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Switch Pitch Issues (I think)


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Hey there,

65 Riviera, 401 base model.

in drive or reverse it is pushing EXCEPTIONALLY hard. It would probably idle at 10 MPH (idling at about 700).

My theory is the the torque converter is stuck in the under-acceleration-mode and the switch is not effecting it...thus a bad converter.

Educate me, oh wise ones.

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4 hours ago, Bill Loeb said:

Hey there,

65 Riviera, 401 base model.

in drive or reverse it is pushing EXCEPTIONALLY hard. It would probably idle at 10 MPH (idling at about 700).

My theory is the the torque converter is stuck in the under-acceleration-mode and the switch is not effecting it...thus a bad converter.

Educate me, oh wise ones.

  If you are idling at 700 rpm while in gear that is too high. Your idle speed should be lower.

Tom

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The torque converter should be in the 'high-stall' state at idle (foot off the accelerator).  Touching the accelerator should switch it to the 'low-stall' state under normal driving until just before the passing gear kick-down, where the switch on the carb linkage will once again switch to 'high-stall' to let the engine spool-up faster.  (Assuming that the '65 controls work like those on my '67).

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In my experience the tendency for creep between high and low stall is minimal and has little effect on idle and certainly not enough to make it stall. I suspect a tuning problem. Ignition carb and/or vacuum.  

When did this problem start?

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Could there be an internal leak between circuits in the valve body?  Is the transmission stock, or has a 'shift-kit' ever been installed?

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"

 I suspect a tuning problem. Ignition carb and/or vacuum.  

When did this problem start?"

Sadly, I have no idea. I purchased the car sight unseen from someone with a good reputation. Trusted my gut. It was supposed to be a running-driving car. It is anything but. Suspension and steering were screwed. NONE of the turn indicators, brake lights, dash lights worked.  Had brake issues. The choke and secondaries are not working.  If I take off in drive it chatters.  If I take off in L or L2 it doesn't. Plus the torque converter isn't "disengaging". 

I got the suspension and steering fixed. Brakes working. Most of the lights and dash working. I was told that the transmission had been removed to fix the front seal. The bolts have the same patina as the engine, no tool marks, plus the front seal leaks. 

Guys, I truly appreciate all of your attempts to assist. 

 

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On 7/9/2021 at 11:06 AM, Bill Loeb said:

If I take off in drive it chatters.  If I take off in L or L2 it doesn't. Plus the torque converter isn't "disengaging". 

 

This makes me suspicious that someone may have been screwing around with the transmission valvebody.  The chatter in D but not L implies that there is a difference in pressure applied to the band that holds the planetary drum depending upon the selected hydraulic circuit.  It might be worth dropping the transmission pan for a look-see...  Gray sludge in the bottom of the pan would indicate normal wear (clutch friction material).  Any brass sparkles would mean bigger issues that need attention.  If nothing bad is seen in the pan, it might be worth removing the valve body for inspection and cleaning.  I haven't looked closely at this section in the shop manual yet, but I recall some details in there about the valve body and proper locations for the various balls, springs and gaskets.

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1 hour ago, EmTee said:

 

This makes me suspicious that someone may have been screwing around with the transmission valvebody.  The chatter in D but not L implies that there is a difference in pressure applied to the band that holds the planetary drum depending upon the selected hydraulic circuit.  It might be worth dropping the transmission pan for a look-see...  Gray sludge in the bottom of the pan would indicate normal wear (clutch friction material).  Any brass sparkles would mean bigger issues that need attention.  If nothing bad is seen in the pan, it might be worth removing the valve body for inspection and cleaning.  I haven't looked closely at this section in the shop manual yet, but I recall some details in there about the valve body and proper locations for the various balls, springs and gaskets.


since I can't count on anything that the seller told me, I have to go by what I see.

What I see is a fresh cork pan gasket and a leaky front seal 

I have been going through the service manual and haven't gotten a feel for what is going on.

My current inclination is to pull the transmission, have a shop go through it and swap the switch pitch for a standard torque converter. 

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9 hours ago, Bill Loeb said:

My current inclination is to pull the transmission, have a shop go through it and swap the switch pitch for a standard torque converter. 

 

That's a good plan, however, I wouldn't be too anxious to ditch the switch-pitch.  I'll bet there is something more basic wrong that explains your symptoms; hopefully nothing to do with the switch-pitch.  It is a slick system when it works as designed.

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13 hours ago, EmTee said:

I wouldn't be too anxious to ditch the switch-pitch.


Several folks share your opinion.

As a cruiser, it seems like an unnecessary complication.

But one only learns from hearing contrary opinions. So please...tell me why it is so great.

Thank you

Bill  

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You can check the operation of the torque converter with the engine off.  Take a 12V hot wire to the solenoid and get out your mechanics stethoscope or a long extension.  Put the listening device on the transmission body and touch the 12V to the terminal. You should be able to hear the vanes in the torque converter “switch.”

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awesome advice!!!

a buddy has his life being used right now but that will be perfect


THANK YOU

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5 hours ago, RivNut said:

You can check the operation of the torque converter with the engine off.  Take a 12V hot wire to the solenoid and get out your mechanics stethoscope or a long extension.  Put the listening device on the transmission body and touch the 12V to the terminal. You should be able to hear the vanes in the torque converter “switch.”

I've done this in wrecking yards with a battery pack to listen for a "click" from both the switch pitch and kickdown solenoids before extracting the torque converter and front pump. One time, this test had me abandon transmission removal. A trans rebuilt had removed the switch pitch. A painted torque converter, another clue.

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On 7/12/2021 at 11:22 AM, Bill Loeb said:

So please...tell me why it is so great.

 

Sure, you can do without it, as Buick demonstrated beginning in 1968.  The reason it was dropped (IMHO) was not that it didn't improve performance, rather it was a simple cost/benefit trade-off.  Most people wouldn't notice, but having the best of both high-stall acceleration and low stall economy in one transmission is something weekend racers would appreciate (i.e., not having to run a compromise stall speed) on their street driven racer.  It's your car and your choice; I'm just saying that the switch-pitch technology is really quite reliable.  Most transmission issues are the usual ones, i.e., failed pump, burned clutches, etc.  If the switch-pitch functions are intact (mainly the torque converter) then rebuild the transmission and keep the feature.  If that's not possible or cost prohibitive, then convert to a standard (1968-up) single-stall converter.

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Food for thought besides cutting costs.  The switch pitch was developed after one year of the TH400  being used behind the nailhead.  I’ve been lead to believe that this was incorporated because little old ladies didn’t like standing on the brake when the car was at a stop and still in gear.  Then one year after the nailhead was dropped in favor of the 430, the switch pitch goes away.  Did the 430 not require the same brake pressure to hold the car at a stop without creeping or did the advent of disk brakes take less foot pressure to keep the car from creeping? 

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I don't know the reason(s) Buick had for including switch-pitch on the TH-400.  Interestingly, it wasn't present for the debut year of '64, but arrived for the '65 model year.  I find it hard to imagine that idle 'creep' complaints from owners of '64 models would have instigated a significant change such as this.  I think a likely rationale was Buick wanting to leverage their switch-pitch technology developed over roughly 15 years of Dynaflow development to enhance TH-400 performance beyond what the other GM divisions were offering.  Again, it's just my guess that the switch-pitch feature may have been planned, but wasn't ready for the 1964 Buick debut of the TH-400.

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On 7/8/2021 at 1:24 PM, JZRIV said:

In my experience the tendency for creep between high and low stall is minimal and has little effect on idle and certainly not enough to make it stall. I suspect a tuning problem. Ignition carb and/or vacuum.  

When did this problem start?

  To the op...this is relevant advice, look elsewhere for a solution to your stalling problem.

Tom

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Does the engine have ignition points/condenser or an electronic ignition conversion (e.g., Pertronix)?  Can you check the voltage at the "+" side of the coil when idling in "N" and then "D"?  If electronic ignition, note that those systems generally want to see 12 ~ 14 VDC, whereas the original breaker-point system used resistance wire to reduce the voltage to ~9 VDC to increase life of the point contacts.  If the voltage at the coil is low and alternator output is low (or battery is weak) maybe the ignition isn't getting enough voltage when the idle falls to ~500 RPM.  On the other hand, the alternator picks-up the voltage at 700 RPM, but the high idle increases coupling of the torque converter (by design).  This is all pure conjecture on my part while simply trying to concoct a scenario that might lead to the situation you describe.  But, if you have a voltmeter you can quickly either confirm or rule-out this possibility...

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2 hours ago, EmTee said:

Does the engine have ignition points/condenser or an electronic ignition conversion (e.g., Pertronix)?  Can you check the voltage at the "+" side of the coil when idling in "N" and then "D"?  If electronic ignition, note that those systems generally want to see 12 ~ 14 VDC, whereas the original breaker-point system used resistance wire to reduce the voltage to ~9 VDC to increase life of the point contacts.  If the voltage at the coil is low and alternator output is low (or battery is weak) maybe the ignition isn't getting enough voltage when the idle falls to ~500 RPM.  On the other hand, the alternator picks-up the voltage at 700 RPM, but the high idle increases coupling of the torque converter (by design).  This is all pure conjecture on my part while simply trying to concoct a scenario that might lead to the situation you describe.  But, if you have a voltmeter you can quickly either confirm or rule-out this possibility...

interesting theoretical thinking 

I have not installed the electronic ignition yet, but I did convert to a modern, internal regulator alternator. It will charge up to 16 amps now instead of the stock 12.

Thank everyone, again, for the input. 

Truly appreciated.  

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6 hours ago, Bill Loeb said:

interesting theoretical thinking 

I have not installed the electronic ignition yet, but I did convert to a modern, internal regulator alternator. It will charge up to 16 amps now instead of the stock 12.

Thank everyone, again, for the input. 

Truly appreciated.  
 

Do you mean 16 volts? If yes that is a bit high. May cause overcharging problems

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