Installed body bushings but have a question.

[MAP]

Greetings,

Sorry I've been away for a while. Dan G., yes, I'll still get my information to you. I'm thinking of contacting GM to see if I can get any of their prints for the frame and suspension, since it would greatly simplify my work.

The chassis/frame/suspension setup I've described has been in service for five years and 40,000 miles now, with absolutely no problems evidenced of any kind.

About my suspension mod's, this was my basic goal:

1.) Raise nominal front roll center from a few inches below the ground, to about 0"-1" above ground. Dropping the UCA inner shafts, and reducing the front ride height by 1" were instrumental in doing this. Raising the front roll center introduces a better camber-gain characteristic, and reduces the front roll-moment for a given centripetal acceleration, which reduces roll angle, or reduces the demand for roll stiffness - as one desires.

2.) Lengthen the front LCA's by 0.56" to make achieving a negative camber easier without many alignment shims, and in order to reduce the front scrub radius. The stock scrub radius designed by GM was huge (about 3-1/2",) and contributes to front-end wander with wide tires over bumpy surfaces.

3.) Important: maintain negligible bump steer, which is easy to miss with spindle swaps and the like.

4.) At the rear, improvements are much more difficult without making radical changes. Here, I took measurements on the stock set-up and found the rear roll center to be an astounding 18.0"
above the ground, and that the rear was designed with 10% roll understeer (i.e., for every degree of rear roll, the axle creates 0.1 degrees of roll-induced understeer.) As I mentioned in an earlier post, the stock design was for 50% anti-squat.

After confirming these facts in a consultation with Herb Adams, we reviewed how to improve matters. Several ideas were discussed. Most involved extensive modifications (which would require cutting the floor pan, for one.) One solution was rejected outright: the GNX rear suspension. Why? because the very short torque arm tends to create unstable tire motion (akin to axle hop) in situations of marginal traction. But the GNX's 11"-high or so roll center is a big improvement on the normal A/G body's towering roll center (although admittedly, a high roll center helps to fit big tires in a small wheel well, by limiting the transverse displacement of the top of the tire under a rear-roll condition.)

The biggest improvement which could be made without extensive modifications, was to drop the LCA attachment points on the axle by 2.0", by welding small extensions to the existing axle brackets.

This creates neutral roll-induced steering characteristics, and 125% anti-squat, which noticeably improves traction under acceleration (but at the expense of unloading the wheels while braking. An adjustable proportioning valve is a must.)

But I'm starting to digress - Dan G., all, I'll get back to you.

Best,
MAP

 

[BJM]

Speaking about bind

Until MAP posted his results I would have said the rear suspension would bind. My personal experience is on a 71 A Body. On those cars the upper arms are much shorter and angled outward much more than on the G body. They are also much closer to the car centerline. As a result the arms twist much more on the A body during normal suspension travel. Polyurethane bushings bind badly on the A body because the arm must do all the twisting because the bushing is so stiff. Note: we are talking about bushing twist, totally different from the torsional motions experience in the bushings of the lower arms and in the 4 front end arms.

My A body was harsh, suspension travel was significantly reduced. The car was almost self supporting without the springs in it, I checked. The poly bushings had the effect of adding a monstrous rear sway bar as well which caused the car to oversteer. They also started to squeak like an old bed, it was awful. The best thing I ever did was to remove them. I left poly in the lower arms and the ride was fine but they still squeaked, so out they came (this was pre polygraphite days, maybe they are okay).

If MAP has no issue with them I suspect its because he hasn't boxed the upper arms. If he has I am surprised its okay. I STRONGLY recommend against boxing the upper arms but if MAP has had no problems I cannot argue with success.

The G body arms must soft enough torsionally to take up the motion. Boxing them would put huge forces into the frame cross member and the axle ears as well as stressing the ends of the arms.

By the way MAP how what rear springs you are using? I would like to use ~140 lb/in in the rear with my 640 lb/in 5660's in the front but I cannot find any the right height.

 

[MAP]

Greetings BJM,

Rear springs are Moog/Federal Mogul 6435 (138lb/in, linear.)

About the rear UCA's: they are fully boxed, but the bushings at the differential end are the stock GN rubber bushings (the other end are black graphite-impregnated PU's installed with that very heavy silicone/teflon grease.)

On another G-body, I used this same type of PU bushing at both ends of fully-boxed UCA's at this location, and never had a problem.

I'm not very familiar with the earlier A-body cars, but I thought the principal difference was that the LCA's at the rear were more nearly parallel with each other (possibly forming a 10-15 degree included angle, instead of the later A/G body's 30 degrees; i.e., the earlier A bodies had less roll-understeer built into the rear.)

Best,
MAP

 

[BJM]

MAP,

I never really thought about it but you are right, the lower arms on the A-Body are quite close to parallel while the upper arms are more splayed. On the A-Body as well the upper bushings on the axle are not much above the axle centerline which with a soft upper bushing allowed massive axle windup and axle tramp (hop) with a posi. I was originally going to poly to get rid of hop, it moved the frequency of tramp from about 4 Hz to about 10 Hz which coupled even worse into the body bending modes. Man, what an awful design. The A Body people like buying the bushing relocating brackets for the uppers. The brackets lifted the UCA bushing up about 2 inches or so. The G body rear is better overall from the factory. I wonder if the same brackets would work well on a G body instead of lowering the rear arm location.

I should have also asked what front springs you are using.

 

[DarkForce]

MAP couldn't be more correct about the effects of braking after lowering the LCA attachment points. After a high speed pass, you have to go through a brief transition period that can get your attention at times. Never had much trouble at lower speeds though. Something I've been trying to picture is whether the twisting motion is greatest on the LCAs at the front or rear of the bar - the rear would be my guess.

MAP, what's your pinion angle? I've been using -3.5* with much success for the street.

 

[MAP]

Greetings Dark Force,

I need your help about pinion angle! How is this referenced? I've made no special attempt to optimize the differential orientation, beside trying to bias the nose of the differential about a half a degree below the crankshaft under a no-load condition. No doubt, your pinion angle is far better optimized!

I can tell you I have the following angles in the drivetrain, with positive numbers indicating a downward inclination from front to rear. The numbers are with respect to the true horizontal, and so the slight inclination of the garage floor, and the nose-down attitude of the car, may give a misleading interpretation:

1.) Crankshaft +5.06 degrees
2.) Driveshaft +2.77 degrees
3.) Differential +4.50 degrees

These are with the car loaded as usual (my weight in the driver's seat, and 1/2 tank of gas,) and, of course, with no torque applied to the rear. To achieve this pinion angle, I shortened the LCA's from their stock 19.25" C-C length to 18.93". I could have lengthened the UCA's instead, but shortening the lowers moves the rear forward in the car, which I wanted for a slightly better overall weight distribution on the tires.

Other matters:

The front springs are still stock, but with roughly 420 lb/in stiffness, achieved by cutting roughly 1/3 of a turn, and re-biasing the bottom seating of the spring in the LCA perch, to complement the increased length of the LCA. As you can tell, I believe in relatively low vertical suspension stiffness, but high roll stiffness.

I received a formal response form GM today about getting dimensioned prints of the A/G chassis and suspension. I guess not surprisingly, the answer was no - they only provide such details to "outside companies under contract." This reminds me of what Lee Iacocca said two decades ago, when he considered to try to buy-out GM. I think he said that he learned it would probably be easier to take-over Greece instead...

But I digress yet again.

Cool84, do you have your car on the road yet? I'm very curious about the results. Also, as more very interesting information gets posted on this thread, I think it's becoming clearer that it's not the PU body bushings per se which are problematic, but rather the combination of PU body bushings and stiff (e.g., PU, Del-Alum, etc.) suspension bushings, and stiff tires. As I wrote several posts ago "you don't want the cabin stiffly suspended right down to the road; you need a compliant, mechanical low-pass filter in the component chain somewhere." Better, I should have said, a "...compliant, *lossy* mechanical low-pass filter...". The factory rubber is excellent at both compliance and loss (with a coefficient of restitution of about 0.10-0.15,) while PU in any compliance is hardly lossy at all, with a coefficient of restitution of about 0.85
(the coefficient of restitution, or ratio of rebound height to release height upon dropping the object on a hard, immobile surface, is directly correlated to loss factor. The higher the C-of-R, the lower the loss factor of the material.)

Coupling two mechanical structures with PU will tend to allow an efficient transfer of energy from one to the other, because of PU's low loss factor. So if the factory's jiggly frame motion is a fact of life for the car, my philosophy is better not to transmit that jiggliness directly to the cabin by using PU bushings at the #2 to #6 positions. But then again, with stock tires and stock suspension bushings, the "other end" of that structure may tend to behave better, and thus yet acceptable results with PU body bushings even at all #1-#7 locations.

Ah, the tricky art of chassis tuning...

Best regards,
MAP

 

[cool 84]

Mine's not running yet but I'm getting so anxious to try out the new suspension/body/frame mods that I'm just before having another car tow me around. . Looks like another 2 months, by then I probably won't remember how it felt before. I'm really curious how it's going to react with the solid #1 and #7 bushings with the stiff tires and urethane front bushings.

 

[GNICETRY]

How bad is this rear end lifting up, losing traction at the transition from accel to decel?? Is it something a proportioning valve can fix or will it make me feel I'm driving my stock suspensioned car again.

 

[darkfa8]

...stuff

- Lee, you're more than welcome to take my car out for a spin. I'd be interested to hear your critque.

- MAP you bring up a good point about the energy absorbtion or coefficient of restitution of different materials, in this case, the rubber vs. poly. I think that unless you have a low miles, excellent condition stock car to begin with, feeling the effects of suspension and chassis tuning in the "comfort" department is kind of a shot in the dark, since unless you replace ALL the stock and/or worn parts, you're kind of only making improvements to sections..and not the whole picture.

In my car, I have the full Energy Suspension body bushing kit (26 bushings, uppers and lowers). All I can tell you about it is that going from disintegrated, partially non-existant stock bushings to the poly bushings, I can feel the road in my seat. Road imperfections and the vibrations from the drivetrain to a degree. However, I also take into account that:

• 
  - My motor mounts could stand to be replaced
  - My trans mount is 1 year old, rubber replacement
  - My seats are out of a 1993 Firebird Formula (they aren't severely worn, but nonetheless, they are 9 years old)
  - My front suspension control arms have stock original bushings in them
  - My front springs are stock/original
  - My front and rear shocks are Tokico Illuminas
  - My front steering linkage is stock/original
  - My front sway bar/chassis bushings are new rubber
  - My front sway bar endlinks are Energy Suspension poly
  - My rear upper control arms are stock with stock decreped bushings
  - My rear springs are Moog Cargo-Coils
  - My rear lower controls arms are BMR tubular's with rubber bushings
  - My front brakes are stock (stock sized rotors, original rubber lines .. need replacement soon!!)
  - Rear drums have all new hardware and star adjusters
  - Rear drums have 7/8" S10 manual wheel cylinders
  - Have converted to vacuum brakes

So given that I still have a lot of stock/original 15 year old parts in there, I cannot say for certainty how good or bad the effects of the poly body bushings are. Again, in that sense it depends on what you're trying to achieve. In my case, consistent body panel alignment is good, they won't deteriorate, and the cabin has a more solid feel that I prefer.

As for the future of the rest of the suspension, steering and chassis, depending on my findings and help from the educated individuals in this thread and others whom I have high regard for, I'll taylor my car to meet my goals all in due time

I think half the battle for most owners of G-Bodies is realizing that unless you replace all the "old stuff" with either new OEM or aftermarket it really is hard to make a good ascertation of how a new peice is working if it is working admist old, typically worn parts.

All about a "system".

I expected the "no" from GM you got MAP, but it seems with your expertise and with help from others, you and/or we could adaquately come up with the prints needed to illustrate the purposes and principles in the how, what and why of suspension tuning for these cars.

 

[DarkForce]

MAP, checked the angle of the frame at several points to make sure it was level then measured off the bottom of the differential with an angle gauge to see what the angle was. Drilled holes in the LCA extended attachment points that permitted -3.5* (degrees of differential slant from rear to front). Rechecked everything after road testing just be sure. Using -3.5* negative angle is as much as I'd feel comfortable with for a street driven car. Obviously the more angle the harder it is on the U-joints. Note: Changing tire sizes will also affect pinion angle.

GNICETRY, on a fast pass when you let off the accelerator the rear end wants to rise up a little and get light. It would appear this effect would be greatest during a ¼ pass because our cars are still accelerating hard when we hit the brakes at the big end and there would be increased inertia and weight transfer to deal with. Seems to me like this is just another one of those compromises you learn to live with. Perhaps lowing the LCA attachment only 1" might help on the top end (braking) but would hurt on the low end (accelerating). Again the choices between street and track applications become apparent. I don't know what the fix would be. Ask MAP, he may know.

 

[HRpartsNstuff]

It seems I caught this thread a little late, but I will try to add some helpful info to the discussion.

Our expertise is on the rear suspension, and we concentrate on street/strip (drag race) setups. We look for mods that help in handling without compromising ride on the street, and also work when you take it out & race it.

Some of the "old" poly bushings did squeak (my Energy Suspensions did) and some bind up as well. The binding happens becuase the center steel tube is pressed into the poly material tightly, and it is a NON-greaseable application. That works like a rubber sheet to open jars in the kitchen (if you have seen those). It grabs it like crazy & won't budge. When it does move, it squeaks, again because there is no lubrication there. Repeated power washes & rain driving, as well as sitting too long between trips makes this worse. With the "newer" poly bushings that contain graphite, this is lessened but still noticeable on some cars.

We have fixed both the binding and queaking with 3 changes to the common poly bushing:

1. We use a bushing (half) inserted from each side. This leaves a small a small space between them. This has less surface contact, and allows the one side to move independently of the other.

2. We added a grease fitting to the thicker outer shell. This allows grease to be inserted and directed to the inner poly bushing surface that the steel tube rotates inside of. The bushings are grooved so that the grease goes all the way around, and the whole length as well.

3. We had the center steel spacers custom ground to a slightly smaller diameter. This reduces the "press" on them once installed into the poly bushings. This makes getting the grease in there easier, and allows the arm to move freely up & down. The side to side rigidity is still retained for handling, but it moves smoothly & won't bind. They can even be twisted out of shape, and they still move up & down freely. The effects are more like a heim joint, without letting it move side-to-side aimlessly.

We used this same design on our new replacement bushings, as well as our new control arms. This way you can have your cake & eat it too We make boxing kits too for those who want to save time & money. We have never heard any problems from having new or boxed upper CA's on any car, including '64-'72 A-bodies. I believe because of our unique bushing design, it can be stiffened up without binding anything up. The ride is also not quite as harsh as the more common Energy Suspension type poly bushings.

Heim joints will let the rearend move side-to-side easily. While this takes the "bind" out of a suspension, it also lets the rear move out of position. The more ends that have heim joints, the worse it gets. Think of a 4-link race car setup. It has heims on all ends, so it moves freely. You also need a wishbone/track locator bar to keep the rearend under the car. Without this, it would move side-to-side until the tires rubbed the frame rails.

Because of the weird braking effects, and the sometimes unnecessary gains, we do NOT recommend lowering the mounting points on the rearend. I drove a friends car once with that setup, and it scared the life out of me. I don't like dancing at 125 mph Our setup has been on Terry Houston's car going 8.60's at over 160 mph. Launches dead level & goes straight as an arrow. My car was going 10.70's with a 1.40 60 ft time, using the stock mounting points & the foot brake. We found that if the suspension is allowed to move up & down freely, and won't bind under twisting, then the mounting points are not as important. The side effects are not worth the gains IMO. I think raising the upper mounting point may be a better choice if you feel that you have to move something.

Wow. Hope that wasn't too long & it helped somebody
Hate to type that much for nothing.
PS- We made a neat tool to change the bushings in the top ears on the rearend housing. In & out in less than 5 minutes tops. Now you don't have to leave it stock worn-out rubber because it's too hard to swap out

Oh yeah, most people that I have talked to say the poly BODY bushings are too harsh, with/without poly in the suspension points. I can't imagine using delrin or aluminum (or hockey pucks) in there. For road racing, it might be fine. For faster drag racing, I would think the body would buckle/crack above the rear side windows. I suppose this would all depend upon how stiff the chassis is, & if roll bar was installed. I would only stiffen up the body bushings AFTER the chassis has been stiffened up, but that may be a drag racing point of view there. Our local guys that go fast without rollbar or extra braces don't launch hard because they buckle/crack under twist. The more you tie a body to a weak frame/chassis, the more this becomes a problem.

Got to go, brain & fingers hurt now
Hope that helped.

 

[HRpartsNstuff]

DarkForce, you seem to have found your correct pinion angle, but here is an easier way to check it:

Jack the car up by the rearend, keeping all of the weight on the rear axle as if it was on the ground (support rearend with jack stands for safety). The car can actually be way out of level, that is not important. Take a reading on the driveshaft, zero out your anglefinder if it has that feature. Now check the pinion gear. If you are careful, you can use the bottom face of the U-joint yoke. Just be sure not to be on the retaining straps. You are looking for the machined surface that would be square to the pinion gear.

The DIFFERENCE between the pinion gear & the driveshaft is your "pinion angle". The driveshaft to the pinion gear should look like a really flattened out V, or both pointing downat the U-joint.

Settings all depend upon your use & what bushings you are using. The harder you launch the car & the softer the bushings, the higher the setting needs to be. The more highway use, the less the angle should be. We made up a chart for recommendations to get you close, and instructions on how to set it & adjust it with adjustable uppers. We include all that with our angle finder and upper adjustable CA's.

Watch out for shortening the uppers and/or shortening the lowers to set the pinion angle. This shoves the driveshaft into the transmission farther. If you drag race a lot, the splines on the driveshaft start to twist & will bind up if you shove it in farther. I had to take mine apart & counter-bore the original "straight" splines out, so they didn't interfere with the already bent splines. That was one reason that we went to +1/4" longer lowers, so the uppers wouldn't need shortened as much to increase the pinion angle. This keeps the wheelbase the same, and helps tire clearance to the front.

Always better to learn from other's experiences than to learn it the hard way

 

[DarkForce]

From what I've learned, a GN that is primarily used for the street should not have the rear LCAs lowered, especially if it is fast - 120+ mph - track use is another story. The handling characteristics and/or transition after a WOT run may catch some lesser experienced drivers by surprise and cause them to have a really bad day. My advice is to stay with the stock CAs and box them with the bushings of your choice. The car will still hook good and handling is improved - that is a fact!

Took the white T project car out for a test ride the other night. Keep in mind that everything on this car is completely shot but I've done the following over the past 3 weeks. Bilstiens (all four corners), all body bushings replaced (2,3,4,6 stock, 5 gnx, 1,7 solid plastic), front swaybar poly endlink bushings, front cross and diagonal braces, boxed LCAs (poly rear bushing, stock front bushings), and ATR rear swaybar.

Results: The ride was substantially stiffer with a slight increase in road noise. Handling in spite of the tires was considreably improved - the above mods were worth the effort. Cool84 was with me during the testing. Tires are the next item to be replaced and the upper control arms may get boxed soon. I'll let you know what happens on the next test rides - if I'm ever able to decide on the "perfect" street tires.

 

[QKRNYRS]

DarkForce


where did you get the Delrin bushings for the front like MAP recommended? Thanks

 

[DarkForce]

QKRNYRS, Cool84 bought a 4' solid roll of polycarbonate "something" which is basically the same as Delrin from Bakersfield Plastics for about $40. A local machine shop drilled and cut it up for us. This was enough for two cars (16 bushings) with very little waste.

 

[charlief1]

Antique bump here for a little reading. This is actually good info if you guys want to go through it.

 

[RIFF RAFF]

just like the old days charlie .. seeing eye dog 1

 

[charlief1]

Did a bunch of searching tonight to fix a bunch of links and this one came up in one of the searches. It's really old but you see this type of stuff come up so often I thought it might be good to do a refresher for some of the members.

 

[just plain john]

I guess aftermarket control arms weren't as readily available tthen

 

[charlief1]

They were but not to many knew about them. The guys that made them weren't known well either. Think about how much the internet has impacted the ability to find info and parts in just the last 10 years and then look at the dark ages of the 80's and early 90's. You can find just about any info on a chasis set up and the knowledge on how to do it if you do some searching to find out about it.