Jump to content
Sign in to follow this  
Nick Jones

Vented Disc conversion

Recommended Posts

Having now cooked several sets of pads on my Vitesse, including some (fairly hardy) Ferodo DS2500, I'm forced to conclude that vented discs are the way forward. It's the track days..... and the Alps..... that do it.

I've bought a pair of Capri 2.8i discs and a spacer kit for the 16P callipers. I've also got full rebuild kits incl. SS pistons as the poor old callipers are looking a bit cooked too.

Usual procedure seems to be to

- space the callipers,

- redrill the discs and fit to the hubs ( centering is an issues a s Capri disc has 2mm larger ID)

- remove the dust shields (spacers used to maintain the original steering arm position

- refit hub/disc

- fit callipers with suitable spacers to centre the them on the disc (5mm supplied with spacer kit)

- find some method stopping the TRE gaiter rubbing on the disc......

 Lacks a certain engineering elegance....

I've measured a 4mm difference between bell height of the OE and Capri disc, with the Capri disc being the larger. On the face of it, machining 4mm off the inside of the hub would appear to correct matters and allow creation of a proper 64mm centring spigot as well. No need to discard the dust shield and no issues with TRE clearance. 

I also note that although the actual increase in disc thickness is ~ 7mm, the spacer kit spacers are actually 10mm - implication being that I either actually need to move the disc out 5.5mm to centre the calliper on the disc - or bin the nasty looking spacers that came in the kit and make some nice ones that are 7mm!

obvious drawbacks

- Not directly reversible (spacers would be needed to refit OE discs)

- All of the extra calliper width will be outboard, which may lead to clearance issues with some wheels

So what haven't I thought of? Anyone done it like this before?

Got some spare hubs and enough stray bits to mock it all up..... but have used all my "stood up" time for today........

 Nick

Share this post


Link to post
Share on other sites

Gday Nick,

Before going quite a different route by changing stubs axles to fit nissan hubs, I made up a vented discs conversion using Saxo vented discs (part number 5815209918) 

I looked at capri discs, but wanted to make the whole lot easier to change discs- using this set up below, all I would have to do is re-drill the pcd on the discs to bolt up to the hubs.

Details of disc as follows- This was mocked up on a herald drum VL and 13/60 hub- because I didn't want to mess with my limited Vitesse bits supply- I have no reason to believe the same wouldn't work on Vitesse hubs and VL's as that was my intention. 

Diameter (mm): 247
Height (mm): 34
Minimum Thickness (mm): 18.5
Thickness (mm): 20
Number of Holes: 4
Centering Diameter (mm):

66

 

 

 Now, to fit I mounted the hub in a lathe and took 5mm off the back face of the hub. Then machined the central locating bore of the back of the hub from 68mm to 66mm. Now re-drilled the disc pcd to suit.

The casting flash was smoothed off the inside of the steering arm, and then that was spaced 2-3mm off the link. With the disc mounted there is plenty of clearance between the ball joint gaiter- it is about the same clearance as OE.

Calipers- I didn't use oe triumph ones as I am more interested in modern ones with bigger pads. I expect they would fit as it sits more or less the same as capri.

 To give you some food for thought, after a great deal of searching I found that Mazda 323/Ford laser (80's 90's cars) use a sliding caliper with big pads that mounts inboard like the triumph type- this is rare in modern OE calipers and is important because it means that you can make a new caliper bracket that is more or less a flat plate, ie; not hard to make. They come in at least two sizes for 18mm and 22mm discs (they are stamped as such on the caliper) I was using 18 and they seemed to fit well. They weigh less than the girling type and cost nothing- they were standard fitment on nearly every ford/mazda co-op car through the 90's. People talk of flex in sliding calipers, these are quite a different design and seem quite solid compared to other types of sliding calipers- also I just couldn't out-brake my old 323 on them and I drove like hell. Wheels clear easily as mazda calipers are even lower profile than girling.

I have few photos of this set up on me as I changed computers- I'll post better pics of clearances as some point. These are pulled off my old photobucket account.

 

Another idea I looked into, but never used, was mounting an mgf vented top hat disc on top of the hub and using the same mazda caliper for clearance. This arrangement DOES work on a herald drum type VL and hub, the caliper bracket is a flat plate at 8mm. Super easy vented disc set up for heralds, spits and it is nice to find a use for all those herald drum type hubs nobody wants. It pushes the wheel offset out about 4mm. A locating ring needs to be made up to fit snugly in the gap between the disc and the drum location ring on the hub.  The same set up could theoretically be used on disc hub cars by machining down the diameter of the hub to fit inside the bell of the disc. Obviously m12 studs with a good shank (Mgf again perhaps). The mgf disc is actually a little smaller diameter than vitesse/saxo so wheel clearance is no issue.

 

mx3caliperfront.jpg

20150820_103002_zpshd9daf4b.JPG

20160612_094837_zpsnx8x1f7w (1).JPG

20150820_103706_zpsfy1uyoat.jpg

20150820_103652_zpsrwvidwta.jpg

20150820_103103_zpsz95x0dq8.jpg

Share this post


Link to post
Share on other sites

Just to add- in one of those pics above there are spring washers under the disc bolts- NO- they don't clear. I drilled the threads out in the hub a couple of mm to bury the shanks, and would loctite them in. 

You will also not that I machined a clearance on the outer portion of the hub to clear the girling calipers before I started messing with mazda calipers. I honestly cant remember if that was necessary or not now, but I have a hunch it wasn't. 

Share this post


Link to post
Share on other sites

 

 

Been mocking things up this morning. There are a number of ways to skin this cat, but they all have drawbacks. My plan A had been to simply machine enough off the hub to shift the disc outboard enough to place the inner face in the OE position.  With the 10mm spacers provided this results in the outer face of the calliper sticking out 6.5 mm beyond the hub face - and interfering significantly with the hub.  Latter possibly fixable, former not fixable without wheel spacers.  I can't used spacers as the wheel/tyre combination I have is on the reasonable limit of poke already.

P1180014MUc.jpg

This supplied "kit" has 10mm calliper spacers plus 5mm washers to move the callipers inboard. This does basically work. The drawbacks of remain as per original post plus the calliper is very close (less than 1mm) from the hub. The kit does not include longer calliper fixing bolts,  which are sorely needed. Not in itself an issue, but kit incomplete!

P1180020MUc.jpg

The 10mm calliper spacers are 3mm bigger than they need to be to accommodate the extra disc thickness (7mm). We've knocked up some 6.8 mm ones from some aerospace Alu alloy we had in stock. Fitted with 2.5mm washers the callipers are now well clear of the hub but disc not central in the calliper. Machining 4mm  from the back of the hub would sort that and allow me to ditch the washers and even fit the dust shields, but then will need to relieve the hub and maybe the calliper slightly and the calliper will again be outboard of the wheel mounting face, though only by 3.3 mm........

Had not realised there is so little to spare in the OE install. No wonder the TRs have big wheels!

Other irritations are new stub axles CNC machined slightly too large to accept the inner bearing (15 mins with wet and dry paper sorted it but really....) and trunnionless vertical links with slightly different dimensions to the bearing-stop boss (the part the inner bearing rests against).  It's "only" 0.5mm but affects the calculations I'm doing above.  Was getting different results side to side - I though I was going mad......

Thought modern machine tools were meant to be more accurate than those from the 60s...... :ermm:

Nick

Share this post


Link to post
Share on other sites

HI Nick

I fitted 2.8 Capri discs to my Vitesse, and from memory bought the caliper spacer kit from Canleys. I had a spacer ring made up that pressed inside the Capri disc to centre it on the Vitesse hub. I then used spacers to gain some clearance between the track rod end rubber and disc. From memory still to close, part of the problem being the repro boots that flatten out to much making the diameter to large. I found some new old stock ones that fit much better. From memory the hub is close to the calliper but a miss is as good as a mile. Hopefully car will be on the road this year, so I'll find out if there are any issues.

Mark

Edited by Mark
Spelling

Share this post


Link to post
Share on other sites

I would shim the stub axle towards the inner wheel bearing

Maybe 2mm will do no harm and give clerance towards the vertical joint.

Hopefully the outset of 2mm will clear the wheel under the wheelarch.

 

Than I would mill the spacers from 10 to 6mm.

The remaining clearance will be enough. I did the same needed 12mm

from calculation and did 11. New brake pads still fit!

Than I would make the spacers under caliper precisely to center the caliper.

This will add clearance of 2mm to front of the hub.

 

We also had trouble with the TR6 swap.

Things became pretty narrow with steel rims, no problems with wire or alloys.

Some added spacers to clear between rim and caliper with steel rims.

That was also a problem with the vented disc set from EBC with 20mm discs.

 

All of the spacers had trouble with the hole for the brake fluid.

It was not drilled where the outlet in the caliper was and in some cases

the canal gasket did not fit properly.

In one case the caliper had the wrong depth for this gasket.

Should be 0.9mm and was 2.1mm!

Share this post


Link to post
Share on other sites

Thanks Andreas,

We made some new spacers yesterday from 6.8mm aluminium.  These do have the holes in the right place/correct depth recess!  They give a disc clearance more or less the same as standard too.

Also noticed that if you measure Spitfire hubs they have 4mm less from the wheel face to the disc face (40mm instead of 44mm) - ie, they are correct for the vented discs.  Of course they have the wrong size bearing bores.....  Then I remembered reading that Dolomite hubs use the same bearings as GT6 but with a different disc position........ Chris is picking a Dolomite hub up later to measure - just in case we are lucky and they will do the job with no machining!  Some hope........

Nick

Share this post


Link to post
Share on other sites

Nick, had a quick look at mine today. The edge of the hub has been machined back, at the same angle as original. Not an issue as wheels do not sit on the edge of teh hub, and it is only a small amount, 2mm reduction in the hub diameter?? And the calliper had seen a grinder in that area, just a tad.

 

My thinking for machining the back of the hubs was to give decent clearance to the TRE's, but that has a consequence of shifting everything out....

I also have a set of gnuine standard 8 TRE's that use metal washers rather than boots. Still in their stanpart boxes. Probably not going to be used by me now.

Share this post


Link to post
Share on other sites

"I would shim the stub axle towards the inner wheel bearing
Maybe 2mm will do no harm and give clearance towards the vertical joint.
Hopefully the outset of 2mm will clear the wheel under the wheel arch."

Andreas,

We did look at this yesterday.  1 - 2mm absolute max due to the position of the drilling for the split pin.  Will using it to do a hard check of my machining calculation though.

Going to have to get machining done by a pro as I cannot get the hub in my lathe with acceptable levels of run-out...... :down:  Can't get below 0.005"....

Nick

Share this post


Link to post
Share on other sites

Oh yes, the split pin! I forgot.

What about putting the hub in the lathe and setting the flange for the outer bearing

2mm to the inside that the outer bearing sits 2mm deeper in the hub?

 

I see the problem of the space between flange for the rim and caliper.

Normally I would try to have 5mm space between rotating and standing parts.

So whereever the space is generated it is not nice, even cutting the flange at the

outside is weakening a critical area.

So I would do a little bit at several positions and hope to stay in the safe area with that.

Share this post


Link to post
Share on other sites

Nick, I too looked at dolomite hubs. The actual axle  and hub is shorter than Vitesse and places the outer bearings in a different place- I dont think you can swap easily. You could use the dolly stubs in the Vitesse link, but I dont think you are gaining much ease unless you could find a top hat vented disc to fit over the lot- but then you will probably have caliper clearance issues. 

Share this post


Link to post
Share on other sites

Yeah, measured one yesterday. Triumph seem to have gone out of their way to create differences. Threads (UNC) in disc rather than hub. Bearing spacing different.

There are ways they could be used but all more effort, so pointless.

Never previously realised that Dolly discs are smaller even than Herald and Spitfire (220mm vs 232mm). No wonder Sprint brakes are "one shotters"!

Nick

Share this post


Link to post
Share on other sites

Hi Nick,

interesting that the spacers you have measure 10mm. I have a kit from Canleys and the spacers are 8mm thick.

My plan is to have 2.4 mm spacer at the caliper mount and to turn / mill back the mounting face of the disc at the hub by another 2,4mm. This then combines with the correct Diameter of the Capri disc.

Then shimming the steering arm as required to free the track rod end.

 

Martin

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×