Blk91Firebird

I picked up an 86 automatic bird for my wife and when I drove it home I quickly noticed that the speedometer doesn't work. Somewhere in its life the cars 700r4 was replaced with a thm350. I found the 4 prong transmission plug and what looks to be a 2 prong speed sensor plug neatly coiled underneath the hood so I assume it has an electric speedometer.

My questions are...

1. Why does all the info I found on the forum while searching for a solution state that I should have a cable speedo because the car is pre 89? (my last 86 car had an electric speedo too)

2. Will the driven and drive gears and all the associated parts from a 700r4 work on a thm 350?

(I couldnt find my answers with the forum search but I could have used the wrong keywords)

Blk91Firebird

I know its only been a day but I'm suprised that I havnt even gotten a "" reply lol

Scorpner

iTrader: (4)

I think there was some cross over for a few years as far as electronic/mechanical was concerned. 1989 might have been a year when they were all switched over?

Don't know about the drive gears off hand but a google search might work since the transmissions were on a wider variety of cars.
This has always been a good website but I haven't checked it out for a while.
http://www.transmissioncenter.org/GM...eter_Gears.htm

This might help too.
http://www.tciauto.com/tc/speedometer-gear-calculator/

Actually, here:

http://www.hotrodders.com/forum/t-35...er-102984.html

https://www.thirdgen.org/forums/ltx-...ml#post4989864

http://ls1tech.com/forums/automatic-...eedo-work.html

http://www.jalopyjournal.com/forum/t...ometer.150893/

bigal55

iTrader: (1)

I think the bullet and the speedo gears for the T-5 and the TH350 are interchangeable so if you get a VSS with the speedo gear drive from a T-5, it should fit the TH350. This doesn't mean it will be accurate but you can change the gears for the correct rear gearing. You need to find out what color gear is in the tranny and then match the driven gear on the VSS to accommodate the rear gearing.

Blk91Firebird

Thank you both very much. After looking through those links you gave me Scorpner, I was able to easily check what you said bigal.

The transmission center website lists chevy thm 350s and t5s as using the same vss housing and gears.

It also lists non chevy thm 350s (Big speedo hole?) and 700r4s as using the same hardware and gears.

I havnt been under the car yet so I dont know if its a Chevy or a BOP thm350. Either way, besides calibrating, I should have everything I need since, I have a t5 (thats now a 4 speed) and a v6 700r4 that was left over from a v8 swap laying around

Thanks again! after the weather clears up and I have the chance to get under the car and try and switch everything I will let yall know how it all works out

stealtht/a

iTrader: (1)

Not sure if anyone clarified this yet but some of the confusion is due to differences between camaros and firebirds.
Firebirds had electric speedos starting in 86 but camaros didn't get them until 89

Scorpner

iTrader: (4)

You're welcome Blk91Firebird.

stealtht/a, technically the Berlinetta was an exception for the Camaro.

Blk91Firebird

Thanks!! It has puzzled me since I first read that if it was a pre 89 fbody it was mechanical.


The housing and gear from my t5 definitely fit in the tailshaft, but I had to rig up a temporary hold down bracket.

The one from the t5 sender needed the bolt hole to be further away from the housing. The original thm 350 hold down needs to be shortened in order to make it work, and even then Im not sure if the bolt head will have room to turn since the t5 sender is much larger.

For now mine is held in place by a long bolt with some large washers holding pressure against the rear of the housing

Wont know if it works for sure till sometime tomorrow

stealtht/a

iTrader: (1)

Just for the digital dash models?

jmd

iTrader: (4)

The bullet does mostly. There are two driven gear lengths; new bullets have a seal installed that can be driven further into the bullet to match shorter style gears.

The T5 gears are not the same as the older TH350 gears. There are two o.d. drive gears and two o.d. speedo gears. The T5 range from 17 to 22 teeth. If you use a matching drive and driven gear, they can replace "the other sized set."

The sleeve is different. O-ring location is different and you may end up with a leak or a sleeve that won't stay (if you try a BOP sleeve in a 700-R4 extension housing, for example.)

To be clear, transmission center is selling correct parts combinations that work if you use a correct matched set.

And I could have sworn I read the other day some 86-88 Firebirds with lesser performance options (V6?) could have cable speedos.

Scorpner

iTrader: (4)

Yes, 84-86. I should have been more clear on that. Thanks.

Blk91Firebird

Thank you very much for all that information/clarification

Distributor problems kept me from seeing if the speedo worked yesterday so I will check it out after while.

Will it matter that the speed sensor came from a car that didnt use the VSS Buffer? (at least I dont think it did) Or are the sensors the same?

Tailhousings interchange between BOP thm 350s and Chevy thm 350s right?

Blk91Firebird

Well still no speedo reading Im going to swap in a 120 mph speedometer and check to see if Im getting a signal at the buffer box

Blk91Firebird

After doing some more research. I figure that im using a 4000 pulse per mile Speed sensor and the buffer box is looking for a 2000 pulse per mile reading so maybe thats why its currently not working. I dont guess there is anyway to just wire it up without having to buy anything is there?

in case no ones noticed im a cheapskate

jmd

iTrader: (4)

The buffer box receives a 4000 PPM speed sensor signal. It feeds a 2000 PPM signal to the early cruise systems, and MAF and TBI ECMs.

The way to wire it up without having to buy anything else is to troubleshoot it by copying your '89 bird.

Take out the VSS out of the '86. Plug the wires in the '89 to the '86 VSS and spin the VSS fast. Does the speedo work off that? If no, then it's either the wrong or a bad VSS.

Blk91Firebird

That is exactly what I should have done! It makes sense and would have done wonders with troubleshooting. Instead of that I went ahead and changed the the gauge cluster, pulled the VSS from my 89 and put it in the 86. Now the speedometer works in the 86 but I was running out of daylight and having trouble getting the other VSS in the 89 so I threw a mechanical sender in it to plug the hole in the transmission

I have no idea which one fixed it but I would guess the VSS. I had to change the connector on the 86 when I first put it in from the twin bullet looking connector to one that I had on my 91 which was a speed density mpfi 3.1, and then back again when I put the VSS from my 89 in it.

Blk91Firebird

Got her car all fixed up speedometer wise and put my t5 vss back in my car. Thanks to everyone for all the useful information and links!

I used the tailhousing from a BOP thm350 and a 700r4 vss. After going through all the transmissions i had laying around I had 3 good Drive gears and 2 driven gears that would fit the 700r4 VSS. Using the above tci speedometer gear calculator I picked out which ones would be right for my application and went with it.

I havnt checked it with the gps yet but according to the math it should be pretty darn close.

Scorpner

iTrader: (4)

Awesome! Glad you got it figured out.

Blk91Firebird

Me too! haha Thanks again!! Im going to refer to this thread for the links you posted anytime I am doing speedometer related stuff.

Im going to hook up the first t5 sensor I tried (without success) to my 89 and check it before I install the one I know is good. I put some more thought into where it came from and that particular sensor came from a 95 v6 t5 camaro