daveg

i have a 86 berlinetta the digital speedo does anyone know how to bypass it to go over 85 mph

John in RI

iTrader: (167)

I've been searching for that answer for over 11 years !!! Finally I installed an aftermarket speed so I could get "real world" speed readings in my Berlinetta !!!

I have heard that it can be accomplished by tricking the speedo read and display MPH - but by using the KPM circuits (or something like that). But,.... I have spoken to more than one electronics guy that says it can't be done.

Get Blown ?

Perhaps if you installed a buffer like the Dakota box you could trick the VSS into reading the proper MPH using the KPH option. Can't see why it wouldn't work, if calibrated properly since you can correct gear ratios with a Dakota box. Or perhaps use different ratio on the tailshaft to obtain the same goal. Even if the digital speedo started to flash at the exuivolent in KPH you'd be good for roughly 136MPH. Anyway it's just an idea you might wanna look into. And I'm sure John will look into this, if he hasn't before. Given his past experience with Berlinettas.


EDIT: OMG I think my idea about using different tailshaft gears will work! Using the 1 to .62 ratio 3.73s would convert to 2.31 and novasourse lists tooth ratios similar to 2.31. That is if my math is correct. Could be backward (and probably is)...Reguardless, these two sites might help you figure out the proper gear ratio to pull this off.

http://www.novaresource.org/speedo.htm
http://www.business2business.on.ca/convert.html
http://www.dorianyeager.com/speedogears.html

John in RI

iTrader: (167)

That makes a lot of logical sense !

Buy dividing the actual rear end gear ratio by 1.6 and then pushing the KPH button on the dash - the speedo would theoretically read the correct speed in MPH (but shown on the dash as KPH)


< REMOVED DATA FROM THIS POST because it could not be verified !!! >>


Now - If I am not mistaken the speedo "DRIVEN" gears for the digital Berlinetta are different from those installed in any other 82-89 camaro with a mechanical driven Speedo. The parts manual I have covers 82-86 cars and lists different part numbers a 42 tooth Berlinetta gear and a 42 tooth Camaro gear.

The 90-92 camaro's were also equipped with the electric Speedo sending unit ( as well as those Digital GTA's !!) and *probably* have the same type of speedo gears as a result. I just don't have that information available to me right now !!!!

I know that in the 84-86 Berlinetta's there were several different speedo gears available including:

DRIVE gears:
7 tooth RED / GM Part # 14071731
17 tooth RED / GM Part # 8640517
15 tooth GRAY / GM Part # 8642620

DRIVEN gears
20 tooth BLUE / GM Part # 14076948 (Sleeve P# 25007350)
42 tooth GREEN / GM Part # 25513049 (Sleeve P# 25007339)
43 tooth PURPLE / GM Part # 25513050 (Sleeve P# 25007339)
45 tooth LT. BLUE / GM Part # 25513052 (Sleeve P# 25007339)


As you can see from my research - not to many speedo gears were offered in the 84-86 Berlinetta !!!! It's up to someone with a parts manual that covers the 90 to 92 camaro's to "pick up the ball" & look into that book for the speedo gears availible for the 90-92 cars and to see if they match any of the combinations I listed above.

I would do it - but my car is getting a T56 and I can't use speedo gears to correct my speedometer reading anymore !!!! I am also using an aftermarket speedo and can convert that speedo for any tire size or gearing combination !


Please - anyone that has some knowledge in this area - feel free to chime in !!


(UPDATE !!) I believe that the speedo gear chart on novaresource.org is WRONG !!!!

Get Blown ?

Don't forget 87+ firebirds with the digital dash. You might be able to get proper tailshaft gears from one...

Here's another site that should help. http://www.tciauto.com/tech_info/speedo_gears.htm

John in RI

iTrader: (167)

Now I am sceptical of the figures posted on novaresource.org !!!!

Based on a 1 & 1/2" DRIVEN gear, The factory Camaro with 3.23 gears and 26" tires (215/65/15) was equiped with a:

17 tooth Drive gear --- 44 tooth driven gear = 3.23 rear gears

But when I look at the chart on NOVARESOURCE it reads :

17 tooth Drive gear --- 44 tooth Driven gear = 2.59 rear gears


The same is true for every other gear ratio I checked,......... example:


The factory Camaro with 3.73 gears and 26" tires (215/65/15) was equiped with a:

15 tooth Drive gear --- 45 tooth driven gear = 3.73 rear gears

But the chart on NOVARESOURCE says:

15 tooth Drive gear --- 45 tooth Driven gear = 3.00 rear gears



What's going on here ??? Is that chart off ??? Are the speedo gears listed on NOVASOURCE aplicable to a Camaro ??

John in RI

iTrader: (167)

My skepticism grows !! After plugging the numbers into

http://www.tciauto.com/tech_info/speedo_gears.htm

I get results that are different than those reported by NOVA RESOURCE !! I would not use the NOVARESOURCE chart for the gearing calculation !!!

I tend to agree with the TCI page as it's results are MUCH closer to the actual speedometer gears that were originally offered with our cars !!!

Based on a 26" tire,.... the TCI calculator shows the following gears will be the closest match for swapping the tranny speedo gears to have the Berlinetta Speedo display KPH but read MPH:

2.77 gear / 1.60 = 1.73 SOL (values to small to calculate)
3.08 gear / 1.60 = 1.925 SOL (values to small to calculate)

3.23 gear / 1.60 = 2.018
15 tooth DRIVE gear and 24 tooth DRIVEN gear
17 tooth DRIVE gear and 27 tooth DRIVEN gear
18 tooth DRIVE gear and 29 tooth DRIVEN gear
19 tooth DRIVE gear and 31 tooth DRIVEN gear
20 tooth DRIVE gear and 32 tooth DRIVEN gear


3.42 gear / 1.60 = 2.137
15 tooth DRIVE gear and 28 tooth DRIVEN gear
17 tooth DRIVE gear and 31 tooth DRIVEN gear
18 tooth DRIVE gear and 33 tooth DRIVEN gear
19 tooth DRIVE gear and 35 tooth DRIVEN gear
20 tooth DRIVE gear and 37 tooth DRIVEN gear


3.70 gear / 1.60 = 2.312
15 tooth DRIVE gear and 26 tooth DRIVEN gear
17 tooth DRIVE gear and 29 tooth DRIVEN gear
18 tooth DRIVE gear and 31 tooth DRIVEN gear
19 tooth DRIVE gear and 32 tooth DRIVEN gear
20 tooth DRIVE gear and 34 tooth DRIVEN gear


This is all theory so please,...... those of you out there with a clearer understanding of speedo gears - chime in and help us out here !!

Get Blown ?

Very interesting, perhaps you could email novasourse about it. The TCI calc should yeild better results anyway, since you know what size tire is actually being used then.

daveg

YOU GUYS ARE GREAT TO GO THROUGH ALL THIS JUST TO GET ME A ANSWER I APPRECIATE IT ALOT I HOPE I CAN FIGURE THIS OUT THANKS AGAIN FOR ALL YOUR HELP THIS MESSAGE BOARD THING IS GREAT BY THE WAY THE REAR END GEARS IN MY CAMARO ARE 2.73 IN CASE THAT HELPS ANY oh and 215/65/15 tires ok so another words i have to change the mph to kph and change the trans tailshaft gears to what?im the type were i need step by step instuctions to do anything right thanks again for all you guys help

redcamaro83

any results?

daveg

i havent tried it yet but it sounds like it would work

levi3

I know this thread is 14 years old but does anyone know if this actually works? I am no math wiz. I know a mile is 1.6 km. But does that mean dividing the rear gear ration by 1.6 and gearing the speed sensor based on that would cause the kph to actually be mph? I put 4.10 gears in my Berlinetta so my problem is two fold. Not only does the speedo start blinking at 85mph but the closest I can get the speed sensor gears to 4.10 is 3.73 so my speedo is 9.2% off. So once I hit 85 I am actually doing somewhere around 75ish but I never really know what my actual speed is. If tricking the car into kph is realistic it would be great!