Packard Forum Index » V-8 (1955-56)

Facts: Drums have more grab (when cool) and reqiure less pressure to operate than single piston disc of the same size.

Drums 10-11 in usually need 600-8-- psi to operate. GM metric calipers need 1000 psi to lock up or there bouts. So why did the top 3 switch in the 70s? Why did I use them on the Willys instead of 11 in drum?
both fit inside that 14 in period correct crest line wheel i was using with the wide polished rim lip. Ahh i love that look. anyome?

I have read some here who want to upgrade the brake system on some packards including replacing spindles and drums with disc spindle frt rotors and calipers and I agree with this on "performance cars, race cars, restomods, street rods" and such but for classics driven normally is there a need? The master however is another issue as safety is concerned.

Need to knoww the DIAMETER of the MC!!! That will determine what pedal ratio can or can not be used. However it mite be possible to combination the wheel cylinders to the MC diameter and pedal ratio.

The OEM 55-56 Packard has a 1:1 pedal ratio, 5/8 diameter (iIIRC 0.675")mc and about a 1" to 1-1/8" wheel cylinders.

I don't know about 55 pedal. The 56 pedal IS DEFINATELY NOT strong enuf for any pedal ratio much over 1:1. SPECIFICALLY THE HINGE of the 56 pedal is very flimsy. Fine for 1:1 ratio but that's about all. I suspect the 55 is about the same but don't really know.

Thanks for that info on the strength of the factory pedal. If I were to take on this venture I would,as has been done by many in the past, prefer to swap a pedal assm and master into a vehicle as a whole rather than mix and match but using the info on ratios will work. I agree with you that the master bore size anw wheel cyl size comes into play but not in the same magnitude as the pedal ratio and booster design. Most masters are right around 1 in and wh cyls 7/8,-1. All else being equal in a system- I had experience with the factory reps reccomending a change on a rear wheel cyl size to suit a condition or cust concern. ie 7/8 to 1 inch or 1-1/8 in to 1 for a sensitive rear brake or a heavily loaded trk (plummers) etc.

If a factory hydroboost sys is used or the above aftermarket hydro boost of which I have no experience- The correct, as used pedal bracket and ratio would have to be used to maintain correct pressures and pedal feel.

Lets remember the btv is a little of an odd bird in that the pedal ratio is 1:1 but it has a DISPLACEMENT type master without a cup seal and the piston size and bore size dont really translate. Lets agree that from here forward we are discussing modern style master cyls and the rules, pressures,guideline,ratios etc are for retrofits of newer equipment into these classics.

Is the GM hydro boost as used thru 1990's and beyond on ALL GM cars or only used on 4 cylinders or maybe small 6's???? Was it used on any cars with big V8'ss or even small v8"s.

Getting back to upgrading the brake system say on a 55 btv 4 wheel drum. Are there many out there who drive at very high speeds or in rush hour traffic stop n go or are on mountainous roads? i guess in colorado or similar the need to upgrade to frt disc may be prudent. Here in this area it seems just the master,booster,pedal assm is what we are talking about here.

If the modern GM hydo boost has the same size MC piston as the OEM Packard BTV then it would work just fine with the oem Packard pedal (set up as oem 1:1 pedal ratio). The next question would be how much STROKE does the GM have compared to the Packard BTV.

let me just say that in a Lg v6 or sm v8 atro cargo van which may be loaded stopping power was not an issue. I have no experience with med or hvy duty trks but I believe they were also used in hvy duty diesel trucks due to no vacuum available. If anyone has any info on theseunits used in diesels- they might know if the hydro boost or master were larger capacity. Surly the weight of those vehicles exceeds any Packard.