Hot Rods Suspension Magicians LOOK HERE...

Curious..... It's been mentioned that the pan hard is not level because the body is off in the photo.
When the body is on how close to level is it?
The reason I ask is that it would have to come down about 2 1/2 - 3" to be level ( looks like it anyway).
If the springs loose 2 1/2 -3" just to get ride height, there's not a lot of travel left for the bumps.

 

All this talk about spring rate and angle is premature. You only have 2.25" between the axle and frame, and .75" is taken up with rubber bumper. I don't think 1.5" of travel is enough, no matter how wonderful the springs are. I think you need more room in there. Time to consider a bigger C or Z-ing the frame.

Try to find some pics of how the Rolling Bones guys do their big C in a 32 frame. They install a thick boxing plate in the area that rises up above the top edge of the frame. This looks like it will add back the lost strength removed when the box section of the frame is reduced.

 

UPDATE: I dropped the rear tire pressure to 25# and this made a difference. 'Still wants to bottom out on bridge joints and dips in the roadway. I have a date Friday to take it to a shop for suspension/shock dyno. I'm hoping that this will be the final step in dialing it in, although I agree with Alchemy in post #32 that 1.5" of travel is not enough. I may try raising the body an inch by going to the middle mounting hole for the lower shock mount, as opposed to the lowest hole where it is now. This will be messing with the stance and the way the wheel sits in relation to the rear wheel well, but if it helps the ride it may be worthwhile. Ah well, life is a series of compromises...

Thanks for the input, it helps to see different ideas.

 

How about some larger diameter tires? Then you could sneak the extra clearance in between the axle and frame, but the larger tire will still fill up the wheelwell lip. I would think a larger diameter tire with less width might ride a bit softer too.

When you adjust your ride height (different spring mount holes, or different springs), make sure to verify your pinion angle still matches your trans output. I'd hate to see you cure one problem yet cause another (driveshaft vibration).

 

Be sure to re-set your caster if you raise the rear ride height.
SPark

 

One of the more informative threads I have seen in a while. Thanks to all have contributed......

 

??? Sorry, I’m not following you here. How does rear ride height effect the caster on a solid axle suspension? I can see how you’d want to do this on an independent rear suspension, but how and why on a solid axle?

 

Lost me too.HRP

 

The frame tilts, typ. down forward, hence a need to add caster° - front end.

 

Caster is measured from the kingpin to the ground. Is not measured from the frame. So, you jack the rear of the car up a bit, the front axle will have less caster. Adjust some back in if you need to.

 

There's a lekker twisty in Cape Town which used to be called De Waal Drive. The last offramp before it becomes Roeland Street all the way down to the Houses of Parliament is a tight left hander onto Mill Street, built some time in the late '40s, and it's on my route home from lots of places. Taking it in the DD at around twice the posted limit always had me riding the entire curve on the bump stops, until I put in a set of German aftermarket springs. Now it'll ride like a shipyard hack* at 40mph but a magic carpet at 125mph, faster than which it will not go, even headed north-west downhill ahead of a Cape black south-easter. And I've got actual suspension coming into Mill Street.

Point is, wheel rate is only half the story. The reason I've got the sort of ride quality my wife sometimes complains about is that I've got no way of separating pitch rate out from bump rate. But that is not so much an entire different chapter as an entire different book.

*Where trucks go to die. As recently as ten years ago there would be savable Bedford TKs and Mercedes-Benz Kurzhauber less plates carrying bits of dead Japanese trawler back and forth. Now it's already moribund FAWs and other Chinese marques.

 

I agree with alchemy. Caster is determined from the vertical plane to the king pin. If my math is correct, using a wheelbase of 106 inches the caster will be reduced by 1.1 degrees for every two inches the rear is raised.

 

You won't notice the caster change, and barely notice the 1" raising in the body.
On the other hand, going from 1.5 to 2.5" travel is a huge improvement.

Talking about harshness with only 1.5" travel is a bit silly...the suspension needs room to move it is to actually do anything.

Raise away! (and report back)

 

I stand by me statement. You will lose caster by raising the back of the frame. I built race cars, I know caster. To prove it to yourself, measure your caster and jack up the back end of the car and measure it again. You just lost caster. Physics don't lie.

It also doesn't matter what type of suspension it is, makes absolutely no difference. You changed the angle/location of suspension mounting points (slightly raised the back of the front radius rods) and the caster pivoted about the centerline of the axle. You just tipped the top of the axle forward, you lost caster. It might be small but it is there.

That's why we tend to focus on changing one thing (raising the rear/gaining clearance) created a new problem (wandering steering going down the road) and blaming the wrong adjustment. Raising the rear didn't make the car drive bad, losing the caster from raising the car did that. Failure to follow thru with what change "A" does to items "B", "C", "D", etc. Look at the bigger picture.

That's where we get statements like "I raised the back of my car and it drove like shit, couldn't keep it in the road, wandered all over the place, never raise the rear of a car or it will drive worse". You can jack up the rear, just put back in the caster you just took out to keep things apples to apples.

SPark

 

When you change the frame angle, such as by raising the rear suspension, you change the caster angle in the FRONT suspension.

When you raise the rear end, you decrease the front caster angle, which could have a negative effect on steering performance.

Caster is the kingpin angle in relationship to the ground. Tip the frame, change the angle.

 

Good advice right there. I run 25 lbs in my rear tires, and it makes a world of difference. If your shocks are not adjustable, get some that are and play with the setting and tire pressure.

 

UPDATE: I found an old pair of shocks that were left over from a former project. They are longer, 17" fully extended vs 13" for the ones that were on the car before. I found a pair of 10" springs to go with the new/old shocks, put it all on the car, and after messing with the ride height for a while, went for a drive a few minutes ago. What a difference! I have much more shock travel and much more axle/frame clearance. I'll measure the new clearances tomorrow, but it's going in the right direction. I intentionally drove over a couple of spots that always caused it to bottom out before and it was smooth as velvet. The back of the car sits up a bit higher and I'm hoping I can fine tune the ride height tomorrow to get it down a bit.

When I got the car up on jack stands to change out the shocks I noticed that one of the sway bar bushings was completely missing in action. So I removed the sway bar. I can tell a slight difference in body lean when cornering, but it is slight...may just leave the sway bar off. I can't tell any difference in the caster change; the car steers fine with this change in rear height. If anything, the steering feels better. Tomorrow I'll check the pinion angle & the panhard bar and adjust if necessary, but in my brief test drive tonight the driveshaft didn't seem to be vibarating.

'Still going to keep the appointment with the suspension shop on Friday, just to have a pro look things over and have the shocks dyno'd if he recommends it. Today was a success and if I can just fine tune the ride height to get it down in the rear just a little bit I'll be content to let it alone. This is sure better than major modifications to the frame.

Thanks for all the advice and input!!

 

Always great to hear a success story!
SPark

 

Keep us in the loop Tom. HRP

 

I thought this was very informative for all.

 

Regarding tire pressure and stock automobiles, the rule is to always use the tire pressure the car has posted in the door jamb. The same tire may be used on several models and that factory rating accounts for the specific weight of that car. Over-inflated tires will tend to ride like basketballs, a lot of bounce and will wear the center of the tread first.

What to do with a custom car, where there are no standard engineering specs? This procedure was outlined in a magazine ... Start with a pressure higher than you should need. Using chalk, color a band across the tread and extending a bit onto the sidewalls. Run the car forwards and backwards and observe where the chalk has been rubbed off. It should be gone in the center of the tread and still have some left over near the sidewalls..Lower the air pressure a couple pounds and repeat rolling the car back and forth. Keep doing this until you have dropped the pressure to the point where the chalk is rubbed off evenly across the tread face, without wearing it off the sidewalls. Add a couple pounds of air back in for a safety margin for incidentals you may load into the car at times, and you should be right on.

Don't forget the front tires too. The same technique would apply. One last thought ... if you do this, and then go on a road trip, carrying another couple people in the back seat and a trunk full of luggage, air the back tires back up a bit.

 

Similar when competing on a road course, inflation press. adjusted by chalking the outer rib and up the sidewall. Height of chalk worn off tells.

 

Wow! Just found this doing a search for coilover shock troubles. Have similar problem with ride. Now I have lots of things to go check and do. Thanks to all.

 

Put it back on, and replace the bushing.

 

Ditto that. Even worse, when an end comes completely adrift. After you exit the turn, the car will stay leaned over to the outside!!! Gary

 

Depends on how the chassis is set up and the hairpins/ladders are influencing the car and it's up to the owner to test under varied circumstances ie. performance driving under a controlled environment to understand what said is capable of for safe driving and decide if livable..

It probably should be mentioned that sway bars affect the under and over steer of a car which ideally should be neutral meaning the front and rear give at the same time while still retaining proper suspension characteristics and sway..

A custom can be difficult to set up under/oversteer with the amount of variables involved, front rear weight distribution, tire size/width, suspension efficiency ect. so a compromise may be in order, part of that may be a reduced diameter bar?? Ultimately it's up to the mechanic/owner to decide and live within the cars boundaries..

If a car Is over swayed to the front I believe it would have an understeer issue?? So if you test the car and it understeers/ front end wash you need more sway bar in the rear to neutralize..

Nothing wrong with setting up a chassis as best as possible but compromise is inherent when considering a car tends to oversteer under power when rear wheel drive and differs under varying degrees so one probably can't be 100 percent anal and must understand the limits of a car at a give time.. it's up to you..

This is an assumption but Seadogs car will PROBABLY handle decent without the rear sway considering it's a Hot Rod but should be tested thoroughly to know what it's capable of and if not acceptable adjust accordingly..

Test and tune time...

 

Correct! Just to UPDATE: I went back to the original shocks & springs, but raised the ride height by about 2 inches. It now rides as it should with no bottoming out issues. I left the rear sway bar off, since it tends to ride better without it. I really can’t tell much, if any, difference in cornering, even in “spirited” driving. There may be a difference if I wanted to auto cross the car, which I don’t.

As said above, the solution was in trying different things and testing!

 

Ah, the magic of travel!
Now get on with enjoying that car.

 

Good to hear it is working better for you. Most people over look the fact that sway bars effectively add spring rate to a suspension, so by removing the rear bar you effectively reduced the spring rate, causing the softer ride.

Have Fun.

 

This is a trick I used when running off road in Jeeps. We ran larger tires than normal and the indicated pressures made them ride in the center of the tire as well as rough. I let air out until I could just pull a match book cover out from the edge of the tire. Tire usually made contact the whole width of the tire and it rode better as well. Hmmm- - - - -That's how I came up with 28 lbs on those 285-15s I run on the back of my coupe.