Yellow Bullet Forums banner
1 - 11 of 11 Posts

·
Registered
Joined
·
5 Posts
Discussion Starter · #1 ·
Hello Ladies and Gentlemen.

My first post here. I have a question about setting up a front engine car with a heavier engine. The car is a 1986 Mercedes Benz 560SL with an M120 V12 from a 1996 SL600. I have been driving this car around for about 15 years now and all runs well. I have had several amateur drivers test it out on the road and they all come back with the same conclusion, that the car runs well balanced and about the only thing they would do is put in stiffer springs and bars to firm up the car like there own track cars. Although none of these drivers has taken it on highways at high speeds.

But I'm not looking for a track car ride. The engine is powerful and smooth with a linear sedate 389 HP, with a nice note.

One of the things I notice is that there appears to be instability at high speeds. The installation of the V12 engine added ~ 300Lb over the front axle, between the engine, transmission and big breaks. All other suspension components are stock with the exception of heavier coil springs up front to recover the ride height. It appears to me, and I am not a driver, that when going down the highway and trying to follow a curve in the road as say 75 MPH, The car wants to keep turning tighter with neutral power. I have to back off on the wheel a bit and sometimes I find myself oscillating back and fourth with the wheel to hold a line. I believe that is called over steer.

So my question are:

1) Is that oversteer?
2) If it is oversteer, would that be the expected result of a heavier engine?
3) Best way to correct for it?

The stock 560SL uses 29PSI tire pressure up front and 34PSI in the back. I am currently running 32/32

Thanks in advance.
John

Land vehicle Car Vehicle Tire Wheel


Car Vehicle Grille Motor vehicle Hood
 

·
Registered
Joined
·
19,463 Posts
Oversteer and understeer generally occurs at the very edge of traction. Rear engine cars like Porsches generally exhibit oversteer, when pushed to the limit the rear end comes around. This is considered an unstable situation and will bite all but the most experienced drivers in the ass. Front heavy cars have understeer and at the edge of traction generally feel as if they're "plowing". This is generally considered more forgiving as the car will simply follow a wider line but stay under control.

What you are describing sounds to me like the front end is not adjusted correctly especially with the oscillations you are describing. Do some googling about how caster/camber/toe-in affect a car's handling and you'll probably find some more information that describes what adjustment is probably most responsible for causing your problem.

Before you have the front end aligned I suggest you go thru every front end component carefully. Worn components such as bushings will affect the way a car handles. The alignment shop will check but I never trust shops 100%. You might consider changing any rubber components to polyurethane if someone offers that. Polyurethane will improve handling though it may transmit a little more noise into the car.
 

·
Registered
Joined
·
5 Posts
Discussion Starter · #4 ·
Oversteer and understeer generally occurs at the very edge of traction. Rear engine cars like Porsches generally exhibit oversteer, when pushed to the limit the rear end comes around. This is considered an unstable situation and will bite all but the most experienced drivers in the ass. Front heavy cars have understeer and at the edge of traction generally feel as if they're "plowing". This is generally considered more forgiving as the car will simply follow a wider line but stay under control.

What you are describing sounds to me like the front end is not adjusted correctly especially with the oscillations you are describing. Do some googling about how caster/camber/toe-in affect a car's handling and you'll probably find some more information that describes what adjustment is probably most responsible for causing your problem.

Before you have the front end aligned I suggest you go thru every front end component carefully. Worn components such as bushings will affect the way a car handles. The alignment shop will check but I never trust shops 100%. You might consider changing any rubber components to polyurethane if someone offers that. Polyurethane will improve handling though it may transmit a little more noise into the car.
Well I certainly don't drive at the edge of traction. So I guess I can rule out over steer or under-steer. This car uses a very complex suspension geometry. The picture below shows the front subframe with the control arm mounts. The lower control arms are canted back about 20°. The upper arms are canted forward about 5°. That means that as a wheel moves up and down there are huge changes in both castor and camber. On the highway it feels like car takes time to settle into a turn and during that settling period it wants to turn in more. If that's the case stiffer springs and bars might be in order. Just keep the car flat. The cars current stock front bar is ~ 1". The car that the V12 came out of was about 1.25". I'm not sure about the rear bars. But I recently read and article on the development of the Boss 429 Mustang. Apparently with the heavy 429 the car handled really badly. To correct it Ford added a 3/4" rear bar. According to the article that made it handle better than all the other Mustangs that had no bar at the time. Since then all Mustangs came with a rear bar.

So how does flattening the ride sound. And if that sounds like a solution which directions should I proceed in springs, front bar rear bar, all bars and springs.

As far as wear all front end parts are new except for the upper control arms. Upper control arm are known to have slight play in the upper ball joints and are on my list to replace. Unfortunately those are $1000 a side and the ball joint is not replaceable.

Automotive lighting Line Art Font Auto part
 

·
Registered
Joined
·
19,463 Posts
I'm not a real expert in this subject but if a car doesn't turn predictably in a normal turn the front/rear suspension need some work. Having a larger sway bar would be my approach. In my opinion sway bars keep the car from leaning too much, springs should be sized as needed to set the proper ride height and shocks control most of the ride quality.

Worn ball joints can change the geometry and if bad enough if will be felt in the steering but not as much as other worn components. I had a 1970 Mustang that when I first bought it I would start a turn and once the car started to turn it would DIVE harder into the corner. I replaced the idler arm and upper ball joints and it stopped doing that. Can't say if one of those or both fixed it but the car was scary until I did.
 

·
Registered
Joined
·
5 Posts
Discussion Starter · #6 ·
I'm not a real expert in this subject but if a car doesn't turn predictably in a normal turn the front/rear suspension need some work. Having a larger sway bar would be my approach. In my opinion sway bars keep the car from leaning too much, springs should be sized as needed to set the proper ride height and shocks control most of the ride quality.

Worn ball joints can change the geometry and if bad enough if will be felt in the steering but not as much as other worn components. I had a 1970 Mustang that when I first bought it I would start a turn and once the car started to turn it would DIVE harder into the corner. I replaced the idler arm and upper ball joints and it stopped doing that. Can't say if one of those or both fixed it but the car was scary until I did.
I had a 1969 and a 1970 Cougar. Pretty much the same as a Mustang. I drove around quite regularly with worn components but maybe I was much younger then. Funny thing is the picture in my first post is me driving on the Tail of the Dragon in NC/TN. I have no problems on those twisty turning roads, but on I 95 it is a different story. At 65 years old I am a bit uncomfortable above about 70 MPH. But I also have a stock 560SL that doesn't seam to have this issue. I'm not trying to make it into a track car, but I would like it to be as close to stock handeling performance as I can get. It will be a while before I can try any changes as I'm moving and the car will be in storage for a few months. I guess I'm just going to have to play the random change springs shock's and bar games, but I will certainly start with my upper control arms.
 

·
Registered
Joined
·
19,463 Posts
I had a 1969 and a 1970 Cougar. Pretty much the same as a Mustang. I drove around quite regularly with worn components but maybe I was much younger then. Funny thing is the picture in my first post is me driving on the Tail of the Dragon in NC/TN. I have no problems on those twisty turning roads, but on I 95 it is a different story. At 65 years old I am a bit uncomfortable above about 70 MPH. But I also have a stock 560SL that doesn't seam to have this issue. I'm not trying to make it into a track car, but I would like it to be as close to stock handeling performance as I can get. It will be a while before I can try any changes as I'm moving and the car will be in storage for a few months. I guess I'm just going to have to play the random change springs shock's and bar games, but I will certainly start with my upper control arms.
I'm 68 and my Mustang goes 175mph in the 1/4 mile. ;)

Good luck!
 
  • Like
Reactions: MB107

·
Registered
Joined
·
685 Posts
I had a ’04 SVT Focus FWD which are considered “neutral” in the over/under steer vehicles as they were somewhat developed as a competitive autocross car from Ford as new. Thinking I could out engineer Ford, I put a larger rear sway bar on it. Man, did it handle better....until...it went to oversteer (at the edge of traction as mentioned above), and then, you couldn't let off the accelerator fast enough! It would throw you into a nasty spin.
 
  • Like
Reactions: MB107

·
Registered
Joined
·
5 Posts
Discussion Starter · #11 ·
I had a ’04 SVT Focus FWD which are considered “neutral” in the over/under steer vehicles as they were somewhat developed as a competitive autocross car from Ford as new. Thinking I could out engineer Ford, I put a larger rear sway bar on it. Man, did it handle better....until...it went to oversteer (at the edge of traction as mentioned above), and then, you couldn't let off the accelerator fast enough! It would throw you into a nasty spin.
Its starting to look like not much of an oversteer understeer issue as I am certainly not putting this at the limit. Don't know if upper ball joints will help but they are the only parts on the front end that have not been addressed and showing signs of play. I also cant rule out the rear end. The car has IRS.
 
1 - 11 of 11 Posts
Top