Spitfire mk2 brake upgrade type 12 to 14

[Benjamin Swatton]

First post after a few years presume the model specific forum has gone so several questions that lead to need for brake replacement:

1 How much trunnion play wobble is acceptable - My mk2 spit has one side with no play but the other wheel has a fair bit of trunnion play - approx 2mm wobble at the seal end

Not disassembled yet but fearing worst the vertical link thread is worn - if so i understand replacement mk1-mk2 vertical links are extinct - if so i'm into a type 12 to type 14 conversion. This coincides with me needing to investigate a possible sticking caliper piston and replace a disc

2 I have persistent disc brake scrub one side only for last 20k miles its only a problem if I turn tight but no where near full lock and disc is 0.006 lateral out of true on outside face I think this is beyond limit of 0.005 I read in a maintenance guide -can anybody confirm limits of trueness ?

3)Can somebody explain why they went from type 12 to 14 system as there is a lot of change - I don't want to change unless necessary but the lack of vertical link availability could force the issue, and I'm just wondering whether  the 12 system has other problems that maybe affecting brakes and I should ditch it all -e.g.  as spitfire graveyard mentioned the caliper mounts can bend and I'm wondering whether another noise I'm getting is not a sticking piston but other issue that will all go away if I blitz the lot and go type 14

This is a car that has done 20k in last 5 years after a lot of rebuilding it's no box of rot and I want it right as it's on motorways regularly the vertical link snapping scares the hell

Thanks

 

[RobPearce]

That much play does sound like the VL is probably shot.

The conversion is really just a case of dropping the whole Mk3 (or later Herald) hub assembly in - the trunnions and ball joints are the same, as are the actual hubs, I think, but everything between them gets changed.

If you have brake scrub only when turning then it's not the disc. More likely some combination of bearings and trunnions being worn.

The factory changed from type 12 to type 14 because the type 14 are a better caliper. The re-design of the vertical link was to reduce assembly cost - the type 12 setup is based on the drum brake bits with some adapter brackets, the type 14 is designed for disc brakes from the start.

[Benjamin Swatton]

Thanks for info,  I don't see how the trunnion can affect brake scrub but yes the bearings could however they are as tight as permissible whereas the wheel on the opposite side has more bearing play but no scrub and the disc is truer hence I suspect the disc on the other side that is scrubbing to be just a little too far out of true to cause a scrub maybe exacerbated by a both pistons not retracting evenly/sufficiently. when I rebuilt calipers years ago I regrettably replaced only the damaged pistons which means that half are the new pistons made from machined (not very smooth) stainless and the other half are the good original ones which are polished chrome and I think I noted back then they don't retract at same rate because of stiction.

Edited May 26, 2021 by 13254
Mistake

[Benjamin Swatton]

Disc brake max permissible runout  is .004 according to P.Olysager motor manual 85, there was no mention of this limit in the Haynes manual I can see. I measure outside face runout total but of course the inside face theoretically should be taken into account however there is no definition on how to measure 

The disc I have that is on scrubbing side is 0.006 runout total measured on outside face with dial guage over 1 revolution . so it's 0.002 over limit . 

It's not a big deal as slight brake scrub is only when U turning and new discs are cheap as chip's, I was just wondering whether anybody checks their disc runout!

[Benjamin Swatton]

Ok , It appears there may have been  a misunderstanding on a telecom - I thought i was told mk2 verticals were no longer available however rimmer parts catalogue clearly shows them to be identical part to later cars through to mk5. Again rimmer bros cat also suggests the hubs are the same for all cars but again I thought I  was told they are  different and I needed to change out along with discs if going from type 12 to 14 calipers. I think I need to double check with  the supplier just goes to show need to check parts catalogue to be sure

[thescrapman]

Do not beleive everything you see on the Rimmers website!

Early Type 12 vertical links are same as drum brake ones, as Rob said. If you have a removable calipers mount it is early, if the caliper bolts direct to the link, it is the later part.

mk3 to 1500 (Mk5?) are the later type and what is available.

seriously consider a trunionless setup if the current standard vertical links are poor quality. Issues can be a poorly cut thread, oiling hole drilled off centre amongst other problems.

I have a memory of a much better source of vertical links becoming available so may not be an issue assuming you buy them.

Later hubs are different to later ones, in that thy are chamfered to clear the larger calipers.

Edited May 27, 2021 by thescrapman

[RobPearce]

As Scrapman says, I wouldn't trust Rimmers. They told TRGB that a Toledo needs a special clutch that's hard to find, when actually it's the same part as a Mk4 Spitfire.

If you want accurate information, go to Canley Classics. They do show different part number for the type 12 and type 14 hubs but the difference may not be that much.

It's easy to get muddled because the early setup (for type 12) looks the same as the setup used on the GT6 (with type 16s) but shares very few actual parts.