1960 Powerglide shift points

[Alexander D.]

What would be the 'normal' shift points (speeds) for a 1960 cast-iron Powerglide.

A friend has a fully-restored 1960 that he bought last year. The car is stock. He started having transmission problems (slipping, leaks) so had it rebuilt. The rebuild seems to work fairly well, but he gets a grinding type noise when moving the lever from Reverse into Park. Also, the transmission seems to upshift from 1st to Drive too soon, sometimes as low as 10mph, causing the car to 'lug' when going uphill.

He took the car back to the shop that did the work and they aren't giving him much satisfaction. He learned that this shop farmed the transmission rebuild out to another shop.

I'm assuming he's running 3.55 gears, which would be stock for a PG car in 1960.

I offered to post his predicament in hopes some of you with C1 experience can help diagnose the transmission issues.

Any suggestions much appreciated.

[Mark E.]

Re: 1960 Powerglide shift points

Regarding the grinding of the shift lever, watch the movement of the linkage as a helper operates the shift lever (engine off). It may be binding or rubbing on something.

The throttle valve and vacuum modulator control shift points. Check the TV rod adjustment. If that doesn't help, check the vacuum modular for a leak.

It's easy for any of these items to be damaged, bent or become out of adjustment during a transmission R&R.

[Edward J.]

Re: 1960 Powerglide shift points

Alexander, I wonder if during the rebuild did they replace the vacuum modulator? There are many different ones, and think the corvette may have it own.some times they are color coded generally there is a strip around modulator. They also make an adjustable modulator so you can Taylor shift points. As Mark said try the TV adjustment first, see if you can boost the pressure a little. When you drive the car does the transmission kick down easy? Keep in mind after about 35 mph the trans. Will Not let it drop down a gear. Also not the shifting point at quarter and half throttle. The shift points should rise.

[Alexander D.]

Re: 1960 Powerglide shift points

Thanks guys for the tips on troubleshooting the Powerglide issues I described.

I'll pass this info onto my friend, who will be grateful for the advice.