Automatic Transmission shift points
Richard Wall
transmission in my '70 Pontiac. Specifically, the maximum RPM that
the engine reaches before the transmission shifts to 2nd or 3rd.
Currently the transmission shifts around 4000 RPM at wide open throttle.
I like to change this to about 5400 or 5500. I've seen the shift
improver kits offered by B&M but they only claim to change the "firmness"
of the shifts. Any tips would be appreciated!! - Richard
EricY
Richard,
I found myself in the exact same situation a few years ago after
having installed a built 400 cu Poncho engine in my 77 TA. The engine
has a mild street performance cam that increased power in the upper
rpm range (well above the ~4000 rpm).
There are 2 components that you can change/alter to change the shift
characteristics of the TH350. An adjustable vacuum modulator (mounted
on the passender side of the th350) will enable you to delay part-throttle
shifts. This promotes later firmer (quicker) shifts and will keep you in
lower gears longer for part throttle situations. There is also a governor
on the driver's side near where the speedo cable attaches. The governor
controls the shift characteristics at WOT. The governor itself has a valve
that is controlled by a pair of rotating weights. As govener rpm increases
the weights swing out ala centrifigal force. Small assist springs help
to fine tune the rate of outward swing.
There are two ways to alter the governor:
1) File the weights (making them lighter and thus require more rpm to
actuate the govenor valve)
2) Swap weights and springs. (B&M makes a kit to do this)
I used the B&M kit. It has some distinct advantages:
1) You can easily return to factory stock condition by re-installing
the unaltered factory weights and spings.
2) The kit includes detailed instructions on the best way to approach
governor shift point changes.
3) The kit come with six different weight combinations and six different
springs that can be mixed and matched to acheive almost *any* shift
characteristic. (both upshift & downshifts)
4) The kit allows you to upgrade the stamped steel pins (on which the
weights pivot) to machined pins with "E" clip retainers.
5) Provides a new O ring seal for the governor cover.
6) Its inexpensive.
I have calibrated my TH350 to delay part-throttle upshifts (1-2) until
~30 mph. (3.08 axle & beefed stock rpm converter) The WOT shifts occur
and approximately 5400 rpm. The thing about selecting the shift point
for a TH350 equipped vehicle will be influenced by the engine output.
Its a pretty wide ratio transmission, which means you lose alot of
leverage as you go from 1st to 2nd or 2nd to 3rd. That being the case,
any modified Pontiac engine that can produce increased power in the rpm
range above 4000 rpm is going to perform better if you can keep the
tranny in the lowest gears for as long as possible. (obviously this
is what you have in mind)
Want more info? I think HP books is the publisher of two very good
books : Tuning & Modifying your TH350 transmission
Tuning & Modifying your TH400 transmission
They cover the governor operation and modification pretty well, plus tons
of stuff on improving the longevity and mtce recomendations.
If you cant locate any of these or the B&M govenor kit email me and
I will look up the book isbn and the B&M catalog address for you.
Happy Motoring!
$0.02
EricY
Frank Evan Perdicaro
But, since they can be used to alter the emissions characteristics of
so many vehicals, they are not common any more. You want a revised
set of govenor weights.
In the past 20 months, somebody posted a good description of how and
why to machine exactly which parts to change the shift points of a
TH350. The machining is easy, but fairly critical -- everything must
balance. I'll see if I can locate the info.
--
Frank Evan Perdicaro Dainippon Screen Engineering of America
Legalize guns, drugs and cash...today. 3700 Segerstrom Ave
inhouse: frank@server, x258 Santa Ana CA
outhouse: fr...@dsea.com, 714-546-9491x258 92704 DoD:1097
wes swinford
I have just placed a 350 Turbo into my car with a 3500 stall convertor.
You can sometime fine tune shift points by adjusting the screw IN the
module that the vacuum line attached to. I will ask the guy who built
mine and get back to you. We are fine tunning mine now and have some
difficulty. I shift about 6300 RPM Manually. Can you now shift yours
manually or just don't want to? I will try to get back to you. Wes
Steven J Orlin
In article <4giva5$o...@server.eng.dsea.com>,
Frank Evan Perdicaro <frank> wrote:
>Kits used to be availabel to do this.
>
>But, since they can be used to alter the emissions characteristics of
>so many vehicals, they are not common any more. You want a revised
>set of govenor weights.
>
>In the past 20 months, somebody posted a good description of how and
>why to machine exactly which parts to change the shift points of a
>TH350. The machining is easy, but fairly critical -- everything must
>balance. I'll see if I can locate the info.
Shift point kits do not alter emissions at all.
The kit is still available through Summit Racing for $25. But it
is easy to grind the weights yourself. most TH350's shift at WOT
around 4400rpm stock. I ground the hell out of the weights -as much
as perscribed in _The Turbo HydraMatic 350 Handbook_ by Ron Sessions,
And my TH350 shift at 5000-5100 at WOT. You simply take off the
inner weights (the thin ones), and grind away metal from both sides
moving in a max of 3/16" towards the little tab that holds the
spring, and a max of 1/2" up from the bottom of the weight.
I didn't "balance" mine by using a scale or anything, I just
ground them to look identical,a nd I took care in making sure that
they did. Also, don't leave any sharp edges or corners, as they
will could cause stress concentration areas.
You will also need two #6 finishing nails to slide back through
the weights, and a crimper to crimp the ends. This is kind of
critical, because you don't want to hold up the weights at all,
or have the crimped ends fall off. So make sure you do it right.
It took me quite a few nails and a few tries. But I finally got
it. Make sure the nails you use are straight.
When you're all done, spray the thing down with carb cleaner, then
dip it in tranny goo, and slide er back in.
Steve
Steven J Orlin
In article <4gllt7$4...@charm.magnus.acs.ohio-state.edu>,
Steven J Orlin <sor...@magnus.acs.ohio-state.edu> wrote:
>
>In article <4giva5$o...@server.eng.dsea.com>,
>Frank Evan Perdicaro <frank> wrote:
>>Kits used to be availabel to do this.
>>
>>But, since they can be used to alter the emissions characteristics of
>>so many vehicals, they are not common any more. You want a revised
>>set of govenor weights.
>>
>>In the past 20 months, somebody posted a good description of how and
>>why to machine exactly which parts to change the shift points of a
>>TH350. The machining is easy, but fairly critical -- everything must
>>balance. I'll see if I can locate the info.
>
>Shift point kits do not alter emissions at all.
Apparently I made an argueable-blanket-statement-booboo here.
Just so I don't get flamed by all the regulars, I could agree that
in some situations, having higher shift points may raise emissions.
But I don't think you would know unless you tested each combination
of emission system/engine/transmission/vehicle. It's possible
that higher rpms for one combination provides more efficient emissions
reduction (and vice versa). Of course I'm not talking about
total emissions production here, just production per volume. there
is some nifty way of designating this, like ppm (parts per million)
I believe. (I can feel the heat now:))
I had heard a while back that the B & M shift point kit was no longer
being sold because of emissions concerns (don't know if it was true
or not). But it is back for sale for sure (in the Summit Catalog),
and if it was for that reason, they probably figured out that changes
in emissions are going to depend on much more than just a change in
shift points.
well anyways...
Steve