vetster86

Looking for speedo gear part number or gear size (teeth) for a 700R4
trans, rear end ratio is 3.45. Its for my 86, changing out the D36 with 2.73 ratio to a D44.

Thanks

Ramrod92

I believe you'll need these part numbers GM PART # 25513050
CATEGORY: All
PACK QTY: 1 CORE CHARGE: $0.00
GM LIST: $6.24
OUR PRICE: $3.56
DESCRIPTION: GEAR


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GM PART # 8642620
CATEGORY: All
PACK QTY: 1 CORE CHARGE: $0.00
GM LIST: $6.24
OUR PRICE: $3.56
DESCRIPTION: GEAR


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GM PART # 10456089
CATEGORY: Speedometer Drive Sensor
PACK QTY: 1 CORE CHARGE: $0.00
GM LIST: $46.19
OUR PRICE: $23.10
DESCRIPTION: SENSOR AS

MrRenoman

I don't think the 10456089 sensor will work in the earlier 700R4 trans. The speed sensor I think you'll need is the 25007308, unfortunately GM doesn't make it anymore and they're hard to find anywhere. You might find a used one, maybe on this forum. You'll also probably need to remove the transmission tailshaft housing to replace the new drive gear if your existing one isn't the right size. The following information was pulled from another thread. It's the aftermarket replacement speed sensors for the 25007308. Please confirm fitment before buying.

Tomco #31018
Standard Motor Products #SC8
KEM #163-416
Filko #SCS-2
GP Sorenson #779-9506
Guaranteed Parts #779-9506

I also read you can rotate your existing speed sensor 180 degrees and make it work for the larger driven gear. The attached link mentions it. Click on "rear axle" and scroll down into the pink text. It's mentioned there. I haven't tried it yet but it sounds like it'll work. I've looked at a speed sensor and the driven shaft is offset from the center. Rotating it 180 degrees allows the larger gear to engage the drive gear.

http://home.alltel.net/wayne/faq.html

Art

vetster86

Thanks for all the good info & part numbers, I guess I'm going to have to research this more. I thought I would only have to change the drive gear and not mess with the speed sensor.

MrRenoman

The other option is to buy the aftermarket electronic device that connects to your existing speed sensor. You don't have to change any gears either. It is an adjustable unit that changes the Vehicle Speed Sensor signal to match the gears you're running. I think MadVet carries it, so do some other vendors.


Art

Pete K

I always thought that those boxes were unneeded and overpriced. In this situation though, they look like a great option.

vetster86

Ya Pete, thats why they can get that price.
I'm going to make a few calls on Monday, I will let you now what I find out.

CFI-EFI

One out of three isn't bad. The 25513050, 43 tooth driven gear is better suited for the 3.54 ratio. What you want for your 3.45 gears is the 25513049, green, 42 tooth, driven gear.

Correct on the changing to the grey, 15 tooth, drive gear, to part no. 8642620.

The 10456089 VSS, besides being for a 6 speed trans, and won't fit his automatic, is the later type that puts out double the pulses per mile than what his older car requires. The 25007308 cited by MrRenoman, is indeed, the correct VSS. I too, have read about rotating the VSS 180° to substitute for the obsolete, correct, VSS. You can take your choice. Either $20.00 to $40.00 for a couple of plastic gears or $160.00 or more for a black box.

RACE ON!!!

vetster86

Thanks for getting the puzzle put together...CFI_EFI.
It looks like my two options are the changing of the gears which is time consuming and less money or spend the extra $100 bucks and keep it simple with the black box. It will boil down to how much I value my time.

Thanks

CFI-EFI

Before you do an assessment on the time the block box will take, do a search. I agree it sounds like the quicker more expedient, albeit more expensive route, but there have been a number of threads questioning the wiring and set up of those "easy" block boxes.

RACE ON!!!

vetster86

Yes, I will do more research on both, I have learned to take more time through the years. I can take my time its not a daily driver.

Thanks

corvette1990

This is exactly why I havent changed anything yet. I changed my D36 3.07 gears for D44 3.55 gears. The tranny shop wanted a fortune to change out the speedo gears. Claimed they would have to drop the tranny, which meant unbolting the C beam and exhaust system. I bought a black box and even figured out the difference in MPH by drving along a measured distance (by signs). I even figured out the dip switches on the black box. The wiring to the VSS and supplying 12 volts and ground is what is holding me up. You need to mount the black box inside, and have to get the wires out to the tranny. It isn't exactly plug and play. I am about to give up and take the car to Tony's corvette shop and pay him to do it. At least it will be right when he is done.....

MrRenoman

Here's a link to the GP Sorensen sensor...

http://www.partsamerica.com/ProductD...e=1179&ptset=A

and Standard Motor Products...drill down to speed sensor...

http://www.smpcorp.com/web_app/catal...ccatalog.asp#p

Art

CFI-EFI

You can figure THAT out by comparing the new and the old ratios. You don't have to drive anywhere, or even change the gears to figure that.

The transmission doesn't have to be dropped. The tail housing has to be removed, which does require the "C" beam and likely the exhaust to be removed, but the trans can stay put. You CAN do this job in your driveway. You already have the obsolete, impossible, to find, VSS. All you need is the two gears. Again, $20.00 to $40.00 worth of parts.

RACE ON!!!

vetster86

I'm thinking now that I'm pulling the rear anyway, whats a few more bolts to remove to get at the speedo gears.
Thanks for all the help guys

sami85L98

Stick with CFI-EFI for speedo part numbers, it was me that i stuck with black box wiring issue but later i figured out with the help of CFI and others. So bottom line u need 15th (grey) and 42 can be ordered from transmissionhead.com as no GM dealer carries these.

MrRenoman

You can buy the Standard Motor Parts SC8 sensor on Ebay item 8026071942, Buy it Now for $34. Can't beat that anywhere. Better buy 2, save some money.

Art

vetster86

I did not think I would need a new speed sensor if I'm changing the drive and driven gears?
Also I talked to two different tranny guys and both said I would need the 40T black and the 15Tgrey for my 3.45 ratio. They told me to look at the driven gear housing to see what gears it will accept. I may have to get a new driven gear housing, the two style housings are 34-39 and 40-45 gears. Starting to get a little confused, maybe old age is setting in.

MrRenoman

The housing they are referring to IS the speed sensor. 34-39 is the speed sensor for 2.59-2.73 gears. The 40-45 is for 3.07 and numerically higher gears like your 3.45.

Art

MrRenoman

The speed sensor you need is offset even further for the larger driven gear. This was one of the reasons that reversing the sensor 180 degrees allowed for the bigger gear. You'll need a new speed sensor for the larger driven gear and have the drive gear on the output shaft changed.

Art