Ok guys I have an 87 Trans am that originally had a 305 TPI in it. When I bought the car that was already removed and an all original CARB 350 out of a 72 pick up was installed with a turbo 350. The car has an electronic speedometer that was working fine with the 350. Now fast forward to present day. The motor has since been pulled and is long gone. It's been replaced with a new 355 with a carb top end and a heavily built 700r4 I had from a previous car. Unfortunately the transmission is already mounted in the car and it has a mechanical speedometer cable. How do I concert the cable to electronic without breaking the bank on a $300+ module or pulling the transmission and swapping the gear and sending unit on the tail shaft? HELP?

 

Your 87 was a factory electric speedo car so; just put all the factory parts back on. Not sure why you would expect to throw $300 + into an aftermarket speedo set-up when your car is already factory designed to use the set-up for the electric VSS ??

Doesn't mater what engine or fuel system you've got, it means nothing to the speedo system. Remove the cable VSS from the current tranny, install the proper electric VSS,... then find and plug in the factory VSS connector ----> Done.

If your cars original electric speedo cluster was swapped to a cable speedo cluster, if the original VSS buffer was removed, or if the original electric VSS wiring/plug was cut off then you will need to correct those things too,..... but keep it simple by just re-using factory stuff and you should be fine.

IIRC the 87 Firebird VSS Buffer got it's ground from a black ground wire located in the original ECM harness...... so you might have to screw the black wire leading from the VSS Buffer to the body somewhere if you completely removed the ECM harness. The 'fix' is as simple as screwing the ground wire to the body anywhere possible.


P.S. Pulling the cable VSS from the tranny is required anyway due to the speedo gears. Even if they were for the same gear ratio,.... Electric speedo gears and Cable speedo gears are NOT the same !!!

 

The problem is I don't have the original parts. I was trying to avoid pulling the transmission back off and pulling the tail shaft apart. I read about changing the gear on the transmission tail shaft and replacing the cable with an electronic part. I don't have the turbo 350 anymore and the ECM is out of the car. Everything runs without the ECM minus the speedo which is where i'm currently at.

 

I'm sure John can hook you up with the parts you need, or you can post in the parts wanted section.

If the speedo gears need to be changed, you can remove the tail shaft housing without removing the trans.

 

Then can someone point me in the direction of where I can buy said gears and the electronic VSS? Stock rear is currently in the car but would like to eventually upgrade to 3.73 gears. Should I just install the drive and driven gears for that setup so I'm only in there once?

 

Thanx NAF, I might have them...... the electric VSS's are getting to be a 'rare' item these days ! instaldave; I'll take a look and report back if I have any of the parts that you might need. To be clear - your looking to get the electric speedo working on an 87 with 3.73 gears ??

I'd say yes,.... there is more then 1 version of the 84-89 electric VSS. The one you need will depend on the tooth count of the DRIVEN gear needed.

Now that the ECM harness is gone the first thing that you will need to do is to be sure that the existing buffer is getting a ground. I wrote this to someone with an 86 here a few years back.

Your car is an 87 so check your C207 connector for a Black/White wire on pin 'm'. That's the wire that needs to get grounded in order to get the electric speedo working again.

You don't have to pull the tranny to swap the speedo gears. With any luck, the DRIVE gear on the tail-shaft will already be the right one. ( it's the DRIVEN gears that are cable/electric specific. ) If the DRIVE gear needs to be changed too just drop the drive-shaft, support the tranny, remove the cross-member, remove the cable VSS, and remove the tail housing from the tranny. Swap your speedo gears and then put it back together - done.

 

Ok sounds good, if it means anything the transmission I have in the car now was originally out an 85' WS6 I had a few years back. I bought the car with the transmission in it. The entire transmission was redone and the car had a 9 bolt rear with 3.23's in it. So I would assume the transmission was setup to match that. Also I do have a pin out of the ECM so I will find that particular wire and make sure I ground it.

To be clear - your looking to get the electric speedo working on an 87 with 3.73 gears ?? Yes, that is the setup I plan on going with so I'd rather get it set up for that now while I'm in there. The speedo doesn't work at all now so even if its off a bit its still better than nothing.

 

I'm finally getting a chance to get the parts in I bought from you back in February John. I was reviewing the information you had provided regarding ground the reference wire at the old ECM harness. I have the pinout from AllData and I'm unable to locate the wire in question. Would you be able to shed some light on this for me?

 

You've got to think of C207 as a "dash" harness and not an ECM harness.

You need to tap into the wire that your looking for on the DASH side of C207. ( not at the ECM ! )


Here is the C207 Pin-out for the 87:

1986 & 1987 C207 ( TPI )

PIN Color From / To (Notes)
A Brn ALDL / ECM (AIR control)
B Red ALDL / Fuel Relay ( TPI )
C Brn/Wht ECM / CE Light ( TPI )
D Tan/Wht Fuel Relay / Fuel Pump ( TPI )
E Wht/Blk ALDL / ECM (test)
F Pnk/Blk IGN fuse / EGR-ECM
G Pnk/Blk Gage Fuse / Burn Off Relay ( TPI )
H Tan/Blk ALDL / TCC-ECM
J Org ALDL / ECM ( TPI )
K Brn ECM / Speed Buffer
L Tan/Wht Fuel Relay / Fuel Pump ( L69 )
M Blk/Wht VSS,P/N switch / Grd
N Org/Blk ECM / P/N switch
P Ppl Brake / TCC
R Ppl/Wht Crank Fuse / Cold Start-ECM ( V6 )

Plug C221

A Pnk/Blk Inj2 Fuse / Even Fuel Injectors
B Lt Green Back Up Switch / BU Lights ( V6-T5 )
C Brn Fuel Pump-Fan Fuse / Fan Relay ( V6 - TPI )
D Pnk/Blk Inj1 Fuse / Odd Fuel Injectors
E
F Dk Blue Back Up Fuse / Back Up Switch ( V6-T5 )

 

I really feel like an idiot asking so many questions. This isn't part of the passenger side engine harness is it? That was fully removed out of the vehicle when the ECM was removed. This would be a lot easier if the car was in front of me now. However I'm at work and the car is at home. I still have all the other body harnesses in the car. Just the passenger side engine harness is removed.

 

When you removed the ECM harness from the passenger side of the car...... You removed the ground connection for the VSS Buffer.

That plug - under the dash on the passenger side of the car, is the C207 connector. There are 2 sides; the dash side and the ECM side. You need to work on the DASH side of C207. ( I'm sure you didn't hack off both the plugs,.... right !?!?! ) When you disconnected the ECM harness you removed the ground for the VSS. That connection was @ C207, a Black/White wire on pin 'm'. That's the wire that needs to get grounded in order to get the electric speedo working again.

Cut that Black/White wire on the dash side C207 connector.

Splice a black wire with an "EYE" at the end to the Black/White wire you just cut off C207.

Screw the new ground wire EYE to the body - anywhere.

VSS Buffer now has ground and should work again.

 

I located the wire in a black connector. I grounded the wire and everything is good to go now. The speedometer and odometer work perfect. Thank you for all the help and answering my endless questions. It's greatly appreciated.