Alfa Ricciardi: How much force goes through the lower trailing arm mounts?

[tjb0274]

Enough to do this, apparently....

[NOTE: Quick update to highlight that the bracket in question is on a Ricciardi (Australian 105-based sports car) - the mount in question is different to the stock 105 item because it allows for adjustment of the trailing arm, and because it is welded to the spaceframe rather than a tub).

[Thevak]

Depends, how big is the driver?

[Colin Byrne]

Like most of life's problems this one can be solved by welding!

Looks like a bit of bracing wouldn't go astray there either, very minimalist mount design...

The trailing arms take the reaction force from braking/accelerating so the go through very cyclic loading

lucky you caught it when you did

[tjb0274]

Like most of life's problems this one can be solved by welding!

Looks like a bit of bracing wouldn't go astray there either, very minimalist mount design...

The trailing arms take the reaction force from braking/accelerating so the go through very cyclic loading

lucky you caught it when you did

  Yep, Hugh is going to improve the bracing during the repair. Will also apply the same improvement to the other TA and to "last" Ricciardi chassis that Monza are currently completing for another customer.

Interesting question of whether this was the result of cumulative wear and tear (car is 25 years old this year) or a particular incident (I did bottom the suspension out in the Winton paddock during the 6hr weekend).

Either way, really really glad that it didn't break at Broadford.

[LaStregaNera]

Been getting any brake hop in the rearend?

[Colin Byrne]

looks like a fatigue failure to me, is there any corrosion at the start of the cracked metal?

[tjb0274]

looks like a fatigue failure to me, is there any corrosion at the start of the cracked metal?

I don't think so, but it's possible. Need to get the bulkhead panel out to get a really good look at it from the top.

Been getting any brake hop in the rearend?

Interesting question - no, but now you mention it I was getting some judder and wheel skip accelerating out of the slow right hander at Broadford. I assumed it was the LSD locking/unlocking as the axle hit the anti-droop strap (which needs lengthening) and picked the inside wheel up a little.

[vin sharp]

Looks like fatigue over bad design....the mounting should have been made at least as strong in all stress directions as the stock 105 mount is, and should be attached to something of equal integrity......this one look like a nice pot-plant hanger, but maybe not a suspension anchor!
Perhaps a good case in point for why changes to club registration rules are being made.
Cheers,
Vin

[tjb0274]

Looks like fatigue over bad design....the mounting should have been made at least as strong in all stress directions as the stock 105 mount is, and should be attached to something of equal integrity......this one look like a nice pot-plant hanger, but maybe not a suspension anchor!
Perhaps a good case in point for why changes to club registration rules are being made.
Cheers,
Vin

No argument that this is a weak point that should (and will be!) addressed, but I'm not sure more inspection of the design/implementation would have made a difference. This isn't a home-made modification, it's part of a chassis that was designed by experienced mechanical engineers to meet the ADRs circa 1990. Both the design and this physical chassis were engineer-inspected by road authorities and approved before the car was originally registered. This particular car has been on hoists in any number of workshops, and this design flaw has never been picked up.

I had thought that the changes to the permit rules were to weed out inappropriately modified or poorly maintained cars. Personally I welcome scrutiny of my car and suggestions to improve it - I certainly don't want to find myself heading into a wall (or worse, someone else's car) because of a mechanical failure - but if club inspections were to start questioning unmodified designs that are road-legal and ADR compliant, I can imagine there may be pushback from some quarters, and I'm not sure where the club would stand. Is it legally defensible to demand a higher/different standard for a club permit than for a standard registration?

[Mick A]

I think this is a can of worms best left unopened for now to be honest.

[LukeC]

For general info:

There are few mechanical components of vehicles that are only required to have physical testing for strength to be certified to the ADRs.

The ones that do are mainly ones related occupant protection: ADR 2/-- (Door latches and hinges), ADR 3/-- (Seats), ADR 4/-- (Seatbelts) etc....

Collision ADRs (69/--, 73/--) are measured with the resulting forces on an occupant (Crash test dummy): forces measured by load cells in the head, neck, legs etc.... How this is achieved is not specified (be it vehicle design through crumple zones, an airbag or blow up rubber duck etc).

ADR 62/-- (Mechanical connections between vehicles) include fatigue... These include the actual coupling components, towbars and drawbars that must be tested by cyclic testing (for fatigue) and/or static loading.

The design and safety of a vehicle outside the requirements of the ADRs (e.g. strength and durability) such as the chassis and suspension components are governed by the Australian Consumer Law (ACCC): Fit for purpose / Will or may cause injury for expected life and usage of the vehicle.

Modified, kit cars and ICVs get a bit greyer: This is where the authorities basically take a bit of a step back and let an Automotive Engineering Signatory decide what methodology they wish to use to certify a chassis design or modification. This may be as advanced as Finite Element Analysis, simpler such as comparison to existing design, or crude as: bigger is better! Whatever method they choose, they wear the risk of litigation if someone gets hurt (hence a requirement for rather expensive insurance that must be maintained by the engineer for several years should they cease certification work).

I agree with Vin. As an engineer, I say it is one piece one of B-grade auto design/manufacturing... A simple visual analysis of the force vectors on the mount shows the likely failure mode (which is what happened).

[tjb0274]

For general info:

...

Thanks - some useful detail 

I agree with Vin. As an engineer, I say it is one piece one of B-grade auto design/manufacturing... A simple visual analysis of the force vectors on the mount shows the likely failure mode (which is what happened).

Indeed - I don't think anyone disagrees (certainly not me!). My point was that a lot of qualified people have looked at the design and the chassis over the last twenty five years and either not spotted that, or not believed it was a big enough problem to change it.

It will be changed now, on my car and on at least one other chassis, and part of the reason for posting this thread was so that other Ricciardi owners might find it if they do a search for Ricciardi material online.

[vin sharp]

On most production cars where problems like this show up, they are generally found in the same circumstances and then the shortcomings and alternative fixes can be worked through. At that point it becomes a check and fix as cars come in.
I don't think there is anything different in this case; yours probably being the first to show the problem. On inspection and with the failure in plain sight it is easy to see why it happened.
The main thing, as you say, is to now notify and or check with others of the model to avoid other failures.
These cars were Rick's (Hardy) pet project in his shed between court appearances......no nothing shifty, he was a sitting magistrate at the time!
I visited Rick at his house when the first couple were being made. I believe that under the SA regs at the time, not a lot of engineering certification had to be done because they used part of the original 105 firewall/front end which allowed a short cut to registration as an Alfa Romeo of whatever year the chassis number was.

[tjb0274]

I visited Rick at his house when the first couple were being made. I believe that under the SA regs at the time, not a lot of engineering certification had to be done because they used part of the original 105 firewall/front end which allowed a short cut to registration as an Alfa Romeo of whatever year the chassis number was.

That would have been interesting! I've heard differing reports on whether Rick still has his car.

My info is the same - there was a registration short cut based on the amount of 105 chassis retained, but I'm not sure what that actually entailed. I've seen documents asserting that the design is ADR compliant for the late 80s/1990, but as Luke points out above, that might not mean a lot!

I know that there was an engineering report done for the overall design - I saw a copy a few years ago and it was certainly long, but I don't know how comprehensive/thorough it was. I recall looking through diagrams of the various chassis sections showing load in the various directions and calculations for the required strength, but I don't recall whether the suspension mount points were part of that. I've been trying to get my own copy of that document for some time.

[giulia_veloce]

Have been reading with interest and the replies.

Just my opinion,,

its not a 105 original front mount for a rear lower control arm.
The pictures show a 3 hole mount to lower or raise the arm,,which is not original,
Originally,a 105 has a single hole to mount the arm to the body.

The above car is a modified car with a modified suspension mount that is not a 105.
As Colin B says,,extra welding,especially above the modified bracket,,would have maybe been better.

The car is not a 105,,it does not have a factory pick up point part (3 hole mount),so I can not see what the fuss is all about.

This topic should be put in another area= modified cars ,so not to confuse Alfa 105 owners,or potential 105 owners about a problem that does not exist.