Front Hub to Steering Knuckle bolts

[Lee]

When putting together my front bearing to steering knuckles (Corvette 86ish) I notice that the holes in the bearing and in the knuckle are different sizes. The holes in the bearing are about 12mm, while the holes in the knuckle are about 10mm. Do they use a special bolt for this job, or do you just use bolts which fit the smaller hole(knuckle)?
Any guidance appreciated.
Thanks

[Malcolm]

My reaction is to say do not use a simple 10mm bolt as that will slop around in the 12 mm hole causing you all kinds of grief. Need to see a picture to give more input as I don't know corvette stuff.

[Peter D]

I am not sure that I have the full picture, but if you are talking about the mounting of the ball joint on the end of the steering rack's arms to the short arms that are part of the hub/upright assembly, then I think you'll find that the stock Corvette "Knuckle / tie rod end" comes with a tapered bolt pre-fitted & that it goes up into a tapered hole in the upright's steering arm.

If you can post a pic or 2 of your problem, we should be able to sort it out.

Kind Regards,

Peter D.

[Lee]

Here are a couple of photos. The bearing is held to the knuckle with 4 bolts (or something). On the picture of the knuckle you can see where whatever was previously attached also had bigger holes. The 4 holes in the knuckle are about 12mm across, while the 4 holes in the bearing are about 10mm across. The 72mm (approx) diameter recess locates the bearing, in that it will stop it moving up and down, or back and fro, but if the bolts were loose, it would allow the assembly to rotate a couple of mm.

[Malcolm]

Well a picture says a thousand words alright! Your query is now a completely different one to the one I imagined!

I have never seen an assembly like this before but it could be that the right hand picture ie upright has enough meat on it so that the holes could be opened up to 12mm. See what others say though before you rely upon my opinion!!!!!

[Peter D]

Aaaahh - now I see what you are talking about ! Are you sure that you have got the correct hub assemblies for the '86 Vette uprights ? I know there were some major changes to the Vette rear hubs from '87 to '88 (handbrake, etc - don't even ask !), so maybe there were some changes to the front hubs as well (eg hole sizes) ?

The reason I suggest this is that your hubs have the toothed wheel for ABS (ie - late model), but the upright doesn't seem to have the access port for the ABS sensor (ie - early model).

PS : Don't be tempted to buy Taiwanese hub assemblies - I got 2 new front ones which had more bearing run-out than the crappy ones I was replacing ! Go for genuine & correct-year GM parts only !

Kind Regards,

Peter D.

[Lee]

Thanks Peter and Malc

As you can see from the picture of the knuckle whatever was previously attached also had big holes, so I guess this is not something out of the ordinary. The bearing assembly is, I believe, now generic - you get the toothed wheel whether you need it or not.
Because the bearing is located radially, which is the important bit, I think it will be OK just bolted up with normal bolts, but I was hoping someone could confirm the usual arrangement, (and confirm that what was previously attached had large holes as well)
All the best

[Peter D]

Lee, my "generic" Taiwanese hub assemblies came with the toothed wheel (& lots of run-out), but the "correct" GM hub assemblies for my '87 uprights came with no toothed wheel & no run-out.

Before you commit to the new hubs & widen the holes, it might be worth clamping them in a vise, bolting a long bar across a couple of studs & checking for run-out (there was no way I could pick up this problem by manipulating them by hand).

Kind Regards,

Peter D.

[Lee]

Thanks very much Peter, I'll do that.

What about the holes on the GM bearings? Are they small to match the knuckle or are they still the large size? I still don't get what the marks on the knuckle are from. Perhaps it had a replacement bearing like this on previously? Can you or anyone confirm the size of the holes on a geniune GM bearing?

[Peter D]

Lee, I managed to measure the ends of the bolts at 3/8" (close to your 10mm hole size for the hub assembly plate - probably is 3/8" as most Vette fasteners were imperial, not metric).

As far as I can remember, the holes in the hub plate & the knuckle were the same, & the bolts were a firm push-fit.

So it is beginning to look like someone has enlarged the knuckle holes.

My guess is that the best approach would simply be to sleeve the knuckle holes down to 3/8". I would not bolt things up with the different sized holes - admittedly, it might be ok for all lateral forces & forward braking, but you can bet that one day, you'll jump on the brakes going backwards & the the whole lot will go "clunk" - then the trouble will start !

Tom Falconer of Claremont Corvette in Snodland seems to the Vette guru in the UK - might be worth touching base ?

(BTW, I can't believe you UK guys have a place called "Snodland" !! It makes some of our aboriginal place names almost sound poetic) !!!

Kind Regards,

Peter D.

[Lee]

Thanks Pete. Actually it would be the bearing which needs sleeving down to match the knuckle. Unless anyone comes back with something different, I think that is what I will do (but first I'll check the runout)

Thanks again
Lee

[Ian Anderson]

How about making your own bolts

12mm shank turned down then with 10mm threads cut

Not too difficult to make

Ian

[Mark Worthington]

I wouldn't want to use cut threads on a critical fastener in the steering/suspension system. I'd go with the sleeve approach.

[Mike Dozier]

Lee

My front suspension is apart...I'll take a look tonight.

MikeD

[Paul Thompson 'Hooligan']

Hi Lee

I have no experience of DRBs, but looking at your problem, if 10mm bolts are considered to be strong enough then as also mentioned, machine a small spacer to slot on the bolt and prevent it slopping about in a hole that would otherwise be too large. Obviously make sure the spacer is very slightly thinner than than the flange into which it is being inserted, so that the bolt clamps the correct parts when torqued up...

I must say though that for what they are doing, (holding bearing carrier'hub to upright) I would have preferred 12mm bolts to be sure...(i.e. 1/2" instead of 3/8")

best..

[Mike Dozier]

Lee

I have several sets of original GM knuckles and bearings...and they are all
the same arrangement as you photographed.

First off...most C4 suspension/brake bolts were metric....no idea why.
The bearing/knuckle bolts are definitely metric (heads are marked 10.9).
The holes in the bearing are indeed larger than need be...again no idea
why...maybe someone at GM had a bad day. However the holes in the spindle
are pretty snug and pretty thick....so those bolts aren't going anywhere
when properly torqued.

As near as I can tell...GM used the same arrangement
for many many years on the Vette....so obviously it must work...and the Vette weighs in a heck of a lot more than any GT40.
If you want to convert the bolts to 12mm, that's up to you...but clearly
it's not necessary for anything resembling "normal" use.
Regards

MikeD

[Lee]

Thanks very much Mike. So Metric High Tensile bolts it is, and I'll get some sleeves made up for the bearings just for good measure.

Thanks
Lee