MainePorsche

Guys,
I get hard shifting most of the time when driving easily from a standstill. I've adjusted the pressure modulator to its max via the T key with only moderate improvement.
What else should I look to ?

Thanks in Advance
Craig

joejoe

Check for vacuum line to the modulator. If no vacuum there is a rubber bit just at the torque tube that may have failed. It is kind of a pain to get to but can be done.

byrdman454

Also check the rubber boot cover you had to remove to adjust the T-handle on the modulator. This cover seals the vacuum as well. If it is original, it is probably dry-rotted and leaking and removing it to adjust the modulator probably made it worse.

WallyP

As both prior posters inferred, the modulator uses manifold vacuum to control the firmness of the shift. If you do not have full manifold vacuum, the modulator considers you to be at full throttle all the time. Best thing is to actually test the vacuum level at the modulator.

If you find that you have very low vacuum and repair that, remember that you must immediately readjust the modulator. If you don't, you may get enough slippage to damage the transmission.

FredR

Wally,

Appreciate if you can expand on this a bit. Fully appreciate what the modulator does not sure how it does it [I run mine a bit on the firm side for more positive shifts]. I did once have the vac line come away and the shifts went to full hard. I did not run that way very long and common sense suggested it might do the tranny damage if left like that. I diagnosed the faulty connection on the multi way connector and the tranny returned to normal- did not [appear] to need any readjustment.

Regards/best wishes

Fred

Kevin in Atlanta

1. Test that the modulator holds vacuum.
2. If it holds vacuum put a tee fitting in between the modulator and the vacuum line and get a reading.
3. If you are not getting vacuum, move the vacuum tester to the vacuum manifold below the air box.
4. If you get get vacuum, it's time to replace the vacuum line to the modulator. Brake line is a good choice.
5. If you get no vacuum, you have a leak at the vacuum manifold or near by.

WallyP

The OP said that he had adjusted the modulator all the way in an attempt to soften the shifts. If the problem was lack of vacuum, and that problem is solved, he would then have the modulator set for fully-soft shifts, and would have vacuum to achieve that. This would result in slippage during shifts, and that would soon result in wear on the clutches and bands.

Firmer-than-normal shifts reduce the wear on clutches and bands, but increase the chances of damage from impact during moderate-throttle shifting. The proper firmness is a balancing act between wear and damage - luckily, there is a pretty wide range of acceptable adjustment.

MainePorsche

Thanks very much guys.
Does anyone happen to have a stock photo or a diagram of where to plug in to test the modulator ?
Also, when testing the vac line to the modulator, what would be acceptable vacuum reading ?

Kevin in Atlanta

I ran a vacuum gauge to a tee with enough vacuum line to get the gauge into the driver side door. So, you need one short 2-3 inches and one long 7-8 feet so you can get the gauge into the cabin. I thought the vacuum should run about 20.

MainePorsche

Thanks a million Guys.