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| 6 cyl Bristol cars Type 400 to 406 - restoration, repair, maintenance etc |
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26-08-23, 07:53 AM
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26-08-23, 09:00 AM
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My 403 was also converted to Dunlop discs by the factory in 1958. It has the cap I pictured so I imagine they used what they could get hold of.
I had endless issues with the Dunlop callipers sticking and finally changed to Coopercraft. It was a huge improvement. I will be interested to hear how you get on. 1:1.9 seems a little low to me. I'm struggling to find a ratio for the original 406 servo 4257-551.
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26-08-23, 12:59 PM
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Mike and David ,
I have front Disc brakes on one of my 400 and the other has discs front and rear. These are mostly 406 parts, but with some variations . I disagree that drum brakes need more boost with the servo than a disc brake car . It needs the opposite !!! If drum brakes are over boosted they will easily lock the brakes, even at touring speeds. Here in Australia all the remote Servo (Booster) are rated in psi . The common booster for drum brake cars are a PBR VH44 at 820 psi , Disc brake front or F&R use either a VH44J at 1270psi or VH40 at 1470 psi. I fitted the VH44J at 1270 psi to both of my 400's . I also fitted a Jaguar vacuum tank (from memory ex a Mk9 or 10) to both , which is very similar to to the one fitted to 406 . The brakes on both are very good and not over boosted . It is a major improvement to the braking system needed if one actually wants to use the car . Does anyone know how the ratings of servos in UK eg 1:1.9 or 1:4 compare with psi valves ?? Geoff
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26-08-23, 02:54 PM
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Input and output pressures for PBR boosters can be found here:
https://d31wxntiwn0x96.cloudfront.ne...4_16032018.pdf This shows your VH44J as 560 in, 1270 out or about 2.25:1
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