GermanV8

Hello from Germany and sorry for my bad english.

I owned an Firebird S/E Coupe 2 Door with the 305 SB carburator. The car had a lot of Pre-Owners and some guys are done changes on the car that i had to fix now. My Speedometer is going wrong. When iam cruisin on the Autobahn / Highway as example, the Speedometer shows 90MPH and this is the maximum. 90MPH must be around 145kmh in German but i testet with GPS on my Phone that i drive only 115kmh. What i going wrong? I dont know if the right Model of Speedometer is installed? My VIN Says that it is an VIN H with Automatic Transmission but in the Car actually is an 5 Gear Manual Transmission and i dont know if one of the Pre Owners does this change. ... On the 5.0 ( with Carburator from 1985, did you know if there must be an 120mph Speedometer or is the 80MPH Speedometer correct? If it will be the correct one, where is the problem? Wheels are in the front 235/60 R14 and Rear 255/60 R15 .

I hope anybody can help me, because here in germany are not so many Firebird Owners an my whish would be to bring the car to an A++ in the next months .....

Regardly from Germany Sascha

John in RI

iTrader: (167)

There are 2 things you will need to do before you can continue on and correct this problem. ( you will probably need to change 1 or both speedometer gears inside the tranny. )

1) Verify your rear-end Gear Ratio.
Open the rear differential cover and count the teeth on the RING/Pinion gears. There are other ways to get the gear ratio from a rear-end but most rear-ends need the fluid changed anyway. ( Cheap maintenance ! )

2) Verify your Speedo Gears.
Remove the speedometer sending unit in the tranny and count the teeth on BOTH the DRIVE gear and the DRIVEN gear ( and check what color each gear is. )


Once you KNOW what rear end gear is in the car and you KNOW what speedo gears are in the tranny you can calculate the proper speedo gears needed ( based on tire size ) to obtain the correct speedometer readout.

Do not focus or worry about the speedometer itself yet. You must verify what the gear ratio and speedo gears are FIRST.

GermanV8

Hi John, thank you. Did you know which Oil i had to use for the rear differential? So i will order a new gasket and the oil and then i will count the teeth. Thx a lot!

Tuned Performance

iTrader: (92)

80/90w gear oil . You can use rtv silicone sealant to seal the rear cover instead of a gasket.

GermanV8

Hey Ho, now it will be tricky but i have informations about the differential. I think a have an very rare Borg M78 because i have 9 Bolts and i found an Serial on the differential. After i googled i found out this datas Serial:10032245 Ratio 3.27 / Std . Good news: I have the ratio ... bad news ... i dont find any chrome covers or new covers original, did u know an dealer? (the actually are not so nice conditioned) . Next days i will open the Gearbox at the transmission to find out how many teeth there. I will inform u as soon i had look. Greetings from germany Sascha

John in RI

iTrader: (167)

If the rear end you've got has a rubber plug on the cover and 9-bolts,... YUP; It's a Borg Warner ! The shop manual calls for 75W90 and NO additive in that rear end.

If I Remember Right there is only 1 aftermarket rear end cover that is available. I don't have any details on it,... but I seem to remember seeing them in the past. Searching thru this website should help you to find information on the aftermarket 9-bolt diff cover.

J.C. Denton

iTrader: (1)

Es gibt einen Aftermarket Deckel für die 9 Bolt. Dieser kommt von TA Performance. Bekommst du aber nur in den USA und musst ihn nach Deutschland versenden. Ist aus Voll-Alu und verstärkt die Differentiallagerkäfige zusätzlich über die äußeren Stellschrauben. Kaufen kannst du den entweder bei http://www.taperformance.com oder über www.hawksmotorsports.com mit deren eigenem Logo auf dem Deckel.
Kostet 150 Dollar plus Versand und Zoll und Einfuhrsteuer und sieht einfach geil aus. Hab das auch für meine 10 Bolt.

There ist just one aftermarket Cover for the 9 Bolt as I remember. Its made by TA Performance. Looks really great and it supports the diff bushings with those preload screws in the cover. You can buy it at TA Performance oder at Hawks with their own Hawks Logo on the cover for 150 Dollars. I have it also for my 10 Bolt that I am actually rebuilding.

GermanV8

Thx a lot!

PS: Hatte mich gestern registriert aber warte nachwievor auf Freischaltung für meinen F-Body-Nation Account. Dauert das immer so lange? ... LG

Drew

iTrader: (58)

It's a little tricky, but you can actually count the teeth on the speedometer drive gear by looking in the sender hole. Might even be easier that way since the teeth are helical and you're seeing them from the profile... A light shined in the hole will usually let you see the color, and since they're color coded.....

As much as I LOVE math... Sarcasm... There are actually charts in the parts manuals that list drive/driven gear combinations. It's in the parts half of the parts and illustration catalog, in the transmission section.

GermanV8

Thx for your Information! I will try it tomorrow ... i had to change the oil pan and at this moment i can look there ... Greetings