I am new to these old beautiful Cat cars, but i’m totally confused. On all my old Mustangs and other vehicles I changed the rear gears to 3.73s, 3.90s, or 4.10s. Nobody seems to do that that with these Cougars…is there a reason? I would love to get my 68 XR7 to accelerate a lil faster, but what seems to be a basic mod is not the norm apparently in the Cougar community? Can anyone explain? The stock gear ratio is sluggish and slow.
I put 3.50’s in my White 70 XR-7 and went soft with 3.25’s in my Blue 71. If one plans long drive in there car high numerical gears are not a lot of fun. But around town they sure can be. As I am not taking my cars out to the weekend drag races I kept them somewhat conservative for what I think was my intended use. I know many that have replaced there rear gear set to a faster set up. But most Cougar owners are not into the stop light grand Prix. I however encourage you to do what you wish with yours and be sure to keep us informed on how it goes. We love the diversity of the owners.
Plenty of guys change the rear axle gears to suit there needs and desires. One thing you need to remember is there are a whole lot less cougars on the road then mustangs and of those even less might feel like modifying them. Hang around a bit and you will see all kinds of fun stuff you can do to your cat to Increase the performance over stock.
My 3.40s with a Yukon Grizzly locker are a good compromise for highway driving and the drags. 3000-3200 on interstates.
Who says that? Mine have 3.91 and 3.50 factory gears. In other Cougars I have used 3.70 gears. A Detroit Locker is maintenance free and silent so I typically use one of those if given a choice.
For cross country or even between cities 30 miles apart Something like 3.00 works well with no overdrive on the highways. Gears with big numbers make more sense at the drag strip.
Funny as it may sound, IMO most are afraid to get into a rearend. I prefer 3.50s. I built a 72 Mav with a home built Boss 302 and used a AOD. That made it possible to run 4.10s in it.
So does anyone know a good website to order said parts from? I wanna get a better differential and I wanna go up in the gears a bit as I live in a small town and don’t take long trips in the Cougar. I’d love to have a lil more go power in the Cougar and gear changes were always my favorite mod in my old Mustangs. Can’t decide what I wanna put in this car or where to even purchase the parts. I’ve yet to find a good website for performance parts for the Merc
It’s a Ford 9” rear. You can probably get parts for it at a 7/11.
Yukon Gear, Currie, Richmond Gear, Summit / Jegs, Amazon. The world’s your oyster.
More than 3.50 without an overdrive is usually not recommended except in motorsports or almost-no-highway scenarios.
Good luck!
If you have a 302 you’ll likely have an 8” rear instead of a 9”. As far as using low gears, I tend to run my Cougar on longer trips with interstate and expressway travel so I don’t want to be cranking to keep up with traffic. 411’s were cool running stoplight to stoplight in town- not so fun trying to get to a car show 5 hours away with the wife in car.
I can recommend Quick Performance in Ames, Iowa. Bright, responsive guy Mike Mortensen runs it. He can build and ship you either an 8-inch (small block cars) or 9-inch (390/bigger 1968s) for you, your choice of clutch type or ratchet type differentials. My 3.40 3rd member with Yukon locker and 3.40s is quiet as a lamb (unlike my own rear axle builds) and came at a fine price. I’m running his axles, too. Yes, I drag and cruise with my upgraded 8-inch!
One great thing about our cars compared to modern 8.8 Mustangs is the modular rear axle - you can swap the new stuff in your driveway.
R.B.
I’ve had 4 different gear ratios in my car. The original was 2.73, but then switched to a 3.50 for quite a while. It was a lot more fun to drive with the 3.50. I switched from the 8" to a 9" and have been running a 3.70 gear since then for street use. When I was doing a bit of drag racing with it I put a 4.56 gear in it. That pretty much topped out my rpm at the end of a quarter. The 3.70 feels like a nice compromise gear to me. It’s high enough that I can cruise at 65-75 without issue. I think most people are used to everything running pretty low rpm at cruising speed, so without an overdrive it takes a pretty high gear (low numerically). Growing up I sat behind a 428 (FE) industrial engine in a tractor that ran 3200rpm all day, so running a small block (289) at that speed doesn’t seem like too big of a deal. If I ever switch to an overdrive transmission I’ll probably end up going to a lower gear, like 4.10 or 4.30.
I’ve run everything from a 3:00 to a 3:50 to a 4:11 in mine. It’s a 9" I swapped into my 68.
But I drive mine distances when I do drive it. I’ve driven all over the eastern half of the USA with the 3:50s, including two Power Tours. Right now I’m back to the 3:00s that I put in when gas prices were closer to $4/gallon around here, but will go to an overdrive trans eventually so that rear gear number will go back up again.
Does the gearing matter as much with a manual?
I’d probably go 3:50 anyways but I wonder.
The RestoMod had 3:50 for years. Rebuilt motor & changed gears to 4:10 Noticed a great increase coming out of the corners, but the temps we higher as a result. Short vid shot w/ the 3:50 gears. Poor Viper…
http://www.cougarbill.com/videos/2017/8/20/restomod-on-the-track
Depends if it’s an overdrive or not. Both a three speed auto and a 4 speed manual have a 1:1 top gear. So it wouldn’t have an overall affect on rpms once in the top gear.
Absolutely matters in a 4 speed, in some cases more. Before stall speed at a given load a torque converter will provide some torque multiplication, a manual doesn’t have any of that benefit
One of the strangest things Ford did was the close ratio 4 speed, my opinion is that it doesn’t work great in anything, and especially a Drag Pack CJ. 1st gear is too tall at 2.32 and if you gear it for 1st, 4th is screaming
I try to stay around 10:1 compound gear ratio in 1st for a pure street car, with a 2.78 wide ratio, that’s 2.78 1st X 3.50 rear. Good all around gear. If you have overdrive, I push to 11:1-ish
Hard to do if you have a close ratio though 10:1 requires a 4.30 gear, and that doesn’t make a drive to the next town over too fun 
In an automatic, you have a little fudge factor there and match the converter to the engine, but you need to look close at the use of the car, because for a C4 or C6, 3rd is still 1:1
Depends on who you talk to I guess. We used to swap in our “fun pumpkins” on a Fri night, then back again Sunday night for the drive to work.
When I worked on a stock car pit crew, we raced at one track on Wednesdays, a different track on Saturdays and then back to the Wednesday track on Sunday.
I would change the rear chunk on Friday night for Saturday and then again Sunday morning for Sunday and Wednesday night. With a drain plug in the housing and floating rear axles, I didn’t even need to remove the rear wheels and tires. I got REALLY good at it.
Ah, the energy of youth. The classic 1960s thing of “weekend” third members.
Up to my 60s, I would swap entire hub-to-hub modern 8.8s on SN95s and S197 Mustangs. I gave that up for once-every-five-years changes of 8-inch center sections.
A close ratio 4-speed is best on a road race track - down shifting doesn’t cause the car to get upset from the RPM change!
It also helps to keep the engine in the optimum RPM range.
I took the close ratio toploader out of my '70 351C cvt and put it in my '67 TA race car. It was a vast improvement over the stock wide-ratio.
The '67 runs 4.11/4.30/4.56/4.71 depending on the track.
