Hey all, after finishing my rear suspension and brakes I felt like looking more into my differential. While working I noticed the tag still on the thing so I got a picture and found out everything. I knew it was a 9 inch, after a few looks I saw it was a standard case with 3:00:1 ratio, not limited slip or anything.
I’d like to beef it up a bit, I’m just making a nice, (mostly) daily with a bit of extra power and fun, so I for sure want to change out the gears. I figure 3.50’s are a good middle ground to have fun and not be a hassle, I also plan to get an AOD in there eventually so I can still highway it. However I know it’s an open diff, and I’d like to change that.
After a bit of research, I found the PowerTrax Lock Right Locker, which they say goes on both 28 or 31 spline axles, and acts as a locker which still lets you go through turns when it unlocks. I was wondering if anyone had use this specifically and what your thoughts were on it. This also led me to find the Richmond Gear 92-0690-3100 Powertrax (P/N 91028000), which is the same thing, except you have to get either the 28 or 31 spline, and it’s a bit more but just seems nicer. I am fairly certain I have 28 splines as it’s a pre '71 setup and has the concave ends on the axles. (1970 Base Cougar)
I’m just wondering if this is worth doing, or if there were any repercussions of it, I know of the clicking through turns but with exhaust and a nicer stereo I’m sure I won’t mind too much. I only saw 1 thread mentioning these options and was wondering if anyone else had some input, thanks!
I have Eaton Trutrac units in 2 of my Cougars. I put 3.5 gears in my White 70 XR-7 and 3.25 gears in the 71 XR-7. I put the lower gears in the 70 because I have a 5 speed in it. I had Randy’s Ring and Pinon do both.
My Shelby is a Detroit locker. They can be a bit rough for daily driving as the inside tire “scuffs” on turns but you can still make turns with no issue. The Eaton would be a decent choice or just the original ford tracklok. It’s pretty forgiving on the street. As for 3.50:1. I don’t know what tire size you’re running but if you drive the freeway you won’t like them. I have 26" tall tires with a four speed trans. My vehicle tachs about 3300 RPM@ 65. I would wait and do your OD trans at the same time you make your gear switch.
No mention of what you have done with the engine and what it is…
-Keith
I’ve never messed with Diffs before but I’ve heard of the TruTrac and that slipped my mind. Part number 912A587? I see it from a few places, anything else I need to get with it?
I’m not on the freeway too much, it is LA county though, I am between 3.25’s and 3.50’s, I occasionally drive a 429 Cobra Jet Ranchero that has 3.25’s and I just feel that it’s not as snappy as I’d like, but I have lots of time to consider my options.
I hadn’t mentioned anything engine wise as I am also unsure of what it will turn out to be, I’m right at the part in a rebuild where I have to choose all the parts and whatnot, but I’m just aiming for a mild build but it’s a 351C 2V, going to be bored out .020, Edelbrock AirGap, HR680, Hyrdraulic roller cam from Brent Lykins, however I am still learning of options as I go so it’s hard to gauge exactly what it’s going to be like in the end.
I had a power trax in my older F250HD you get the clicking noise at really low speed turns and when backing up it kinda makes a ratcheting noise, you get some hop out of the inner wheel if you are making a sharp turn when pulling away from a light or stop sign. during regular driving while making turns or going thru corners you dont have noise or hop. I acts like a locker. I bought it used and put well over 100K trouble free miles on it. That being said on a 8 lug rear it was easy just pull the cover and install the unit and posi units for that rear get expensive it was the best bang for the buck, on a 9" you have a lot of options something like a Tru Trac or may be the way to go.
Unless you are doing lots of track time the 3.00 ratio is ideal. I have 3.50 (factory ratio) in my GT-E and it is revving very high at highway speeds. Quite unpleasant on any kind of long trip. I have a Detroit Locker, it was new in 1994 when I built the rear end. Very good unit, utterly quiet. The Detroit Locker is a little stiff in the rain / wet pavement so you need to be aware it will understeer or oversteer unexpectedly, especially when decellerating in the rain. No issues on dry pavement.
I use the Yukon Grizzly locker with a less aggressive oval track spring in my modern street-strip car (you can contact Yukon about the spring topic; it has to be swapped in before setup). It never fails me on the strip, and has not been any issue in winter driving. With most ratcheting lockers you will scare passersby in supermarket parking lots occasionally when it releases.
Before the locker, I had a True-Trac that failed to stand up to the rigors of frequent track use, but it was a real sweetheart on the street. For normal performance driving sans the 5000 rpm launches, it should last as long as Traction-loc clutches.
Yukon makes Ford-style clutch limited slips now, BTW. Two variants which they call aggressive and street.
No I have had a half dozen or more Detroit Lockers over the years before and since in other cars. The only ones that make any noise at all are either the “H” series ones that you can buy used on eBay or the old ones that came new on Shelby Mustangs in the 1960’s. Anything Detroit Locker / Eaton made since around 1975 has the (way back then) new design so they don’t make any noise.
Well from the responses here it seems like the TruTrac or the Detroit Locker would be the more widely used options, I most likely won’t be on a track with this car, so I’m sure the TruTrac will be the best for my applications. I’ll also keep the 3:00:1 gears and after driving it a bit I’ll see how I feel. Thanks for the recommendations!
The locker in my Shelby is from 1967. I can assure you it’s noisy at times. I’ve had the car since 1982 and I just completed the ground up restoration and the differential was rebuilt. It still makes noise in tight turns and sometimes backing up and turning tight from a parking spot.
Do you have documentation on the locker being installed in 67? All Shelby limited slip or optional gear ratio were dealer installed. All production 67 Shelby’s came from factory with open rear ends, except engineering cars and the 3 427 GT500s.
Yep they will pop every once in a while out of nowhere. It was funny the reactions you would get when random strangers would hear it. It sounds like the axle snapped. I have owned a few and while they work great they are not quite all the time.
For a street car go with a true trac. A locker is somewhat of a pain on a street car that can see all types of weather. The locking and unlocking action can be annoying, more so if you have a manual. While nothing beats a locker for traction unless you need it I don’t recommend them over a limited slip like a true trac.
I lost a right rear tire on my bronco on the highway doing about 70. Between the tire blowing out and the locker unlocking on decel it was a white knuckle ride!
Another thing to concider if you ever snap an axle it will almost always take the Detroit with it due to the violent unloading/unlocking when the axle breaks. It shears off all the locking teeth and Detroit(at the time) would not sell just the parts. I lost 3 before I got sick of buying Detroit’s and patching up broken ones…
I did drive my Yukon version of the locker (Grizzly) commuting in winter for three seasons in MA/NH. It was no big deal, but winters aren’t like upstate NY’s. I did swap the spring that came with it for a less aggressive circle track spring, which still works fine at the strip.
Kinda high-jacking the thread a bit here, but doing some research into why I have noise coming from my 3.25 limited slip, (with 390 & 4 speed) and the above quote describes it quite well except I have not noticed the hop spoke of on the inner wheel in a sharp turn though (could be there)
I’ve read multiple threads on a couple different forums, and am a little unclear if this is common on a limited slip or just common on a true locking differential?
It sounds like the newer ‘kits’ some folks offer are noise free?
I have 80/90 weight oil in the rear jug says it’s good for all GL4 and 5 apps, and have the required amount per capacity of friction modifier. Not the stuff Ford sells, just better priced parts store stuff.
Thanks for any input!
