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PostPosted: October 3, 2016, 9:46 pm 
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Joined: November 11, 2013, 4:47 am
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Location: No. Nevada
Bet this has never been asked before!

Need to convert my front hubs from 4x114 (4x4.5") to 4x108.
"Large" Triumph to Alfa Romeo Spider.

The brake rotors on each car are nearly identical for diameter and thickness.
Car will be too light to worry about swapping to vented rotors as they do need to reach operating temp.
May slot or drill them.

I see a couple of ways to do this.
Plug and re-drill the TR hubs, 3mm off-set per hole.
Would be happier with this if I could get virgin metal but the way TR hubs are cut that is not possible.
Might be able to use a different wheel stud with a larger shank for less eclipse of the hole?

Make new TR hubs with the correct PCD in steel or Aluminum.
Possible but a lot of work.

Make custom TR to Alfa front stub axles to take the Alfa hubs.
This may actually be the simplest answer, have to figure out what steel to use and possible heat-treat?
Could probably alter the profile to make them stronger at the same time.
Some claim an issue with stock causing brake pads to back-off in heavy use.

Cool to have CNC tools handy, not so cool to have to make custom Geometry/G-Code for only a pair of parts. :ack:

Which solution is the consensus for "Best"?

Something I have not thought of?
I deliberately left out adapters as asking for trouble.

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PostPosted: October 4, 2016, 12:35 am 
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If the flange offset works out you might be able to find a way to swap hubs by building bearing sets, Bearing 7C, Race 19A.... something like that.

The TR6 and the Spitfire Mk1 use the same front wheel bearings (but different grease seals), Spitfire hubs can be redrilled to 108mm but I disremember the flange offset.

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PostPosted: October 4, 2016, 12:49 am 
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You can get Cateringvan front hubs in the 108mm PCD that use the Triumph Spitfire hub bearings. But, as stated, you might able to mix and match hub bearing to make things work. Failing that, if you're using Triumph spindles, you could also look into making up custom stub axles to suit the Alfa bearings.


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PostPosted: October 4, 2016, 1:08 am 
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'Web was frustrating today.
I had hoped to look up some studs with larger shanks so that I could re-drill the TR hubs by 3.15 mm.
No luck at all finding out what the TR shank dimensions are, or even what is available in new replacement.
If I can avoid unsupported shank area re-drilling is the simplest way.
Looks like I have to pull a TR stud then head to NAPA.
keeping it simple will get it done a lot faster.

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PostPosted: October 4, 2016, 10:48 am 
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Richard,
The reply at the bottom of this thread should give you an idea of stud dimensions:

http://www.britishcarforum.com/bcf/archive/index.php/t-68564.html

TR3 through 6 use a 7/16" UNF thread, but I'm sure you know that already.


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PostPosted: October 4, 2016, 12:21 pm 
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Thanks!
That gets me a lot closer.
You win the arcane knowledge link of the day award. :cheers:

If I stay at 7/16 thread I can take up half of the shifted off-set diameter.
Original .517".
ARP .580"
Ideal would be .640".
So .060" shy of ideal but still fully supporting the flange at the head of the stud.
Manufacturer's Part Number: 100-7702
Part Type: Wheel Studs
UPC: 672036000400
Wheel Stud Style: Press-in
Wheel Stud Thread Size: 7/16-20 in. RH
Knurl Diameter (in.): 0.580 in.
Underhead Length (in): 3.200 in.
Knurl Length (in): 0.300 in.
Quick-Start Nose: Yes
Quantity: Sold as a set of 5.
Notes: Fits late model GM disc brake and early drum brake applications.

If I go to 1/2" stud I can get more than enough knurl support.
Going to mag wheels so 1/2" stud is probably fine to use.
Part Number: ARP-100-7703
UPC: 672036000417
Wheel Stud Style: Press-in
Wheel Stud Thread Size: 1/2-20 in. RH
Knurl Diameter (in.): 0.625 in.
Underhead Length (in): 3.500 in.
Knurl Length (in): 0.400 in.
Quick-Start Nose: Yes
Quantity: Sold as a set of 5.
Notes: Fits Ford rear disc brake and Chrysler front brake applications.
Ideal would be .640".
I don't think .015" would be an issue in the real world.

Knowing the OE use I can probably get these individually at NAPA or at least look at examples.

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