I am fairly new to the racing world and have been studying as much as I can about horsepower, engines and their mechanics for about a year now. I recently bought a '70 Chevelle with a 4-bolt 350 and a powerglide transmission and am in the process of restoring her.
I have had many questions regarding the powerglide transmission, but have gotten different responses from various people. My biggest questions are:
What is the difference between a powerglide and a regular tranny besides the number of speeds? Does the powerglide provide better performance on the quarter-mile? How does it perform on the highway? What are the advantages and disadvantages of the powerglide?
Thank you in advance for any answers you can supply.
Otis J. Ayala
In your 1970 Chevelle at 3300-3400 lbs, the powerglide is probably a little short on gear ratio. It has a 1.76 low gear and a 1-to-1 high gear, which isn't a lot. A high power, lightweight car needs less gear ratio; a low power, heavier car needs more gear ratio.
The TH 350 has a 2.52 low with the same 1-to-1 high gear, so it gives you much more mechanical advantage at low speed. In your case, a nice turbo 350 would be a good all-around performance set up.
The three speeds will give you good bottom end "get up and go" with a good high gear for the highway.
I have built some powerglides. They all work in low, but don't have high gear. I have looked at everything, but can't find out why they don't work in high. Maybe you can help me. They all have new parts. One has a new pump. What could I be doing wrong?
I have been building performance automatics for 25 years. Just when I think I've seen it all, I get a new one.
Really, you need to get into the systems in your glide, especially high gear. You need to double-check everything, even things you already checked-sealing rings, lip seals, valve body mod's, etc.
You can also set up pressure gauge on the servo cover to run a pressure check in low and high gear, which can possibly help you zero in on the glitch.
Go back to the basics and work out from there. Understanding the high gear circuit is very important.
I have a powerglide that blows trans fluid out the vent when the car makes a quarter-mile pass. Does not do it in the eighth. I put a hose from vent to carbs and wrapped with a rag to catch the fluid.
It's built with a Dedenbear case in a mid-eight-second door car. What would make it do this?
When an automatic trans blows fluid out the breather, there are a few possible problems:
1. Over-full condition. The fluid is whipping up on the drums and planet, then foaming up and bubbling out.
2. An internal pressure leak: sealing rings, pump halves, etc.
A lot of people get over excited about fluid out the breather. On some applications, such as high "G" load cars or wheelie cars, we actually run the trans over-full so it doesn't suck air under a load or high G's.
In these applications, we run an overflow tank, or puke tank, to catch the fluid. As the trans breathes you can set up this tank so it drains back into the transmission.
So, barring major internal problems, just make sure the fluid level with the car running is about 1/4-inch to 1/2-inch above the pan gasket.
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