What would you have done?

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Bender351

Member
Joined
Dec 3, 2012
Messages
19
Reaction score
1
Location
Austin, TX
My Car
1971 Mustang Mach 1
351-4V Ram Air 4-Speed
3.25 Standard Rear
Light Pewter Metallic, AC
Orig. Magnum 500s, Tilt Wheel
So I've got my '71 Mach in the shop to have 4-speed clutch replaced. Shop is also rebuilding the 3.25 standard rear end. Basically, the whole drivetrain is out of the car from the block back. Also getting the radiator replaced because the original is now leaking pretty badly. Shop has a very good original out of a '72 Q-code Torino Gran Sport. I brought them a lower hose spring I had purchased a while back but never installed. While there, the lead mechanic asks me if I want a posi rear. I think about it for a few minutes, and decide to leave it as is. I don't race it, it never sees inclement weather, and it is a very original car which is how I like it. Mechanic even believes that the exhaust is the original from the factory including the mufflers.

My question to y'all is, what would you have done? Stay original or go posi?

 
posi. the car will be more stable in the rain.

example... my car came with a damaged posi. i didn't know it was damaged at the time. but i was climbing up a steep hill it was wet out and i ran over some leaves on the right side of the road. car lost control and slid right almost hit the guard rail. the posi acted like an open rear end. after that incident and the rear end noise i would get i decided time to drop that rear end.

once i got inside everything was fubar, i bought a ford racing posi to replace the one i had, night and day, rear end locks up like its suppose to car has much greater straight line stability, and climbing that hill wasn't an issue after.

somethings you don't know are better until you try them out, the posi is one, the next is a rear sway bar, if you do not have a rear sway bar install one, monster difference.

 
I have a several cars with posi one is the Ford Limited Slip and the other is a Ford 9" Detroit locker. When I got the Mach 1 new in 73 I had to learn how to handle the limited slip, lol. I lived just across a four lane road from a gas station. I can remember all the traffic and I revved up the engine dropped the clutch got about half way across the four lane did a 180 and was back in the gas station before you could blink an eye.

The locker is not the way the average guy should go cost more and the clicking noise bothers some, you have sticker in glove box with info on it.

After you get to know the locker you can scare your friends drifting on an interstate clover leaf. I think we invented drifting back in the 60's when the interstate came through our town.

My 2002 F-150 has a limited slip I pass front wheel drive cars stuck in the snow and just keep going and it is not 4 wheel drive.

The 20th. anniversary mustang I have also has limited slip and it saved me from getting hit in rear once. I was sitting first at a red light in Myrtle Beach, left lane, with wife and two kids in the car. Car beside me. I always watch the rear view mirror. The first car to approach stopped but I could see the headlights of the next car not slowing down. There are cars in the intersection so I cannot go into it. I revved the engine dropped the clutch jerked the wheel and made the car do a 180 and spun right in front of the car beside me at the light. The car hit the car behind me and the wife thought they had hit us but did not. I would liked to have seen it on video. I backed up and started to try to slow my heart rate.

I also have an 85 SVO with limited slip and with the wider tires it had it would get a little wiggle in the rain if it was hard so had to watch it.

Your car do what you want not something that can been seen but it for sure can be felt and does come in handy for something besides racing.

For racing you can make a Ford rear posi by adding another set of axle shims but would not want to run on road. A friend did with his Henry J with 454 and big slicks and worked great. Read it in one of the car magazines in the past back in the 60's.

Makes me want to go do burn out. I go back to Charlotte Sunday for 20 laps on the speedway if it doesn't rain again. They frown on doing burn outs, lol.

David

 
I'm not at all familiar with the posi units that came in our cars, but my experience with open vs. limited slip vs. posi (locked) rear ends is this: limited slip is the best of the bunch when it comes to the compromise between power & control.

Open diffs typically only allow power down to one wheel (usually, the passenger side), which steals power and can create control issues (as Dan mentioned), but they usually doesn't lose control under acceleration since while one wheel loses grip under power, the other maintains a level of traction by not spinning (under normal conditions). The whole purpose of an open diff is to ensure smooth operation going around corners (since one wheel travels further around the corner than the other - the open diff allows this to happen without any binding of the driveline).

Limited slip uses centrifugal force to attempt power transfer to both axles during acceleration - usually does it really well, and will often allow a variance in traction when the road surfaces are different between the 2 wheels (one grip, one slip). Limited slip still allows unloading of the axles around corners without dramatic events (clicking, popping, banging, etc.)

Posi-traction is a locked-up rear diff, meaning that both axles are engaged and should receive equal power, which is good for power, but can create control issues by allowing both wheels to lose grip equally. Factory lockers are often more 'forgiving' than aftermarket lockers, in the way of less clicking, popping, and banging that occurs when the axles load up and release tension from making turns. I think the factory posi units have 'some' slip built-in so they don't feel like they're exploding when unloading the axles.

I have Detroit Lockers in my 1980 Jeep CJ-7, and after installation, the first few corners I went around scared the living crap out of me. A few years earlier, my transmission literally grenaded on the freeway at 70mph - cruizin' along and with no warning a loud BANG with a bounce, loss of power, and a trail of 90-weight behind it from where it let go to where I finally stopped on the side of the road. A few years later (with a new tranny), I installed a new rear axle (got a smokin' deal on it) with the locker. Took it for a spin, and after the 2nd or 3rd corner, I felt the rear end start to bind-up then BANG! It unloaded. No loss of power or tranny fluid or anything out of the ordinary had happened, and it took a few seconds before I remembered what I'd read about the lockers unloading with dramatic events - and to calm back down as well.

Personally, I'd get a limited slip diff for normal driving, but if I were into racing, I would save up the money and get an ARB Air Locker - the diff runs 'open' all the time... until you hit the switch, then the included compressor 'locks' the diff and you have posi.

Sorry for the novel, but I hope this helps.

 
If it was a fair price and had the cash I would have opted for a Ford style Traction-Lok unit. Ford offered it for many years on production cars. A Detroit Locker still provides differential action albeit in rather coarse increments and the ratcheting action can be heard if mufflers are used. A spool provides Zero differential action as both axles are locked together by the spool. Just my opinion. Chuck

 
I installed a traction lok unit along with motive 3.50 gears a month ago,it was a great upgrade,. When you stomp on it she leaves nice and straight now. It almost feels like a locker now because both wheels spin pretty much constantly now.

 
I would go with the Ford Traction-Lok. Has been offered in various Ford car and truck lines and has been a very reliable performer for many years. Your car would probably feel more stable when driving through various traffic conditions. The Detroit locker is expensive and noisy and really unnecessary unless your serious about racing. Friend I grew up with had a 70 Mercury Cyclone SCJ 429 with the Super Drag Pak. That means it had a Detroit Locker 4:30 rear end. Fine for straight lines, but was noisy and made strange clunking sounds when turning and would scare you on wet roads.

 
'Posi' is shortening of the Chevy term used for their limited slip diff. The official name as 'positraction'. What your mechanic probably meant was the ford 'traction-lok'. Both are limited slip. I know the ford uses a clutch type system, I am not sure what the actual chevy positraction uses.

I would (did) upgraded to a traction-lok. (To answer your original question)

 
I would recommend a new Eaton TruTrac Limited differential setup over the classic Ford TracLoc with the clutches. I have the vintage TracLoc in my 73 vert and an Eaton TruTrac in my 69 vert. The TracLoc does every just fine, but over time the clutches will begin to wear and slippage will eventually start to compromise performance. The Eaton TruTrak uses helical gears and does not have any clutches. It also works very well but I'll never have to deal with slippage down the road.

Cost is probably about the same for both units when converting from an open rear end.

 
'Posi' is shortening of the Chevy term used for their limited slip diff. The official name as 'positraction'. What your mechanic probably meant was the ford 'traction-lok'. Both are limited slip. I know the ford uses a clutch type system, I am not sure what the actual chevy positraction uses.

I would (did) upgraded to a traction-lok. (To answer your original question)
I was just quoting the mechanic about the use of the word "posi". I am sure he meant going limited slip.

I agree that for weather purposes, Traction-Lok would be the way to go. BUT, if there is any chance for rain in the forecast, neither the '71 nor the '11 goes outside, and the '71 never goes far enough to get caught out. Why the original owner didn't order Traction-Lok is beyond me. He (or she) loaded it up with an M-code engine with 4-speed, ram air, Magnum 500 wheels, AC, deluxe interior w/instrumentation & tach, console, AM/FM radio, intermittent wipers, and tilt wheel, BUT no Traction-Lok.

I have decided to keep it as is for originality's sake.

BTW, can't use the radiator from the Gran Torino. In '72, with the body change, the Torino's radiator got 2" wider than the Mustang. Gotta' go with a repro until I can get the original re-cored.

And to Mister 4x4, maybe I'll get a chance to see your Mustang some day. It's only 200 miles between San Angelo and Austin.

 
'Posi' is shortening of the Chevy term used for their limited slip diff. The official name as 'positraction'. What your mechanic probably meant was the ford 'traction-lok'. Both are limited slip. I know the ford uses a clutch type system, I am not sure what the actual chevy positraction uses.

I would (did) upgraded to a traction-lok. (To answer your original question)
I was just quoting the mechanic about the use of the word "posi". I am sure he meant going limited slip.

I agree that for weather purposes, Traction-Lok would be the way to go. BUT, if there is any chance for rain in the forecast, neither the '71 nor the '11 goes outside, and the '71 never goes far enough to get caught out. Why the original owner didn't order Traction-Lok is beyond me. He (or she) loaded it up with an M-code engine with 4-speed, ram air, Magnum 500 wheels, AC, deluxe interior w/instrumentation & tach, console, AM/FM radio, intermittent wipers, and tilt wheel, BUT no Traction-Lok.

I have decided to keep it as is for originality's sake.

BTW, can't use the radiator from the Gran Torino. In '72, with the body change, the Torino's radiator got 2" wider than the Mustang. Gotta' go with a repro until I can get the original re-cored.

And to Mister 4x4, maybe I'll get a chance to see your Mustang some day. It's only 200 miles between San Angelo and Austin.
One of our other forum members Jeff has the red well optioned 73 Mach 1 and only thing they left off it was traction loc. It was a Ford Corporate order car.

David

 
Posi is Chebby term. Ford factory version for our cars is called Traction lock. it is a great setup and I would have done added it. However, I have no need for a locker for a street driven car.

 
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