Packard Forum Index » V-8 (1955-56)

I purchased relined brake bands as part of my Ultramatic rebuild. When I installed the reverse band, I noticed that it was easier then the removal of the old one. I then did the following comparison of the original and replacement bands. The picture shows all of the bands with the left sides aligned to show the variance on opening gaps. The relined bands are the top two.

The gaps, in inches, measure, from top to bottom band: 0.575, 0.865, 1.310, 1.329.
The force, in pounds, to reduce the gap to 0: 6, 9, 15, 15
When closed around the ring gear, the gap is 0.33
The force to close around the ring gear is 2, 5, 10, 10
The unbound (not held by the operating lever and the adjusting screw) clearance between the band and the ring gear is: 0.040, 0.085, 0.155, 0.155
I haven't measured the bound clearance when adjusted per the service manual because it requires everything to be assembled.

I would think that you would want as much spring to the band as possible as that is the only thing that retracts the band. If the band does not retract you would have drag and wear. With the pressure test range for the low brake of 75-100 pounds and the mechanical advantage of the lever arm it easily overcomes the spring force of the band.

I have found no mention of the correct brake band spring rate, spring force, clearance or unbound gap to know what is appropriate.

Does anyone have any information on this?

Thanks.

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Interesting! My first thought would be to order the factory blue print for that part number and see what specifications are given.

The only bulletin mention of a change in bands happened early on. The strut was pinned to the band for easier installation and the width was reduced by approx 1/4". Packard said the old and new were fully interchangeable. Any evidence of the narrow ones maybe getting so hot they lost their temper and that is the reason for the smaller gap?

All of the bands are the same width, 1.75.
I do not see any indication of extreme heating. See the picture of the back side of the bands (still in the same order)
In the second picture you can see that there is a noticible difference between the two sets of bands. The original bands have a very smooth surface while the relined bands have a rough surface. There was a differnece in production and possibly material.

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If there were running changes to the part and it kept the same part number, the changes will be noted on the blue print as dated revisions.

When in use the bands are almost closed. There is and never has been an issue with spring rate etc. The steel texture on the back is as important as the texture on the side web of a brake shoe, that is, nothing.

Put your car together correctly and it will work fine.

> When in use the bands are almost closed.

As noted, the band closed around the ring gear yields a gap of 0.33 which is pretty far from closed. In order to reach 0, the friction material would have to compress 0.05 and with that being the approximate average thickness of the lining, I wouldn't expect it.

> There is and never has been an issue with spring rate etc.

Then please tell me what the factory rating is so that I can do the comparison.

> The steel texture on the back is as important as the texture on the side web of a brake shoe, that is, nothing.

So you are saying that the same material and manufacturing process yielded different results and gap variances of 0.290, 0.435, and 0.725, and closing force and unclamping force variances of up to 500% and that met the quality standards.

The servos are both power on and power off so the band has only to spring away from the surface of the drum. Due to the toggle action of the band struts the band is always resting against the drum at some point or another, usually at the gap judging by the typical wear patterns.

I would guess that the difference in the surface texture of the band has to do with the relined ones being shot or sand blasted before relining.

The one band where the edges are not parallel needs a good tug to straighten it up.

The spring RATE is determined by the dimensions of the band and can not be changed unless the metal is thinned. The preload is of course determined by the how much the band has to flex to reach its working position. I submit that as long as the relaxed band is larger than the drum, you are fine. If you feel they don't have enough preload, hold one end in a vise and spring the band open a bit.

Bands are among the least of your worries concerning Ultramatic longevity. All of the various clutches have ample holding capacity----if they receive their design pressure. Now that is the Achilles heel and deserves your full attention, not the bands.

> The servos are both power on and power off so the band has only to spring away from the surface of the drum.

I just want to make sure that they spring away well and a good distance. The distance should be determined by the band setting as defined by the service manual while the spring is determined by the band.

> If you feel they don't have enough preload, hold one end in a vise and spring the band open a bit.

If the band acts as a spring, I shouldn't be able to bend it easily. If it is easily bent, I would expect that the decrease in gap would be a sign of wear.

> Bands are among the least of your worries concerning Ultramatic longevity. All of the various clutches have ample holding capacity----if they receive their design pressure. Now that is the Achilles heal and deserves your full attention, not the bands.

I am planning to add pressure sensors to all of the outside measurement points so that I can check and track the pressures.

Thanks.