Topic: 68 Fastback Ride Height

[68GTFastback]

What are the options for lowering the rear ride height? My car has new coils on the front and new leaf springs on the back. 

[67350#1242]

You can use a lowering block kit but it would be best to have them dearched at a spring shop.
Lowering blocks will affect handling negatively and make rear of car less stable.
Dearching will actually add stability and keep original look.
Kurt.

[Bob Gaines]

You can use a lowering block kit but it would be best to have them dearched at a spring shop.
Lowering blocks will affect handling negatively and make rear of car less stable.
Dearching will actually add stability and keep original look.
Kurt.

I do agree on de arching maintains a more stock look . I disagree on the rest. FYI the 65 R models and 66 -68 Trans Am Shelby team cars used the lowering blocks . Given the race incentive of successful teams if there was anything to be gained by a de arching advantage I am sure the Shelby team and privateer racers of the day would have taken advantage of it over the lowering blocks.

[preaction]

Kurt, what would be the negative effects and loss of stability with the lowering blocks ?

[preaction]

The 68 assembly manual has the ride heights listed for standard and GT models.

[67350#1242]

Kurt, what would be the negative effects and loss of stability with the lowering blocks ?

It's about the leverage increase when the axle housing is farther away from the mounting point on the leaf.  Increased leverage makes it easier for the spring to wrap up under power or braking.  There is also side to side leverage increase during cornering.

Leaving the higher arc in the spring combined with lowering blocks even adds more leverage as opposed to having less arc in the spring (especially side to side). 

I suspect with the R models and Trans Am cars that the blocks served to help correct understeer as well as lowering the roll center, both of which would be an advantage on the race track.  If the leafs were stock they also wouldn't have had too much arc.

The OP says he has new leafs and the car sits too high - means to me more than ideal arch.  Dearching will lower the car and roll center without adding unwanted side to side leverage and movement, as well as decreasing tendency to tramp under power.

I am sure there are situations where lowering block may be a choice (easier, more economical etc). But anything over an inch or so IMO too much of a compromise.
Kurt.

[Building 3]

I had the same problem with my 1966 convertible. As suggested in an earlier post you should get the proper ride height and tolerances from the Assembly Manual so that you can see how far you are off. Once I had that data I found the front coil springs were in spec but the rears were too high.  We loosened the rear springs a small amount and then added weight to the trunk. About 200#.  We used sand bags. We had several more months of work to do on the car in other areas.  When the car was drivable we drove it very carefully in the neighborhood with the loosened springs.  Over and over. Then tightened the rear leafs and added weight to simulate 1/2 tank of fuel. The rear was now in spec. On the high side, but in spec. With a full tank of fuel it was even better. That worked for me. My springs came from Eaton Detroit Springs.