OK, so I check the tranny fluid level in my TH350 after it has been sitting for a month or more and the engine is OFF and completely cold. The fluid reads very high on the dip stick. I start the engine and let it run for 30 minutes and get to engine operating temp of around 155-160 deg.(checked with laser temp gauge) after the thermostat has opened and it doesn't register on the dip stick. I cycle it through the gears as it is running and still no change. Is this the correct reading? Is it actually low on fluid and I probably have a leaky gasket? It only drips after its been driven and parked I'll notice some drippy's on the floor. Should I ignor the completely cold reading and only use the hot reading? I know it sounds stupid, but the reason I ask is because I have a little tranny fluid loss under the car and was wondering if it is blowing out cause it is over full.

 

Trans has to be warmed up before you can obtain an accurate reading. I'd add more fluid until it's between the marks on the dipstick. Letting the engine idle may not be enough to actually warm the trans up, so I'd add some fluid, drive it around the block, then check it again.

 

Rely on the warm fluid with the engine running reading. Cold with engine off reading on a transmission are not relevant.
A common area for a leak is the o-ring on the speedometer bullet or the seal around the driven gear in the speedometer bullet that goes into the transmission.

 

I have that exact leak on my TH350 now. Bought a new speedo cable "bullet" with new O ring and seal.

 

Will the gear come out with the bullet when replacing o ring and bullet gear seal? Like to check condition of gear and count the teeth. Does the gear just pull out?

 

There is a single bolt that holds on a retaining bracket then the bullet pulls out, usually with the gear in it.

 

Sounds to me the o/p is checking the fluid with the engine off, which is wrong. you always check the fluid with the engine running, and of course warmed up.

 

o/p?

 

"Original Poster", aka, "Thread Starter."

AT Fluid level should never be checked with engine off. Always engine running in "park" and warmed up.

 

If you check, I'll bet the actual dipstick tells you how to check it.

It should say something like:

"Check when warm on level surface with engine running" or something like that.

 

Not usually but sometimes. See my post started today. Pulled the bullet to get the original gear out. No problem. Inserted new gear in bullet (for new rear end gear ratio), inserted bullet, seemed to hang up so pulled bullet out. Gear didn't come with it. Had two chances to retrieve it as I could just see it. Missed on both tries.

Need to keep an eye on the end of the gear shaft when you're pulling out the bullet. Problem is it's virtually impossible to see it with your hand in the way. Might be best to pull it out a little at a time and keep checking.

If it does drop in, keep an eye on my post to see if I ever get it out or just leave it loose in there and hope for the best.

Sign me off as flyguyPA28 (if it were an airplane I wouldn't leave it and hope for the best)

 

Pull the bullet with the cable attached, the end of the cable should retain the gear. Same for putting it back in, cable on bullet with gear in bullet then install.
Also if you jack the car on the left side it’ll keep fluid from running out, or at least minimize it.

 

I changed my rear differential also to a 3.55 from a 3.08. How do I know what is the correct gear or tooth count to replace it with? My speedo doesn't read correctly now, I suppose this is why.

 

Since you went from a 3.08 to 3.55 I think you likely have an older vette than my '80 as the Dana rear end ratios are 3.07 and 3.54. But percentage change in tooth count should be basically the same. On mine I went from a 19 tooth to 21 tooth gear (a 10.5% increase). But even that change is only approximate because the gears are rarely exactly optimal.

To get a more precise answer, the starting point would be to pull the driven gear out (i.e. pull the bullet to get the gear that drives the speedo cable). Count the teeth on it.

Then go to a speedo gear calculator like this one at TCI http://www.tciauto.com/tc/speedometer-gear-calculator/

Put in the basic tire information they are looking for in the tire diameter calculator - width, aspect ratio, wheel diameter (e.g. for my '80) that was 255 60 15. That will get the tire diameter calculated.

Put that value into the tire diameter box in the speedometer gear calculator.

If you can see the color of your drive gear, the one that's still in the transmission, then you can look in the chart for your transmission on the page and find it's number of teeth. Put that in along with your old gear ratio. The calculation for the driven gear should come up with a number of teeth close to the one you pulled out. It won't be exact but should be within less than half a tooth (e.g. mine was 19 and the calculation was 18.67). If it is close you can now change the gear ratio and recalculate and it will give you the number of teeth for the new driven gear you need to get.

If you don't know your drive gear size because you can't see the color of it in the tranny or the number the calculator came up with didn't match your the tooth count on the driven gear you took out, you need to work a little backward. Put in your old rear end gear ratio and tire diameter. Then pick one of the drive gears from the chart for your transmission and put that number of teeth in and run the calculator. If the tooth count for the driven gear comes up within a half a tooth of what you have, then you have the right drive gear tooth count. If not, try another drive gear tooth count and keep doing this until you find the one that calculates a driven gear tooth count that is within a half a tooth of the one you have. At that point change the gear ratio to your new ratio and you'll now see the tooth count needed for the driven gear for your new rear end gear ratio. This isn't as bad as it sounds.

A couple questions might help to narrow the search. What tranny do you have? What is the tire size? Do you know how far off the speed is?

If you have that a good starting point can be found. And it's likely someone with a similar set of numbers and equipment already did the swap and has your answer.

 

Had some time at lunch so I checked on this a little more. Assuming you have the original size tires (8" - about 203 mm), 70 with 15 inch rim) and either a TH350 or TH400 (the L48 would normally have the TH350 but apparently rare cases where it was TH400) then when you pull the driven gear out it will be a 17, 19, or 21 tooth gear. I'm guessing a 19 as combined with an 8 tooth drive gear it is near perfect for the 3.08 gear ratio and the 8" 70 tires on 15 rims. If it is a 19 tooth then you need to get 22 tooth for the 3.55. It it's 17 tooth you'll need to replace it with a 19 tooth.

If it's a 21 tooth then it indicates the drive gear is 9 tooth and then you may have a problem because the replacement for the 21 tooth driven gear would be 24 or 25 tooth and I don't think they make those. So you would have to also replace the 9 tooth drive gear on the transmission output requiring removal of the tail shaft housing. your options then become:

7 tooth drive gear and 19 driven
8 tooth drive gear and 22 driven

If it's a manual transmission the same numbers apply but I didn't look up a chart to see what gears are actually available.

 

 

If you have a leak in or around the bullet and you are replacing the inner and outer seals make sure you check the driven gear shaft for wear. I found my wife's 78 still leaked after seal replacement and it was shaft wear at the inner seal location. Just place a straight edge like a ruler along the gear shaft to check for wear. On her 78 you could see the wear without the straight edge.

 

It does say that in the manual with fluid cool 65-85deg room temp, it should read between the the two small punch marks below the full mark. I miss interpreted cool being "engine"off". It meant engine on, but fluid warm not hot yet
. duh!

 

I have to change my driven gear because I changed the differential ratio anyway, so Ill just install the correct one. They're cheap.

 

No, reread his post, he went TO a 3:55 FROM a 3:08