dave R. said:

Sounds like a fun combo also.   Dave R.

That combo was in one of my older brothers 69 Mach 1 back in the early 1980's.  He was one that would street race almost every weekend.  On Saturday mornings I'd see all the rubber stuck to the rear quarter panels and rear inner fenders of the car.  At first he'd clean off all the rubber before our father saw it.  After a while he didn't care and left it on there.

[stangs-R-me 120]

My 351W has a Wide Ratio Top Loader, 3:50 Gears, and 225/60-15 (25.63" Dia.) tires.

2840 RPM @ 60 MPH or 3551 RPM @ 75 MPH in 4th.

OK on 55 MPH back roads but screaming on the 70 MPH Interstate !!  

Doug

 

[RPM 1,190]

14 hours ago, stangs-R-me said:

My 351W has a Wide Ratio Top Loader, 3:50 Gears, and 225/60-15 (25.63" Dia.) tires.

2840 RPM @ 60 MPH or 3551 RPM @ 75 MPH in 4th.

OK on 55 MPH back roads but screaming on the 70 MPH Interstate !!  

Doug

Put some 27 inch or bigger tars on the back. 

[1969_Mach1 333]

Update,  I've decided to go with a 3.70:1 ratio.  After being use to the 3.89:1 gears it might feel lazy in 1st with a 3.50:1 gear.  Now just to select from who.  I've had good luck with Motive's performance series of gears and I've had good luck with buying some no-name brand stuff from shop near me that does rear axles and manual trans.