Mr C
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| posted on 5/9/13 at 07:58 PM |
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Well done Jeremy for persevering with this. Hi again Ash two nights in a row   ..get on and get that car fixed.. ..
How easy would it be to do the calcs with willwood parts, maybe powerlite calipers, or the other option is another AP caliper on the back...?
Girl walks into a bar and asks for a double entendre, so the barman gave her one
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jeremy
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| posted on 5/9/13 at 08:18 PM |
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My calculations suggest the car needs 50/50 bias on the brakes. So two possible options are:
1) Replace the tandem master cylinder with dual cylinders: 0.688" bore front and 0.5" bore rear. However, I don't think we'll
find a 0.5" bore and serious modification would be needed on the pedal box.
2) Replace the rears with the same callipers and discs as the front. This presents the issue of a separate handbrake calliper (and the AP callipers
aren't the cheapest). (And the master cylinder would need changing for a 50/50 bias version).
There is also the option of replacing all the callipers!
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MarcV
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| posted on 9/9/13 at 03:18 PM |
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From my basic calcs along with a few assumption I get a brake pressure distribution of 38% front and 62% rear. This is for 1.1g deceleration which
gives 55% front load and 45% rear load.
Also, the 1 1/16" MC will give a very high pedal effort. In the starting post however I noticed a 60/40 MC with unknown diameter.
So this 60/40 split seems ideal (with 40 at front and 60 in the back), but I am quite sure that the diameter will be too large (in general for boosted
brake MCs) and probably the available stroke is the wrong way around.
With 0.625" being the smallest MC around (well available), you'd need about a 0.8125" for the front. If my calcs are correct this
will balance out your brakes and seriously reduce pedal effort (less than half of what it is now).
Is the rear brake radius correct? I'd assume a 126.5mm disc radius - 18.5mm piston radius = 108mm brake radius, maybe a bit less if the brake
pad overlaps the piston.
I would think that the calipers aren't too far off and going to separate MCs would be well worth the effort. Probably quite a bit cheaper than
changing calipers.
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Mr C
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| posted on 9/9/13 at 05:15 PM |
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quote:
Originally posted by MarcV
From my basic calcs along with a few assumption I get a brake pressure distribution of 38% front and 62% rear. This is for 1.1g deceleration which
gives 55% front load and 45% rear load.
Also, the 1 1/16" MC will give a very high pedal effort. In the starting post however I noticed a 60/40 MC with unknown diameter.
So this 60/40 split seems ideal (with 40 at front and 60 in the back), but I am quite sure that the diameter will be too large (in general for boosted
brake MCs) and probably the available stroke is the wrong way around.
With 0.625" being the smallest MC around (well available), you'd need about a 0.8125" for the front. If my calcs are correct this
will balance out your brakes and seriously reduce pedal effort (less than half of what it is now).
Is the rear brake radius correct? I'd assume a 126.5mm disc radius - 18.5mm piston radius = 108mm brake radius, maybe a bit less if the brake
pad overlaps the piston.
I would think that the calipers aren't too far off and going to separate MCs would be well worth the effort. Probably quite a bit cheaper than
changing calipers.
Thanks Marc,... interesting, quite different to Jeremys calculations,.. Marc, are yours based on getting the existing calipers working properly and
does this mean that Russ original idea of swapping the connections on the MC might be a goer?
How do the calculations work out, say if we used the AP four pots all round with 275mm discs? (and put in a bias valve to tweak)
Girl walks into a bar and asks for a double entendre, so the barman gave her one
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jeremy
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| posted on 9/9/13 at 05:19 PM |
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Swapping the ports on the master cylinder will do nothing for the brake balance as the bore is the same.
All it will do is mean the rear piston could move a lot more if able to as it has the longer stroke
1.1g is quite high deceleration. 0.8g is more commonly used.
[Edited on 9/9/13 by jeremy]
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MarcV
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| posted on 11/9/13 at 06:36 AM |
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Yeah, with 0.8g decel (which I would think is on the low end, 1.1g is surely on the high(est) end of the range) a load distribution of 50% / 50% is
found.
With the current calipers that turns into the rear pressure being twice as high as the front.
If you'd assume the front calipers are also used at the rear, you'd logically end up with equal pressure front and rear (assuming the
0.8g, with 1.1g you'd need 56% front and 44% rear)
However, pedal force still remains high (albeit lower than the current setup) and I would suggest going to a smaller bore tandem MC in that case.
So yeah, matter of price / work etc I'd guess. Both routes could lead to a much improved brake performance.
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