Mustang MonthlyHow To Tech Qa
Vintage Ford Mustang Tech Advice - April 2014
Beyond the Basics
Question About Ride Height
The left rear of my ’67 Mustang hardtop sits approximately 1-inch lower than the right side. I have had all four shocks and the rear springs replaced to no avail. I have heard that this is a common problem with these cars. Do you have a solution?
Since you have already replaced the rear springs, I would suggest that you look at the ride height at the front of the car. Ride height is determined by the springs’ weight load and can be altered diagonally. As an example, if weight is removed from the right front, it will be transferred to the left rear, changing the ride height at both ends of the vehicle.
I find it is much easier to see a Mustang that seems to sit too low from the back. The front ride height goes unnoticed. Try measuring the distance between the front upper control arm and the front suspension limit bumper to determine the front suspension ride height. The distance should be equal on both sides of the car. You may find that a front spring has weakened, creating a diagonal weight change.
A 1-inch difference in ride height should not hurt the driveability of your Mustang to any great degree, so the car can be enjoyed as-is.
Carb and Intake Fit
As a long-time subscriber, I need to know how to deal with the interface compatibility of an Autolite 4100 Hi-Po carb and a Cobra high-rise intake manifold. With the carb installed, there is a gap between them. Can you help me understand this and come up with a solution?
A carb spacer plate inserted between the carb and intake manifold will correct any interference and fit issues. There are many choices between those available from aftermarket sources and OEM applications. Most factory spacers were also used as the source for PCV vacuum as well.
I typically use the Boss 302 spacer because it is thin and does not create hood clearance issues with the high-rise intake. It is also made from a plastic material that is a good heat insulator for the carb and incorporates a clean, convenient spot for the PCV hose. However, any carb spacer should correct your compatibility issue.
I have a problem with a non-original 351 Windsor engine in a friend’s ’67 Mustang. The engine runs fine except it starts to shake badly when you give it a short hit on the accelerator. It is especially bad when idling in Park, when it starts to run like it is missing several cylinders and shakes so badly that you think the engine is going to jump out of the car! The shaking lasts for approximately one minute, then slowly the engine starts to run find again. The cylinders check out fine with a compression test, the distributor is stock with a PerTronix electronic ignition conversion, and modifications include an Edelbrock carburetor and intake. The rocker arm lift checked out okay and I double-checked for vacuum leaks. Could there be an internal oil pressure loss which would cause lifter leak-down, preventing the valves from opening properly until they build up pressure again and allow the engine to return to normal operation?
Via the Internet
This is an odd problem. Your hunch about valve operation is valid. However, I believe the lifters may be "pumping up," not leaking down.
If the lifters are indeed bleeding down, the valve clearance would increase, resulting in a loud clattering noise when the engine is running. However, when the lifters pump up, they simply hold the valves open (no clearance), creating a dead cylinder but no noise. When the engine is shut off, the lifters bleed down to normal and the engine runs okay until accelerated, causing the lifters to pump up again. Lifter bleed down is related to valve spring pressure, so if the valve springs are incorrect or installed too high, the lack of pressure can cause lifter pump-up.
A quick check can be performed by operating the engine with the lifters completely full, or extended, so they cannot fill, or "grow." Loosen all of the rocker arm fulcrum nuts and adjust the valves at top-dead-center so the rockers barely contact the valve stems. Run the engine briefly and your problem may disappear. Only run the engine for a minute or two as the fulcrum nuts may back off, causing a rocker or pushrod to come loose.
Lifter pump-up is more commonly noted as "valve float" at higher rpms, hence the higher valve spring pressures for performance camshafts. But it can also occur at any rpm if there is a valve spring issue.
Boss 302 Swap
Can a ’70 Boss 302 engine be installed in a ’65 Mustang using the factory cast-iron exhaust manifolds? Shorty and long-tube headers are not available for this application.
Fairview Heights, IL
The stock Boss 302 exhaust manifolds will interfere with the shock towers on an early Mustang. However, the interference is slight. The shock towers can be cut and a plate welded in such a manner to allow for the extra clearance. This will permanently alter the engine compartment but not drastically. The manifolds will not fit without trimming the shock towers.
I performed this swap many years ago utilizing Hooker long-tube headers designed for a ’69-’70 Boss 302 Mustang. The headers required some modifications to a couple of the tubes but at least this method did not require trimming the shock towers. You may want to investigate current header sources and modify the headers, not the car.
Let us hear from you.
Send your ’65-’73 Mustang questions to: Beyond Basics, c/o Bob Aliberto, P.O. Box 205, Salt Point, NY 12578. Send email to email@example.com.