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Switch-Pitch shifting issues when hot


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Posted (edited)

I own two - 1965 Buick Skylarks.  One with a two barrel carb and one with a four barrel carb.

The two barrel carb Switch-Pitch is a new thing for me to understand.

As the transmission heats up the switch-pitch transfer makes the car more difficult to get going.

I guess that is called stall speed.  When transmission is cold and I first start out you can stop and go with no issues.  I can hear the switch-pitch wine.  As the transmission gets hotter it is harder to get going.  It takes a lot of throttle to move the car.  Especially difficult when stopped on a hill.  Really need to wind up the revs to get going.

The four barrel just gets up and goes no issues.

Edited by Skybeatle1965
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There are TWO switches on the SP transmissions, as I recall.  Many times, both on the carburetor, for vehicles with a "rod" throttle linkage (i.e., not a cable).  One switch is on the idle side and the other switch is on the WOT side of things (which might also double as the Kickdown switch on THM400s?).

 

When the car is at hot, base idle, the "front"/idle switch is activated.  This puts the converter in what might be termed "high stall" position, for less creep in gear and less load on the motor, as a result.  When the accel pedal is depressed a certain amount, that switch is deactivated and the converter then goes into "low stall" position, for a tighter throttle feel and more efficiency in power transmission.  When the throttle reaches WOT/kickdown, the rear switch is activated and the converter then goes back into the "high stall" position for a bit more torque multiplication and power.

 

The reason I term it "WOT/kickdown" is that on a THM400, which has an electric kickdown function, the switch might do both?

 

In reality, the differences in the torque multiplication between low stall (about 1.9?) and high stall (about 2.6?) might not make that much difference in throttle response unless you know what you're feeling or not feeling.  Reason is that normal torque converters usually had a 2.0 torque multiplication and maybe up to 2.2, back then.   IF you have the ST300 2-speed automatic, then the differences might feel greater, with the 1.76 low gear ratio, I suspect, but the car would still move decently well, just not quite as well as it would with the SP working correctly.

 

ONE thing which is not usually considered in an older automatic transmission is "valve body seepage" between the circuits.  Which can cause two holding units to partially apply together, when one should not be applied.  To fix/diagnose this, a competent transmission shop would be needed.  Usually, though, this is most apparent when a shift is made, as in the normal 1-2 shift, not on initial "breakaway" activities.

 

Some other issues might be the rear axle ratio on the 2bbl car vs the 4bbl car, with the 4bbl car possibly having a lower ratio than the 2bbl car, as 2bbls were usually geared for highway fuel economy.  The difference between a (2bbl) 2.56 and a (4bbl) 3.08 would make the 4bbl feel better in normal driving, for example.

 

First thing would be to get a test light and check the continuity of the idle and WOT switches at the carb location, to verify their correct operation.  Might also check the wiring going to and from the transmission connectors, too, plus checking the integrity of all of those electric plug-ins.  Then go from there. 

 

Is the transmission fluid still a deep crimson color with a pungent smell?  Or has it darkened with a more-burnt smell?  Just curious.

 

Just some thoughts,

NTX5467

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Went for a drive this afternoon.  About 83F today.  The drive was great for about 45 minutes.

Car would excel from a stop no issues.  About 45 minutes later it would barely move.

 

Ran thru 3 stop sign getting home.  If I had stopped, it probably would not have got going again.

Stopped short coming into the garage.  It would not excel over the 3/8" bump at the door.  Had to back up and get some momentum.

 

Upsetting.  But I the drive was wonderful when working.  

 

The transmission fluid is fairly new.  But, I do not recall the last time the transmission was serviced.

 

 

 

 

 

 

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Thanks for the description.  When the car does not want to accelerate, with the added throttle, does the engine labor or does it rev too-freely before any vehicle movement happens?  Probably best to get the vehicle to a competent automatic transmission shop for a look-see, possibly one that is reasonably close by.  A shop where they are more attuned to the older 2 or 3-speed automatics, although most of what they might see are the "gazillion-speed" newer ones.

 

Just some thoughts,

NTX5467

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Just an inquiry:  when you had the issue in drive range, did you happen to shift to low range ? And if so, was there any major difference in transmission response?

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Transmission shop it is.

I am passing the 2-bbl on to my Son & his family.

They are moving to Texas next this month, so the push has been on to fix all the ills.

This one was a little unexpected.  It will just have to ship later.

I had asked the transmission shop in the region to look at it, but he was unable to get to it for 3 weeks.

 

New dual exhaust, tires, brakes, hoses and a carb rebuid.

She was sounding and running sweet.

I was looking forward to driving her around in Texas when I visited.

 

Now I will begin the restoration of the 4 bbl hot rod.

Paint, new top, interior, wheels, tires and exhaust.

The 4 bbl runs great, looks bad.

 

I tried low gear.  The engine did not overrev, you could feel it the transmission trying to engage.  Once it got rolling, it was a sweet ride.

At first it would not engage until rev'd quite high, it would slowly engage, but when it did you were moving 25 plus quickly.  Not tire spin quickly, but quickly.

 

I was debating unplugging the solenoid at the trottle, just to see what would happen.  But, I made it home.  Now that is has cooled down, I am sure it will make it the five miles to the transmission shop.

 

Appreciate the words.  I am not sure the 4 bbl has the same switch-pitch unit or not.  I have never heard it do the wine up as the vanes move.

It just goes.

 

Off to the bank I go.

 

 

 

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The transmission in both cars should be the same transmission. For the Special, Skylark cars though , basically there were three different ST300 transmissions.  There was a MJ model for all 300 v-8 models , except Sportwagon. The Sportwagon used a MR model transmission. I think the difference was that the transmission for the Sportwagon had a long tailshaft. Internally these two used the same torque converter, valve body plate and same number of driven and drive plates in the both reverse and forward clutches. 

 The third ST300 transmission was for all v-6 engine and the model was LS. It had a different valve body plate , identified with a notch in it , a different reverse clutch pressure plate and reverse clutch piston.  Also the number of driven and drive plates was one less than the transmission used behind the 300 v-8 cars.

 From your description, it sounds like an issue with either the idle stator switch being out of adjustment or an issue with the stator valve body or solenoid . 

 The purpose of the idle stator switch is to reduce engine creep, by changing the stall speed of the torque converter. By changing the stall speed, it  makes for less force needed to be held on the brake pedal when stopped.

 My thought would be to check the adjustment of the stator switch first.

My thought process may be flawed here, but thinking about your issue, a cold engine and transmission would have a heavier transmission fluid and create a bit more pressure internally. As the engine and transmission warm up, the transmission fluid would thin, resulting in an increase in accelerator to get the car to move. 

 

 Loren

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21 hours ago, Loren@65GS.com said:

As the engine and transmission warm up, the transmission fluid would thin, resulting in an increase in accelerator to get the car to move. 

 

...which would be consistent with an internal hydraulic leak or low pump pressure.

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Posted (edited)

Could use same advice from those that have been there, done that, have the T-shirt.

 

Do I rebuild the existing transmission:  Cost at aprox. $4,500.  Could be less.  Shop said $3,500 plus parts and tax.

 

Do I take one from the parts car I have.  No idea of its condition.  Used the engine in another 65, that was 20 years ago.  I have used the rear axles also.  But no idea on the transmission.  It would cost $800 to find out if it would work.

 

I have been quoted $1,200 for a used from the "salvage network"?  Who knows if that is any good.

 

Do I find a three speed automatic that will bolt in?  Is there such an animal?

 

We did pull the pan on the existing.  Full of thick dark sludge and some shiny particles.

 

Skybeatle

Edited by Skybeatle1965
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Oh man, I am so far out of touch. $3,500 in labor?  Are they pulling the trans or did you do it?   For that type of money I'd crawl under there and unbolt the dozen or so bolts and drop the trans myself.  Then I'd take a stab at putting the front and rear seals in the spare tranny, and bolt that up.  But that's just me.  

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There's a retired tranmission wizard in my area who builds transmissions for all kinds of older applications.

If you want to get an idea of whst an ST300 rebuild would cost, I will be happy to put you in touch with him. He built my 700R4 for about $1400 last year, including a new GM performance torque converter.

Might be worth shipping it to Michigan for that kind of $$$ difference.

Send me a pm if you want to get his input.

Joe

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Shop around you should be able to beat that price. There is a BCA chapter in Lynnwood, WA (the North Cascade chapter) and a club member may have a good source for a shop to rebuild your transmission (assuming you are not set on using the shop you have referenced). Good luck!

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There are actually several Buick clubs not to far from you. Two of them right in your back yard. Gene mentioned one and there is another 'The Puget Sound Chapter'. There is a third down in the Vancouver/Portland area and a fairly new one in Spokane. I am sure some of the members of those clubs could give you some ideas. The price you mentioned seems high to me, but I have not been looking for many years, so who knows...

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On 7/12/2021 at 8:17 PM, Skybeatle1965 said:

Could use same advice from those that have been there, done that, have the T-shirt.

 

Do I rebuild the existing transmission:  Cost at aprox. $4,500.  Could be less.  Shop said $3,500 plus parts and tax.

 

Do I take one from the parts car I have.  No idea of its condition.  Used the engine in another 65, that was 20 years ago.  I have used the rear axles also.  But no idea on the transmission.  It would cost $800 to find out if it would work.

 

I have been quoted $1,200 for a used from the "salvage network"?  Who knows if that is any good.

 

Do I find a three speed automatic that will bolt in?  Is there such an animal?

 

We did pull the pan on the existing.  Full of thick dark sludge and some shiny particles.

 

Skybeatle

WOW! $3500 just for labor?  I am certainly out of touch.

A ST300 is a simple transmission. I've rebuilt them and with the proper tools it is not a big task. 

Loren

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  • 5 weeks later...

OK.

Had to deal with several family emergencies.  The car had to be put on hold.

I do like the idea of going with the Turbo 350.

I am a little concerned about the loss of the switch-pitch feature.

For some reason I am having a heck of a time with V8 Buick formum.

They will not let me in.

 

I have read before all the health issues there is a turbo 350 with a cable connection?

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If you go with the TH350 you won't miss the switch-pitch since you'll gain a third gear.  The TH350 uses a kick-down cable.  You'll need to connect the cable to the throttle linkage.  I don't think that you will have any issues with that since aftermarket suppliers such as Lokar make kits to handle such conversions.

 

https://www.lokar.com/assets/instructions/INS0003-GMhitech-KickdownKit.pdf

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