1966 LeSabre transmission - need advice

[JonW]

I have a 1966 LeSabre sport coupe with the 340/2-speed drive train. When I am coasting to a stop, the downshift to 1st gear is very hard. It just slams into 1st. The 1/2 up shift is fine and the car runs well. My mechanic is competent, but he is not an expert on switch pitch converters. Any thoughts?

[EmTee]

Does the 1 --> 2 shift happen normally under light throttle, or is it delayed?  The first thing I'd check would be fluid level (just because), next would be the vacuum line to the modulator.  It doesn't sound like a switch-pitch issue to me, as I wouldn't expect to feel any 'clunk' associated with that.

[NTX5467]

Agree, NOT a switch-pitch issue.  More of a valve body issue.  Might get some cleaner/additive to put in it for a while and see if it might get better.  You can always put it in "N" while slowing to a stop, then back into "D" to drive off, if needed.

 

We used to use Berrymans B-12 (pint) to put into atf before it was changed, to clean things out.  Not dirt or debris, but varnish accumulated over time and such.  Turned the atf black quite quickly.  Then a full-drain and new filter usually fixed things, back then.

 

Might check the vac lines going to the vac modulator, if it has one.

 

If the car has a two-piece drive shaft, also check the u-joints and center bearing assy (and its mount) for wear/looseness. 

 

Just some thoughts,

NTX5467

[EmTee]

I looked at both my '67 Buick shop manual as well as a '64 Motor Manual I have.  Both mentioned checking the vacuum line to the modulator.  The Motor Manual also said to check the modulator itself.  The other causes (e.g., low pressure, maladjusted band) would be unlikely if the hard downshift symptom appeared suddenly.  Last thing to check would be proper idle speed.

[JonW]

It's the down shift that's the issue. The up shift is fine. My guy says he checked the modulator, back lash for the differential, about everything he could check. His opinion is that the converter is making the switch too abruptly, and he doesn't know how to fix that. I know he's a competent mechanic, but this sort of thing is not his specialty. I'm going to look into the Berryman's.

[JonW]

10 hours ago, NTX5467 said:

Agree, NOT a switch-pitch issue.  More of a valve body issue.  Might get some cleaner/additive to put in it for a while and see if it might get better.  You can always put it in "N" while slowing to a stop, then back into "D" to drive off, if needed.

 

We used to use Berrymans B-12 (pint) to put into atf before it was changed, to clean things out.  Not dirt or debris, but varnish accumulated over time and such.  Turned the atf black quite quickly.  Then a full-drain and new filter usually fixed things, back then.

 

Might check the vac lines going to the vac modulator, if it has one.

 

If the car has a two-piece drive shaft, also check the u-joints and center bearing assy (and its mount) for wear/looseness. 

 

Just some thoughts,

NTX5467

When I search for the Berryman's B12, all I find is a fuel system cleaner. Is that what you used?

[NTX5467]

Berrymans B12 is basically a fuel additive, but also had the automatic transmission cleaning functions mentioned elsewhere on the bottle, back then.  Basically, a "varnish remover/liquifier in nature, whether in the fuel system or elsewhere, to me.

 

There are other transmission "clean up" additives on the market now.  How well they might work, I'm not sure.

 

NTX5467

[NTX5467]

As to the "pitch switching too suddenly", from what I found years ago, the "low stall" pitch is the same as a normal, non-switch pitch torque converter with a torque ratio of 2.0 or 2.1.  The "high stall" (i.e., looser) pitch is right at 2.8.  Not a large difference but just enough to allow for higher rpms when needed.

 

Ideally, the converter should be modulated by intake manifold vacuum, but in this case, it is done by electrical switches.  Seems like the "Idle" is at the "high stall" position to decrease creep in gear, but as soon as the throttle comes off idle, it goes into the tighter position, for better throttle response and fuel economy.  Then goes back into "high stall" near WOT.  All electrically.

 

For diagnostics, you could unplug the switch-pitch connector, somewhere?  To de-power the system for testing.

 

NTX5467

[Pete Phillips]

11 hours ago, JonW said:

When I search for the Berryman's B12, all I find is a fuel system cleaner. Is that what you used?

Buy it in the pint can or quart can that you pour; do not buy the spray. Yes, it is fuel system cleaner but also good for automatic transmissions.

Pete Phillips

[old-tank]

Lucas Oil 10009 Transmission Fix

I usually tell folks to stay out of the additives isle, but this one works.  And is made for transmissions unlike the B12 and no fluid change is needed.

[avgwarhawk]

Concur with Willie.  Lucas does work.