New governor for a TH 425

Got a new Allison AT540 governor to see if it would adapt to an TH425 transmission. It does! The Allison governor has no speedo gear but the gear from a TH425 fits on it. The Allison governor has no can as it fits inside the transmission in it's original configuration but it will fit inside a TH425 can. It does fit, shift and the speedo works. The Allison governors were available in several different rpm ranges to go with whatever engine was driving it. This particular governor is for 3000-3400 rpm and is a code 462. Sonnax makes them new.http://www.makcotransmissionparts.com/Allison-AT540.html

Part number on the Allison governor

Speedo gear swapped from the broken TH425 governor on to the Allison.  I think the weights and springs could be swapped and then it would act like a TH425 governor.

vacation in the shop

                                               Uncanning governors

                                                             Making chips

                    Governor can parts...It took me three days to make 17 of them.
                    Used carbide insert bits for the first time. They cut fast but did                               interesting things with thermal distortion of the parts.

                 Shaper cuts a key slot for a belt pulley reduction.

Testing Corvette style "windowed" primary governor weights

Modified the primary weights to have a "window" like GM did for Corvettes with 700R4 transmissions. This was a removal of about 20% if the weight.
Windowed weight and a B&M kit.
Installed for testing, I found the effect to be very small. If anything it may make the light throttle shifts later. Hardly noticeable..... real changes need to be made with secondary weights and springs.

Governor weights

Drilled a 1/4 hole in the primary weights and could not tell any difference in how the gov acted.
Swapped in this lighter weight and there was a slight difference. Mostly the 2-3 shift was later.
Parts swapping
A few parts. Spring color seems to be somewhat random, same color different spring. Some springs are wound left hand and some right hand. These are random turbo hyramatic governor springs and weights from the junkyard except the tagged spring. The tagged spring was behind the vacuum modulator spool, took that out in 2007. Removing it gave more range on the vac modulator.

TH 425 governor cans part 6

A few chips
GMC outside
New Driven gears installed. Notice two styles of shafts. The two on the left are different then the three on the right. The spools are different also.
Nylon gear sets the operating axial position (runs against the dowel in the trans case). The gear with the most wear was .050 different than new. shoulda used the camera flash
Brushing out the bore,
Some of these needed a good wire brushing to get them clean
Sludge
Cleaning out an orifice in the valve spool

TH 425 Governor cans part 5

3 1/2 schedule 80 pipe to make seal retainers out of. Pretty close to what is needed I.D and O.D. This stuff doesn't machine as good as some other, gummy like.
Chuck it up short.
Boring to fit over the can top.
Parting, out kinda far so bull nose center to stiffen it up.
Going slow here, no support.
Ring and can top
How it fits on, hold an O ring seal and has a lip to get a screwdriver in to pop it apart.
Together with a slot for prying it back open. Need to tack weld the retainer on. Ripe for weight and spring changes...tune it like you want.
Bail holds it together and in the hole.
can parts.
how the originals fit.


parts ring out.

TH 425 Governor cans part 1

Leaded steel to make governor cans out of. Machines nice.... lots of chips to come, About $10 a linear inch delivered.

TH 425 Governor cans part 2

Old school calipers
Parting, Used a power hacksaw to complete the cut
Dial in and center drill after a cut
Last two top to top
cutting cans apart

TH 425 Governor cans part 3

Patients. These are Turbohydramatic 425 transmission governors.
Last two just a stub left
all that is left over
Blanks and a sample
Zero check

TH 425 Governor cans part 4

Oil it!
Boring
Carnage
Ready to machine the top
Some done. These are the new bottom part of the cans and will seal with an o ring to the original tops. The original was crimped together and not serviceable.