1973 AC Model 70 Invacar, Visitors & Occasional Distractions

Had a chance to have a closer look at the new hub today.

Felt like a bit of a vandal peeling off the waxy coating which has kept it looking like new for decades, but needs must and it's done its job very well.



Once this was removed a rather interesting number appeared.



This appears to relate to the actual technical service drawing numbers rather than an actual part number. This is one of only two parts we've seen these stamped into so far. Doesn't actually mean much, but it's the sort of detail that's interesting to find for a marque enthusiast. I'd assumed this was just an internal AC part number until a friend) who I reckon has memorised pretty much every technical drawing and parts catalogue for these cars by now) corrected me.

Looking closer it's obvious that while the studs have not been welded in, the ends have been stamped to prevent them from being unscrewed easily.



I have a feeling that if I go start trying to pull these with the tools I have here I'm just going to make a horrible news - even after I figure out how to hold onto the hub assembly without a working vice just now.

I'm a bit hesitant to just attack the rear face of these with the grinder or to apply brute force without knowing for certain what the best way to remove these actually is. I do wonder if the correct answer is to go in with a lathe and just machine off a tiny sliver around the rear head of the stud to release it. Sadly I don't have a lathe so am looking in your direction glenanderson - you reckon getting these out is something that would be easy enough with access to your kit? Obviously I'm more than happy to give you something for your time.

Second that, would follow Blackpop's advice and do pull-through studs which allows you to just drill and ream plain holes- and if the stud gets mashed up in the future, you are a hydraulic press away from new ones.

Phil

definitely get an imperial gauge, otherwise you'll get me this monday, very-nearing and thread-pitch-gauging a land rover front spring U bolt, then confidently declaring it M11x1.4, which doesnt exist.

7/16” x 18tpi - BSF. 😉

If it were mine,I would take the hubs off,put them in the milling machine, Machine the holes out to the desired size for press in studs,counterbore the holes from the back to get rid of the 45 degree chamfer, and press off the shelf available studs in. End of grief...😊

I'll need to take a closer look at things this evening and have a think.

Switching to press in studs will require machining of the hub. To get that done I'll need to find someone willing to do the work. The first three machinists I spoke to around here weren't willing to make modifications to a suspension component, presumably due to worries over liability is something failed down the line.

I think rather than just milling away material to eliminate the 45 degree slope on the hub it may be necessary to build it up with a welder. I fear that if you milled it away you'd be left with a hub that's effectively about 5mm thick. The holes are already quite close to the edges as it is given the hub was originally designed for a 4X98mm bolt pattern, so things have already been pushed towards the outside.

Sadly it won't make changing studs in the future a ten minute task as the hub will still need to be removed from the car as there's virtually no clearance behind it. I suspect this may be why screw in studs were originally used. Hopefully there would be just about enough clearance to allow the head of a press fit stud to clear the brake cylinder.

I'll try to get a few clear photos later today and hopefully get the hub pulled.

If you need them doing, pm me and I will let you know what it will cost.
Cheers
Johnny 😊

^^^^agreed!

Right, I've actually had the opportunity to sit down at an actual computer this evening so have been able to do a bit of proper research for information on the hubs themselves. Specifically I wanted to try to get better to the bottom of what the deal is with the hub pre-load. 99.9% of the time these days I'm only able to work from my phone, and I only have so much patience for trying to figure things out on a tiny touchscreen.

I'm glad I did.


The rear suspension arms, springs, stub axle, driveshafts, wheel bearings, bearing carriers and hubs* are straight off the Fiat 500 and I believe latterly the 126.

(*With modification carried out at the AC/Invacar factory to suit the BMC stud pattern).

This is a good thing and a bad thing. Firstly is that it means that the driven hub assembly is actually relatively readily available in new or reconditioned form at a reasonably sensible price.

The less good part of this is that a sacrificial crush washer used when initially during the assembly - which allows the precise setting of the preload (to 0.36 lbft of rotational resistance), and sometimes results in issues with play in the hub assembly if the washer is reused.

The bit we're looking at is the stub axle, the inboard end of which is bolted onto the driveshaft itself and the outboard end held in place by a carrier. There appear to be two types of these - they're basically identical in every way except for the number of splines at the driveshaft end. One has six splines, the other considerably more (haven't seen an exact number quoted yet), I'd expect this to be the one with the finer splines as it *seems* that the six-splined version was only used on the Fiat 500D.


None of this actually affects the fact that I'm going to pull the hub next time I get a chance, but it's nice to reduce the number of surprises waiting for me - and to have actually figured out what the vague "you must use special tools or the world will end" waffle about bearing preload is actually about.


Given I've had a very generous offer to "sort the hub out" here, I'll definitely be taking advantage of that. Between lack of experience and lack of equipment to really deal with this I'm most likely just going to make things worse. It's the sort of thing that in the future as my workshop situation improves I'll hopefully be better able to look at more closely...but not now!

I basically want this car to be usable, and as such I don't really honestly care whether splined studs are fitted or whether the hub is drilled and tapped with a completely new set of holes to take widely available bolts. That decision is one I'm happy to leave in the hands of those who are actually doing the machining work. Given one of the holes is already quite mangled courtesy of my ham fisted attempts to drill things out, the latter may well be easier.

My intention would be to get both the rear hubs done - though given the way the car is situated in the garage it will have to be done one-at-a-time as I can only get to one side at a time without completely blocking off access to the far end of the garage which is also used for storage.

I really appreciate the offers of help and patience folks have shown here.

With the next update that we should hopefully have a dismantled hub in front of us!