Anyone here running 2.47 rearend gears?

I just purchased a late seventies Ford Granada rearend for my 55 Fairlane. It's one of those oddball 8.7 ten bolt diffs that were only produced for a few years. What I'm looking to get by converting the diff is a highway flyer. The motor is a 352 with a 68 Cougar 4 speed and 215/75/15 tires. I'm not to sure if these gears are to tall. Anyone else running this gear ratio?

 

I used to run the model A salt racer on the street aswell when I first put it together,it has the 2.47 gears,I was turning them with warmed up naturally aspirated caddy 500,it ran great. Your fairlane might not be the fastest in the traffic light grand prix,but down the highway it will cruise along great without the engine buzzing.
Tim

 

I have stupid high gears in my model A, its a nova rear end something like 2.30's. I have a double wide ratio 4 speed. this helps, but its slow off the lites!! I have a set of 3.42 gears with new bearings ready to put in....but i'm getting used to the high gears and i love go'n down the road! 11,000 miles the last 2 summers! this thing cruises at 70 MPH!! I stick it in the left lane and the telephone poles look like a picket fence!!!

 

I've run 2.75s quite a bit. 2.47 would be a 10% reduction in engine speed from there. I have a set of 2.50s but never put them in my car.

As long as the engine works ok at low rpm (not too much cam or too big of an intake manifold) it should be fine. You'd get much better off-the-line acceleration with more gear though.

 

Engine should be fine at low RPM. Bone stock 352's have good torque. My concern has more to do with eventually frying the clutch off the line.

 

With lots of torque you shouldn't have to slip the clutch much at all. I used 2.79's behind a Merc 276 inch flathead in my '47 Ford coupe and while I could tell the gears were a bit tall on acceleration, it wasn't really a struggle to get underway.

Ray

 

I had 2.73's in my 66 skylark and I had a few different engines in it. The first was the stock 340 and a 2 speed tranny. You could run faster than it could get off the line up to aout 30 but from there it pulled hard and cruised down the freeway at 90 mph all day long. Literally I did it a few times. then I switched to a couple a different smallblock chevy's and a th350 it was better off the line but I wish I had the money then for a set of 3.73's to really see how fast it would have been.

To answer your question It will be a great freeway gear. It may be a bit tougher on the clutch but time will tell you that.

 

I have a 54 Ford with the original 239 3speed trans. I was told by the previous owner the rearend is from a Granada. Dont know the year. The tag is missing from it. But there is a stamping on it. D5AWB
The gear ratio is the 2.47
Well at the lights it takes a little bit of work to feather the clutch and get her going. But when it does no problem. Highway speeds are nice! But once I determine if it is the 8.7 or 8.8 I would like to go upto the 3.08 gear.

 

I bought a new 77 Ford F100 that came with 2.47s. I hated them and replaced them with 3.70 for towing over Donner. I had 2.47s in the race car and at Bonneville with a big motor they were fine.

 

Yeah, my '57 Chevy 1/2 ton cobbled up Frankintruck (350/350 auto) has a 2.42 12 bolt rear. Not great off the line, but with the auto trans that's no big deal. I know I'd get better mpg around town with a 3.08, but changing it out hasn't been a priority.

OTOH, doing 70 out on the interstate, I've got lots of top end to go.

Hah! Just realized this was a two year old Zombie Thread!

Later, Kinky6

 

Hi Run with 2.47 in a 56 Ford with 428 CJ....The car was set up with propane and could run 1200 miles for $90...this was about the same as running a 1.5 L car on petrol.....

 

Someone gave me a Mopar 8.25 rearend from an A body. Its under my 39 Plymouth truck. Imagine my surprise to discover a 2.45 gear ratio. It is a narrow rearend. I run 15x10 wheels on the rear and it had a 4.5 bolt circle. In traffic lot of the time I run in second gear. Cruises at 70 at about 2200 rpm. I do know one thing about these Mopar rearends, If I wanted to change gear ratios I would have to change the carrier housing because the ring gear is thinner than lower ratios which would make a gear change a lot more expensive.