Hi All I saw a post from 2016 and BlueBird428 had a good discussion going on replacing front springs and rear leafs. My 68 400HO (no a/c) is a 50 year old lazy bones and is nearly dragging her belly. I will admit I like the lower look. Aggressive, but don't want to body surf.
I need to replace shocks and springs, but get the height just a little lower than spec. I did see that one poster mentioned that springs should outlast the car, so I'm wondering if maybe its just shocks I need. I know that's a definite because the nose bobs relatively easily when I sit on the fender. Should I even need new coils?
I saw all the conflicting, or at east differing, results from people's preferences to published specs. So at risk of re-opening that can of worms from '16, what was the final purchase, and where did your stance finish up at from the ground to fender lip?
'68 400HO Coupe, 4 spd, 259 interior, Windward Blue. My other car's a Johnson 15 outboard on a '61 Starcraft rowboat... Just sayin'.
Now days you can get all different front spring sizes that will lower the car an inch or two from stock or raise it from stock to 1-2 inches higher. This is also true for the rear leaf springs. You can also buy the coil over spring/shocks to set your front height where you want it. You should also be careful in asking what others have as far as height from ground to fender lip because tire size will also changes those measurements, so make sure to ask what tire size they are running to gauge it accuratly. I do not believe that your springs will outlast the car. I had the same problem as you with the front and rear bobbing up and down and and how the car handled going around corners and how the car sagged. New springs will make a big difference if yours have never been replaced. I put some stock size leaf springs from Eaton on the rear and put in some stock size front springs from eaton and I am sitting about an 1 1/2 inch higer then I want to sit in the rear so I am going to replace the rear with a set of global west L-2 leaf springs that are suppose to drop the back 1 1/4 inch which should be perfect and I am sitting about an inch to 1 1/2 -2 inchs too high in the front so I am going to replace the front springs with some coil over spring/shocks so I can set the height where I want it to be. I am running 17X8 inch wheel with 4.5 back spacing in front with 245/45-17 tires and 17X9 wheel with 5 back spacing with 275/40-17 tires in the rear. I havent measured my ground to wheel lip yet, but I will if you want me too.
Good advice. Yes, I'm thinking same on the springs...50 years HAS to have an effect! You have very large wheels compared to my 14" Rally's. Don't bother with floor up measurements...probably wont help me much, but thanks a lot for your insight!
'68 400HO Coupe, 4 spd, 259 interior, Windward Blue. My other car's a Johnson 15 outboard on a '61 Starcraft rowboat... Just sayin'.
I found the best way to compare different springs and not have to take the tire diameter come into play, is to measure from the center of the wheel to the bottom of the fender lip. If spring X creates Y inches from the center to the lip it will do it whether one has 20 inch diameter tires or 29" diameter tires.
I've had my front springs out about ten times now. Between trying to find the right height or the correct geometry, the A arms and springs were frequent R&R items. It's almost as if I should have purchased twenty sets of coils, then R&Red them until I got the ones that gave me the stance I wanted. There were a gazillion different coils made for our cars, most manufacturers only supply a few. I installed the Moog replacement for a 68 non ac, manual brakes, power steering car and they were about two inches too high. Go figure.I installed a set for a car with every option available and it sat too low??? Some guys buy a set and they are perfect, every car is different and I'm starting to think two sets of springs with identical part numbers from the same manufacturer will be different. The correct height of a stock car can be found in the AMA specs section on this site. It is measured so many inches from the front and rear wheel centers and so many inches from the ground to the rockers. You have to remember the stock FGF where a little high in the front so ordering a stock height spring may be a bit tall for your taste.
One has to look at the condition of the chassis as well as the springs. Worn, bent A arms, sub frames and cross menbers will also affect the ride.
As far as the coils, it would be handy if you could measure the spring rate of the springs you now have on the car. Take them out and add force/weight until they compress one inch. You would then now what the spring rate is and if it's too soft or stiff you could get a set plus or minus what ever it would take to get the stiffness you want. That wont help with the ride height though.
You could call Eaton Spring, they have a good variety and can make springs for a dropped or raised look.
One thing to consider when lowering the body is whether the tires are going top rub on the fenders.
I R&Red mine a bunch of times, cut some, put spacers under some, replaced then modified the A arms and continued to get tire rub unless I had the car sitting too high for my liking. I finally bought a set of adjustable coil overs with a higher rate spring and now it sits where I want with no rub. I should have done that from the start but didn't think I should spend all that $$$. Would have been cheaper if I spent all that $$$ from the get-go. My car has been bashed up at least once so things are not quite as they were from factory.
The rears were replaced some time ago, mono to multi. They were so worn out air shocks were needed to keep the body off the tires. The mono spring perches were not replaced when the conversion was done so I had to weld some repairs there. The only place near Sidney I could find rear leafs for mine could not get Firebird springs with the rate and load I wanted but said they had good luck putting Nova springs on Firebirds and Camaros. I bought a set, plus a couple shackle/bushing kits, and installed them last winter. Bushings didn't fit so that was another $100 but I got it all installed. It sits a little high at the back but I like the 70's Muscle car look with the back raised a bit and larger tires on the rear than the front. I'm happy with what I have now but it took about eight years and a lot of skinned knuckles to get it.
The shocks are not what keeps the car at the correct height, it's the springs, the shocks keep it from bouncing, keeping the tires on the pavement. If yours is dragging it's belly the springs are sagging. Replace the shocks as well.
The springs did out last some of the early Firebirds, the ones that were wrapped around power poles. Every thing wears out eventually.
Wow! Well, BB, terrific info as usual. I'm more in the dark now than when I was unaware of the possible suspension nightmare I'm facing.
I don't want to venture into coil-overs now because I don't need or want to change the arms to ones with a coil over shock seat. Just stick with stock arms. But agreed, adjustable coil-overs would be the one-and-done move. But I'm historically too stupid to take good advise. I dunno.
I do think this though: change the rear to new fresh 4 leafs, heard 5 leaf may be too high. I have air shocks too in my rear right now for the very reason you described. Lazy butt. Hoping the new 4 leaf sits the rear higher than the front or at least the same when I change to 1" drop coils. But after reading your post and ORDY's I'm totally guessing. So I'll say a prayer and spend some more money. Yikes.
PS: USMC_Ordy If you're what I think, thank you for your service. My dad's a Marine. Turned 81 last week. Semper Fi
'68 400HO Coupe, 4 spd, 259 interior, Windward Blue. My other car's a Johnson 15 outboard on a '61 Starcraft rowboat... Just sayin'.
You can get adjustable coil overs that will fit right into the stock control arms. They are pricey though. You may buy a set of ordinary coils that slip right in and give you exactly what you want for ride and stance. Didn't work for me but my car has a black cloud that follows it wherever it goes.
PS: USMC_Ordy If you're what I think, thank you for your service. My dad's a Marine. Turned 81 last week. Semper Fi
Thanks ReverendRW, you are correct, I am a retired Marine and thank you, and please pass onto your Dad, a grateful Thank you and a SERIOUS SIMPER FI Devil DOG!!!!! And thank you for his service during those tenacious years! Was he in the Korean war (long shot, probably not) or Vietnam war?
No, no..."out" prior to Vietnam getting real active. Timing is everything. I arrived in '63, and pretty sure he was going to night school by then. Became a shop teacher. God Bless those that weren't so...
'68 400HO Coupe, 4 spd, 259 interior, Windward Blue. My other car's a Johnson 15 outboard on a '61 Starcraft rowboat... Just sayin'.
I know this is a old thread but I would HIGHLY recommend you check out Eaton Detroit Spring: https://www.eatondetroitspring.com/ you give them how your car is spec'd out (engine, accessories, etc. for weight reasons) and what stance you want (I went 1" lower in the front and 2" in the rear) and they will build the coils and leafs to meet your needs. If you go with anyone else it's pretty much a one size fits all recipe except for the coilovers which are adjustable.
They are not all that wonderful. I had issues getting the correct front springs for my GTO vert. They gave me way too stiff springs which looked comical. I tried to help them understand the issue but the girl I had to keep dealing with did not have a clue. On the 3rd attempt I just insisted they provide hardtop springs since the hardtop vs convertible weight is essentially the same. I’m sure they are continuing to sell the wrong springs to GTO vert customers
I have CRS so I have to write stuff down. This is what I did to my '68. Sorry the cut & paste from my build notes came over kind of funky. Please note, I'm running an iron head big block Chevy, no A/C, aluminum manifold, headers, 700r4. (all weight counts, went through several front spring swaps and one rear spring swap to get what I wanted.)
Notes Moog front springs are relatively cheap - $62 today from Summit for a pair of Moog 6312's. I toyed with changing to Moog 6308 but decided to leave well enough alone. X2 what USMC Ordy said - If you want the car lower in the back look to aftermarket. Global West and Hotchkiss make great lowering springs. Mine are 1 1/2" drop but I might go 2" if I had to do all over again. I recommend Polyurethane bushings in the rear spring shackle. Using the softer rubber bushing in the front spring eye will transmit much less road harshness to the body of the car. I strongly recommend the use of the GM spring cushion pads. Much better differential housing to spring locating than aftermarket Polyurethane spring pads. Still available from GM. I decided to save some money and use KYB gas shocks. These are very harsh shocks. Recommend staying away from them. Someday I'll buy some really good shocks - right after I change the control arms. The springs are the muscle, shocks are the brains.
Hope this helps.
Build Notes:
Stock Front Suspension Rebuild: • Moog K5250 Upper Control Arm Kit – Shaft & Bushings • Moog K6076 Lower Control Arm Bushings • Moog K5108 Upper Ball Joint • Moog K5103 Lower Ball Joint • Addco 1 1/8†diameter front sway bar Part No. ACO-599 • KYB Gas Shocks Part No. KG4515 • Moog #6312 Coil Spring ’67-’69 Firebird 400 – shortened 1 coil. Tried Moog #5246, 400 convertible w/AC but too tall.
• 6312 Spring Specifications: o ID 3.68†o Bar Diameter .64†o Spring Rate 337 lbs. per inch o Load 1800 o Installed Height 10.75†o Free Length 16.06†o Spring Type Constant Rate
Pozzi Racing recommends a much heavier spring rate, especially for a big block equipped car. They recommend Moog #6082 however the spring rate is very high at 722 lbs. per inch. They also recommend Moog #6308, which is a cross reference to the original Z-28 spring. It has a spring rate of 380 lbs. per inch. Might be a viable option with a little heavier rate as current springs are 337 lbs. per inch.
• Moog 6308 Spring Specifications: o ID 3.68†o Bar Diameter .64†o Spring Rate 380 lbs. per inch o Load 1607 o Installed Height 10.75†o Free Length 14.98†o Spring Type Constant Rate
• Moog 6082 Spring Specifications: o ID 3.68†o Bar Diameter .75†o Spring Rate 722 lbs. per inch o Load 2406 o Installed Height 10.0†o Free Length 13.18†o Spring Type Constant Rate – one end pigtail must cut off
Stock GM Alignment Specifications: • Caster +1/2 deg • Camber + 1/4 to 1/2 deg • Toe-in 1/8" to 1/4" (Radial tires need less toe-in, use 1/8" or less for them)
David's Pozzi Racing Alignment Recommendation (Google Pozzi Racing) • Caster 5 deg positive, or as much positive as you can achieve up to 5 deg, can use .5 deg additional positive on the passenger side to compensate for road crown. A common setting would be: LF 5 deg positive, RF 5.5 deg positive. • Camber -.25 degree for mostly freeway driving, • -.5 for street and frequent hard cornering or mountain roads, • -1 deg for street, Autocross, and Open Track, this will wear the inner tire tread if you drive a lot of freeways. I use -1.5 deg quite often on cars that we frequently autox and do only a little street driving. you can use even more if tire temps show outside edge of tread is hotter than inside after a track run. If the inner edges of tread show excessive wear, use less negative camber. An autox only car would use -2 to -3 degrees. If you have not done the Guldstrand mod, you can be more aggressive with negative camber and increase negative camber by another -.25 to -.5 degrees. • Toe in, 1/16" to 1/8".
Differential & Rear Suspension Components • Ring and Pinion: Richmond Gear #4900961; 3:73:1, 4 Series Carrier • Bearings, Seals: Richmond Ring and Pinion Installation Kit #8310191 • Axles: Superior Axle and Gear Axle Kit #EV12-2; Direct fit 1541 carbon steel 30 spline axle kit complete with 7/16" press in studs, Torrington axle bearings #DB-67309 and National Oil Seals #86605 • Rear Axle Bearing: BAC #5707 (alternate number) • Rear Axle Seal: National #86605 • Wheel Studs: Moser #8002; 1/2-20 x 2" long screw in studs • Cover Gasket: Fel-Pro #RDS55029 (Autozone) • Leaf Spring: Hotchkiss 1.5" drop spring kit # 2407-C (Front & rear bushings, rear shackles, heavy duty 1/2" U-bolts) • Tee Bolts: NPD #C-7529-1A (4 pieces) • Traction Bars: Competition Engineering J Bolt Traction Bars #2101 (Replacement J bolts Competition Engineering #7032 - 2 per card) • Traction Bar Bump Stop: Energy Suspension #9-9132G (3/8" tall) • Leaf Spring Cushion: GM #3930052 (Schepel Buick) • Leaf Spring Bushings: Rear: Energy Suspension Polyurethane #3-2101G; Front: Rubber bushings supplied with Hotchkiss leaf springs • Front Spring Pocket Mounting: Front J Nuts Rick's Camaro #RC-469; Mounting Bolt Set Rick's Camaro #RC-470 • Rear Shock Absorber: KYB Gas #KG5521 • Gear Lube: Valvoline 80w-90 High Performance Gear Oil, Limited Slip #VV831 (Synthetic lube not recommended with factory clutch plate style gear carrier) • Gear Lube Additive: GM Limited Slip Axle Lubricant Additive #1052358 (4 oz. bottle) • Driveshaft: Custom built 3" diameter by .083" wall steel Performer Series by Driveshaft Specialists, San Antonio, Texas. Universal joints 3110. Transmission slip yoke #6081X, 3110/27 spline.
Differential Installation Competition Engineering traction bars – use GM spring cushions only. GM cushions have a steel locator ring molded into the cushion. Locate rear end to leaf spring much better than aftermarket polyurethane cushions. GM part number 3930052. Still locally available from GM. To install, follow Competition Engineering installation instructions. Competition Engineering’s J bolds are really soft – follow torque specifications and use anti-seize or risk damaging threads. Evenly tighten J bolts to 50 Ft. Lbs. then tighten Tee bolts to 50 Ft. Lbs. Once all fasteners are at 50 Ft. Lbs., torque rear nuts of J bolt to 70 Ft. Lbs. Competition Engineering’s J bolts come with (4) Ny-loc nuts. Used an additional (6) grade 8 SAE flat washers and (4) grade 8 nuts per side. Due to lower curb height of Hotchkiss rear leaf springs, original tall traction bar bump stops must be replaced to gain recommended bump stop to spring eye gap of 1/4". Use Energy Suspension Polyurethane 3/8" tall bump stops. Competition Engineering traction bars must have locator holes bushed. Factory hole in bar is 1†diameter. Used 1â€od x ¾†id bronze bushing, 7/16†long. Work well with GM cushions.
Wheels & Tires Front: (Includes Spare) BF Goodrich g-Force Super Sport All Season Radial; 225/45R17 mounted on American Racing Wheel Torq Thrust M Anthracite W/Machined Lip. 17" x 7" x 4" Back Space Tire Part # 245WR7GFASXL-26483; Wheel Part #AR105M7761AML
Rear: BF Goodrich g-Force Super Sport All Season Radial; 255/45R17 mounted on American Racing Wheel Torq Thrust M Anthracite W/Machined Lip. 17" x 8" x 4.5" Back Space Tire Part # 545WR7GFAS-11671; Wheel Part #AR105M7861AML
Nice looking cars you guys have. I have several of mine as I was going through all the spring changes but for some reason haven't taken one since I finished with the suspension. When the wind quits blowing trees over I'' take it out and get a picture. I also installed the competition engineering J bolt traction bars. When I redid the rear springs and welded the spring perches I changed the J bolts for thicker U bolts as I couldn't get the J bolts to fit in after the mod. I left out the rubber spring pads, couldn't get those to fit either. With the combination of no spring pads, solid body bushings, weld in subframe connectors, tubular a arms with the stiffer sprung coil-overs with adjustable shocks, new higher rate rear springs with new bushings and shocks, the car corners really flat. It starts to slide before I get much roll going around a tight curve at speed. When I first bought the car it rolled changing lanes on the highway. I think replacing the transmission mount with a boxed unit may have tightened things up as well. One problem I had with the Moog springs was the springs in the boxes were not what was printed on the box. I didn't realize that until I installed the springs and the car sat at about two inches different height. Had to take them out again and return them. I changed the alignment from stock as well, handles better and helped with tire rub. Had to take all the shims out on one side to get it, the other side is stacked. I don't think my frame is exactly straight, I did drop a plumb bob down from all the alignment points on the frames, marked the floor and measured. It's straight on the horizontal plane within a sixteenth, not so sure on the vertical. Weakest Part of mine is the rear axle assembly, it's a 373 C clip posi from a 69 Camaro, I swapped a girdle for the rear cover but I fear if I ever get real good traction the thing will come apart.
A friend of mine owned an auto parts store at the time. He ordered me several boxes of Moog springs. He let me return the "unused" springs. lol wonder if I returned them in the right boxes.
Nice timing and the reason I popped on these forums, I have the same process in mind with my newly acquired 68 that has the sag going on in the rear. In the trunk I can see the stock air hoses not even connected to what could be original shocks, which prompted the look for an upgrade within the stock look, but maybe lowered.
Hi all... So here's where I am after all this: I've got the front suspension all the way off and disassembled... pulling the springs is just scary ( even WITH a chain holding them there), pressed in new urethane bushings and ground off the rivets to install new ball joints (upper CA's). Washed, wire brushed/grinded/sanded, primed, and will get Eastwood 2K Chassis Black on them hopefully this weekend. Bought Viking 2-way adjustable shock and 2" drop coilovers. But I hope I didn't foul up. The spring rate descriptions from Viking steered me to 550s. AMA spec looks like 380ish. I could have gotten 450s, but they said that was small block and race rate, and 250 and 350 were drag racing specs. The spring itself is about 1/2 the size of the original. Maybe the rates are interpreted differently based on the shorter geometry? Wishful thinking? I guess I'll know when I lower it back down. Side note: These cars are such money pits After pulling the CA's off, I got into it with my tie rods. Little too sloppy, and while I'm under there.... well, you know...new tie rods! Rear will get done after I get the front sorted out...
'68 400HO Coupe, 4 spd, 259 interior, Windward Blue. My other car's a Johnson 15 outboard on a '61 Starcraft rowboat... Just sayin'.
Hi Dennis, They sit on the same spot, and line up with the same bolt holes, that the original shocks did, but I had to grind down the fixed nuts flat (ever so carefully so as not to remove any metal but the two nuts there). You have to drill out the bolt holes about a 1/16" more, but still leaves plenty of meat for a strong hold. The coil sits on the shock body via the adjustment ring. Planning to install them this weekend. I'll post pics.
'68 400HO Coupe, 4 spd, 259 interior, Windward Blue. My other car's a Johnson 15 outboard on a '61 Starcraft rowboat... Just sayin'.
Thanks for the pics. I didn't realize coil over mounted on top of the lower control arm but makes sense. Does shock mount area get reinforced? Get yourself a fat sway bar for the front. I used an Addco #599 1 1/8" diameter. Relatively inexpensive (compared to others on the market) and what a world of difference.
Hey Dennis~ Yes... did consider a beefier sway.... stock does look puny. But after reading up on stabilizers, sounded like you could easily overdo it and actually lift the inside tire enough to lose grip in a tight corner under speed. And since I'm planning to cruise "straight and easy" anyway, figured I'd just clean up and paint the original! Maybe at some point I might change it for a little stiffer twister. The only real goal of the shock and spring change was because the orig's were understandably shot. I just wanted to be able to have adjustability and get away with doing this once! So far the result looks great. It's a whole lot stiffer (I haven't had it out yet so haven't played with the shock compression and rebound-- just set that at the manu's recommendation) and still plan to drop the nose about an 1" to get a lower stance. You're pic above is way beyond my skill level, btw...very nice work!
'68 400HO Coupe, 4 spd, 259 interior, Windward Blue. My other car's a Johnson 15 outboard on a '61 Starcraft rowboat... Just sayin'.
BTW... shock mount location did not require reinforcement... although I understand your concern. Both the spring and compression of the shock are sitting on the same two points...instead of the spring in the pocket and the shock on its mount, albeit hanging below it from two nuts.... Viking is confident that as long as the lower control arm is in good shape (pocket area is solid and as thick as spec) they would perform as specified. I will monitor the shock pocket going forward....but it looks solid.
'68 400HO Coupe, 4 spd, 259 interior, Windward Blue. My other car's a Johnson 15 outboard on a '61 Starcraft rowboat... Just sayin'.
Did those coil overs come with a bearing above the adjuster nut? Mine did not so I had to buy them after the fact. You will want them when you are adjusting once the car is all together.
Yes- Came with a washer, and bearing ring and another washer. That "sandwich" is what the base of the spring sits on so that adjustment is "easy". That's debatable though.... it's still a good crank to raise/lower.... Cant imagine trying to adjust it without the bearing kit...
'68 400HO Coupe, 4 spd, 259 interior, Windward Blue. My other car's a Johnson 15 outboard on a '61 Starcraft rowboat... Just sayin'.
Yeah it's a bit of a grunt when you're laying under the car with those spaners. If there wasn't any other parts under there to get in the way it may not be too bad, but always seem to be in a position where a good grip is hard to get.
Took it for its maiden voyage with new suspension on Saturday..... WOW. What a difference!! Drives like my MKX! (almost...) Smooth, responsive.... incredible. Stance I like now. Compression dial set at 5, rebound at 7... feels good to me! Recommend it!
Correction, rebound is set at 9.
Last edited by ReverendRW; 01/30/1907:00 PM. Reason: bad memory.
'68 400HO Coupe, 4 spd, 259 interior, Windward Blue. My other car's a Johnson 15 outboard on a '61 Starcraft rowboat... Just sayin'.
Thanks for sharing. I keep thinking I want to switch to aftermarket control arms to gain more caster and coil overs but just not sure. Nice to hear you are pleased. A couple questions about front ride height. What size are your front tires? How much more adjustment down is left on the coil overs?
Why yes it is. Good eyes. I cut a “rubber band†from a truck inner tube and tie on with wire. Makes for two layer protection Cheap, easily replaced and works well.