Front brake puzzle

[Orsom Weels]

Gent?s,
I have spent age?s searching archives but can?t seem to find a definitive answer to a bit of a puzzle my friend has uncovered with his S3?s front brakes. As this is taking up time that really should be being spent working on my +2, I thought I?d try a plea for help from those of you with much more knowledge than I.
Having purchased new calliper seal kit?s, pistons, pads & discs, he found the new pistons were bigger than those in his callipers, he then checked every thing else & consulted the workshop manual, not much about calliper piston sizes but it states the discs should be 91/2 inches, his old ones are 91/8 inches, & guess what, so are his new ones.
From what I?ve been able to find, I think he should have type 14 callipers with a 48mm piston from a later Spitfire , but he has type 12 callipers with 43mm pistons from Herald/early Spitfire, but I couldn?t find anything definite on disc sizes.
From what I remember, & a quick look on the interweb, it seems that Spitfires used a 9inch disc & GT6?s used a 91/2 inch item & I had always been led to believe that the Elan used a GT6 disc, which ties in with the manual, & the +2 used a special 10 inch item peculiar to it, so I checked the +2 manual & confirmed that their discs should be 10 inch, which is what I?d always assumed my +2?s discs were. I measured them & found they are actually 95/8 inch But obviously with the bigger type 16 calliper. Basically a GT6 set up
Now, were Lotus just being a bit optimistic with their stated disc measurements or have we both got the wrong size discs & did the Elan ever use the type 12 calliper, as this is what Triumph were fitting to the Spit at the time my friends Elan was built (1966), it?s an early S3 dhc. & finally , if we both have the correct discs, is it that the Elan actually uses Spitfire discs & the +2 uses the GT6 items

Thanks in advance, Tim

[john.p.clegg]

Just a note,the type number refers to the piston diameter in 1/8ths of an inch...

i.e.
type 16 2",type 14 1 3/4"...

John

P.S. my Plus 2 discs are not 10" but rather 9 5/8",maybe the 10" refers to the diameter available within the calliper?

[rgh0]

S1 and maybe some early S2 had smaller piston calipers that I presume were type 12. The rest of the Elans had type 14 calipers. I guess it is possible that somehow a S3 ended up with the early calipers either due to Lotus running out of the right ones or more likely due to a later rebuild when the wrong ones were fitted when an exchange of calipers was done with a brake rebuild company.

cheers
Rohan

[garyeanderson]

Lotus Limited (U.S. Lotus club) used to send this chart out with new memberships in the last century. It may be of help to some. The SP12 calipers were fitted to 26/0001 to 26/4109 (Ross and Robbinshaw book). Lotus felt the need to upgrade to the LF14 and I would look for a pair to replace the ones your friend has.

Gary

[Orsom Weels]

Hello chaps,
Thanks for the replies, they would seem to confirm my suspicion that my friend has the wrong callipers, so a pair of type 14's are on his shopping list.
Are we saying that his discs are correct at 9 1/8 inches ? It sounds like two of us have +2's with 9 5/8 inch discs, 3/8's less than the w/s manual suggests, the same discrepancy as between the Elan manual & the old & new replacement discs he has, does anyone have a definitive answer to this ? I'm guessing the discs are correct & the manuals are wrong, any thoughts on this ?
John, an interesting note on type numbers relating to piston size, however, my type 16's have a piston diameter of 54mm, which equates to 2 1/8 inches ? Is this where some of the discrepancies come from ? converting from metric to imperial & the rounding up or down to the nearest inch or whatever ?
Anyway, thanks again for all your efforts
Tim

[CBUEB1771]

John, an interesting note on type numbers relating to piston size, however, my type 16's have a piston diameter of 54mm, which equates to 2 1/8 inches ?

The +2 front calipers are 2 1/8 inch bore. Whenever I check dimensions on parts that were designed using English units (i.e. Girling calipers of this period) I set the micrometer or caliper to display inches, similarly I set to display in millimeters on modern parts. This helps to eliminate rounding or truncation confusion.