105 Targa Car Version 2.0

[Evan Bottcher]

Looking forward a little bit, Colin, are you going to replicate your old car? 2000GTV front grille and Alfa red?

Also, what's the reasoning behind the steering box change?

[Colin Byrne]

Hey Evan,
yea just for something different the car will be 501 red (exactly the same as my old car) and 2L grill, tail lights ect, i have to make it into a 2L so i can run the engine, and diff within the regs.

Couple of reasons for fitting the rack. the first and most important is I like making my life as difficult and complicated as possible.  Second reason is the steering box and idler arms arm attached to a very weak point on the chassis creating significant compliance in the steering.  The idea is to attach the rack to the super strong engine cross member.

The old steering box's are getting a bit worn now too, so doesn't matter how many times you re build them, they will always have some slop.  I've found a rack specialist in Queensland who can fully rebuild the rack I've chosen, even to the point of adding special arms with the correct thread for my rod ends.

a rack is generally more efficient, i'e less steering force required, and there are also less tie rod ends to keep track of, should be a bit lighter too.

cheers

[Colin Byrne]

got onto the brakes this weekend,  coming up well

Also will be putting my original brake pedal box up for sale so let me know if your interested

http://105rally.wordpress.com/2014/10/19/the-cat-mrrreeeooowww-is-out-of-the-bag/

[tjb0274]

a rack is generally more efficient, i'e less steering force required, and there are also less tie rod ends to keep track of, should be a bit lighter too.

cheers

Hi Colin -

Have you worked out a location for the rack that allows good steering geometry? 

The Ricciardi has an Alfetta rack mounted on the 105 crossmember, and uses the standard 105 uprights (with shortened springs), tie rods and steering arms. The bump steer has always been pretty bad, and the Ackerman doesn't seem to be correct either - very bad understeer at extreme steering angles, which doesn't affect me on the track, but would be a pain in motorkhana events. The bump steer was significantly improved by installing "quick" steering arms (I think they're Vin's design, but can't remember for sure now), but it's not completely cured. I think the rack would need to be moved to fix it properly, but there isn't really the scope to do that with the Ricciardi chassis layout.

[Colin Byrne]

as you can imagine there's not a huge amount of options for rack location, but from preliminary fitment it looks like it will end up in a very similar location to the steering/idler outside points but a bit lower.  This may actually help with bump steer as it will be in a closer arc to the lower arm, but i'm sure there will be much adjustment to get it right

very early on i did look at an Alfetta rack but from memory it was much much wider than the outer pivot points of the original system so not really suitable, maybe this is were the Ricciardi runs into problems with ackerman?  The rack i have selected is from a Ford laser, i got into contact with a very helpful guy in Queensland who helped out with the selection

http://www.ultimatepowersteering.com.au/

although this will help with geometry, it makes for difficult fitment as the output pinion is very close to the relatively wide ali block, but if it was easy everyone would do it!

[tjb0274]

Ah - I'd never thought to check the rack width, but I daresay you're right.

I should dig out the suspension modeling software and set up a few scenarios to try....

[Colin Byrne]

nearly finished off the brake pedal assembly this weekend

http://105rally.wordpress.com/2014/10/26/the-cat-mrrreeeooowww-is-out-of-the-bag-2/

[tjb0274]

Ah - I'd never thought to check the rack width, but I daresay you're right.

I should dig out the suspension modeling software and set up a few scenarios to try....

Happened to be thumbing through my copy of "Tune to Win" the other day, and re-read the section on Ackerman. Interestingly, according to Carroll Smith quite a few race engineers in his day would modify steering geometry to dial the Ackerman correction *out*, in order to avoid scrub in medium and fast corners. Smith's view was that it wasn't a big enough deal to worry about.

[LukeC]

The old steering box's are getting a bit worn now too, so doesn't matter how many times you re build them, they will always have some slop.

I will disagree on that one... If they are reconditioned properly, not just selecting the best bits available and shimmed to suit: they will have NO play. 40 odd 105 steering boxes over 25 years under my belt including 10 this year says I have the authority to state that. It is a very cleverly designed steering box that apart from wear in the sector shaft bushes/shaft and ball races in the column shaft self adjusts itself.

But yes, the mounting is not as rigid as it could be. Sorting out positioning to dial out bump steer is fun stuff with rack conversions is callenging though if you want complication. I've only done it a couple of time myself... plates, dial indicators etc......

I agree re Ackerman: I remember from reading Milliken and Milliken (race car vehicle dynamics) that race cars normally had minimal Ackerman. But I think we are talking full purpose built circuit racing cars here.

[Colin Byrne]

apart from wear in the sector shaft bushes/shaft and ball races in the column shaft self adjusts itself.

The wear in the ball races themselves was what I was sort of referring too, do you find this isn't an issue?

[LukeC]

The actual bearing running surfaces (cone and cup parts) can both be resurfaced. The case hardening is very deep (> 1.5 mm) so will cope with this. I used to have this done in engine shops on crankshaft grinders, but since have made tools to do this on my own lathe.

The 9/32" (shudder - imperial!) balls are about 10 cents each (~$5.00).

The lower shaft race is the first usually to wear, which while is a bit dearer than resurface is easy to replace with a tapered roller bearing which will outlast most of us. The top is more tricky.... It is possible to do this and retain the steering lock or just delete the steering lock (OK for race and rally applications). Non-steering lock cars are a snap to add tapered top and bottom bearings.

[LaStregaNera]

To confuse the Ackerman thing even more, some go to a reverse Ackerman to reduce the drag from the very lightly loaded inner front, given that the outer will be working at a couple of degrees of slip angle....

[Colin Byrne]

I was more concerned with the ball race within the actual re-circulating section, pretty much impossible to fix that up once its worn?

To confuse the Ackerman thing even more, some go to a reverse Ackerman to reduce the drag from the very lightly loaded inner front, given that the outer will be working at a couple of degrees of slip angle....

From my experience, Ackerman is very much tyre dependant and whilst it can make a big difference at lower speed tighter corners, isn't as critical at higher speeds.  In our Formula SAE car we ran over 200% Ackerman due to the tight "motorkana" style course

Latest update to the build here

http://105rally.wordpress.com/

[Evan Bottcher]

Excellent video Colin, and you only dropped the f-bomb once!

[LukeC]

I was more concerned with the ball race within the actual re-circulating section, pretty much impossible to fix that up once its worn?

I have never seen significant wear here... Only time I have seen one unserviceable nut was from one that was left in the weather with no oil or filler plug. But then, the only part of the whole box that was useable was the aluminium casing.

Apologies for the long winded explanation, but I will try to explain for general info: The axial load on the recirculating ball nut when turning is the same as that on the shaft cup and races. However, whereas the races have only several bearings each over 360 degrees (I can't remember what actual number top and bottom), the nut has 540 degrees of balls (at a larger diameter). My guess is that the force transmitted through this part is shared over about 20 balls. The result is that this part never gets pitting on the bearing faces. Likewise the worm on the shaft (and that the loadings are constantly shifting along the worm).

The shape of the actual bearing surfaces (worm and nut) do not mirror the bearings (i.e. radius ½ 9/32"). While the groove that the balls run in looks like a "U", it is a bit closer to a "V" than a "U". The result is that the balls bear on the side of the "V" not in the root of the "U". Inspection of the bearing marks on the worm confirms this. This shape gives that advantage of when the nut is loaded from above (by the spring under the small elliptical cover on the top of the box), all play is removed between the nut, balls and worm. The clever thing is that where spring load is (the top of the nut), is where there are two rows of balls. This is why I say the box "self-adjusts" itself.

One a box develop play, it is wear in the bushes/sector shaft and or the column shaft bearings. Removing shims (as some people attempt will not solve the real issue).

When setting up a Burman box, the final adjustment is the clearance between the top of the sector shaft and this elliptical cover. Alfa specified .2 mm. I set them up to even lower, as long as there is no bind anywhere from lock to lock. This prevents that sector shaft riding the up the nut under load.

One of these boxes set up with ~.001" clearance on the sector shaft bushes, slight preload on the worm shaft bearings and the top cover adjusted as above will give a box that is silky smooth and no perceptible play.

I initially started rebuilding these boxes by using the best parts on hand from cars I had parted out. Now I find this is near impossible. Besides, I now use a superior synthetic lower bushing material.