R/C 107 w114 w115 lower ball joint size? - PeachParts Mercedes-Benz Forum

rwd4evr · #1 08-23-2017, 04:07 PM

I'm trying to find a lower ball joint with a longer stud to use on my SLC drift/track car to lower it properly without destroying the geometry and camber curve. There are rebuildable lowers ball joints available for most older gm,Ford and Chrysler vehicles used for dirt track cars with various stud lengths to tune the suspension. Does anyone have a r/c107 lower ball joint out of a control arm to measure the diameter of the press fit area that fits into the arm? I've got dozens around but they're all in cars that still roll and would be a ***** to get at for two seconds of measurements. No one has them in stock locally to check on a new one. The taper off the stud could be an issue but the spindle can be reamed to the right taper as long as the Mercedes original stud isn't larger than the Chevy full size Moog k6117. I believe this will be my best bet. If the ball joint isn't too far off in it's press in size it can be machined down or the arm could be opened up a bit.

Frank Reiner · #2 08-23-2017, 06:48 PM

Quote:

Originally Posted by rwd4evr

I'm trying to find a lower ball joint with a longer stud to use on my SLC drift/track car to lower it properly without destroying the geometry and camber curve.

If you will, please view the suspension links as a four-bar linkage, i.e., a parallelogram. If the stud of the lower ball joint is made longer, that side of the parallelogram is also made longer, and when the linkage is deflected (bump & droop) the arcs through which the ball joints move are changed from the original configuration. As a result, the camber curve(s) is/are also changed.
To lower the chassis without altering the camber curve, raise the spindle on the upright.

rwd4evr · #3 08-23-2017, 07:30 PM

Yes that is true, in an Ideal World I would put lowering spindles on it that simply move the axle up in the relationship to the ball joints. But nobody makes those for a r/ C107 chassis. So practically speaking if you look at it as a parallelogram with unequal length sides, simple lowering springs put the lower control arm in a position pointing upward from the chassis out. So when the suspension compresses in a corner it will actually decrease negative camber (bad). The lower control arm must be pointing downwards to keep some semblance of the correct curve. Unfortunately I doubt that with the 2-3" lowering I will have I do t think it will be downward anyway. The increase in the distance (with a longer lower ball joint) between the outer upper and lower suspension pivots will however change the angle of the upper control arm at ride height and change the arc the upper ball joint sees effectively increasing the camber curve. I haven't run the suspension program yet because I don't have the measurements but it will be no worse than if it was just lowered by springs only.
High amount of camber are good for drifting because of the way the outer tire contacts the ground at opposite lock.

A bit crude but here's the idea.

97 SL320 · #4 08-23-2017, 10:31 PM

Get some pegboard, wood strips and bolts then play around with control arm locations.

With an unequal arm system ( upper shorter than lower ) raising the upper ball joint pivot will give better ( more towards negitive ) camber on bump.

Lowering the lower ball joint pivot will do the same.

It isn't a " lower control arm must point down towards the wheel to reduce positive camber", like a Mac strut car.

rwd4evr · #5 08-24-2017, 02:34 AM

yes i understand its not cut and dry where the lower needs to be pointed. I have a suspension sim and i actually use coroplast graphed out and push pins for real world geometry checks. the issue with a r107 front suspension set up is, the anti dive built in throws any 2d model out of whack. I just dont want the car riding at the end of the usable geometry height and going positive under roll. I plan on removing the spring and rigging an adjustable height lower joint to run it through its travel to see what is ideal, or as close as i can get for decent performance lowered. Plus the change in lower control arm angle (relative to the upper) raises the roll center reducing body roll, same effect as anti squat or anti dive but sideways. Im not even getting into steering arm geometry yet and ackerman reduction for drifting. i'm not a suspension expert but i did stay at a holiday in last night!:-)

so does anyone have that lower ball joint out to measure please?!

97 SL320 · #6 08-24-2017, 09:15 PM

In your case, remove the spring, loosen the pivot bolts ( so the bushings don't bind ) then cycle the suspension full stroke.

If you use stiffer springs, suspension travel will be reduced over a stock car so bump less bump travel might not be an issue. Just be sure the suspension bumpers catch the suspension before ball joints bind.

rwd4evr · #7 08-25-2017, 12:52 AM

Well i'm using cut springs(for now at least) which does increase the spring rate though. i'm going to use the last of my liquid polyurethane epoxy for some new bump stops if i have to. also have custom poly bushings planned, they're easy to turn on a lathe(freeze them first!). I've always hated the bonded type rubber bushing with no free sleeve in the middle. stupid design under constant bind.

so i talked to a guy at moog today and got the specs i was looking for. the r/c107 lower ball joint is 48.5mm diameter at the compression area and 57mm high to the beginning of the threads from the shoulder that sits against the bottom of the control arm. the chevy ball joint i think will be best is 50.19mm diameter and available in 65mm,68mm and 94.7mm height. so it loewers the car instantly 8 , 11 ,or 37mm. only have to remove .845 mm to fit it in the arm. larger end of the taper is 18.5 on the r107 ball joint and 22.148mm on the chevy so reaming 1.8 mm should not be an issue and it will have the correct taper after that. looks promising i think. the actual ball size will have an effect on geometry because it changes the pivot point, so ill have to check that. forgot to ask moog today.

rwd4evr · #8 08-25-2017, 12:54 AM

Quote:

Originally Posted by 97 SL320

In your case, remove the spring, loosen the pivot bolts ( so the bushings don't bind ) then cycle the suspension full stroke.

If you use stiffer springs, suspension travel will be reduced over a stock car so bump less bump travel might not be an issue. Just be sure the suspension bumpers catch the suspension before ball joints bind.

oh yes i will have to check the upper for binding since it will be at an increased angle. good call.

rwd4evr · #9 08-25-2017, 05:05 AM

well, i found the info i was after so i'm going to continue any other developments in my build thread. thanks for any helpful input! check it out if you haven't.

http://www.peachparts.com/shopforum/performance-paddock/379765-1978-450slc-super-beater-lemons-race-car-9.html

97 SL320 · #10 08-25-2017, 09:22 PM

Quote:

Originally Posted by rwd4evr

Well i'm using cut springs(for now at least) which does increase the spring rate though. i'm going to use the last of my liquid polyurethane epoxy for some new bump stops if i have to.

Bump stops need to be progressive ( cone shape or Michelin Man looking ) otherwise if you hit them, the suspension goes from compliant to solid instantly. this can lead to snap under / oversteer.

Quote:

Originally Posted by rwd4evr

I've always hated the bonded type rubber bushing with no free sleeve in the middle. stupid design under constant bind.

Not really, they are a great design. If the sleeve was free to rotate, it would squeak. For a road car, the movement is minimal as at ride height the bushing is in an relaxed state. This is why tightening pivot bolts at ride height is critical.

rwd4evr · #11 08-25-2017, 09:38 PM

Originally Posted by rwd4evr View Post
I've always hated the bonded type rubber bushing with no free sleeve in the middle. stupid design under constant bind.

"Not really, they are a great design. If the sleeve was free to rotate, it would squeak. For a road car, the movement is minimal as at ride height the bushing is in an relaxed state. This is why tightening pivot bolts at ride height is critical."

Road cars use more suspension travel than a road race car. Roads around here suck too. So it's always trying to rip the bushing out while twisting and distorting it.
I've had poly bushings in multiple cars and as long as you use the correct grease I've never had squeaks. Gm uses the free sleeved design, in older cars at least, and when they start making noise it's time to replace them. My bump stops will be cones. Red Solo cup shot glasses work great. The poly I have is shore 60 not the really hard stuff you get from energy suspension for trans mounts. Reynolds advanced matierials has tons of options for poly and silicon or even plastic epoxy matierials for so many different uses.

Roncallo · #12 09-17-2017, 04:52 PM

Quote:

Originally Posted by rwd4evr

Yes that is true, in an Ideal World I would put lowering spindles on it that simply move the axle up in the relationship to the ball joints. But nobody makes those for a r/ C107 chassis. So practically speaking if you look at it as a parallelogram with unequal length sides, simple lowering springs put the lower control arm in a position pointing upward from the chassis out. So when the suspension compresses in a corner it will actually decrease negative camber (bad). The lower control arm must be pointing downwards to keep some semblance of the correct curve. Unfortunately I doubt that with the 2-3" lowering I will have I do t think it will be downward anyway. The increase in the distance (with a longer lower ball joint) between the outer upper and lower suspension pivots will however change the angle of the upper control arm at ride height and change the arc the upper ball joint sees effectively increasing the camber curve. I haven't run the suspension program yet because I don't have the measurements but it will be no worse than if it was just lowered by springs only.
High amount of camber are good for drifting because of the way the outer tire contacts the ground at opposite lock.

A bit crude but here's the idea.

How much are you trying to lower. You could extend the upper control arm mounts if you are good with fab. But do increase the bracing.