I'm curious about the broken spindles. It seems beyond the laws of probability that you broke two spindles in two years of normal street driving. I mean they made several million of these parts and they've been in use for ~40 years which has to account for billions of miles. SOMETHING had to have been exerting undue force on them with your car in my mind, one could break due to "bad luck", but two?
I would agree with you if it did not actually happen to me. I do not think my car is completely unusual, but it is not 100% stock.
My car is a daily driver, I've owned it for about 15 years. I was not the original owner so I do not know what type of abuse it might have seen before. I probably have averaged under 100 miles a week on the car -- commuting to and from work. If my math is right that comes out to around 80,000 miles while I have owned it. The car was "well used" before I bought it, so maybe the spindles have 200,000 to 250,000 miles on them ?
My modifications to the front
suspension are:
* Koni shocks (adjusted for moderate/mild rebound).
* 600 lb/in springs
* lowered about 1-2 inches.
* 235/60R14 tires -- on wider than stock steel wheels.
* 1 1/8" front sway bar
* porterfield r4-s brake pads
* "performance" alignment (slight negative camber, several degrees of caster)
I do not recall any major recent curb hits or anything near the failures, but the car is driven... I cannot say I never bumped into a curb while parking over the last 15 years. The "curb bump" theory would generally only apply to the passenger side spindle.
The passenger side one cracked about 75% through but did not actually break completely. The symptom was a metal-on-metal rubbing noise of the rotor against the caliper bracket when hitting dips at low speed (at high speed I suppose I could not hear it) -- at first I thought I was hearing things, but it got worse over a few day period to where I knew I was not crazy. I was surprised to find the spindle cracked when I took the wheel off to see what was going wrong. It cracked in the narrow section of the spindle just about where it starts to increase in diameter.
At the time I debated upgrading to the 70-73 or granada spindles, but the car is my daily driver and I wanted to get it back on the road quickly. And using the same logic as you above, I thought a cracked spindle must be a one in a million thing, so there was obviously no chance I would see another one break. Also it was the passenger side spindle which would get banged against curbs more often. So I found a used 68 spindle and replaced mine. I thought maybe I would upgrade the spindles in the future sometime when/if I ever upgraded my brakes/wheels.
Less than 2 years later while going about 45-50? miles an hour around a sweeping (and busy) highway interchange (not completely smooth but no major bumps) the other spindle broke suddenly. In this case the end of the spindle broke off completely and suddenly (my guess it was probably already cracked but was not flexing enough that I had noticed it yet). Luckily the wheel did not come completely off (disc caliper was holding it on) and I managed to get over to the side of the road before there was a pile-up. Scary. Not an experience I would like to repeat.
My guess is probably 40 years of use (and unknown abuse) combined with the wider wheels and high rate springs were all factors contributing to the failures. Probably combined with very bad luck on my part. I decided not to tempt fate again, and upgraded to new 70-73 style spindles.
I had one person email me and tell me that had a spindle break on their 68 mustang in 2005. The other references I have to broken spindles seems to be second-hand anecdotal type reports (such as various mustang magazine and web articles).
Chris