Speedo Gear For 4.11 Gear 700r4

[fasterthanu]

I had a 3.23 gear in my vette. I converted my car to a 700r4 trans. I have a 1976 vette. They had the proper gear in the trans for the rear end. I then just added a 4.11 gear. At 60mph, speed is off by 20mph. At 75mph, the speedo is off by 25mph. I was told there is no way you can make up 20+mph with a speedo gear. I can get one to put me close, but will never be dead on.

Is anyone out there running this setup with a stock speedo that is dead on? I mean, hell, there should be some gear or something. Camaros and vettes had this trans, and I am sure with a 4.11 they were right...

 

[69MyWay]

If you don't mind dropping another $300 or so on the car (less if you are real creative), you can easily convert to a fully electric speedo from Autometer.

If you run that (I have one in my car), the sending unit screws into the trans just like the stock one, but instead of a cable you have wires going to the speedo gauge. You can calibrate the gauge with a touch of a button. So, if you change tire size, gears, etc, you can simply go in and recalibrate to your desired accuracy level. Plus, they look so COOL.

You need the 5" diameter unit, and it will take you the better part of a saturday to build the retainer brackets, pull the dash, and install it. Go for the gold while you are at it and install one of their fully electric tachs as well.

One thing you will love about the speedo is that it sweeps when you turn the key just like the C5.

 

[page62]

Don't be so fussy. Every speedo is off by a couple of mph -- unless it's a modern bone-stock computer-based unit like the one in my truck. Remember, even changing tire sizes can put you off somewhat.

Do the best you can (and that IS possible) and enjoy...

By the way www.700r4.com has a speedo gear calculator that might help you.

 

[77-4speed]

Depends on the size of your driven gear. As a rule of thumb, every tooth on the driven gear changes the speed by ~5mph. So if you are 20mph too fast, you'll need 4 more teeth. Check your local Chevy parts dealer and see if they carry the speedo gear that you need. You can also check online at www.docrebuild.com
http://www.docrebuild.com/dr-r-web/ASH-TRAY.PDF

He has a bunch of different speedo gears. I don't see why you couldn't fix the problem with a simple speedo gear swap.


Russ

 

[fasterthanu]

whats the difference between drive gear and driven gear?? Bowties site shows I need such and such drive gear, and such and such driven gear.... I've changed the gears on a TH350, its the same for a 700r4, isn't it?

 

[77-4speed]

The drive gear is the gear that is mounted inside the transmission. The driven gear is the plastic gear that the speedo inner cable slides into. I'm not sure about the gearing in the bowtie transmissions. If you call them I'm sure they can tell you which driven gear you'll need.

Russ

 

[barrier5]

Well heres what I did,but I went from 2.72 to 3.70. I've got the yellow drive gear,bought the biggest driven gear I could get which is 45 tooth (green).Then I went to the bone yard and got an external speedo reducer, 1.25 to 1 and took it apart and reversed the gears inside to get it down to .75 to 1 and the speedo is dead on now.

 

[vms4evr]

Try this link. He has a speedo gear calculator.

http://www.bgsoflex.com/speedo1.html

And this link. The math is explained.

http://www.chevytalk.com/tech/transmission/calibrate.html

I think you'll find that with 4.11 gears it will be hard getting the drive/driven gears to make it right. But you can get a lot closer than 20mph off...

Sounds to me like you'll need to get 15 tooth and 45 tooth. Pretty much the max you can go with GM. I converted my92 with 7000R4 trans from 2.59 to 3.54 rear gears. I'm using 15 tooth x 43 tooth and it's pretty accurate. 17in wheels. Tire diam. is 27.5in.

Sounds like barrier5 has the right idea using a reducer because you won't get the tooth count you need...

Now if you could run 50in tires this problem would be much easier to solve :L

Graham

 

[crebo]

fasterthanu,
I know this is not your issue...but I have a small question. How big was the difference between gears as far as off the line? I went from a 350 to 700r4 from bowtie. I'm currently running 3.08 I believe. Thinking about going to 3.73. I'm looking for recommendations.
Ashman

 

[fasterthanu]

unbelievable difference! The pull! WOW. Before I had all the wrong setup I mean I had dual quads, full race cam, Pro Action Heads opened up. The cam alone kicked in at 3500. So, with my 3.08 took too much time to get there. With that 4.11 wow. The pull keeps you pinned in your seat. I am sure I will break into the 12's with no problem right now. Before I did the gear, I could brake torque with my 3.08, and the tires wouldn't budge. Now I will sit there and roast them if I try to use stall speed by brake torquing to the stall speed.... I was going to go 3.73 just like you, but then i thought about it. I wanna have some fun with it, and even if I do do expressway driving, with OD I am taking the same as my 3.08 before OD =) On those terms I said, lets do it =) That gear swap will be the most noticable difference you can do. Hell, when you are on a ten speed bike, which do you start off faster in, 1st, or 5th? Thats basically the difference.

 

[page62]

Crebo, I have a 3.55 and a 200-4r OD from Bowtie. And I'd go to 3.70 or higher in a heartbeat...but I'm still paying for the tranny!!!

 

[crebo]

Thanks fellas,
I like the sound of that. That will be my next project. How much would I be looking at for the gear exchange? I'd imagine it would be rather difficult for a novice like myself.
Thank you very much....Ashman

 

[fasterthanu]

its actually not too bad. Where ya from? There is a guy in beloit that does it cheaper than ANYONE, or ANYPLACE I've seen. His work is first class. He was a machinist and really knows his stuff..

Hi Joe, i don't do the rear window conversion, so i can't help you there. But to change your 3.08 to 3.70 is no problem. It would be $375 for the rebuild (includes new bearings, seals, clutch pack) and $260 for a new set of 3.70 ot $150 for a used set. UPS is usually around $40. Add $100 for 4.11 to change carrier to 4 series. Rebuild is usually 3-4 days. Hope this helps. Gary Watson---CORVETTE PERFECTION