Any thoughts on adding a DRAC

[Big Port Jimmy 6]

The speedo on my crew cab has always been 4-5 MPH slow. (01 5.3 /4L60E). The tune was supposed to be set up for the tire size but? I am using a 91 cluster. I just went bigger on the rear tires and now the speedo is 10ish MPH slow. I wonder if adding a modified Drac would correct this.

As I understand it I would install the Drac in between the VSS and the PCM
And would have a separate out put for the speedo. I have seen the article about modding a drac for my input. The question is if the later 4l60 outputs 40 pulse per rev/4000 per mile. . Jay

[BR3W CITY]

4L60e's are 40ppr, which IIRC is the same as what the 90-91 cluster uses. You need to go from ac-sine wave to DC square wave for the thing to work though.

Thing is, to recal the speedo, don't you have to change the teeth on the 8pin plug on the cluster? Cuz you'd have to get a new one of those, which matches what you need or hasn't been setup (destructable), and they don't make them anymore. *This is just from reading misc junk while looking at swaps*

I thought all the modified drac would do was let you have outputs for the ecm AND cluster etc, not to actually change the function on the cluster? I may be confused on this, as the information seems to change heavily from 89-95 in terms of HOW it needs to happen.

[Big Port Jimmy 6]

Let me clarify I have a R body cluster (square body) not the 91 CK cluster so I don't think they calibrate that way, but I will check my spare. You can modify a drac for different in put value that you calc with your tire info. Jay

[ls1nova71]

The '91 cluster should work perfect right out of the box. You say "The tune was supposed to be set up for the tire size but?" makes me think it's just not set right. If you have the tuning software it should be relatively easy to get right.

[BR3W CITY]

Originally Posted by Big Port Jimmy 6

I am using a 91 cluster.

Originally Posted by Big Port Jimmy 6

not the 91 CK cluster

hence, I'm lost.

[Big Port Jimmy 6]

I feel like the tune is right, but that the speedo is inaccurate. a problem that I exacerbated with changing the rear tire size I did not do my own tune and do not want the equipment as a means to keep me from screwing with it all the time. And really do not want spend a lot to redo the tune

Brew City the 1/2 tons in 88-92ish are the new body style the 3/4, tons Burbs and Blazers are like the 81-87 trucks. Some of them have electric speedo clusters, which is what I have. Jay

[BR3W CITY]

Originally Posted by Big Port Jimmy 6

I feel like the tune is right, but that the speedo is inaccurate. a problem that I exacerbated with changing the rear tire size I did not do my own tune and do not want the equipment as a means to keep me from screwing with it all the time. And really do not want spend a lot to redo the tune

Brew City the 1/2 tons in 88-92ish are the new body style the 3/4, tons Burbs and Blazers are like the 81-87 trucks. Some of them have electric speedo clusters, which is what I have. Jay

oooooh its like the whole "silverado Classic" thing on the NBS trucks....gotcha.