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I am bringing a 1979 back to life this winter. Sometime in the cars past the Turbo 350 was removed and a Turbo 400 installed.
The Speedo driven gear where the cable attaches was leaking. I pulled it out today and have a new seal and o ring. The driven gear that came out is a natural color 36 tooth.
In browsing, it appears that the 1979, L48 had a rear end ratio of 3.55:1, and I am using stock 225/70/15 tires.
Now is the time to change the driven gear if need be. I cant get the car on the roa due to snow and ice.
What rear end ratio is the Natural color 36 tooth for. As mentioned, no idea what this Turbo 400 came out of ?
My only other choice is to wait till spring and try it on the road and see what the speedo show compared to GPS. I sure would like to get it close now while apart.
Willcox; great charts. But they dont show a 36 tooth driven gear, natural in color. I dont believe 78/79 used a turbo 400, rather they sued a Turbo 350.
Do you have a chart like you posted that covers the Turbo 400 Tranny.
I just swapped mine out since I changed the rear gear ratio to 3:55. I has a 42 tooth in there from the factory 3:08 rear, I upped it to a 44 tooth to drop it 10mph. If yours has a 36 in there and the speedo was even close to accurate, than you probably have a different drive gear. Mine is a 71 big block with a TH400. If you haven't driven it, you might want to do the GPS route and then adjust from there versus guess and then have to buy another driven gear.
All of my Chevrolet parts books list the "natural" colored gear as having 19 teeth, not 36. Could it be that the gear you have is a discolored white gear, because my Parts Books show the 36 tooth driven gear to be white? The GM part number for the white gear is 1359270, and 3987919 for the natural one.
The chart below is from the 1980 Corvette Parts Book. Based on the 1974 chart, I would guess that you'd want to use a black, 40 tooth gear, part number 1362048. I chose the 74 chart because 74's used the Turbo 400, were available with a 3.56 rear gear, and 1974's GR70-15 radials, are roughly the same diameter as the modern P225/70R15 radials.
As I said, this is just a guess, because obviously the drive gear you have, will determine which driven gear you need. Unfortunately I can't seem to find a tooth count for the corresponding 74 drive gear.
Thanks for the chart. I think the best thing is for me to see what the speedo reads vs GPS in the spring and then make gear changes if need be.
8Valve
Originally Posted by gbvette62
All of my Chevrolet parts books list the "natural" colored gear as having 19 teeth, not 36. Could it be that the gear you have is a discolored white gear, because my Parts Books show the 36 tooth driven gear to be white? The GM part number for the white gear is 1359270, and 3987919 for the natural one.
The chart below is from the 1980 Corvette Parts Book. Based on the 1974 chart, I would guess that you'd want to use a black, 40 tooth gear, part number 1362048. I chose the 74 chart because 74's used the Turbo 400, were available with a 3.56 rear gear, and 1974's GR70-15 radials, are roughly the same diameter as the modern P225/70R15 radials.
As I said, this is just a guess, because obviously the drive gear you have, will determine which driven gear you need. Unfortunately I can't seem to find a tooth count for the corresponding 74 drive gear.
When I installed my 700r4 I called and talked to bowtie overdrive and gave them all the information without my car. They sold me the correct gear. Here's the number if you want to give him a call.
When I installed my 700r4 I called and talked to bowtie overdrive and gave them all the information without my car. They sold me the correct gear. Here's the number if you want to give him a call.
02-08-2016, 01:37 PM
Which Speedometer driven gear
