I need to do the same thing...assuming we are talking about the transmission. Can it be easily done without a lift?

 

I only have 2 jackstands. Is it okay to check the fluid while the car isn't horizontal?
I YouTubed the process, I think I can handle it, but every video I watched was for a truck with enough clearance to crawl under without jacking, or a car on a lift.

 

I assuming we're talking 4-speed transmission and rear axle fluids. Not really the best method as 2 stands puts the fluid to one side/end or the other and is an unreliable indication of quantity. If you can get it up on 4 stands at the same height setting that would be OK. Level is the key to getting a good indication of adequate fluid. If you have a reliable shop that works on your regular car then they could put it on a lift and easily check fluid levels. You don't have to have them do any other work but it is a simple solution. Ask them to show you what they are doing too for educational purposes. Should only take 15 minutes or less.

Automatic trans is checked on the ground while the engine is idling with the dipstick by the firewall.

 

Yes, 4 speed.
Is rear axle fluid something different from transmission fluid?

Which one should I be checking based on my description of sound?

 

Well... once it's up in the air, check both for the knowledge. Transmission is by your knees and is directly connected to the engine via the clutch. The rear axle (I should really be calling this the differential) is between the rear wheels and converts the straight back power from the engine/trans sideways to each rear wheel. It also does some multiplying of the rotations depending on the mathematics of the internal mating gears.

Transmission noise will likely be evident all the time to varying degrees of volume from idle to acceleration. Differential will only be evident when driving. If noise is from differential then it will probably change tone or characteristic when cornering vs. straight line driving; transmission doesn't care if it's going straight or not so the noise should only differ in volume in relation to the car's speed.

Checking both is a simple one-bolt removal and putting your finger in the hole to see if the volume is near the bolt hole (which they should be).

 

Here's a pic and labels to illustrate the major components of the drivetrain between the engine and rear wheels:

 

Raining the next 2 days. As soon as it clears up I'll take audio of the sound I'm hearing, but to be honest it does sound exactly like a big dump truck. It's that whirring whining noise.
I guess for the sake of a quick test I can jack up the front of the car and test the trans fluid, if it's low at an angle then we know it's low. Or maybe I'll just buy another set of jack stands.
You guys are costing me money.

 

I just autopsied 4 junkyard C3 differentials. ( Yes, I confess, I am a C3 addict! )

3 of the 4 had leaky seals, so visibly messy on the outside. The insides ran from great to horrible. One was full of oil and the oil that came out still looked transparent and the metal parts inside looked silver in color. Yeah that was the good one.

The worst one had major messy seal leaks everywhere, so hardly any oil came out of it, it was almost "dry". The oil inside looked more like taffy or molasses than oil. A brown sticky varnish was stuck on everything inside, and it stuck like super glue. It took hours to scrub off. It was almost "burned" on there! Yeah it probably was. Oh BTW the gears overheated and had chipped teeth, surprise! Probably all caused by oil leaks from a leaky seal, and never checking the oil, until it died. Must have been a little noisy with 6 chipped teeth. LOL

 

So the next question would be, if the oil is low in either of those things, what kind of oil do you put in them?

 

use google like
c3 corvette differential fluid change

here is one..get the gm additive and recommended rear lube..it has to be sucked out
https://www.corvetteforum.com/forums...-question.html

your transmission should have drain and fill..make sure fill opens before drain. Not sure if yours has both heres my 79

strongly suggest a new thread with specifics of your car year etc manual auto and ask questions if needed


2 open holes

 

Are you hearing the noise while idling with the trans in neutral and clutch out?
Is the noise variable by speed?
Is the noise variable whether going straight or turning a corner?

Depending on how the car is tilted on the stands, you can certainly overfill a trans or differential –– or have them underfilled and not realize it. Car being level is really the only proper way to judge the levels.

• Trans oil... I don't recall what's called for for the manual transmissions. I haven't changed my '67's since 1990ish. Guess I should but when the car has only added a couple thousand miles in that time, it's hard to see the need. My '72 has an automatic which is a completely different beast.
• The differential uses two products: one is a gear lubricant 75W-90 and the other is an additive specifically made for the GM Posi-traction differential. Both are available from a number of places, even at your local GM dealer.
• 
  
  Changing either the trans or diff fluids are not particularly difficult but they can be messy and you'll need to get a suction tool to pull the old fluids out. Unlike Interpon's trans, my '67 only has an upper fill plug and must be suctioned out like the differential. Let's hope yours has the lower drain!

 

I’m aware of how to use Google, but thus far I’ve found the advice on this forum 2nd to none.

Just got back from picking up another set of stands, if weather doesn’t permit going to the car show happening tomorrow morning I’ll put her up and check levels. Even if they aren’t low I might change them out as I have no idea when if ever it might have been done in the past.

If neither are low and the sound persists I’ll start a new thread to get more input.

All said and done I’d like to give everyone that posted help in this thread a HUGE THANK YOU!

 

I think you may have set a record here on the Forum, 112 posts on just changing belts has got to be way up there.... .

 

the point of referencing specifically c3 corvette google (insert topic) is because 95% of the time it brings you to this forum and i find it much better than the search function in this site..
i figured you knew how to use google
good luck
113

 

Then you’ll love this trick. Go to google.com and put “site:corvetteforum.com” in front of your search.
ALL your results will be limited the this site.

 

Question: is it possible you have an M22 transmission? The noise you hear may be the melodious whine of the M22, aka Rock Crusher, which got it's nickname because of the noise it made.

Some suggestions (115 posts I apologize if these were covered. already)

1. Drain the fluids into a clean pan and look for shiny materials and other debris in the oil
2. It looks like you are buying tools piecemeal. If you intend to keep this car, get yourself a decent set of tools like Craftsman. You'll go broke buying tools piecemeal. Craftsman quality is good enough for what you are doing.
3. If the plug doesn't come out easily, as some have suggested, run the car and get the trans hot. The case is aluminum and will expand more than the steel plug with the heat.
4. If the plug still doesn't come out get yourself a square socket for the plug and use a 1/2 drive breaker bar with a cheater. (pipe over the handle of the ratchet) Ya, I use the ratchet instead of the breaker bar. Be careful how hard you pull so you don't break the case
5. It is sometimes difficult to check the oil level with your finger. I use a piece of wire bent into and 'L' . Make sure to lay the horizontal leg flat on the threads. You'll be able to see the oil on the vertical leg. 12 or 14 gage single strand wire works real well and the oil is readily visible on the insulation.
6. Look around the Trans and rear for oil leaks. Transmissions and rears don't use oil. If it is low, it is a leak somewhere. You'll want to identify where.
7. Don't overfill the transmission. The excess will come out the front. GM used a funky method of keeping oil in the trans at the pilot shaft.

Good Luck
Greg

 

I thought about that, how do you find the makings to see if it’s an M22?

The one thing all 3 mechanics I’ve taken the car to agree on is that everything under the car leaks, I just don’t know how much or how fast.
Oil, PS fluid, transmission, diff…

Does the trans take a certain amount? Videos I watched said to fill until it spills out the fill hole.

 

My 73 AIM says "LUBE HYPOID" 2.8 lbs. (3 pints metered full) and "Fill to level of filler hole". It looks like some of the Googled sites are recommending 2.5 pints. Full Disclosure: I never ran my Muncie. I put an Autogear trans in it so I don't have the front seal design the Muncie does.

I don't know if or how you can tell if it is a M22 with the trans in the car. Others will likely comment on this.

 

Yep. Fill both the trans and differential until the fluid starts to barely dribble out the fill hole. (That's another reason hoisting the car in a level attitude is important.)

Without pulling the side cover off the case, about the only way to identify the M20/M21/M22 is going to be the factory stamping code with the date and VIN portion. An "A" is the M20 (wide-range 4 sp), "B" is the M21 (close range 4 spd), and "C" is the M22 (also close-range 4 sp but with differently machined gear angles for high strength in racing situations). There was also a "P" indicating a HD case.

 

Might as well throw in my 2 cents worth and keep it going....

- Belts many have started making noise after the previous owners anti-noise spray started to wear off.
- Don't just rely on the jack stands they can fail especially the cheapie ones from Harbor Freight. I leave the jack itself in position just in case. I have also put a large block of solid wood under as well.
- Usually when the differential is going out you hear a whine from the back when going slightly on or off throttle when cruising.

Good luck and welcome to the club.