I know the transmission on my 420SEL has a front seal leak, but I'm trying to determine if it's bad enough to warrant pulling the engine and trans in order to replace it, or if I should just keep topping off the fluid.

The transmission shifts nicely. I serviced it about a month ago, and found virtually no material from the discs or steels in the bottom of the pan when I did so. Of course I topped off the ATF at that time. Today I checked the fluid level. I went through the whole drill: warmed the car up, ran it through the gears while parked, and put it in "Park" before checking the fluid level. The dipstick showed no fluid at all, so I figured it had a pretty bad leak and would take at least a quart. But when I added a quart of ATF and checked it again, the level was quite a bit over the "full" mark on the dipstick.

What could account for this? Am I doing something wrong?

Thanks in advance.

Very simple - You added way too much fluid. Unlike the marks on an engine dipstick the marks are not calibrated in quarts.

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78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
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B/w the high and low mark is 200ml's.

Also, you'll have residue from adding fluid in the dip stick which makes getting a solid reading difficult right after adding fluid.

I'd add fluid and go for another 10 min drive.

Jonathan

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Jonathan Hodgman
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When reading the dipstick hot, the level should show full at 80C. The only way to get the trans to this temperature is to drive a bit. A small change in temperature will result in a significant change in fliud level thus giving you a false reading.

If the fluid level doesn't show on the dipstick when COLD, it is definitely a full quart low. It is difficult to "read" dipstick right after adding fluid, so make sure when transmission is cold, you have at least added a half quart- drive car a bit to warm up and get a good reading after new fluid drains off the stick.

It will run for years if you watch level and add as necessary. I have had a new trans (84k) miles waiting to put in but transmission in the car is still perfect after leaking 5 years from front seal. Hope that helps.