Brake-Drum Backing Plate Fixings / Bolts - Where to buy?!

[cunning plan]

Does anyone know where I can buy the backing plate bolts for the rear brake-drums?

There is x1 bolt holding the wheel cylinder on and x2 bolts going through the backing plate to the hub.

The measurements from the old bolts are:

Wheel Cylinder Bolt:
Diameter: 7.25mm = M7?
Length (Including Head): 26mm
Threaded Length: 20mm

Backing Plate Bolts:
Diameter: 9.22mm = M9?
Length (Including Head): 33mm
Threaded Length: 25mm

I can only find the wheel-cylinder bolt on VW Heritage, C+C and Cool-Air, but they are all too short!!

I've asked Volksbolts but they said they do not have them.

Any help? :sign0009:

 

[tomedwar72]

M8 X 20
M10 X 25

(assuming the items in the image are the ones you need?)

 

[RePhil]

As above.

Just a pointer for future reference:-

Metric bolts usually come in standard sizes.
M3, M4, M5, M6, M8, M10, M12, ... Usually in even numbers from here. The only other variable is that they are sometimes 'fine' pitch. You will know when you hold it next to others.
(Just to prove myself wrong - the 2 screws which hold the drum to the hub are M7. Little buggers)

Also metric bolt lengths are measured from under the bolt head (i.e. Excluding the head).
This may be why you thought the supplier's bolts were too short.

I hope this helps.

Phil.

 

[cunning plan]

M8 X 20
M10 X 25

(assuming the items in the image are the ones you need?)

Yes, they are numbers 11 and 9 in that diagram and the lengths seem to be correct against my measurements:

Wheel Cylinder Bolt:
Diameter: 7.25mm = M7?
Length (Including Head): 26mm
Threaded Length: 20mm

Backing Plate Bolts:
Diameter: 9.22mm = M9?
Length (Including Head): 33mm
Threaded Length: 25mm

Although, can someone confirm that a bolt with 7mm diameter (or just over in this case), is an M7?

This maybe where I am wrong?

As above.

Just a pointer for future reference:-

Metric bolts usually come in standard sizes.
M3, M4, M5, M6, M8, M10, M12, ... Usually in even numbers from here. The only other variable is that they are sometimes 'fine' pitch. You will know when you hold it next to others.
(Just to prove myself wrong - the 2 screws which hold the drum to the hub are M7. Little buggers)

Also metric bolt lengths are measured from under the bolt head (i.e. Excluding the head).
This may be why you thought the supplier's bolts were too short.

I hope this helps.

Phil.

Thanks Phil, I thought I was possibly wrong with my measurements, so I took two, one including the head of the bolt and the other just the threaded area.

This is one of the M7 bolts available from VW Heritage:

http://www.vwheritage.com/vw_spares_Bolt-for-T2-T25-rear-drum-71-M7x12-N0102276_act_shop.product_pID_189280.htm?crumbStartPage=1" onclick="window.open(this.href);return false;

It is 12mm long which is way too short

 

[RePhil]

Yes, just to confirm each side, you need:-

1x M8 bolt to secure the brake cylinder & backplate to the axle,
2 x M10 bolts to secure the adjuster housing & backplate to the axle,
2 x M7 bolts to secure the drum to the hub (these are the Heritage ones you list).

Phil.

 

[cunning plan]

Yes, just to confirm each side, you need:-
1x M8 bolt to secure the brake cylinder & backplate to the axle,
2 x M7 bolts to secure the drum to the hub (these are the Heritage ones you list).
2 x M10 bolts to secure the adjuster housing & backplate to the axle,


Phil.

Thanks Phil, but on my '68 there are no fixings from the drum to the hub.

Here is my hub:

So, the only M7 bolt I can find IS that VW Heritage one which is 12mm, where as I need it 20mm to go all the way though to fix the wheel-cylinder.

I cannot find the M9s either. :|

:sad2:

 

[dubdubz]

m9 is a very odd size - so it should be M10??

also if it is M7 and not M8

http://www.ebay.co.uk/itm/M7x20-Bolts-7mm-Metric-Thread-zinc-20mm-long-x5-bolts-/271505886487?pt=UK_Motorcycle_Parts&hash=item3f37030d17" onclick="window.open(this.href);return false;

 

[RePhil]

Being pre 71 your drum & hub are one unit therefore no need for the 2x M7 bolts. This doesn't affect what you are having issues with.

The item you labelled as the hub is in fact the rear wheel bearing housing.
The 2 larger holes are M10 & the small one is M8.

As for length of bolts don't forget to add thickness of lock washers.

Phil.

PS I assembled all this lot on mine yesterday.

 

[cunning plan]

The 2 larger holes are M10 & the small one is M8.

As for length of bolts don't forget to add thickness of lock washers.

Thanks for your help Phil, but I'm confused, are you saying that a bolt with a diameter of 7.25mm is a M8 and not a M7?

Also, the same for the bolts with a diameter of 9.22mm being a M10 and not and M9?

:shock: :? oke:

(Those dimensions are from the original bolts that I have taken out of the bearing housings / backing plates).

m9 is a very odd size - so it should be M10??

also if it is M7 and not M8

http://www.ebay.co.uk/itm/M7x20-Bolts-7mm-Metric-Thread-zinc-20mm-long-x5-bolts-/271505886487?pt=UK_Motorcycle_Parts&hash=item3f37030d17" onclick="window.open(this.href);return false;

That's what I thought, so I started this thread

Good find on the M7s, although either my understanding of bolt sizes is wrong OR the bearing housings on my bus are super weird.

:sign0009:

 

[tomedwar72]

Did you measure the diameter with vernier calipers by any chance? They often have sharp edgess that sit within the thread.

You need M8 X 20 & M10 X 25

See the major and minor thread diameters listed here:

http://mdmetric.com/tech/M-thead 600.htm

You won't measure 10mm and 8mm even on fresh bolts.

 

[cunning plan]

Did you measure the diameter with vernier calipers by any chance? They often have sharp edgess that sit within the thread.

Yes!! :lol: Right, okay, I think we had found the issue! I am fairly sure the 'blades' of the vernier went into the thread instead of sitting 'on' the thread. :?

Thanks for confirming that, it was annoying me to wonder how the measurements could be so different, but I am sure if I measured on the thread it would push the sizes up 1mm to 8 and 10mm. :msn4:

You need M8 X 20 & M10 X 25

Roger that!

See the major and minor thread diameters listed here:
http://mdmetric.com/tech/M-thead 600.htm

You won't measure 10mm and 8mm even on fresh bolts.

[/quote]

Understood.




Thanks all for the help! arty0047:

 

[cunning plan]

Once I knew what I was looking for thanks to the guys above, I have found these bolts which I thought I would post here in-case it helps someone else:

M10 x 24mm
http://www.vwheritage.com/vw_spares_Bolt-M10-x24mm-" onclick="window.open(this.href);return false;[10]-N90369801_act_shop.product_pID_175190.htm#esp_pg=2

M8 x 20mm
http://www.vwheritage.com/vw_spares_Bolt-M8-x-20-Multiple-uses-GolfCorradoT2T2-" onclick="window.open(this.href);return false;[37]-N01024016_act_shop.product_pID_196048.htm#esp_pg=3

 

[RePhil]

Result.

What's next ?

 

[cunning plan]

Girls and beer! :lol:

arty0047:


(I wish)