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Original GT40s You know if you belong. If you don't we'll tell you.

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Old 21st May 2017, 08:03 PM   #1
Ryan Love
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Originals brake specification and development

I am trying to find out some details about the original brake system specifications and the like. Tyring to spec my replica in the spirit of the original to some extent.During the course of the search I have been unable to determine what the disc sizes are, so I guess the next interesting question is, what do original cars do for maintenance items
Can you still buy the discs? Or are owners getting them custom made to original specification?

Can anyone point me to a good book that would give the details?
I see some mention in Jimmy & Alistair's Cars build thread about original 4 piston Girlling callipers and see a vented rear disc, but just about every other photo I see shows a solid rear disc?
when was this change made on the original cars, what chassis numbers got them?

Cheers, Ryan
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Old 22nd May 2017, 03:07 AM   #2
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Re: Originals brake specification and development

Ryan,

Others will be far better equipped at answering than I am. I just got here first.

Early GT40s used three-Piston Girling BR and CR calipers with solid discs. Later cars used four-piston calipers (I think?) with vented rotors.

The early three-Piston calipers were the same as used on the 427 Cobra. Dunno about the discs though.
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Old 22nd May 2017, 04:49 AM   #3
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Re: Originals brake specification and development

Mike is correct. Earlier cars had solid discs. Vented discs used from '66 on if I remember correctly.

Check out bgdevelopments.co.uk

They can supply most of the original spec calipers and discs.
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Old 22nd May 2017, 06:16 AM   #4
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Re: Originals brake specification and development

Vented discs are 304mm x 32mm and use separate bells (steel originally,but everyone uses ally now). Calipers were Girling 18/4 all round or 18/4 front and 16/4 rear. CR and BR calipers are two piston, the three piston caliper on the Cobra was a 16/3 and 12/3 set.
The reason you see so many cars running the lesser solid disc setup is that this is mandated by FIA historic regs for the pre '65 class, which is what Goodwood runs to. How this is reconciled with cars running Weslake head sets is a puzzle that's beyond my pay grade.
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Old 22nd May 2017, 08:22 AM   #5
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Re: Originals brake specification and development

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Originally Posted by sfm6s View Post
The reason you see so many cars running the lesser solid disc setup is that this is mandated by FIA historic regs for the pre '65 class, which is what Goodwood runs to. How this is reconciled with cars running Weslake head sets is a puzzle that's beyond my pay grade.
Is it because they wanted to slow them down?

Do the T70 spiders run solid disks at Goodwood as well? Never seemed like a fair fight against the GT40s.
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Old 22nd May 2017, 11:01 AM   #6
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Re: Originals brake specification and development

Goodwood likes to present itself as a stickler for authenticity but the reality is rather different. Pretty sure the T70s run solids as well,but then they're over 400lbs lighter.
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Old 23rd May 2017, 08:37 AM   #7
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Re: Originals brake specification and development

Thanks for all the replies. Interesting reading.

i have been going through this today
Ford GT40 and GT Ultimate Portfolio 1964-2006 : R. M. Clarke : 9781855207431

I can find references to 11.5" as well as 11.56" discs. i can only find one mention of a width in the book at 0.75', which i assumed was for a vented disc.

However when looking on the BG Developments site, i see that the vented stuff was used with the 18/4 and 16/4 calipers which required a disc of 1.1 to 1.25" thick. this certainly looks to be inline with what Racing Icons have fitted to 1049.
Ford GT40 Restoration - Chassis 1049

has anyone here fitted an 11.5" x 1.25" disc in the 18/4 or 16/4 caliper? Just curious if that sounds doable.

Ryan
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Old 23rd May 2017, 09:13 AM   #8
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Re: Originals brake specification and development

After having driven cars on the track with solid non-vented rotors in the past, I would flat refuse to do it again as it can be very dangerous. With a car as expensive as a GT40 - well - originality be damned..
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Old 23rd May 2017, 09:51 AM   #9
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Re: Originals brake specification and development

Even with the thicker disc the pads were pretty hefty (ds11) as in thick.
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Old 24th May 2017, 01:14 AM   #10
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Re: Originals brake specification and development

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Originally Posted by Big-Foot View Post
After having driven cars on the track with solid non-vented rotors in the past, I would flat refuse to do it again as it can be very dangerous. With a car as expensive as a GT40 - well - originality be damned..
It is pretty remarkable the lengths the teams go to in order to cool the solid discs. Very elaborate boxes are fabricated which wrap around both sides of the disc and are connected to flexible hoses which in turn feed them fresh air from ducts in the bodywork. Evidently it is effective judging by the extreme. Raking you can see at all the races.

Brake cooling pays ENORMOUS dividends, but particularly with solid discs.
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Old 24th May 2017, 06:57 AM   #11
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Re: Originals brake specification and development

I'm in agreement with everything you said Mike...
They may have also used forged steel rather than cast iron rotors. Steel would be much more stabil at higher temps than iron would. I worked to try and get shrouds and ducting to be effective and was only marginal in making it work (at the expense of more than an inch of steering travel).. The brake rotors would still warp, pulsate, flat-spotting tires and just flat-out locking up unpredictably...
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