Packard Forum Index » V-8 (1955-56)

I appreciate that there are other topics covering brake issues, but I thought I might start another as I'm not sure how to dig the relevant info out. I think I have mentioned previously that since reconditioning the brakes on my car (drums honed, new linings, wheel cylinders reco'ed, new rubber hoses), the car pulls rather strongly to the left under brakes. No amount of adjustment seems to be able to compensate for this unnerving tendency. So yesterday, in an effort to try and eliminate some variables from this seemingly complex equation, I swapped the front drums, shoes and bearings left to right, and readjusted. I then took the car for a short test drive and was astounded at the difference. Instead of transferring the strong pull to the right as I was expecting, braking is now so close to neutral that it's close enough for me. Can anyone enlighten me as to why this would be?

Also, as my next step was going to be changeover of the wheel cylinders, I was looking the spec's up in the service manual and noticed that the fronts are 1 1/8" and the rears 1". Why so? Presumably there's a good reason but I thought you would have all four the same to give even braking. Wouldn't smaller cylinders on the rear reduce braking capacity at that end (and maybe increase pedal pressure), and thereby reduce overall braking efficiency? I acknowledge in advance that I'm no expert in the science of braking, although I have often pulled them down and rebuilt them. Regards, John

quote:
" I swapped the front drums, shoes and bearings left to right, and readjusted. "

Were the wheels and tires swapped from front to rear or side to side too or strictly the drums, shoes and bearings only????

As for the wheel cylinder size variation spec that is the way PMCC designed it based on their testing. I wouldn't change it. Smaller wheel cylinders on rear is typical across nearly all manufacturers. It is because of the way the car is balanced out from front to rear weight wise. Usualy more braking effect is needed on the front. With the single line master cylinders pressure is always equal to each wheel cylinder. The smaller WC acts FIRST and moves fastest but applies less pressure to the shoes. The bigger WC applies more pressure to the shoes but slower. Its a balncing act of shoe pressure, and speed of action that is determined by rigorous testing. Front of car heavier than rear of car.

Changing the wheel cylinder size from spec is ok up to 1/16" variation but no more than that. Prefer OEM spec. Unless u're pulling 7000 pound trailers thru the Rockies or trying to win 24 hours of LeMans i would not change the wheel cylinder size.

Sometimes aftermarket wheel cylinder parts-book reference will vary by 1/16" and that's ok but not prefered.

Sounds like the cause of the pull didn't involve a problem with any part, in and of itself, then. Perhaps it was just a matter adjustment. Drive carefully and continue to monitor the condition. Give the new linings some time/miles to wear into the arc of the honed drums and check adjustment again.

As Keith noted, the factory's selection of wheel cylinder size was used (for decades) to proportion braking action relative to the weight bias of the vehicle - front-to-rear. Unless otherwise advised by factory bulletin, I'd stick with stock sizes.

Thanks for the advice guys. Now that we seem to be braking pretty evenly I won't be touching the wheel cylinders unless something unforeseen occurs, even though a little less pedal pressure would be nice. The wheels and tyres were not swapped so whatever has changed would seem to relate to the braking components. I previously did try swapping the front tyres over but that resulted in a bit of drift to one side, more noticeable when coasting, so I swapped them back again.

There are two things that could possibly have some impact that I have thought of. The side of the brake shoes that rubs on the backing plates is now the opposite to what they were before. I actually made sure the rubbing pads on the backing plates were as smooth as I could get them, and lubed, so I wouldn't have expected this to make much difference. Secondly, I am now running a different power steering ram and the steering seems a lot smoother than before (with no leaks now). I can't see why this should have any effect on braking, but possibly could with the steering drift I mentioned before.

When all said and done, even if it can't be explained with any certainty, I very happy with the outcome as pulling up is much less stressful. Regards, John

JP -

Are you saying the pedal feel is too firm? That could indicate a problem with the power assist or the vacuum supply required to accomplish such.

Vacuum supply issues could be anything from failing check valve (at back of carb) to leaking hoses or reservoir (latter mounted on rear of left fender splasher).

OR, are you saying that the pedal action delivers too much pressure to the wheels - that the brakes are grabby?

G'day Brian. The pedal is a little too firm, but not dangerously so if you have a reasonably strong leg. I have had the booster rebuilt, fitted a new check valve and replaced all the vacuum hosing, so I think the issue is how the BTV was setup when it was rebuilt a couple of years ago (by Karps, CA). I don't think there is a problem with the reservoir, but that's something I should investigate. I'm pretty sure that there are no vacuum leaks otherwise, and am toying with the idea of fitting an alternator with an integrated vac pump, similar to what Peter Toet (Peter Packard) has done. This is only an idea at this stage but I would like to find out whether hooking up an auxiliary source of vacuum might be helpful (ie, stronger vacuum = reduced pedal pressure). Apart from this, as I have A/C and an electric pusher fan wired in with it, I have been thinking that an alternator might be an asset, especially in summer when the A/C and lights are on. The generator seems OK most times, but it's hard to read the instruments when idling at night in traffic because they are so dim. Regards, John

For summer AC use and lites on try setting idle speed to as high as 800 rpm, especialy with automatic trans. The higher idle speed will allow for better cooling (AC and engine) as well as correct the dim dash lites or at least brighten the dash lites to an acceptable level.

JP -

OK, that jogs my memory of your firm pedal issue from another thread. I only asked because some people complain that the power brakes seem touchy.

There's no factory-provided adjustment that I know of - not even internal. I suppose there's a way the assist could be tweaked, but have never needed to do so. More likely, there's a problem somewhere.

To check the integrity of the reservoir, just remove and plug the hose and then test drive to see if that has any effect on pedal feel.

You really shouldn't have to add a vacuum pump to the power brake system. The V8 should develop more than enough vacuum to operate the power booster - UNLESS there's a pretty substantial vacuum leak somewhere. The vacuum reservoir (tank) is only there as a reserve. The vacuum pump on the OE oil pump is only there as an auxiliary source for the vacuum wipers.

Also, make sure the horsehair filter on the side of the booster shell isn't clogged. For the power piston to move in the direction of vacuum (and help apply the brakes), there has to be a way for air to enter the opposite side.

I should add that I once experienced a loss of power assist in one of my V8s, and when I removed the toe plate and end cover, with the BTV still in-car, I found that the hose that supplies vacuum to the power piston had slipped off the fitting that goes through the shell. Turns out some PO had foolishly replaced the large-diameter, thick-walled, formed vacuum hose with common fuel hose. Not only was the fuel hose a bit hard/stiff, but it didn't fit the booster fitting very well - even with mechanic's wire that had been twisted on each end (when the OE part never used any clamps). I slipped the hose back on (until I was able to scavenge a good used OE hose) and problem was solved.

WRT to dim instrument lights, are you sure you don't have a problem with the rheostat in the headlight switch? That's a common failure. Decades ago, as parts had become scarce in this area, rather than replace the entire switch on his 56 Exec, my dad removed the common (black?) feed wire for the instrument cluster lamps from the headlamp switch and plugged it into a separate rheostat control that he scavenged from an old electric heater. However, I can't recall where he picked up the feed for that rheostat - perhaps another terminal on the headlamp switch. Just as a test, you might temporarily unplug the dash light feed wire form the headlamp switch and wire it up to a hot circuit just to see the full brightness possible within the current limits of your electrical system.

Hope this helps.

My 56 Pat pulled to the right after a very complete brake job. The solution was to round the shoes....

Got rid of the pull, but they squeak now...just when you are almost (but not quite) stopped....

Sounds like they are still not square, any long hills around, with a long straight get up 60 mph, put brakes on firm,, till you stop.

this has something to do with "setting" the shoe to the drum. its worked for me.