# 66 GTO 461 Stroker Rearend - Good to go, Rebuild, or Replace?



## Elwood GTO (2 mo ago)

Hello all, long time lurker here. I was hoping to get some opinions or what to do. I have a 66 GTO that I picked up a couple years ago, it has a 461-stroker, born with 4-speed M20 muncie and 3.55 safe-t-track rearend. I going to replace the clutch this winter with Centerforce 2 clutch kit. However, I am concerned about the rearend and if it's going to hold up. I mostly just cruise but occasionally like to open up the secondary's and a once in blue moon burnout. Am I asking for trouble and living on borrowed time? Do I need to rebuild the stock 3.55 safe-t-track or replace with a ford 9" or ? TIA


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## lust4speed (Jul 5, 2019)

If you run street compound tires and stay away from slicks and drag radials the odds of the rear lasting go way up. The limited traction of the street compound tires act as a fuse and helps the rearend survive. The original limited slip with the cone clutches works really good right up to the day it doesn't. Eventually the cones wear down and one day it goes from leaving two nice lines to one very long line. Mine lasted 53 years and about a 125,000 miles of spirited driving before the cones started slipping and it had to be refurbished. If this happens please don't toss it - either have it fixed or drop it on eBay and give others a chance to buy the wounded carrier. If the carrier is original to the 4-speed car it will have the 4-pinion spiders which takes more abuse than the 2-pinion spider gears that came with automatics.

If the limited slip gets weak the rear reverts back to an open differential and you can continue driving around since the weakness doesn't affect day to day drivability. The critical failure point is when enough shock load is applied to the ring and pinion that the case spreads and pulls the ring gear away from the pinion with the resulting sheared teeth and catastrophic failure. This does require a flatbed tow home. The BOP 10-bolt units are still pretty strong but when the old irresistible force meets the immovable object, the unit will fail. That's where the hard compound street tires can save things.

I ran the 10-bolt and the Muncie until a few years ago when I replaced them with the TKO-600 and a Dana 60. Both the Muncie and rear end were original to the car and are still intact and now stored away in case a future owner wants to change everything back to pure stock.

Link is to a clip that was originally an 8mm movie of the first burnout done with my GTO in March of 1967 after getting the 500 mile break-in out of the way. First of many abuses the rearend handled without coming apart. Your mileage may vary...
First Burnout in March 1967


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## Baaad65 (Aug 29, 2019)

Elwood GTO said:


> Hello all, long time lurker here. I was hoping to get some opinions or what to do. I have a 66 GTO that I picked up a couple years ago, it has a 461-stroker, born with 4-speed M20 muncie and 3.55 safe-t-track rearend. I going to replace the clutch this winter with Centerforce 2 clutch kit. However, I am concerned about the rearend and if it's going to hold up. I mostly just cruise but occasionally like to open up the secondary's and a once in blue moon burnout. Am I asking for trouble and living on borrowed time? Do I need to rebuild the stock 3.55 safe-t-track or replace with a ford 9" or ? TIA


I'll have a '66 Chevelle 12-bolt out of my '65 gto for sale soon, it was completely rebuilt in 2017 and has Strange axles,1350 yoke and a nice cover but needs a posi unit and gears which I just broke at the track.


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## PontiacJim (Dec 29, 2012)

lust4speed said:


> If you run street compound tires and stay away from slicks and drag radials the odds of the rear lasting go way up. The limited traction of the street compound tires act as a fuse and helps the rearend survive. The original limited slip with the cone clutches works really good right up to the day it doesn't. Eventually the cones wear down and one day it goes from leaving two nice lines to one very long line. Mine lasted 53 years and about a 125,000 miles of spirited driving before the cones started slipping and it had to be refurbished. If this happens please don't toss it - either have it fixed or drop it on eBay and give others a chance to buy the wounded carrier. If the carrier is original to the 4-speed car it will have the 4-pinion spiders which takes more abuse than the 2-pinion spider gears that came with automatics.
> 
> If the limited slip gets weak the rear reverts back to an open differential and you can continue driving around since the weakness doesn't affect day to day drivability. The critical failure point is when enough shock load is applied to the ring and pinion that the case spreads and pulls the ring gear away from the pinion with the resulting sheared teeth and catastrophic failure. This does require a flatbed tow home. The BOP 10-bolt units are still pretty strong but when the old irresistible force meets the immovable object, the unit will fail. That's where the hard compound street tires can save things.
> 
> ...


Keep in mind that those tires were the old bias-ply type which smoked real well and didn't grab quite as well as radials. Never seemed to get quite the good smoke show out of radials, but they did grab better. 

Bias-ply.


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## armyadarkness (Dec 7, 2020)

Baaad65 said:


> I'll have a '66 Chevelle 12-bolt out of my '65 gto for sale soon, it was completely rebuilt in 2017 and has Strange axles,1350 yoke and a nice cover but needs a posi unit and gears which I just broke at the track.


Perfectly proving that anything can and will break, under the right (or wrong) circumstances.


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## armyadarkness (Dec 7, 2020)

PontiacJim said:


> Keep in mind that those tires were the old bias-ply type which smoked real well and didn't grab quite as well as radials. Never seemed to get quite the good smoke show out of radials, but they did grab better.


My 67 roasts the tires, but BFG's never seem to smoke well, for me. My Vette was the same.


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## Elwood GTO (2 mo ago)

Thanks for the feedback, good to hear it shouldn't grenade on me, I would prefer to keep fairly close to original as possible. I'll check the rear axle bearings and go from there.


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