An Ultramatic experiment

Posted by Ross On 2010/4/9 6:52:43

The majority of 56s tend to run their shifts together when using drive, unless one accelerates hard. I usually find that low winds out longer than I'd like, and then direct comes too soon.

For years I have been bumping up the direct engagement speed when doing rebuilds by shimming the direct shift valve piston spring,roughly as outlined in ibn the February 56 Service Counselor. Except that I put my shims down in the piston so as not to restrict its movement, and I end up using a lot more than they call for--usually about .120". That raised the direct engagement point about 6-7 mph which prevented a lot of lugging, and made for a neat return to convertor when accelerating out of slow uphill corners on the twisty roads around here. Coasting, my 56 Packup shifts to direct at about 25, and in normal acceleration about 35. With the 3.07 rear, I don't want it any earlier than that.

I was still not satisfied with the low-high shift point. Like most 56s I've driven, at medium accleration it would raise much further than the direct shift point and the shifts would run together. Bump-bump. I hate it. I had an early production 56 400 in last week where the shifts were all but simultaneous under most conditions.

Both cars have now had 1/4" cut off their low-high shift valve spring ("B", figure 208 in the shop manual). This has proven quite satisfactory and the cars have a shift pattern reminiscent of a Torqueflight. Under light acceleration, there is a 7 mph gap between shifts, and the gap spreads as you horse on it. To the floor you shift to high at about 55.

I find this makes the tranny much more flexible in traffic and back roads, also it does not attempt direct while I am still accelerating. That comes in as I ease off the gas a hair as I near my desired speed. Some of you might like to try it.