Is it dangerous to stick a spacer betwixt disc and hub?
Discussion
I need to move the disc back in order to line up with the centre of the caliper. Long story short; I have a set of new discs that are c.50mm height, but of course should be c.70mm. Would it actually be dangerous (as opposed to not ideal/bodge job etc) to bolt a 20mm wheel spacer between the front face of the brake disc and the rear face of the hub? Will it work or am I missing something obvious? I need an 'emergency' solution ahead of a full front brake rebuild over the winter - 'emergency' in the sense of two track days I really want to do before the end of the year and my current discs are shot...
Thank you,
Thank you,
As long as the disc is properly centered on the hub (either by being the correct bore, or sitting on a lip in the spacer), and you use longer bolts (proper high tensile) it should be ok.
The spacer also needs the faces to be properly flat/parallel too - steel/alu plate this thick can be pretty rough.
We did something similar to this on a TR7/8 upgrade years ago.
EDIT to add: Also if it's a modern disc with a thin mounting flange which you're going to bolt though rather than bolt "into" like the original, I would get some large, thick washers under the nuts/bolt heads to spread the load as much as you can.
The spacer also needs the faces to be properly flat/parallel too - steel/alu plate this thick can be pretty rough.
We did something similar to this on a TR7/8 upgrade years ago.
EDIT to add: Also if it's a modern disc with a thin mounting flange which you're going to bolt though rather than bolt "into" like the original, I would get some large, thick washers under the nuts/bolt heads to spread the load as much as you can.
Edited by Keri on Monday 26th November 19:28
lear said:
I need to move the disc back in order to line up with the centre of the caliper. Long story short; I have a set of new discs that are c.50mm height, but of course should be c.70mm. Would it actually be dangerous (as opposed to not ideal/bodge job etc) to bolt a 20mm wheel spacer between the front face of the brake disc and the rear face of the hub? Will it work or am I missing something obvious? I need an 'emergency' solution ahead of a full front brake rebuild over the winter - 'emergency' in the sense of two track days I really want to do before the end of the year and my current discs are shot...
Thank you,
thats rather a thick spacer your putting in 20mm. I have a 5mm spacer to bring my disk out, and found my studs were no long enough so 20mm is abit excessive. Thank you,
Thank you for your views. I finally got around to pulling the discs off over Christmas, only to find that the centre bore on the new discs is 63.5 as opposed to 69! I think that is for the later Granada hub with front mounted discs. However, I'm glad I did as I discovered the old Tower View 300mm upgrade is not what you might call beautifully engineered! I'm assuming disc has not been subsequently replaced but looks like they started with a massive disc - centre bore over 80 - and then drilled a new PCD and inserted an alloy spigot ring to reduce the bore. However, the new holes are so close to the edge that there is less than 2mm of metal - and worse it is drilled on the tapered part of the bore. So I found that every single bolt hole is cracked all the way through to the edge. It has lasted a good few years but if you have this upgrade fitted (same as pictured in the SH bible), you might want to check the disc mountings from time to time.
I'm going to get BG Developments to make up a custom disc now.
I'm going to get BG Developments to make up a custom disc now.
lear said:
I think that is for the later Granada hub with front mounted discs.
That doesn't sound correct. I ca't find a reference for Ford increasing the G/S pcd and it would be an odd thing to do. Don't know what you've got but glad that you found about the problems before trying to fit it.TA14 said:
That doesn't sound correct. I ca't find a reference for Ford increasing the G/S pcd and it would be an odd thing to do. Don't know what you've got but glad that you found about the problems before trying to fit it.
Sorry, I meant to say different centre bore hole rather than PCD. The centre bore on the discs I bought from Hispec is 63.5mm (same as Wedge wheels) whereas the mounting to the back of the hub is 69mm (and the discs are shorter than the wedge originals). Not familiar with Ford models but thought I remembered a change in the centre bore diameter and height between Granny models when looking for discs some time ago. I think Hispec make them for kit car conversions using newer Granada hubs. I've got some nice 300mm paperweights now though!To be honest the strength of the bolts is irrelevant as the disc doesn't hang on the bolts. It is not the bolts that stop the rotor from moving. For a start there is about 1 mm gap between the bolt and the hole.
The bolts provide a clamping force between the the hub and disc faces and it is the friction between the two surfaces that determines if the disc slips. If it does it will be stopped by the bolts acting like a peg. The mounting holes are not a tight fit on the bolts and if it was the bolts simply acting as pegs, the disc would have considerable play and vibration. The size of the bolts determines how much clamping force can be applied which with the size of the bolts is quite immense. That means that the rotor and hub stay together. You can see that by looking at the bolt holes themselves.
Look at the holes and they are not elongated or oval. Yes there are cracks but that is more to do with the drilled ventilation holes which is why many prefer grooves rather than holes. With that disc design, the number of holes and the size of the disc coupled with pad knock back due to the taper roller bearing and once they start to crack, they crack through very quickly. When this happens it is like having ABS on the car as you can feel vibration through the pedal.
Yes I have cracked them... and the Hispec replacements as well. It's all down to how much abuse they get.
The bolts provide a clamping force between the the hub and disc faces and it is the friction between the two surfaces that determines if the disc slips. If it does it will be stopped by the bolts acting like a peg. The mounting holes are not a tight fit on the bolts and if it was the bolts simply acting as pegs, the disc would have considerable play and vibration. The size of the bolts determines how much clamping force can be applied which with the size of the bolts is quite immense. That means that the rotor and hub stay together. You can see that by looking at the bolt holes themselves.
Look at the holes and they are not elongated or oval. Yes there are cracks but that is more to do with the drilled ventilation holes which is why many prefer grooves rather than holes. With that disc design, the number of holes and the size of the disc coupled with pad knock back due to the taper roller bearing and once they start to crack, they crack through very quickly. When this happens it is like having ABS on the car as you can feel vibration through the pedal.
Yes I have cracked them... and the Hispec replacements as well. It's all down to how much abuse they get.
Look like discs from a german barge to me, redrilled with the pcd for the granada hubs. works fine on my granada with a similar setup too 
As Steve says, the bearing design makes pad knock back more noticeable with bigger discs, as well as making the first pedal press a bit spongey if there is enough knock back
As Steve says, the bearing design makes pad knock back more noticeable with bigger discs, as well as making the first pedal press a bit spongey if there is enough knock back
TA14 said:
You sound like you've had a bad day here. These are supposed to be new discs so it's not surprising that the holes are not elongated. Not only are there cracks on the pad area of the disc but the holes drilled for the studs have cracks through to the centrebore.
I think you will find that the discs in the photos with the cracks are the old ones and have had a lot of wear and tear. 
I work for Mercedes-Benz and selling discbrake axles is my fulltime job. All I can say to the visitors of workshops is tell your workshop to use parts that are built for the purpose and not modified by a workshop and fitted because "they think it wil be ok". This is a horrible picture and anyone defending this as a safe product should get help. That is my strong advice. I do not know who was the suplier of this disc, but it must be a workshop that does not like to see customers come back.
So that spacer sits outboard of the disc (between disc and hub) with a part protruding back inboard towards the chassis to concentrically locate the disc?
Were the bolts threaded into someing like a ring or were there just nuts and washers etc?
Were the bolts threaded into someing like a ring or were there just nuts and washers etc?
Edited by Keri on Saturday 2nd February 14:09
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