1965 Mustang: Rear Suspension – Take 2

After redoing the rear suspension on the 1965 Mustang for the second time, it’s the moment of truth.

 

Part 10 of Jeff’s series on rebuilding a 1965 Mustang. Click here for Part 1.

No rattles and no shakes, but the ride is way too stiff and one rear tire is still scuffing the inner wheel well when turning into uphill driveways.

Hey, just because we’ve measured twice, cut once, tacked everything in place and checked everything again — and again — before final welding, doesn’t mean that our new rear suspension is all done.

 

Jeff Melnychuk’s 1965 Mustang – work in progress

 

 

There’s still some tuning left to do.

The beauty of the 1965 Mustang’s new watts-link setup is that we can easily move the rear differential left or right, and forward or back in relation to the body, to perfectly position it. You just can’t do that with leaf springs.

The watts-link system uses coilover shocks and while the ride height is adjustable, the spring rates are not.

 

Starting with a blank canvas, the realization is that there’s really no turning back.

 

Buying springs and shock absorbers is a huge grey area when you start a project like this, and you can usually count on replacing the springs twice, and once if you’re lucky.

Consider that racing teams have complete facilities to test different shock/spring combinations and you can see where most regular folk come up short: We have no means to fully optimize the combination for this particular car.

Our adjustable shocks came from Aldan American, so a call to them to get ‘lighter’ (softer) springs only cost us $100 or so, plus shipping. We chose lighter springs only because the ride was so stiff.

Installing them means taking the shocks off the car, but the process is pretty straightforward… if you were the one who put it all together in the first place, that is.

 

BEFORE: It looks pretty tidy under there, but to get the car down to the desired ride height meant the exhaust came in contact with the rear sway bar (circled). And although we carefully measured for tire clearance, the leaf springs allowed too much lateral travel. The result? Tires rubbing the inner wheelwell in some situations.

 

There was a substantial amount of refitting that had to be done to other parts of the car to make the package work.

A set of subframe connectors were welded in to strengthen the chassis as well as to provide a mounting point for the lengthy torque arm running up the middle of the car.

We had to do some surgery to the trunk floor and also had to build a whole new differential/rear axle, which means more work trying to adapt the driveshaft to it. Instead of the 8.0-inch rear end that came with the Mustang, we used an 8.8-inch unit fitted with 3.50:1 gears and an Eaton Detroit Truetrac limited-slip differential.

 

We’d like to say that we took all the parts to the paint shop to be covered in satin black, but we found a great rattle-can product that covers well and is reasonably tough. After some test driving, I ordered softer coilover springs.

 

The housing was also narrowed four inches to get the wheels and tires to fit within the wheel wells.

Then there’s the exhaust. The most difficult part was running the tailpipes through the maze of bars and lateral links while leaving enough room for everything to move up and down without contact. Lots of work and science-ing.

The best thing I can say about the new rear suspension is that there is so much lateral grip — now that the tires are squarely planted on the road during spirited driving — that the car tends to understeer a bit, pushing out the front tires in a corner.

 

 

AFTER: Beginning with a clean sheet of paper also means cutting and welding on the car itself. The white strip at the top pf the photo is daylight from the slot we had to cut in the trunk floor. The result is a more modern suspension design that decouples the ride function (using coil springs) from the lateral stress (using control arms). Leaf springs have to accomplish both these tasks, so to make the lateral control strong, the ride suffers. A rear sway bar with the new setup is not necessary, which means more clearance. The lateral control arms mean the exhaust system has to be rerouted, however. Here, during final assembly, the shocks and brakes have yet to be installed.

 

Even with no rear antiroll bar, the 1965 Mustang corners very flat, and with the long torque arm there is no wheel hop under hard acceleration.

The car no longer dives forward under braking; the overall balance is much better than with leaf springs.

It’s a huge improvement, but the one unfortunate reality is that the package will likely never be fully optimized since we just don’t have limitless days at a test track to cover all the variables. We might be able to get to 90 per cent, but without knowing where the ideal tune-up actually is, how would we ever know if we’re at 90 per cent?

We’ll know just how good a similar system will be with the Project 1970 Plymouth as the package for that car was engineered, completely computer-modeled, track-tested and tuned. That’s worth the extra money, right there, in our books, knowing that the setup is bang on right out of the box.

For the Mustang, full rear-suspension installation and parts cost about $8,000, which included the rear-axle housing. The price also included: fabricating a new bolt-in filler panel to cover the slot cut through the trunk floor to accommodate the bar for the shock mounts; making and installing subframe connectors as well as a handful of mounting brackets.

 

After spending plenty of time and money trying to make the stock leaf springs work, we gave up and took it all out. That’s OK as we’re more than pleased with the replacement.

 

We were able to save the rear brakes from the previous setup and we intend to recover some of the cost by selling everything we took out as a package. Otherwise, we’re exactly where we wanted to be the first time around when we had leaf springs.

In the next installment, we build an engine that rivals what’s under the hood of a new Mustang.

 

1965 Mustang Rebuild – Catch up on the series here:

Part 1, click here.

Part 2, click here.

Part 3, click here.

Part 4, click here.

Part 5, click here.

Part 6, click here.

Part 7, click here.

Part 8, click here.

Part 9, click here.

Part 10, click here. (You are here)

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