Front Control Arm Bushings Slipping

[NitroDann]

It can only do what you're describing if the bush is able to slide within the arm itself.

There are millions of people using these and must be hundreds of thousands in track cars. Poly bushes are not new. It has to be something with your car or install.

You mentioned painting the arms, did you paint the surface the bushes sit in? Im just trying to work out why this is such a rare problem but yours is doing it nonstop.

Dann

[Luke]

I painted them before removing the original ones.
There is factory paint in the holes. Super shiny and smooth.

[Ned Loh]

The bush is moving in the arm. Pin the bush in the arm. Many have done it. No need to reinvent the wheel.

[Luke]

The bush is moving in the arm. Pin the bush in the arm. Many have done it. No need to reinvent the wheel.

I would pin the bush in if I were to continue using Poly.
But as many of the other experienced MX-5 racers have told me they perform worse ie slower on the track than standard rubber ones let alone hard rubber competition ones. I have proven that to myself as well so I'm not going back to Poly.
Like the link earlier in this thread for the bushing mega thread, I now also agree Poly is the worst material to use for this application.
The car feels like crap with the Poly ones up front.


I have never heard of anyone pinning rubber ones in. Only Poly and Delrin.
I would imagine with the rubber being flexible and the fact that it flexes within the arm whilst the centre pin is locked the bolt or screw used would just tear through the rubber over a very short time.
Anyone done it with rubber???

[greenMachine]

Luke, I would measure the internal diameter of the housing, just to be sure there is nothing funny there.

In your post above you talk about something that is 'super shiny and smooth' - if that is the bore of the housing, I think we have the answer to your problem! I don't think it is meant to be 'super shiny and smooth'.

First up, I would thoroughly clean the inside of the housing (all of it in fact) to get rid of any traces of grease, and then maybe rough it up a little, bit like honing a bore. You need a surface that will grip the rubber/poly/whatever, but don't go overboard - maybe just use a light touch-up with fine wet and dry.

If you really want to make the rubber grip, then get a rubber/steel adhesive and use that as your lube when installing the bush. I have never heard of anyone doing that, but desperate situations call for desperate measures ... I am not sure how much would remain after the bush has been inserted, but as a last resort it would be worth a try.

I agree, I would not pin a rubber bush. The way the rubber deforms between the bonded-in pin (the one held by the suspension bolts) and the surface (hopefully) held by the housing as the arm (housing) rotates would have the effect you describe. Poly/delrin are different because they are not intended to deform in the same way.

[StillIC]

I would use a Sikaflex polyurethane adhesive and bond the rubber bushes into the arm. Follow the directions, clean and prime the surfaces properly then cross your fingers.

[Magpie]

http://sadfab.com/bushingpackages.html

[Luke]

Yes the bore of the housing is shiny and smooth.
They were full of Mazda factory black paint.
There was not a spot if rust or anything in the bores when the originals came out.
I would be very confident to say that no one has touched the bushings in this car before me as I bought it at 5 years old with very low k's from a one owner who never once drove it in the rain.
I cleaned the housing with brake clean before putting the rubber ones in to make sure there was no contaminants from the poly grease.

[Luke]

Through a couple of guys I have been talking through PM's we may have found a contributing factor on my Lower control arm bushings issues.
It seems the more Caster I have the worse the problem is.

I have read that generally the maximum you will get is 5.5 degrees on most US Miata performance sites and they all say max out the caster if it does not sacrifice your targeted camber. This figure would be with reduced negative camber to achieve it. Most running lots of negative camber without any arm or bushing modifications are lucky to get 4.5 degrees of caster as increasing negative camber takes away caster.
See below factory workshop table for front alignment specs.
It indicates you achieve more Caster as you lower the car but stops well short of my ride height.
I am at about 310-315mm centre of wheel to fender height so I gather that's why I can get more Caster plus my upper offset bushings would likely change the geometry as well.


I was able to achieve 7.5 degrees caster maxed out with 3.25 degrees negative camber and I could have taken the negative camber even further.
This is how I had had it aligned the first and time when I absolutely destroyed the ES bushings at both the Rear Caster Mount and Front Camber Mount.
The 2nd time with Superpro I just had the Caster backed off to about 6.5 to 7 degrees with the same effect but at a lower rate.

Now the part that led us to the Caster causing the issues.
The third go on Poly with Superpro on the Caster and ES on the Camber, I only destroyed the right side bushings. The lefts were perfectly fine. For some odd reason the aligner adjusted the left Caster to adjust the camber which minimised the left caster. I just ignored it and took the car with it. I don't have the printout but the left caster was about 4 to 4.5 degrees or so. The right was around 6.5 degrees.


Now at the rear caster point I don't believe the Poly was being initially cut by the arm after further analysis of the bushings.
Looking at the way the bushing sits I am more inclined to say the Subframe mount point is where the bushing started being cut. It overhangs 2 parts of the edge which have a 90 degree angle on it. It looks like my cuts started at these points then were further by the arm shoving into these initial cuts. The cuts were always a V shaped chunk taken out of the bushing which can be seen in my first post quite clearly.
I would take a guess that under braking forces the arm would want to move back causing the Poly to flex over the mounting point and then with the arm moving up and down over the bumps, the steel edge of the mounting point would slowly dig into the Poly.
These below pics should give you an idea why I am saying this.
Mounting point with no bushing.


Max Caster it overhangs.

Min Caster it is well within the mounting area.


The front Camber mounting points are different. They have more steel around them so the bushings never overhang.
I think they would have started cutting through once the rears were already gone as all the forces would have been going into them at this point. These ones are definitely the arms going through the lip as they just cut a perfect round lip off where as the rear points always had a V cut out off them at the outside edge.


That leads me back to the rubber bushings sliding.
I'm inclined to go with the Turbo Miata Bushing thread regarding rubber ones sliding around a bit being normal when using R-specs, race pads etc.
The rubbers ones don't even have a lip on the rear Caster point to help prevent the sliding.
The front Camber points do, my OEM ones were cut off after 13 years of use. The new I.L ones are still nice and pliable so no damage to them observed.

I had 6 Degrees 10mins of caster on the right and 5 degrees 50 mins of caster on the left with the I.L rubber bushings.
The rights side bushings moved more than the left as below.
Top of pic is front of arms, left is left arm and right is right arm.
Front camber mount.

Rear Caster Mount



Where I go from here.
Well I have figured I can just reposition the rubber bushings with a vice or threaded rods using a 36mm socket.
I already have centred them using a bit of degreaser as lube.
I may move them 1/2 to 3/4 out to apply some adhesive as suggested then push them back in.
I don't want to push them all the way out as I won't get them back in just with a vice requiring another visit to someone with a press.

I still will try the washer and it looks like toilet cistern seal at the rear caster point to physically prevent some of the sliding.

The next alignment I will go for 5.5 degrees of caster as a max figure.

[Magpie]

Why do you need so much caster? It sounds like there are other issues at play down there...

[Luke]

More caster is supposed to be better is it not???
Active camber whilst steering.
Better steering feedback and self centering.
More stable at high speeds.

I know the disadvantage is less rear traction the more caster you go. When I Was at 7.5 degrees the traction in tight corners was crap.
Also heavier steering which is invalid to me because of power steering.

Wheel alignment computers come up with 5 degrees 50mins +- 1 degree as the recommended range for a NB8B which is probably because that is the Mazda spec at standard suspension height.
I'm not exactly going to any value that is not possible looking at the workshop manual.

Its just I have never read anything in forums, online etc about people running more than 5.5 degrees on track.
So I tried it anyway and have seemed to found the result of doing so.

So my question is has anyone else tried to run more than 5.5degrees of caster on a NA or NB for track use?

[Magpie]

Most track cars will run 3-5 deg caster.

The outside wheel in a turn to gain negative camber, while the inside wheel gains positive camber. However it is possible to go too far. Further, greater caster causes steering effort to increase whilst aiding straight line stability. Less caster makes the steering effort easier.

[Luke]

Ok.
From my understanding low caster is for Manual or de-powered racks. Generally they want about 3 to 4 degrees max otherwise it just becomes to heavy.
Steering effort does not affect me so much because of the power steering.

The extra Caster I have had has been really good at the high speed SMSP GP and North circuits.
Most corners are just big sweepers with lots of straights.
Around the high speed turn 1 the car is so easy to drive compared to before on the original bushings where I Only had about 4.5 degrees of caster. It is much more stable with the 6+ degrees. I made up heaps of time through Turn 1 alone. The 2 hairpins have been a struggle for traction though.
Around the tight and twisty SMSP South circuit I had more traction issues than ever with higher caster values.
So I have probably gone to far.

From what I have observed the extra Caster would seem to be creating more stress on the bushings, so I will go back to 5 to 5.5 degrees and see what happens as SMSP GP is up next again.

[Magpie]

I had about 3 deg of caster at SMSP last year, with a depowered steering rack with no issues. Car went well, not fast but a 1:53 around 160 apex T1 and 72 T2.

Caster will have little impact on grip (puts on fire suit), camber/toe/damper settings, tyre pressures and spring rates will have more impact. Is the lack of grip under/oversteer?

[Luke]

No grip problems. I don't think I was complaining about grip other than traction in tight corners??? Well here is how my car feels anyway.
I do 1'49s around the GP circuit. My T1 Apex hovers between 165 to 172. My T2 is around 67-71.
I would say I have more front grip than rear grip. Understeer is not a problem.
Initial Turn in is good.
I suffer inside wheel spin in the tight corners. I know higher caster values affect this as the outside front lowers as you turn more, causing the inside rear to raise. Stupid Torsen is probably the biggest problem here though but I'm stuck with it for the category I run.
I can get sideways on the exit of the low to mid speed corners, but that would be more due to power than anything else.
I would summarise the car as a little on the oversteer side. But very stable at high speed. It has been very rare that I have even put a wheel off with the current setup.
When the car was completely standard suspension wise the car oversteered badly as all standard SE's did and felt unstable at high speed leading to a few offs.

My Last Alignment which by the way felt awesome at Wakefield Park was:
Front
Left Toe: 0.0mm Right Toe: 0.0mm
Left Camber: -3°19' Right Camber: -3°20'
Left Caster: +5°49' Right Caster: +6°10' Aim to make these 5°30' next time.
Rear
Left Toe: +1.6mm Right Toe: +1.9mm
Left Camber: -2°26' Right Camber: -2°37'

Note the rear end was not touched as it was done a couple weeks before where Toe was exactly +2mm each side.
And its Positive Toe In at the rear, not Out like I said in my first post.

Suspension
Front/Rear rake angle of a tiny bit lower in the rear, a few mm from memory. Sill heights can't be measured at the moment as the car is on stands. Lets just say low for now.
Tein Street Flex, Front 7kg and Rear 6Kg. Dampers I set per track and fuel load. Between 9 and 12 out of 16.
Standard 23mm Front Sway bar with 949 adjustable links and RB brace blocks.
No Rear Sway Bar. No rear was to balance out the bad front/rear spring ratio Tein supply. With the rear installed there was no traction on the inside wheel and the car was easy to spin. Even on the out lap.
Tires are adjusted to Maximise wear. Around 30 to 31 PSI on the Yokohama A050's. I wear the rears more than the front at SMSP and Wakefield they wear more evenly front to rear.