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Pete, Auto Service Technician
Category: Chevy
Satisfied Customers: 24142
Experience:  14 years GM dealer Technician.
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I have a retro mod truck sitting on a 1988 S10 w/4.3L. The

Customer Question

I have a retro mod truck sitting on a 1988 S10 w/4.3L. The speedometer reflects a 10% faster speed than my actual speed and it shifts a bit prematurely eventually gettin into overdrive sooner than I think it should. They added low profile tires, so diameter surely changed from stock, but not by 10% so probably rear end as well. Is there a thread or a document I can reference to address this? I also don't mind paying a professional to do this, where can I identify one of those? Afraid of shade tree types, so understanding the process will help me know I found the right service provider.
Submitted: 29 days ago.
Category: Chevy
Expert:  Pete replied 28 days ago.

My name is ***** ***** I am a professional here at Just Answer. I noticed that your question had not received a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.

The biggest issue is usually the smaller tires that will cause this.It only takes a small amount to cause speed change signals like this here and smaller tires will change the speed to a faster speed as well as cause upshifting and over drive operation sooner then desired.

The other issue I have seen is a fault with the drac module as some of these vehicles used.Usually this is a calibrated module that is installed (obtained from a dealer) that matches the transmission and differential gear ratios and tire sizes.You can get these checked to get the numbers you need from these and have a GM dealer order in a correct fit drac to correct this here.It is usually situated behind the glove box area and is white in color with wiring connected to it.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service,your 5 star rating is appreciated.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

Expert:  Pete replied 24 days ago.

Hello I am just checking in with you to see if there is anything else I can help with here?

Let me know,thanks Pete.