Limited Slip 8" Rearend

mchnplt · Apr 17, 2017

I have a 66 coupes and would like to upgrade from the stock pony kicker rearend and put a limited slip in it without breaking the bank, I don't have alot of horsepower, when all said and done just under 300hp, any suggestions?

rhutt · Apr 17, 2017

Do you have a budget in mind?

mchnplt · Apr 17, 2017

somewhere in the $500.00 range, and not sure what # spline on my axles, maybe you know ?

rhutt · Apr 17, 2017

If it's all stock, you're undoubtedly looking at a 28 spline unit. You will have to look for a used unit or start collecting the parts to build one, although I don't think you will find much out there in good running order for that money. A rebuilt or new unit would typically set you back about $900-$1500. I paid closer to the high end of that range for a Currie 3.55 TrackLoc.

Paxton.5oh · Apr 17, 2017

I am too looking for a rear end for my 1966. Does anybody know a vehicle that has a similar sized rear end that is boasting a ford 9"? If there is not one that is similar size what would be my best bet to get a new 9" rear end.

rhutt · Apr 17, 2017

Paxton.5oh said:
I am too looking for a rear end for my 1966. Does anybody know a vehicle that has a similar sized rear end that is boasting a ford 9"? If there is not one that is similar size what would be my best bet to get a new 9" rear end.

How much horsepower are you making? Torque? All new including housing, center section and brakes, you could easily be looking at $2000-$2500+. You could do it for less using used (salvaged) parts.

zookeeper · Apr 18, 2017

Paxton.5oh said:
I am too looking for a rear end for my 1966. Does anybody know a vehicle that has a similar sized rear end that is boasting a ford 9"? If there is not one that is similar size what would be my best bet to get a new 9" rear end.

1957 Ford rear ends were 9" and bolt right in (after new U-bolts and U-joint) and as a plus they often came with 3.98 or 4.10 gears.

Paxton.5oh · Apr 18, 2017

rhutt said:
How much horsepower are you making? Torque? All new including housing, center section and brakes, you could easily be looking at $2000-$2500+. You could do it for less using used (salvaged) parts.

Currently, I am at 218.04 HP and 258 Torque at the tires. My goal is to eventually twin turbo and supercharge the engine so I would prefer to build the rear end right the first time to save me from having to do it twice. I would like to eventually have about 450 HP to the ground.

zookeeper said:
1957 Ford rear ends were 9" and bolt right in (after new U-bolts and U-joint) and as a plus they often came with 3.98 or 4.10 gears.

I would just have to change the 3rd member to a closed differential rather than an open differential correct?

rhutt · Apr 18, 2017

If you can afford a supercharger and twin turbos, why are you so concerned with saving a few bucks on a salvaged rear end?

Paxton.5oh · Apr 18, 2017

Currently, the supercharger is not in my budget. I would prefer to save some money now on the rear end. The supercharger or turbos would most likely be done in a year or two but I don't want to have to redo the rear end when I get to that point. My main concern is just having a closed diff because this car is my daily driver and it does get a bit treacherous to drive in the rain.

7991LXnSHO · Apr 22, 2017

No to locked rear axles on the street in your situation. A clutch type or gear type limited slip in a 9" would keep you happier and hopefully going the right direction in a turn.

GT1966 · Apr 23, 2017

I installed a Eaton TruTrac in my 8" rear with 28 spline axles and 3.25 gears. The engine makes 315 at the crank; 260 at the rear wheels. Eaton tech told me the 8" with this diff would be good for up to 350hp at rear wheels no problem. The TruTrac is a Torsen unit where there is always power to both wheels, which actually is a handful in the rain such as a slick off-ramp because there is no "clutching" and operates more like a straight-up locker (although they are turning at different rates). You can really slide the car around and apply predictable power when roads are slick, but you have to be on your game on the street. I went with this diff because I wish to track the car this year (installing the multipoint cage now) and a previous 8" limited-slip diff didn't perform well at all. Look up Torsen diff and you'll get the idea of this parallel helical gearing. The unit was around $700 and I did the install with a dial indicator, a good workbench, oven for heating ring gear, etc.

foxbobby · May 10, 2017

Did I miss something? Ten years ago I got a 3rd member on EBay. For 8 inch it was just plug & play and couldn't of been easier.

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