Unibody Mk4 Spitfire 6

[BiTurbo228]

So I've been playing around with various different options for the handbrake cable and come up with a least-worst option.

Modified a 19mm deep socket so I could compress the belleville washers to swap the Peugeot pivots about:

One of those times when I was very glad to have bought an absolute monster of a vice as it only just fit between the jaws!

I tried swapping over the pivot arms side-to-side, but they get too close to the flexi union:

Initially I thought welding on the old pivot arms like this might work:

Before my brain finally caught up and realised that this would be pivoting the wrong way...

So I tried an underslung option which might work ok...

...before deciding on this arrangement:

The reason I prefer this one is that Markus mentioned having to keep the cable tensioned tight enough to make the brakes drag to get the handbrake to work at all. By setting the arm back at a shallow angle the effective lever arm is very short for the initial bit of travel, helping take up slack in the cable quickly. The effective lever arm increases as you apply the handbrake, helping the last few clicks of the handbrake to put more force on the cylinder.

The downside to this setup is I'll have to mount the caliper upside-down to get the cable orientation right, but I figure you use the handbrake more often than you bleed the brakes, so the compromise is in the right direction.

So with that decided I set about copying the shape onto the other side. Bent up another piece of 7mm plate and drilled some holes to align it up:

Bit of work with a flap disc and we end up with this

Next step is to weld it up, though I figure I should test it on the car first...

[BiTurbo228]

Weldy weldy

Goes on something like this:

Will need a bit of the caliper tickling with a hacksaw to let it move through its full sweep, but it's only the superfluous Peugeot cable mounting lug that needs to go.

[BiTurbo228]

Well it's been yonks since I've done anything on the Spitfire, but flitting between my place and my folk's place for childcare has afforded the opportunity to give it a bit of attention.

I'd picked up a Sure-Trac Subaru R160 quite some time ago, but they all come in too high of a ratio for my needs, so the plan was to swap the LSD centre into a 3.54 open diff:

Normally this is really quite a straight forward job as Subaru's manufacturing tolerances are usually good enough that you can just keep the shims and bearings together and swap things over. However, I noticed that some of the welds on the LSD core had cracked:

Apparently this is quite a common thing. So I pulled the bearing off that end (wrecking it in the process as it was super tight), and vee'd out the welds ready for repair. At this point I read a little more about how the LSD is constructed, and I don't actually think any of that is necessary. The end cap is screwed into the centre tube and the welds are just there to stop it coming undone. There's limited force on the welds as the threaded portion takes the majority of the load from the pawls inside, and the cracks probably occurred due to differential cooling rather than application of force while driving.

Oh well, too late now.

So I pinched a bearing off the open diff core, actually took some time to set up the backlash properly, and now have a diff that is very nearly in spec (0.21mm backlash where the spec is 0.1-0.2mm).

I've ordered some more shims to just sneak it over the line.

Next up is making up the hybrid Rover 100/Subaru driveshafts to connect to the uprights I've had machined for MGF bearings. Then the car should be rolling again (though I'll need a different prop again).

[Escadrille Ecosse]

Always something else on the go! So nice to see a bit of progress.

Similarly frustrated on the lack of progress with mine. Latest for me is a combination of injury and the relentlessly pish weather.

[Nick Jones]

16 minutes ago, Escadrille Ecosse said:

Similarly frustrated on the lack of progress with mine. Latest for me is a combination of injury and the relentlessly pish weather.

Can relate! 

[Escadrille Ecosse]

Just now, Nick Jones said:

Can relate! 

It's bollocks isn't it. My Dad always used to say that age didn't come alone. I am increasingly seeing his point.

I hope your back is improving

[BiTurbo228]

Yeah I count myself lucky that mine's not injury-related! I'm only early 30s, but I've already put my back out once or twice already (lifting and twisting...stupid boy). It's no fun at all, and always takes at least twice as long to heal as you expect (plus the rest of the time it takes to build back the strength you've lost during the healing process).

Pish weather I can relate to especially at the moment! Most of my time recently has been taken building a driveway so I can build a garage and actually work under cover and not lying on the wet ground outside. Just maintaining the old crocks that are currently running is tricky from a puddle.

I shouldn't complain mind! It's not everyone that gets the opportunity to build a garage, let alone have one already (that's full) and building another.

[Nick Jones]

D

8 hours ago, BiTurbo228 said:

Next up is making up the hybrid Rover 100/Subaru driveshafts

Have you got the inner CVs and do they fit the Rover shafts? There are some that do ….. the trick is finding them….

[BiTurbo228]

I have a set of inner CVs that should fit the LSD, but I've not yet tried them on the Rover shafts 

[Nick Jones]

Good luck with that. I’m told that the ones that are 75mm OD are the ones. I can tell you that 73mm ones are not….

[BiTurbo228]

13 minutes ago, Nick Jones said:

Good luck with that. I’m told that the ones that are 75mm OD are the ones. I can tell you that 73mm ones are not….

Useful stuff. Will pop out with a set of verniers tonight! Wish me luck 

[BiTurbo228]

Well aren't I a jammy sod! Pair of 75mm OD driveshafts on the first go!

If it helps these were ones badged for the Sure Trac diff. Won't work with the viscous version, but it's my understanding that the splines are the same as the open ones (not checked it personally though).

[BiTurbo228]

Inching forwards on the rear suspension. Popped some polybushes in the rear housing (had to get some new ones as I sold the last set with my old diff).

I'd also read that, if you're driving them really hard (e.g. as a club racer), the conversion plate spring mount can tweak side to side slightly. I doubt I'll ever get anything like that amount of g-force in my car, but adding some gussets felt like a good safety precaution:

I also took the opportunity to get some more shims and actually tweak the backlash down into spec. Didn't measure it this time, but as it was at 0.21 and the top of the spec is 0.2, just bumping it 0.05mm in one direction should be fine.

Just waiting on the right thread nyloc nuts and it can go in the car!

[Nick Jones]

Yeah, was considering doing something similar. More because the Vitesse is a weightier beast, especially 4 up (rare!) and/or with a boot full of luggage!

Does the spring sit flat on the bracket or is it wide enough to catch on the  arch?

[Escadrille Ecosse]

Nearly there with that. Looking made at the makers style.

But I do hope you are going to clean up the diff casing before putting it in. 

[BiTurbo228]

19 hours ago, Nick Jones said:

Yeah, was considering doing something similar. More because the Vitesse is a weightier beast, especially 4 up (rare!) and/or with a boot full of luggage!

Does the spring sit flat on the bracket or is it wide enough to catch on the  arch?

That's a good question. I haven't tested it on a spring yet. I suppose if it doesn't sit nicely you could cut a C into it and bend the edges down to reweld in more of an arch...

17 hours ago, Escadrille Ecosse said:

Nearly there with that. Looking made at the makers style.

But I do hope you are going to clean up the diff casing before putting it in. 

Haha I am definitely guilty of leaving diffs and axles and things unpainted and just rusty. I'll see what I can do, though part of the reason I've picked this up again is there's a risk of me losing the storage where it lives at somepoint soon. Getting it on its wheels and mobile would definitely help in relocating all of my junk (as would finishing my garage build so there's a place for all the junk to go!).

Oh, also, something that might help if someone's using the same cast rear plate. On mine the clearance between the mounting lugs and the two closest rear cover bolts was a bit tight. You can get a spanner in to tighten it, but only with the flats and not brilliantly. This might vary between castings, but I thought a socket head bolt would be better.

Unfortunately, the thread is a weird M10x1.25 fine pitch (seems to be a Japanese trend, like using 12mm and 14mm bolt heads instead of 13mm). You can get this readily enough in stainless, but I really don't like stainless for bolts. Turns out that a lot of Japanese bikes use this thread for various casing bolts so I managed to pick up some in BZP. You need ones that are 30mm long.

[Nick Jones]

Lots more manufacturers using metric fine these days. In some “unusual” sizes too. VAG now use M7 and M9 in occasional weird places. Often with some wacky splined head on it requiring a new tool (or whole set because can’t find singly).  Usually discovered on a Saturday evening. Bastards.

I like metric fine. “Normal” metric from M10 up is pig thread. Ok for farming and building but not engineering! I despise multiple head variations on the same vehicle though.

[BiTurbo228]

1 hour ago, Nick Jones said:

Lots more manufacturers using metric fine these days. In some “unusual” sizes too. VAG now use M7 and M9 in occasional weird places. Often with some wacky splined head on it requiring a new tool (or whole set because can’t find singly).  Usually discovered on a Saturday evening. Bastards.

There's a special circle of hell reserved for these people. Weird heads is one thing, but odd-numbered bolt diameters is just psychotic.

Definitely makes me grateful that the newest car I've ever owned is a 2002 

1 hour ago, Nick Jones said:

I like metric fine. “Normal” metric from M10 up is pig thread. Ok for farming and building but not engineering! I despise multiple head variations on the same vehicle though.

There's metric fine and then there's metric FINE. Regular fine thread is 1.5. This is some weird extra fine 1.25mm thread designed mainly to irritate people who think they have a decent stock of bolts  the Jag rear subframe is the same and uses some of these, interspersed with proper bolts.

Agreed that M10 and up coarse threads are good for building pigsties and not much else. They're 1.75 I think...

Oh, and I dislike multiple head varieties as well, though I've somehow managed to end up with a brace of cars where that's unavoidable. The XJ40 is almost entirely metric except the driveshaft flange bolts and the rear propshaft flange which are Imperial (the driveshafts by original design, the prop because I've used an XJS flange). The SD1 is entirely metric apart from the engine which is Imperial. The Spitfire is entirely Imperial except the diff and driveshafts which will be metric (and maybe the engine as well if I go for the Rover 2600).

At least they're mostly hex heads or allen keys, not these newfangled torx or even-newer-more-fangled male torx (which the M57 in the Jag is guilty of using, as well as 11mm bolt heads on the inlet manifold).

Edited April 30 by BiTurbo228

[BiTurbo228]

Still only tinkering with this inbetween other more pressing things, but there's been some progress made.

First thing is I sorted out the shimming of the R160, but that highlighted a tight spot around the rotation which is unfortunate. I'm hoping I just didn't clean the back of the crownwheel well enough when fitting it, which is a possibility as I had it on and off a few times in quick succession cleaning the threads. The other possibility is that the tiny but of (turns out unnecessary) welding done had warped the flange ever so slightly. Would be no issue if I had the lathe up and running, but I do not have the lathe up and running...

In more exciting news I got the handbrake widgets for the 106 calipers back from the zinc platers:

Needed to do a bit of clearancing to get them to fit properly across their whole travel:

Fiddly old job getting all the various widgets back into place. Special cut up socket, some needle-nose pliers, a small screwdriver and a lot of delicate fernangling got everything in the right place at the right time:

Done and looking shiny 

Hopefully these should work fine with the stock handbrake cables (maybe with some light modification). The action pulls directly back into the centre of the car:

I'm hoping these arms will alleviate some of the issues Markus had with his iteration of these calipers. He said he had to keep the handbrake cables wound so tight they would bind to have any workable handbrake at all. By having quite an oblique angle to the arm, the first few millimetres of travel on the cable will turn the pin a lot of degrees, taking up the slack quite quickly. Then, as it actually starts applying pressure the effective lever arm should get longer, applying more torque for a given cable travel (up to 90 degrees of rotation).

Time will tell if it's a bit too aggressive, but the whole thing wasn't too difficult if I need to make them again.

[Escadrille Ecosse]

That looks very 'made at the makers'.

Nice

[BiTurbo228]

Thanks! Definitely pleased how they came out

Let's hope they work!

[BiTurbo228]

Next step is to actually try a trial fit with the correct disc before I pull the trigger on a machined caliper bracket. Too many different things measured here (some of them in quite challenging ways) to be confident it's precise. I'd at least like to make a wooden mockup to test things.

The disc I'll be using is a front disc from a base spec 205/306. It's 247mm wide so fractionally larger diameter than the MGF disc, and has a 66mm centrebore which should locate onto the MGF hub spigot, but the top-hat section is shorter. That makes the whole thing just a smidge lighter (disc and caliper bracket) which is nice.

However, the PCD needs redrilling. As this is something I might have to do a few times I've been designing a tool for it:

The PCDs covered (in order) are:

• 4x95.25
• 4x98
• 4x100
• 4x101.6
• 4x108
• 4x114.3
• 4x130

The holes are 12mm and it's 20mm thick, so it should guide an M12 drill acceptably. There's 60-degree chamfers on the top surface to match wheel bolts so it should locate in a similar manner to lug-centric wheels (i.e. well, but with a bit of care). For brake discs I'm planning on buying a set of M12 wheel bolts and M12 wheel nuts to bolt through the disc with chamfers on each side to locate them. It'll be made in steel to prevent wear from the sides of the drill.

As a singular piece I've had it quoted at about £170, but if there's a couple of people who want to buy in then it gets cheaper.

If there's 5 other folks who want it then it gets down to £60 each (plus onward postage). If there's 10 then it's £50 (plus onward postage). These are cost figures, I'm not trying to make a profit.

I've posted it in a couple of places to see what the interest might be  

[BiTurbo228]

So I've been fettling with the design of the PCD adaptor tool, and found that 3D printing it was a lot more affordable so ended up ordering a prototype. I went for nylon, which reading about it isn't the best choice of material for this, but hey ho I'd already ordered it. I use Xometry for machining, mainly because it's easy to use and finding local machine shops that are in any way interested in one-off private work is difficult. Same reason I want to be able to redrill discs myself rather than giving them to a machine shop. I can't find one nearby!

This is what I ended up with:

Learnt a lot from the prototype. Firstly, I'd ordered it before the wheel nuts I'm using to attach it turned up and it turns out the taper on their seat doesn't start until ~16mm out so it only just contacts the locating portion of the tool. It still worked, but could be better.

Second issue was that the tool would need to be much taller (and made out of steel as original) to locate the drill properly. It just about worked for marking the starting point and then drilling the rest by hand, but the tip did wander a bit and required fettling and correction with a centre punch (which was a bit of a stab in the dark, though aided slightly by the ability to bolt the tool back on to check concentricity).

Pretty proud of managing to get it so that with 12mm holes it slipped over the studs of the M12 MGF hubs, though it took a lot more care, effort and luck than I'd like.

I've since discovered that transfer punches are a thing. I'd been searching in vain for ages trying to find a straight-shanked centre punch with an OD I could trust and found nothing. Was even looking at the cost of having something made up. Then, I was idly talking to my mate about this and he said 'what, like a transfer punch?'. Lo and behold I search for that and tons come up for affordable prices! There's a set on order for doing disc number 2.

Anyway, I opened up the holes to 13mm and they slipped on fine. Turns out the MGF disc uses the hub OD for centreing not the spigot so the 66mm centrebore of the Pug discs does nothing, but I can get a set of spigot ring adaptors to sort that out.

That allowed me to trial the whole setup together. Disc, calipers and pads. Just as well I did! Turns out I'd made the assumption that the disc sits central in the machined cutout in the Peugeot calipers, but it really doesn't!

Luckily for me, that actually moves it in a much better direction. It means I can use a single flat plate to mount the calipers, which is much easier to make (and thus cheaper if you're not making it yourself). Ideally it would want to be spaced away from the upright at its base by 1.5mm to get the sliders in a central position, but I can do that with shim washers if necessary.

Last challenge is I'd got the measurements wrong for how far away the pad sits from the lug chord, so the whole thing needs to move in by a couple of mm. That means it's back to being very close to the upright where I clearanced it earlier. I've drawn up another CAD model that's skewed 3deg upwards to try and remedy this, so I'll transfer that to an MDF mockup and test if that fits.

Goes to show that it's worth mocking up the entire assembly before ordering anything, rather than relying on measurements upon measurements. Not sure where the error crept in but crept in it did!

[BiTurbo228]

Oh, for reference if anyone wants to use these Peugeot 106/Citroen Saxo calipers for their brake conversions, the relevant dimensions are:

Peugeot caliper dimensions
Lug spacing: 82mm
Bolt size: M12 (needs to thread into the adapter)
Lug centreline chord to outside of pad: 57.5mm (take this dimension away from your disc radius to tell you how far out your lugs need to be)
Lug mounting face to back of disc (34mm high Peugeot 205 front disc, 6mm face thickness, sliders centred, full thickness pad): 17.8mm

GT6 upright dimensions
Drum plate mounting face to front of hub face: 45.8mm
Mounting bolt pattern: 4x101.6mm