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Discussion Starter #1
Problem:
I’m getting a “clunk” from the rear when I start from standing still. It can be felt as much as it can be heard.
Car:
’68 GT 390. Marti says 3.25 w/ Equa-Lok. It has a 3.50 installed by PO. The case has only one vertical rib so it’s not a Nodular Iron case. The engine is fairly stock (Edelbrock and DuraSpark added) and I have with no plans of upgrading. The top-loader has been replaced with a TKO600.
Diagnosis:
I jacked up the rear and turned the wheels with the transmission in gear. The driver’s side is solid with no slope. The passenger side has a couple inches of sloop.
My mechanic says it sounds like the Equa-Lok has a broken pinion gear. Internet research suggests it might be a cracked differential case.
Options.
I haven’t taken it apart, so I’ll assume it has the original Equa-Lok. It is not a well-regarded differential.
Assuming that the differential needs to be rebuilt I plan to replace it with either a Ford Traction-Lok or Detroit/Eaton Truetrac. I’m also considering getting a fully rebuilt 3rd member. I will probably never race or autocross this car. It is a cruiser and I plan to do long road trips.
Questions:
First, Ford Traction-Lok or Detroit/Eaton Truetrac. The price seems about the same. I like the idea of not needing friction modifier or worrying about clutches. But I also like the idea of a factory Ford unit.
Second, should I have my mechanic rebuild the current unit or buy a fully new/rebuilt unit. If I buy a new unit, a recommendation please. And should I get a nodular iron case even though I don’t plan on updating the horsepower?
Thanks in advance for any advice.
 

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I previously installed a Eaton TrueTrac in a 8.8 as part of a Factory Five Cobra build. I had no issues with it for the 4000 miles of my ownership. The 2nd owner has the car up to about 10K miles total, no issues with it either. I have read some have had issues, not sure if that is a result of a design or use issue. I like the way it worked, with the Cobra's 90 inch WB, I wanted traction to both well as these cars are notorious for swapping ends in a blink of the eye. That said, for my Mustang restomod, I have gone with the TrueTrac again, this time a fully built up third member with TrueTrac by Strange. I figured if Ford included these in their GT500s, they must have had a good reason.
 

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I believe most will steer you in the direction of the TrueTrac. I had Currie build my Trac-Loc when they were still offering their own nodular gear cases and I ended up with a great 3.55 third member. I personally like the Trac-Loc in my application. I run it behind a small block.
 

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i went the truetrac route in my 70 about ten years ago and have had no issues. if i had to do it again, i would. i also like not having to worry about clutches.
 

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I have a 69 390 that came with a 3.25 Trac-lok axle. While going through the powertrain I installed a TruTrac from Currie. Clutches are a thing of the past for limited slip. I don't know an instance where I would ever use the clutch type limited slip. They certainly don't hook up better and they are definitely less reliable.
 

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Having done both, there is several $100 difference with the trutrac being more expensive. If you build it, and have the tools and center section, a complete tracloc and gears is roughly $700, a trutrac and gears is $1000. Gear prices vary allot, no name generic vs high end. Eaton is an awesome setup and well worth the money.
 

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Discussion Starter #10
Yup. Talked to Allan this morning. He's building me a new complete 3rd member. His advice was to simply use a standard trak-lok (clutches) as he said that for what I do I won't notice any difference and I won't wear it out. I am upgrading to a nodular iron case. He is only 2 hours away, so one morning the rear will come out, we'll drive up and do a swap (turn in my old unit for credit), return and replace. This might be a one day operation, but properly two.
I'll report in when done.
 
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