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MG Midget and Sprite Technical - Big brake upgrade advise

The 9" brake conversion saga continues, the discs that i have have a slightly larger PCD, also they have clearance holes rather than threaded as per the spidget ones.
So do i redrill & tap at the correct PCD (at 90 deg to the clearance holes) or elongate the existing holes, which i don't think is too good an idea.
Then again i could use the existing Pcd, elongate the clearance holes in the discs & put a threaded adapter plate behind the disc as i think theres room.
Anyone have some first hand experiance with all this as i'm looking at the options, procastrinating & working on my Triumph instead.
cheers
Brad
B Richards

I definatly would not elongate the stud holes in the rotor...

My guess you got the wrong rotors, should be triumph spitefire rotors if the PCD is not 4x4 then there not spitefires

the adaptors will work, but if you got a swa midget....measure carefully, or your going to be doing some suspension mod work or body re-work if the rear wheels rub.


while your there Id upgrade from 3/8 to 7/16 wheel studs

prop
Pro P

I'll go & check part numbers again, should be correct though as they came from a proper Triumph shop.

I think the best way out of it is to redrill at the correct Pcd, which is they way i was thinking, but sometimes you just need a second opinion.

Time for a remeasure.
Brad
B Richards

I wouldn't expect spitfire discs to use 4x4 as the Triumph wheel PCD is 3.75" x 4, although the disc mounting may be something else.
David Billington

Brad,

Regarding your query I would be inclined to redrill and tap but it depends on whether there is sufficient depth of material to take the thread. IIRC you want about 1.5 times the thread OD in CI or what the original disc have as thread engagement. Otherwise if the 9" disc is intended to have nuts seating on the inside then what about redrilling clearance holes at the correct PCD to match the spridget hub and use nuts and bolts to hold the discs on.
David Billington

If I am wrong...(I do have blond hair) But didnt we have a huge discussion about a month ago for making a big brake upgrade modification using spitfire rotors and MGB calipers, and making a special spacer block....If not, then What am I thinking of,,,that was here on this forum wasnt it???

If I gave bad advice...im sorry!!!

prop
Pro P

Prop, Your right, that previous thread was started by the same fella just he procrastinates sometimes ;-) as he wonders how to find more speed and power

Shaun
Shaun

Thanks Shaun, your right as ever, never enough time for all my projects.
By the way I've been drooling over my new 1.5:1 titan rockers tonight :-)you'd like them, but then again you'd need a serviceable head to put them on :-)

Anyway back to the disc saga, the sprite wheel pcd is 4' but the bolts which hold the hub to the disc are not.
On the sprite the disc is threaded with the set screws coming in from the bub/ wheel side. On the spitfire discs the hole is a clearance fit & a slighty larger pcd, so i either have to drill & tap the disc, which as Dave points out leaves little metal between the thread & the inner hole of the disc, or i make another adapter which fits on the inner side of the disc & make this with the threaded holes. I think there will be enough room to do this as the spitfire discs have a deeper inner dish than the sprite ones. Then again i could be going in the wrong direction. Anyone got a better idea?
cheers
Brad
B Richards

Brad,

Not sure you took my previous comment on the thread engagement correctly. By 1.5x thread engagement I meant that the length of thread in the disc the bolt engages should be 1.5X the bolt diameter so as IIRC the bolt is 3/8" UNF the tapped thread should have a length of about 0.56" minimum. On checking my GT6 manual the discs are held to the hubs by bolts so the disc should have a machined surface for the bolt head to seat against so retaining the discs with nuts and bolts should be OK, I might look at all metal locking nuts if used for severe service where the temperature rise is higher.
David Billington

Thanks Dave,
it was getting late when i wrote my last post & i'd been having a lot of grief with my other project, which as Shaun could tell you is an ongoing 14year saga.
Your right though, nuts & bolts seem the way to go with the brake mod.

Prop, your not losing it yet, i work away from home & have just got back after two months, so a lot of spritely jobs catch up on.

This week i debumpered the Sprite (which the wife still hasn't noticed) & added a wing vent which did the job niecley of stopping her overheating in summer traffic jams.

cheers
Brad

B Richards

B Richards, Grampian,

I would love to see a pic of that wing vent, if at all possiable....Im going to harbor fraight this week end to get some sheet metal tools to try and make another (good looking) heat vent, That I have recently put pen to paper to try and create...5th time Im hoping is a charm...I must say, they are looking better each time I make one...so Im starting to get the feel for them.

sorry for the high jacking

prop
Pro P

Prop,
I've spent ages researching all the various options, some very nice examples out there, but i was after someting that was easy to fit, would look reasonable & wouldn't require any re-painting.
I have a fully welded shell (even the wings are seam welded by the PO) so it had to go in situ on the car as well.
Having a black car has let me get away with a bit more than a car in a lighter colour, so it kind of looks ok, for now anyway.
I'll go start the camera hunt & post a pickie later.
cheers
Brad
B Richards

Prop,

if i had the time i would have inset the vent into the wing, it would look better.
A used spark plug will be your reward if you guess the vent origins, correctly first time around.
cheers
Brad
B Richards

Is it my dyslexic fingers or is uploading a photo awkward?!
B Richards

Prop the file is too large, i'll take another tomorrow.
cheers
Brad
B Richards

Brad

I find this tool ideal for the job.

http://fileforum.betanews.com/detail/Resize/1042979619/1

it's freeware and easy to use. Poor Bes with no chrome.......

How about fitting a splitter on the front to cure the lightness and you could join the jetty boys.
Shaun

Shaun,
very funny, you know your there every saturday yourself in the 'Yellow Peril'.
Here's some photo's:
One hub done.




B Richards

Prop, one for you.


B Richards

Land Rover!
Tarquin

Thats right Tarquin, i've left enough metal behind to scroll the edge & have the vent flush, if i ever get back to it.
Brad
B Richards

This thread was discussed between 03/09/2008 and 07/09/2008

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.