Trunnions. Angles and greasing

[661]

26GTS build for FIA racing.
I have to say I feel uncomfortable loading the trunnion abnormally by pushing the ball joint rearwards any further in order to gain castor. I found that with the ball joint centred on the top chassis supports it took 2 and a half washers each side to 'nip' the spherical bearings, whilst using 2 std AN washers each side of the ball joint. The ball joint appears to need probably at least 1 std and one thin washer each side to avoid the rubber fouling the TTR wishbones on suspension travel.
I've, therefore put 3 washers on the back support and 2 on the front. The trunnion seems to be OK with this but moving the ball joint back further ( by following TTR suggestion of moving more ball joint washers to the front)seems to make the suspension travel quite rough and the trunnion's poly bearings are trying to distort as the trunnion is angled. That really doesn't look like good engineering principle. So, I'll settle for the chassis ' determined castor plus the 2mm from the 1 extra rear washer.

And for greasing.........
With the solid vertical links, has anyone put a stubby grease nipple in the centre of the bottom surface of the trunnion?

Does anyone use M8 bolts for the ball joint to wishbone connection instead of 5/16 as the ball joint holes appear M8?

[vstibbard]

Hi Graeme,

I ended up running less caster than TTR suggested due to the loading of the trunnion/wishbones. Note the trunnion is designed to run with heavy gearbox/diff (NON LSD) oil NOT grease. My replacement shell is about to leave UK, with the rebuild we'll bring slight offset into bottom wishbones trunnion bolt holes to allow the trunnion to sit at the TTR recommended caster angle and then yet to be worked through either offset bore the lower wishbone nylon bushes, fit a spherical inside the inner wishbone bush with dummy bush like covers!!.

I understand the cars are less nervous with more caster.

V

[661]

Hi Graeme,

I ended up running less caster than TTR suggested due to the loading of the trunnion/wishbones. Note the trunnion is designed to run with heavy gearbox/diff (NON LSD) oil NOT grease. My replacement shell is about to leave UK, with the rebuild we'll bring slight offset into bottom wishbones trunnion bolt holes to allow the trunnion to sit at the TTR recommended caster angle and then yet to be worked through either offset bore the lower wishbone nylon bushes, fit a spherical inside the inner wishbone bush with dummy bush like covers!!.

I understand the cars are less nervous with more caster.

V

I saw your shell at TTR.
I must speak to you in more detail about the castor stuff. I'll P M you when I've thought it through a bit more

[patrics]

Hi,
I was very unhappy about loading the trunnion so on mine I fitted spherical joints to the bottom arms.
No idea if that's okay with FIA

Regards
Steve

[elandoc]

Hi Graeme,

I ended up running less caster than TTR suggested due to the loading of the trunnion/wishbones. Note the trunnion is designed to run with heavy gearbox/diff (NON LSD) oil NOT grease. My replacement shell is about to leave UK, with the rebuild we'll bring slight offset into bottom wishbones trunnion bolt holes to allow the trunnion to sit at the TTR recommended caster angle and then yet to be worked through either offset bore the lower wishbone nylon bushes, fit a spherical inside the inner wishbone bush with dummy bush like covers!!.

I understand the cars are less nervous with more caster.

V

It hasn't left yet? A mate up here had to replace the front chassis member and built in extra castor with angled uprights and matching angle in the bottom wishbone mount. I understand the Series 1 had a lot more castor than later models - not sure what TTR has engineered into his. I use the top and bottom spacer technique in my rally car, but of course am limited by binding.

[661]

The first chassis were about 7 deg I understand and later, including the TTR replacements, about 3 deg.
I want to add degrees without straining/binding the trunnion/vertical link shaft. I may have a solution but it requires some bespoke bushes for the trunnion.

[vstibbard]

Hi Graeme,

It better be on the way by now! Apologies Iv'e not replied to your email, I've been sucked into a work vortex.

V

[vstibbard]

Hi Graeme,

It better be on the way by now! Apologies Iv'e not replied to your email, I've been sucked into a work vortex.

V

[MarkDa]

An old thread now but for the record replacement of 5/16 bolts with 8mm Stainless is almost a no brainer especially in terms of practicality and availability.
I appreciate that the ultimate strength is reduced but in this location not an issue I'd say.

[Frogelan]

I have been watching this subject with interest and have just bought new ball joints from a reputable supplier.

To test out the sizing theory (with thanks to those above), I "innocently" asked for the correct bolts and the supplier was as rattled as much as the correct bolts in the ball joint were...I think this will very shortly become officialised as a metric conversion rather than cheap stock from the wholesaler.

I now need to work out how to deal with the castor angle. As I am about 18 months behind you chaps...all tried and tested ideas welcomed!

[Vali]

With the solid vertical links, has anyone put a stubby grease nipple in the centre of the bottom surface of the trunnion?

Yes, just did it yesterday.
Carefully fitted a 1/4 UNF grease nipple there.
Together with 2K metal glue on the surface to be safe.

[661]

Interesting!

[Billmack]

What you describe is exactly the thing that breaks the uprights. Adding caster on a trunnion type suspension requires a ball joint at the bottom or reworking the inner pivots so the upright stays at 90 degrees to the control arm (looking from face of wheel) a lower ball joint gives the system an extra degree of freedom that it needs to cycle up and down without binding on the trunnion. I applaud that you cycled it up and down without the spring and damper. Probably saved yourself a broken upright and all the extra trouble that goes with it.

[Billmack]

The right way to increase caster using the stock parts would be to cut off the front crossmember and weld it back on at a different angle. I am a fan of extra caster but you gotta be careful how you gain it.

[snowyelan]

Alternatively you can twist both lower arms so the bushing bores aren't perpendicular to the trunnion bushing mounting face (think vice holding the outer mount surface flat and bar thru the bushing bore) and shim the upper arms back to suit This keeps the suspension geometry (pretty much) the same. It does put the shock lower bushing into a distorted state, but the rubber should take up a couple degrees easily. Globally tilting the suspension back will (marginally) increase dive under braking.