'69Z Coil Spring Suggestions

[69302DZ]

Hello, I am a new owner of a pretty correct / older restoration '69 Z28 and brand new to the site. Reproduction E7015 tires that were on the car when I bought it rubbed when turning sharply.  Measuring from the fender lip, the drivers side is approximately 1/4" lower than the passenger side measured at the wheel centerline. I haven't found a good reference to what the stock ride height is supposed to be but feel that my springs have sagged.

I bought a set of 235/60-15 BFG Radial T/As to run on 15x7 rally wheels based on several tire size references with positive experience (no rubs) within this group. Unfortunately, the new tires, shorter but wider than the E70s, also rub.

I am thinking it's time to replace the coil springs. I have found references to a couple of different Moog part numbers - 6308, 6320, and possibly others. I am interested in other's experience and advise on whether spring replacement is the right move and if so, what the recommendation is. My goal to be clear is to have a stock height and no tire rubbing with my new tires. Thank you!

[william]

Trim height chart is in section A10 page 0 of the Assembly Instruction Manual.

Front trim height [+/- .38"] is measured 33" from the CL of the front wheel to the bottom of the rocker. Z/28 should be 9.13" with full fuel tank.
Rear  trim height [+/- .38"] is measured 20" from the CL of the rear wheel to the bottom of the rocker. Z/28 should be 8.75" with full fuel tank.

Spec states "Pull vehicle up 3 or more times, allow to settle, then measure."

Not unusual to be off more than 1/4".

[69Z28-RS]

Hello, I am a new owner of a pretty correct / older restoration '69 Z28 and brand new to the site. Reproduction E7015 tires that were on the car when I bought it rubbed when turning sharply.  Measuring from the fender lip, the drivers side is approximately 1/4" lower than the passenger side measured at the wheel centerline. I haven't found a good reference to what the stock ride height is supposed to be but feel that my springs have sagged.

I bought a set of 235/60-15 BFG Radial T/As to run on 15x7 rally wheels based on several tire size references with positive experience (no rubs) within this group. Unfortunately, the new tires, shorter but wider than the E70s, also rub.

I am thinking it's time to replace the coil springs. I have found references to a couple of different Moog part numbers - 6308, 6320, and possibly others. I am interested in other's experience and advise on whether spring replacement is the right move and if so, what the recommendation is. My goal to be clear is to have a stock height and no tire rubbing with my new tires. Thank you!

When I removed my front springs, I found that one of them had a broken coil (the bottom coil) was lying in the bottom of the spring pad area.   I compared all the commercially available coil springs (the ones yuo mentioned and others), and found all of them lacking in meeting the 'basic physical parameters' of the spring (coil dia, # coils, unloaded height, etc) and a company (Coil Spring Specialties in KS) was recommended to me.  I sent my one good coil to them and they measured it's spring rate, height, #coils, coil dia, etc) and made me a pair to match... They probably still have the specs on it in their files which should save you a few $$)...

[z28z11]

Hello, I am a new owner of a pretty correct / older restoration '69 Z28 and brand new to the site. Reproduction E7015 tires that were on the car when I bought it rubbed when turning sharply.

What offset rim are you running ? Are these original YH 15 X 7 rims, or aftermarket (or FW's) ? I ran F70 Goodyears on my stock suspensioned Z fronts for years, with H60-15's on the back, with no rubbing whatsoever, with original to-the-car YH Rally wheels. Goodyears are really flat on the sidewall when properly aired, radials have a bit more "midriff" bulge to them.

Car an RS ? Rubbing on the actuator shields can be a problem with certain tire combos. 235's are fairly tall -

Your height difference could be stock factory springs - driver's seat usually gets the most seat time, suspensions can wear over the years. Swap springs side to side if you don't want to replace original sets (if they are originals).

Pic of said combo. Developer reversed the image when it was copied. Note the traction bars and bullet mirrors - thank goodness the mods stopped there - 

Regards,
Steve

[ZLP955]

I sent my one good coil to them and they measured it's spring rate, height, #coils, coil dia, etc) and made me a pair to match.

Gary are you happy with how the car sits with the new springs? Just wondering about using an original spring, even if the car had low miles, as a reference for free height, in case it had settled after years of weight on it.

[69Z28-RS]

I sent my one good coil to them and they measured it's spring rate, height, #coils, coil dia, etc) and made me a pair to match.

Gary are you happy with how the car sits with the new springs? Just wondering about using an original spring, even if the car had low miles, as a reference for free height, in case it had settled after years of weight on it.

Tim,

The alternative to having CSC to make my springs was to use the OTS Moog springs and their physical specs were nowhere close to the factory springs;  nothing matched, and the cars running them do not 'sit correctly'  in my eyes...

I'm happy with the way it sits, but the fenders / hood are not on the car right now...  I'm fairly certain I will like the way it sits with all the weight on the springs. After their calculations and tests, and using the factory spring rate specs, they gave me a couple of options and I chose the higher of the alternative spring rates that they offered me, and they matched all the physical specifications as closely as possible. 

[ZLP955]

Thanks Gary. Sounds like the best available option. I'm interested in front spring selection for my car too, as the originals each had a coil or two cut out, so I'll need to replace them. I have some originals out of a base small-block coupe that I will trial, but would rather it sits a little nose-high (esp given it's race history!) than too low.

[69Z28-RS]

Tim,  you're trying to reproduce your car's history as a drag racer, whereas I'm more attuned to the road racing stance, thus we probably have totally different goals in mine for our front springs.   I want to reproduce the factory original stance of a Z28, and I can remember explicitly the new first generation Z28's always sat a little lower in front than standard or SS models..  and of course the design logic for that was the *reason* the Z28 existed at all..  for the Trans Am road racing series!

[69302DZ]

Guys - I really appreciate the responses and help. To answer a couple of questions, i have the original wheels with E70 15s repro tires; they rub a little now. I just bought a second set of aftermarket 15x7 (4 1/2" backspace) rally wheels to run the 235 T/As for periodic driving. What I have subsequently measured (full tank) with the T/As installed (probably a mistake) is the following:

Floor to bottom of fender and hub centerline to bottom of fender respectively (at wheel centerline)
RF = 24 11/16" and 12 7/16"
LF = 24 7/16" and 12 1/8"
RR = 24 1/8" and 12"
LR = 24 3/16" and 12"

Compared to the AIM specs recently found - 33" rearward of front wheel centerline, 20" forward of rear wheel centerline:
RF = 8 5/8"
LF = 8 5/8"
RR = 8 3/4"
LR = 8 5/8"

Note: I am a tad unsure about where / what to measure to regarding the bottom of the rocker panel. There's the bottom of the trim, the bottom of the finished edge (a 45 deg. bend), and the very bottom of the panel (at the right angle to horizontal). My AIM-relative measurements are to the middle of the three listed as they seem to match my actuals. I believe my coil springs to have sagged, the (4) leaf rear to be close to correct. Having just realized I did all of that with the T/As installed, I am thinking the AIM-relative values will all be off as the T/As are shorter tires. Oh well, I still think my coils are tired. Thanks again!

[HustleRussell]

Not sure if it makes any difference but John Z has said that the closest to original metric tire size is 215/65-15.

[ZLP955]

Tim,  you're trying to reproduce your car's history as a drag racer, whereas I'm more attuned to the road racing stance, thus we probably have totally different goals in mine for our front springs.

Short term, I need to build the car to stock specs to be able to register it legally for the first time in Australia. Although the car came here over 20 years ago, it was never registered so the techs will go over every aspect of it, including suspension heights and ground clearance, against factory specifications. Once it can be driven legally, I'll do the day 2 updates, although those still need to pass a simpler safety inspection.