89formula350tpi

I'm going to be swapping a set of 3.73's in my rearend. I know what speedo gears I need, I was just wondering if the new gears just go right in, and work with my current VSS, or if I need to buy something to make them work. I've seen some places selling sleeves for different speedo gears, but I think that is for cable driven speedometers. Thanks for the help.

Dyno Don

iTrader: (7)

You will need a different VSS with the offset for a larger driven gear. (I think it's 15/45)

89formula350tpi

Does anyone have the part number for the right VSS.

Z28 Boy

really? i've never heard of this in all of my research i have done on this...i have to do my speedo gear change within a few weeks.

is this with all electronic speedo thirdgens?

-Brian

89formula350tpi

Z28 boy, I've been doing some research tonight, and by the looks of it all you have to do with an electric speedo is just change the gears. I saw that a few people said they bought a different VSS but it was the same as their original one and it didn't matter which one they used. I'm still not 100% positive that this info is correct. But I'm just going to buy the speedo gears and see what happens.

Z28 Boy

ok good deal...i will do the same. if i need a new VSS, i will get one after i KNOW i need one.

later..

-Brian

caleb

I havent actually done the swap, but as far as I have agathered from my custom EProm burning, you shouldnt need to change the VSS the VSS gets its reading off of the back of the speedomoter, which is turned by a cable off the trans, so as long as the cable off the trans is turning the right revolution the VSS wont see a difference! Thats why you can swap guage clusters and not have the speedo be messed up, and the VSS is like $75 at least thats the cheapest I could find when I replaced mine.

GMTech

The reason you can swap gauge clusters is because the circuitry in the speedo converts Pulses Per Mile for electric sensors and RPM of the speedo cable for manual setups into the appropriate amount of needle sweep based on wether its an 85, 120, 145, etc... MPH speedo. However, you still need to provide that "circuitry" with the proper PPM or RPM for it to be accurate, and this is done via speedo gears.

I have yet to meet anybody who needed a different sender to install the two gears needed for 3.73s. I did the swap myself and my stock VSS on my '87 T/A worked just fine.

Z28 Boy

well, for what it's worth, i went to the local chevy place and ordered a new VSS, GM PN 10456089. it seemed to be the general consensus that IF there is a different VSS needed, that that is the correct one.

i should get it tomorrow, and will hopefully get it all apart this weekend. i will definitely update you guys with what i come up with.

by the way...the VSS only ran like 24 bucks. I get it at the "cheap" price from the dealer...i think the regular cost is like 42 bucks.

like i said...just in case i do need a different one...i will have it.

i also got a new clip to hold the gear on. i read in earlier posts that these were no longer available...that's not the case.

ill let you guys know....

-brian

OMINOUS_87

Z28 Boy

What was the outcome of the swap? What rear axle gear do you have? I will being going from a 3.27 to a 3.73 in a couple of weeks and am hoping to have all my info lined up first though. Does anyone know what the 2 gears I need are?

Thanks

OMINOUS_87

Well I did a bunch more digging. I assume the following info is correct but not posititve.

Here is what is known to be true.

1. 87 Formula 700R4 with factory VSS on trans and factory 3.27 BW axle.

2. I have swapped in a 10 bolt with 3.73s.

Assumed Info

1. I have not cracked open the trans yet

2. According to the TCI speedo gear calculator the following combinations would work for the original 3.27 setup with a 25.7 inch tire.

15 teeth drive/38.45 teeth driven or 17 teeth drive/43.58 teeth driven

3. GM only makes 15 and 17 teeth drive gears and 18,19,20,22,26,27,28,29,30,31,35,40,42,43,44,45 driven gears.

4. Since there is no 38 or 39 teeth driven gear from GM the 15drive/38.45driven combo is not possible and I must have according to the math a 17drive/43or44driven setup.

5. Ed Maher states from his situation that there is specific VSS for 41 teeth and larger driven gears. I assume I already have the right VSS and possibly the right driven gear as my new setup 3.73 with 25.7 inch tire will require a 15drive/44driven setup and the only change I will need to make is to a 15 teeth drive gear.



Anyway that is what I found out. If anyone would like me to run the numbers for their setup just post your questions.

Ed Maher ThreadTCI Calculator

87Formula4bbl

Z28BOY,

Do you have a part number for the clip? I'm looking for that.

Also, is the VSS you're talking about the electrical unit, or the cable driven, because as far as I know, all the VSS's that the dealerships list is $112 something odd cents.

Thanks,
Ben

firedawg225

ok here the answer to the original question. Since i just did this same thing on my 1992 camaro w/electric speedo. It simple just take your time

here are the gears you need for a 3.73 rear.

driven p/n 25513052
drive p/n 8642620

this is all you need no sleeves. and this is a web site with pics to help you out some.

http://sethirdgen.org/vss.htm

hope this helps and if you have any question fell free to ask.

Nick

87Formula4bbl

Ok nevermind. I have the gears for the swap. But I accidentally broke the little clip that keeps the drive gear from spinning on the output shaft. I just needed that. Just wondered if you had that, I coudln't find it on any online diagrams (like gmpartsdirect.com, etc).

Thanks anyways,
Ben