brake piston sizes
Discussion
OK I've just been reading up on brakes and have made a quick spreadsheet to calculate bias etc.
Does anyone have any dimensions of master cylinder and caliper piston sizes for any configurations fitted to Wedges?
In particular I'd like to know figures for the following.
The original solid disk setup.
The vented ford caliper upgrade.
The AP (Princess rocking horse do-do) caliper.
Jag calipers.
I understand that in usual TVR tradition there were loads of different master cylinders used but were they all using the same diameter piston?
Does anyone have any dimensions of master cylinder and caliper piston sizes for any configurations fitted to Wedges?
In particular I'd like to know figures for the following.
The original solid disk setup.
The vented ford caliper upgrade.
The AP (Princess rocking horse do-do) caliper.
Jag calipers.
I understand that in usual TVR tradition there were loads of different master cylinders used but were they all using the same diameter piston?
shpub said:
Errr why not fit an adjustable brake balance thingy and adjust it do your hearts content. A lot easier than trying to work it all out theoretically...
A valid point but I'm just trying to get my head around the subject and wanted to use some real world numbers. I was told once that the AP 4-pot calipers were a direct replacement because they had the same total piston area as the original 2-pot Ford calipers and wanted to mathematically investigate.Anyhow not sure how you'd do safe testing on the road for getting a balance bar set up correctly. I can imagine severe forms of death resulting from getting it set up biased too far to the rear. Speaking of which that Ultima 0-100-0 in 9.4 seconds video definitely had the rears locked so I guess a slight tweak would be in order. Bally impressive all the same!
Edited by leorest on Tuesday 6th November 20:05
Wedg1e said:
I have some Princess calipers in bits at home (Im at college at the mo!), can have a measure later. I think they're something like 32mm, maybe a bit more but I doubt as much as 40mm.
Much appreciated. What are you studying at college BTW? I'm guessing it's not the art of sarcastic whit as you've got that one polished to a professional edge LOL.leorest said:
Wedg1e said:
I have some Princess calipers in bits at home (Im at college at the mo!), can have a measure later. I think they're something like 32mm, maybe a bit more but I doubt as much as 40mm.
Much appreciated. What are you studying at college BTW? I'm guessing it's not the art of sarcastic whit as you've got that one polished to a professional edge LOL.Doing AutoCAD; I've been fiddling with it for 10 years, thought it might be nice to have a bit of paper to go with it.
Oddly enough I don't seem to write anything funny any more...
leorest said:
Anyhow not sure how you'd do safe testing on the road for getting a balance bar set up correctly. I can imagine severe forms of death resulting from getting it set up biased too far to the rear.
You don't need to be at warp 9 to set it up. I did mine initially at low speed on a deserted road. Then slightly tweeked it on a track. kevsmev said:
Leo,
The original solid set-up with granny calipers are 54.0mm diameter pistons. The later vented calipers were the same diameter pistons but had bigger pads. The Princess calipers are 1.5" diameter.
Kev
Area of grannies = 2290mm^2The original solid set-up with granny calipers are 54.0mm diameter pistons. The later vented calipers were the same diameter pistons but had bigger pads. The Princess calipers are 1.5" diameter.
Kev
Area of princesses = 1140mm^2 x 2 pistons = 2280mm^2
Wow - less than 1% out.
GreenV8S said:
shpub said:
The brake balance valve replaces the decel valve (which isn't that much cope in the first place).
Remember that neither of these will correct that static balance if you have got that wrong.Leo (learning a little every day... I hope)
leorest said:
By brake balance valve do you mean dual master cylinders connected by a balance bar arrangement? ...and why doesn't that affect static balance. ...or maybe the better question would be "So what's the definition of static balance then?"
Leo (learning a little every day... I hope)
The static balance is determined by the mechanical and hydraulic geometry of the system i.e. what size pistons you have, the disc/wheel size etc. This defines the distribution of braking effort under light braking, so this determines what happens when you're tip-toeing around a slippery corner and need to brake. If you have a twin master cylinder setup with a balance bar then you can use the balance bar to set the balance, otherwise you have to get the piston sizes right and/or move the calipers around to get the balance right.Leo (learning a little every day... I hope)
The dynamic balance determines how this distribution changes as the amount of braking increases. The brake distribution needs to change to reflect the weight distribution. For example under gentle braking your brakes may have a 50:50 split, under hard braking this might need to change to 65:35. This change is achieved by the bias valve. They usually work either by sensing either deceleration or line pressure, and restricting the flow to the rear brakes.
You need to get the static balance right, and then sort out the dynamic balance. The bias valves used to adjust the dynamic balance won't fix the static balance if that is wrong. Likewise, a balance bar can correct the static balance but doesn't affect the dynamic balance. They're separate problems that require separate solutions.
leorest said:
Thanks for the data all.
I always thought the AP callipers were 4-pot? Must be thinking of something else!
Anyone know master cylinder piston size and what about the Jag callipers?
...and just for completeness what are the standard disk diameters front and rear?
The Princess calipers ARE the AP ones... and yes they're 4-piston.I always thought the AP callipers were 4-pot? Must be thinking of something else!
Anyone know master cylinder piston size and what about the Jag callipers?
...and just for completeness what are the standard disk diameters front and rear?
Incidentally I got a brand new pair of rear discs from an Ebay trader (ie not private) for £12.
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