Packard Forum Index » V-8 (1955-56)

The 13/16 bore of the Honda unit compensated for the shorter stroke of the Honda unit relative to the rather LONG stroke of the BTV.

Note that any attempt to fit a modern MC unit to the OEM BTV power unit will create cleaaarence problems at the frame.

LOOK at the 55 56 frames. The very front most point of the OEM BTV MC haas maybe 1/8 frame clearence. That is why the BTV mc is rather SHORT compared to most master cylinders. LOOK at the frame!!! There is a slight indention in the frame to allow the BTV mc to fit and clear the framee.

Got into the BTV last night, looks like there was brake fluid in the can. Lots of orange goop at the bottom. Looks to me like the booster was sucking fluid through the outer seal of the master into the back of the can. When I pulled the can off the master the triangular gasket and rubber ring had dried brake fluid on them.

My BTV looks like it was rebuilt sometime before I got the car, the piston is shiny no rust a couple of wear streaks in it but smooth.

Haven't gotten the master apart yet though, I should have pictures to post when I'm finished disassembling it.

The BTV is 11", so that's about as long as I can go with the space provided.

Found a couple 5/8 masters from wildwood that I'm interested in.
However both are single outlet.

One is 3 3/8" long, and the other about 5 1/4".
The 3 3/8 inch master I believe had a 1 1/4" stroke.

How do I accurately measure the stroke length of the BTV master?

With the BTV mc fully assembled then pull the ram all of the way out until it stops. Measure. Then push ram all the way in until it stops. Measure again. Subtract last measure from first measure and that will be the travel.

My personal opinion at this time is to forget about any DOUBLE outlet mc.
Add not any more complication to the this R&D project. The dual can come later. OR let me put it another way:
Suppose the BTV had NEVER become the controversy that it IS. THEN, we would all be driving around happier than a pig walllowing in shit with confident BTV's as a SINGLE outlet cylinder.

On ANY of the BTV mc's that u encounter be sure to put a magnet to the MC ram to determine if it is stainless steel or regular steel.

NOTE THAT some SS IS magnetic. I have no idea as to wheather or not the reproduction rams that are SS is magnetic or not. NEVER tried one. VERY high grade SS is NOT magnetic at all. Low grade is somewhat magnetic but not as magnetic as a similar piece of regular steel. I don't know what your experience level is with metalls relative to making such a determination of SS v regualar steel. But what i have explained above is the best i can do to explain it.

Just a wild idea here to keep in mind:
IF the stroke of the Wilddwood mc's is to short then see what kind of DUAL outlet mc's are available that will fit the space restriction. MITE BE POSSIBLE to convert the dual outlet to a single outlet thereby allowing for additional stroke.

As i side note, even 11/16 or nothing greater than 3/4 diaameter MC mite be just fine.

Also to to be more specific the BTV ram is not exactly 5/8. IIRC it is something more like .685" diameter slightly bigger than 5/8. But measure it with a mic if u hace one to be sure about the diameter.

Measure the ram travel and the diameter. If u can't compute the diplacement then i can. Knowing the displacement might allow for some "wiggle-room" when choosing an aftermarket MC of "best-fit". i.e. any final decision that mite be difficult say between two different mc's then knowing the displacement, stroke and diamter comparisons mite help in the final decision.

You really can't go by the stroke distance of a BTV because the operation is so different. Conventional masters will generally not have as long a stroke because the larger pistons push more fluid in a shorter distance. IIRC, the BTV is around 3 1/2" +/- max but PackardV8s method of checking is the way to be sure.

Your booster limits will determine part of the new max stroke available. You will have to decide on which booster you are going to use and see if it will work with the master you choose. The adjustment at the wheels will determine part of how much stroke you actually need or use. If the shoes are properly adjusted the master will move a small distance before brakes apply and conversely, wear or a bad adjustment where the wheel cylinders have to move the shoes quite a bit will require a large movement of the master. That last part is one thing to be concerned about with a small diameter master. Figuring worst case, can the small master move enough fluid before bottoming that the brakes can fully apply.

You also need to factor in mechanical design compatibility between master cylinder and booster. The bolt pattern, centering pilot arrangement, and spacing and size of the bolts connecting the two are important. The relaxed point of the booster has to be far enough back that the piston rod adjustment can ensure the master piston is in it's full relaxed position yet the actuating rod to master has to be the proper length so the booster doesn't have to travel far before the master piston starts to move.

It might be worth calling ABS or Master Power Brakes and speaking to one of the technical people to see if the Wilwoods will work with the 7" universal booster -- or the booster you are thinking of getting -- before spending any money. If not, maybe they have another option.

IIRC it was HH56 in one of the above posts that indicated the rod in the POWER unit will need to be supported if a conventional MC is transplanted. SO maybe need to allow for something like a 1/8 or 3/16 thick spacer between the NEW MC and the power unit can to act as a support for the end of dhe rod in the power unit. That mite effect the final overall length (shorter) of the new MC chosen.

IT is quite possible that he can use a SLIGHTLY dhorter stroke aftermarket MC. Note that the OEM BTV usess up, i'm guessing, about 3/16 of the stroke before the compensator is fully closed.
On a conventional design cylinder it is probably only about 1/16" to cover the pee hole from the reservoir.

He will just hace to measure the BTV to see how far the ram moves before the Comp port is fully closed. Then compare that to the movement of the aftermarket mc.

Hopefully any aftermarket MC he chooses will be close enuf in all aspects to retro fit without having to worry about much fine or precision measurements.

can you give us more details ? what mc did u use ? how did you hook it up . etc, etc thanx