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Lots of progressing being made and I'm now waiting for for a new cable and Heater / AC switch to come from the US.
I've turned my mind to replacing fluids with engine and trans completed. My understanding is there isn't a drain plug for the diff however when I climbed underneath I noticed a small Allen Key grub screw in the bottom towards the front.
Before I undo it and see what happens I thought I should check that its not connected to something that will result in me having to pull the entire diff apart to rectify the situation.
Lots of progressing being made and I'm now waiting for for a new cable and Heater / AC switch to come from the US.
I've turned my mind to replacing fluids with engine and trans completed. My understanding is there isn't a drain plug for the diff however when I climbed underneath I noticed a small Allen Key grub screw in the bottom towards the front.
Before I undo it and see what happens I thought I should check that its not connected to something that will result in me having to pull the entire diff apart to rectify the situation.
Thanks
David
There is a rubber bushing on the front of the diff, there should not be a drain unless someone added one. You will need to suck the fluid out via the check plug hole, most builders recommend dyno oil and a couple bottles of limited slip. Either 80-90 or 80-135 GL5 oil.
I'm not 100% sure of the current part number for the GM Additive?
Not sure there is a difference between the positraction additive and limited slip additive?
The part numbers have changed over the years.
Most add 2 4oz. bottles when changing differential oil.
I’d say take the bolt out and see what happens. I put a drain plug in the bottom of the diff when it was opened up to replace one of the C-clips. Mine is in the midline also, but a couple of inches rearward. The installation kit came with a template but it was nice to see what on the inside of the diff I was drilling towards. Cost less than $15 and took less than 15 minutes. The heat shield bolts are farther up on the front.
Charlie
Dave1977vette
Here. Compare your location to the one for my drain plug. About a year ago I found that I had one after like 38+ years of ownership. Looks like about the same place as mine. Unscrew it and see what comes out. Mine was even magnetic with minimal "fuzz" on it. https://www.corvetteforum.com/forums...ferential.html
Originally Posted by Dave1977vette
Bugger, I was hoping someone would say I’ve never seen that, someone has put in a drain plug 😂
One step forward and one back. Car only came with one key and that key doesn’t fit the lock for the spare tire so has to drill the lock out to get it off.
I went to bed last night hating the car and when I took that bolt out this morning and saw fluid drain out I’m back in love.
Thanks again for the guidance and support of the people on this forum. I really appreciate all the help.
I looked for a decent side on photo of my 77 for you to compare. This one is from about a year ago.
Note that my rear looks similar to yours. But the front definitely sits lower. The car has 3/4 inch of rake when parked. These cars raise the front and squat the rear under power.
They sit about level with stock springs. Here is my 77 with 255's front and 275's rear and one coil cut off the stock springs. One coil dropped the nose 2" and really didn't change the ride quality.
Since I reconnected all the vacuum lines properly I have this strange rattle when I start the car. I’ve worked out it’s the EFE actuator.
This wasn’t happening when they had the vacuum advance connected to it :-)
As the car isn’t registered I can’t drive it so I can really test if the TVS valve is working or not.
In the picture posted above which shows the pipe routing it shows 2 pipes to the TVS, one from the carb and one to the actuator. My TVS has 3 ports for hoses. I have the carb connected to the top port, then the actuator to the second port and I’ve blanked off the third port. What’s that supposed to be connected too?
If the TVS isn’t working I guess I can block them all off for the time being while I get another TVS.
Last edited by Dave1977vette; Mar 13, 2023 at 12:44 AM.
The lower port is the exhaust port, it must remain open!
On a cold start or water temperature at or below 180*f vacuum passes through the TVS switch.
Vacuum the pulls the rod of the actuator up thus closing the heat riser exhaust valve (sandwiched between exhaust manifold and exhaust crossover pipe).
At or over 180* the TVS switch changes state, closing vacuum source to the EFE actuator...
You now have trapped energy that needs a path to escape...
Your original TVS switch when new had a foam cap filtering the 3rd or lower port.
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