I would like to know was is the easiest way to access the brake proportioning valve on a 1979 308 in order to clean the electrical connection . Thank you for your help . P.
Straight from underneath. There should be an access panel right behind where the battery is bolted to the chassis. Lots of cars have this panel missing but you can access the valve easiest from this angle.
Is that the proportioning valve? My QV manual calls it "device for light signal or differential oil pressure in the brake circuits" and then shows another item in the rear brake lines near the rear called "pressure regulator".....but the parts manual doesn't show the pressure regulator and I'm pretty sure my car matched the parts book diagram not the diagram in the manual.
I went through this a year or so ago https://www.ferrarichat.com/forum/threads/brake-bias-proportioning-valve-clean-rebuild.671478/
Image Unavailable, Please Login Not sure Image Unavailable, Please Login Image Unavailable, Please Login But in the parts manual it's call a brake failure indicator.....I'm pretty sure there is no proportioning valvevin a 308. Image Unavailable, Please Login
Just looking at the guts of disassembled units (in the threads linked from this one) it surely looks like a differential pressure switch and not a proportioning valve.
It is just a differential pressure switch. The "proportioning" happens with the bias valve. There is a bias valve in the rear circuit after the switch that limits the rear circuit pressure the harder the brakes are applied. On my '77, the bias valve is located in the front by the switch, not in the rear of the car. See picture below. Differential pressure switch on the left, bias valve on the right. Image Unavailable, Please Login
I'm confusing things a little by calling them different names than the Parts book. You are right...what I am calling the pressure differential switch is the "Brake Failure Indicator" and the bias valve is the "Pressure Regulator".
What "parts manual" are you referring to here? Are you mixing 308QV and Mondial QV? The "pressure regulator" shown in the Modial8/QV WSM does seem to be shown in the Mondial QV parts manual: https://www.ferrariparts.co.uk/diagram/ferrari/mondial-qv-coupe-cabriolet/029-brake-system-(valid-only-for-lhd-up-to-chassis-no-43011) https://www.ferrariparts.co.uk/diagram/ferrari/mondial-qv-coupe-cabriolet/030-brake-system-(valid-for-rhd-for-lhd-from-chassis-no-43013)
Absolutely. I have 3 books: Mondial QV shop manual 308 QV/328 shop manual (which is really just a supplement showing what changed) US QV parts book So clearly not an actual complete set. The point is though the 308QV parts book doesn't show a proportioning valve and I didn't find one when I was pulling out the factory stuff to do the brake mods so I just assumed 30-8s don't have them, but there is a valve in the pic of the 77 308 setup. Now I wonder when it went away and why they made that change? or if the new style "failure detector" included a proportioning valve....I might go take mine apart and look.
Thanks. It seems such an odd design choice for a street car that it just never occurred to me before this thread that they had done that. .......I guess they figured that since most cars were GTSs its a safe bet most don't drive in the rain and will never notice or care about longer stopping distances on wet roads where no proportioning valve means the car is giving up about 15-25% of possible braking
