1965 Mustang: Rear Suspension Take 2

If you told your better half you were going to spend four weeks and triple the money replacing something you just spent two weeks (and two weeks salary) on, what do you think he or she would say? “Get out. Now.”


*Part 9 in our series on rebuilding a 1965 Ford Mustang. For Part 1, click here.


Yes, things would get ugly in a hurry and I don’t mean maybe.

The good part is, by reading this series of stories, you might be able to keep your current address and your better half and still have a decent project car in the end.

We’re also much better at making mistakes you can learn from than we are at relationship counselling, so please pay attention because we’re likely not going to get a third shot at this and live to tell about it.

After a bout of ‘what does it all mean’ existential crisis in the last instalment of the Project Mustang, we’ve run face-first into the reality that we’ve tossed out our rear suspension — leaf springs, high-performance axles, narrowed rear housing and all — for something much better and much more costly.


After tirelessly working to make rear leaf springs work, we threw it all out and started from scratch.


Why? Everything from ride quality to the fact the rear end was tracking all over the place, because that’s just the nature of rear leaf springs. It was terrible.


Terrible rear suspension tossed out for something we should have done from the start

So, we sucked it up and purchased a new multilink package that replaces the buggy (leaf) springs with coilover springs and modern adjustable shocks. There’s a lot of measuring and welding to do but the result is nothing short of phenomenal. We should have done this right from the start.

I also chose to upgrade the rear axle to a Ford Motorsports 8.8-inch unit, replacing our modified stock 8.0. The 8.8 is needed to mount the Grigg’s Racing watts link suspension and it’s stout enough to handle our new 482-horsepower 331-cubic-inch V-8 that replaces the original 289 . . . that we just rebuilt. Yes, we built two engines, too, but that’s another story.



Once the leaf springs and the rear axle have been removed, the key, as with anything, is to measure twice — or thrice — before committing to cutting anything for the installation of the new hardware.

At the risk of making this sound painfully technical and boring, the main components that must be welded to the car include the crossbar to mount the top of the coilover shocks, mounts for the new lower control arms, and a transverse bar that supports the four-foot-long torque arm.



There are also axle mounts for the lower control arms and, sadly, some not-too-subtle cutting of the trunk floor to make it all fit. The wildcard is the coilover shock length, which must be determined to get the car close to the correct ride height where it can be further fine-tuned with the threaded adjustment collars.


You’re probably scratching your head right now, or drifting off, and no one would blame you, but if you consider what the system has to do, it makes pretty good sense.

The watts link positions the axle laterally in relation to the car while still providing the up-down motion and the pitch articulation when the car leans, however little, when going around corners.

The lower control arms position the fore and aft location of the axle while still providing free up-down motion. The torque arm controls the rotation of the axle housing caused when the tires bite the ground.

Aside from cutting a four-foot-wide lateral slot through the trunk floor to make the system fit, we had to redo the exhaust system to snake through the watts link assembly. We also had to shorten the driveshaft to mesh with the new 8.8-inch rear end.

Oh, and while we were at it, we filled the rear end with 3.50:1 gears. When coupled with our T5 manual transmission purloined (and rebuilt) from a 1991 Mustang GT, the new rear end provides quick acceleration and low-revving highway driving in fifth gear to save both our eardrums and our new engine.


Redoing the exhaust system to fit through all the lateral bars is more complicated that it looks because we have to take into account up-down travel of the axle.


Did they get it right the second time around?

We also felt it was a good time to join the front and rear subframe assemblies together to make the car more rigid. The new subframe connectors also provided the perfect mounting spots for the torque-arm crossmember.


To mount the crossbar that connects the torque arm, we bent some tubing to make connectors that join the front and rear chassis subframes.


This is a huge deviation from the original leaf springs — century-old technology, by the way — but these changes bring the ride and handling quality ahead 50 years while providing the right stance and nearly infinite adjustability.

So, did we get it right the second time around? In the next instalment, we’ll polish off the details of the installation, including the cost, and take you for a little ride to find out.


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. (You are here)

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