RTGTA

Howdy and Happy New Year! I have a question about rear end ratios in relation the the speedometer. When i bought my car the prev owner told me that 2.92 was installed in the rear to get better fuel economy which in turn caused the Speedo to read higher than my actual speed. I purchased a new carrier, crown and pinion, and bearing kit to install the original 3.42 in the rear. So if I'm corect this will fix my speedo problem. Does this sound correct or was the speedo maybe a completely different problem and I blew money on a rear end that I dodn't even need to replace? Please help

RTGTA

I also forgot to mention that my engine sounds like it's redlining when my tach says about 3200 rpm... and when doing 110 km/h (actual, 140 km/h on speedo) the tach is saying about 1400 RPM.

alloy

iTrader: (16)

Depends on what the original gear ratio was. If it was 3.42 and you went back to the sameratio then your fine. If not then you will need to either change the speedometer gears, or you can have a speedometer ratio adapter made up to correct the ratio and have the speedometer read correctly.

I have a speedometer shop here and they put my car on the rollers and checked to see where my speedometer read, then they built a ratio adapter so my speedometer read correctly. This cost me $75 about 5 years ago. Since then I had pulled my old T5 apart and got rid of the adapter and put the proper gears in it. Now I have a T56 and used Bob Hanlon's T5 speedometer utility to choose the proper gears.

Here is a link to it.

http://www.hanlonmotorsports.com/t5speedo.asp

JamesC

iTrader: (5)

2.92 isn't a ratio that I'm familiar with. Alloy is correct about the change.

JamesC

subroc

iTrader: (2)

If the car your are talking about is the Trans am i dont think that 3.42 was a ratio that came with a V8...only a v6 and lower. So..check your codes and figure out what ratio your car came with, then find out what you have. If he put highway gears in it is probably 273 (10 bolt) or 2.77 (9 bolt BW).

RTGTA

Yeah he said 2.92... I thought that sounded wrong but whatever. And yeah i got my build sheet and it's a 305 TPI with the T5 with 3.42 rear ratio. So as soon as I put that in my speedo should be good. Also, what should I be expecting when crusing at 110 km/h on the highway with the 3.42... about 2100 rpm?

JamesC

iTrader: (5)

A speeding ticket .

JamesC

subroc

iTrader: (2)

110kph is about 70 so your rpms will be closer to 2500rpms. At least thats where mine fell with a 700r4 and 3.42s. Since you have a T5 you will probably be a bit lower than that...maybe by 1-200 rpms.

RTGTA

Thank you all for the help. Greatly appreciated. I can't wait for spring so I can get my baby back on the road. And hopefully with those 3.42 She'll be a bit more fiesty. I was just scared I spent money and maybe the rear was still stock and it was just a speedo problem but good to know I have the solution to the problem. The prev owner falsified a lot about this car so now I'm not too sure. But with the RPM and everything it all points to the rear being changed out. I have about $2000.00 worth of parts sitting in my shed for her so I'm itching for spring.

RTGTA

I was reading old work orders that came with her and it has had a transmission put in in 2000 as the speedo gear heated and disintegrated senting metal through the tranny. They reported that when they put the tranny back in it had the same red speedo gear as the one which was pulled out yet the speedo was not accurate. With the tranny detroyed I;m sure they towed the car in and I'm also sure that if that was different then before the owner at the time would've said something. ANy thoughts. Does this all seem to be pointing to the Rear end being swapped before??? Opinions and knowledge greatly appreciated