Customs 1949 Mercury New Project Engine/Tranny/Rearend Question

Hmmm I see some folks being a little off in their comments.

4.27:1 gear with 26" tires, 1:1 trans, no OD = easily over 4500 at 60-70mph.

Now...

4.27:1 gear with 28" tires, AND OD, = something much more manageable.

My OT TrailblazerSS with 4.10's and factory 30" tires and OD is doing 2000 rpms at 70mph.

 

I am running a stock 49 merc rear end with a 350/400 combo in my 50. Run the 700. i have been wanting to put a 9" rear end in but havent had the time or wanted to spend the money. I figured i would keep it till it grenaded. I should have gone and found a 700 when i put in the motor/tranny but the sbc and the 400 were too good a deal to pass up. I was kicking myself as i was screaming at 70 mph on the 405 tonight. Do yourself the favor and get an extra gear.
I have a 49 project that will have highway gears if i can ever get it on the ground.

 

I think the 700R final drive is .75. I have had it both ways, my 51 had the stocker non OD rear with a 350/350 and sucked ass. It wasnt terrible, but going 20 minutes on the highway seemed like an all day trip. My 50 had an OD rear and when the flatheads OD wasnt connected it was WAY unbearable. With the OD connected it wasn't bad at all. Now the flip side being that the R10 unit which was the factory OD trans has a doozie of a gear reduction in OD, I believe .6 Thats so far the highest rev cut Ive seen in a factory trans like that. The AOD I believe is somewhere in the middle, either .65 or .7, I remember it wasnt the R10 but just edged out the Chevy.

Any rear 61" hub to hub (wheel mounting surface) is good. A direct bolt in after you flip the spring perches is an earlier F100, I did that once and it fit well and retained the stock bolt pattern, it is a 9", the downside is that I think most all were 3.73 gearing so you aren't getting much of a break on revs at all.

 

I don't know what the exact ratio is with the 700R, but you're fairly safe in figuring a 30% drop in rpm with OD engaged.

30% holds true for the stick ODs from back in the day as well.

 

OD + 4.10 + 28" tires is actually a nice combo personally speaking, car won't be a total turd when accelerating. But if you are driving long distances a 3.23 or something would be pretty nice.

 

A 700R4 trans has a .7 ratio in 4/OD.

-KatsAss

 

10 bolt rears from 69-72 Novas work great under mercs,. A couple of friends are running them under theirs. Most had low gearing. 51 Mercs with MercoMatic had 3:31 gears too. Kind of hard to find though. Iflooking for a Granada w/ 9 in, look for a 6cyl with tow packge. Most have 9 in and some are limited slip.

 

I am running a sbc 350 ...bored .40 over and 20 over on the crank...3/4 comp cam with matching edelbrock intake/carb.
The trans is a 700r4 w/ OD. Stock driveline to a 7.5 GM rear. The rear in it is 2.56:1 which is totally wrong now....so I am swapping out for 3.73 rears.

 

My 51 Merc came stock with OD and has a rear axle ratio of 4:27. A 700R4 has an OD ratio of .7. Mutiply 4:27 times .7 = 2.98 which is what the final ratio in overdrive will be with a stock 4:27 Merc rear. Engine RPM's will depend on tire dia. The standard rear end for a 49-51 Merc with OD was 4.27 to 1. A 3.91 to 1 ratio was an option. Automatics came with 3.31 ratio. Station wagons had an option 4.55 ratio. Here is a very helpful chart.
http://forum.eastwood.com/showthread.php?6092-Ring-and-Pinion-RPM-MPH-Chart

http://www.superlift.com/library/gears.asp

 

I am running a 9" that came out of an Econoline van. the width is perfect. i have a 9" from a Versailles but it was going to require me to move a bunch of crap around as far as spring hangers go.

 

You guys think he's still wondering about this 2 years after he originally posted the question?

 

I have a 283 sbc with a turbo 400 and a stock rear end it dives fine.

 

I know its been years but what the heck. What rear end did you finally consider for your combo. im in the same boat looking for a on budget buy for the same setup if any one has info on the same setup please msg me or post it thanks.