Gear ratio for 35 inch tires.

[Shaun Neubert]

Please advise. I put 35's on my 90 Burb and the Speedo is off. Can anyone tell me what ring and pinion would put my Speedo back on the money? Now is the best time for me to change them on both ends since my carrier, ring gear, and pinion gear in the rear diff self destructed recently.

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[Vbb199]

Since its a 1990 you're truck uses a VSS
The vss is what reads the digital signal (rotation of the drivehaft) the drivehaft creates pulses.
Those pulses are then sent to the DRAC module and turned into a analog signal that the computer or whatever can read.

Even changing gear ratios won't quite fix it completely.

You need to reprogram the DRAC.

Go to harristuning.com and read about reprogramming your drac.


As far as a ok ratio for the 35's, 3.73 I think would be fine.

 

[Vbb199]

There is a reluctor ring inside the trans tail (2wd)
Or the t case (4x4), the vss reads teeth counts on the reluctor ring... That is what your pulses are.
VSS is vehicle speed sensor.

 

[Vbb199]

Most anywhere on the web you can find one of these handy references.

Really 4.10 would serve you better. I just guessed off the top of my head

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[Vbb199]

Reprogramming the drac is very easy if you have a soldering iron.

Or you can purchase a dip switch and make short work out of it. But that will also require soldering.

 

[C10MixMaster]

Since its a 1990 you're truck uses a VSS
The vss is what reads the digital signal (rotation of the drivehaft) the drivehaft creates pulses.
Those pulses are then sent to the DRAC module and turned into a analog signal that the computer or whatever can read.

Even changing gear ratios won't quite fix it completely.

You need to reprogram the DRAC.

Go to harristuning.com and read about reprogramming your drac.


As far as a ok ratio for the 35's, 3.73 I think would be fine.

you can add dip switches to the drac module and change the speedo reading with the flips of a couple switches (I was modifying and selling these on ebay a while back)

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[bucket]

Most anywhere on the web you can find one of these handy references.

Really 4.10 would serve you better. I just guessed off the top of my head

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That doesn't take into account overdrive though. 4.56 or 4.88 would really be pretty good.

 

[Vbb199]

That doesn't take into account overdrive though. 4.56 or 4.88 would really be pretty good.

You're right. Wasn't thinking about OD

 

[Shaun Neubert]

That doesn't take into account overdrive though. 4.56 or 4.88 would really be pretty good.

Are there any videos where I can find out how to properly modify my DRAC module?

 

[bucket]

Are there any videos where I can find out how to properly modify my DRAC module?

Beats me, @C10MixMaster is the one that modified them. I'd like to know as well.

 

[C10MixMaster]

Are there any videos where I can find out how to properly modify my DRAC module?

haven't seen any videos its just a matter of unsoldering the jumper wires and replace them with the switches. the switches can be found on ebay

this link will show how to calibrate it once converted. https://harristuning.com/Tbi/vssb-drac-calibration/

 

[nvrenuf]

I have a 91 crew cab with 35’s, 4.56’s were perfect for it. No DRAC mods, it shifted normal like before the lift and felt great driving.

 

[gmbellew]

my 1990 v1500 did not like the highway with the speedo off after a lift and going to 33s. i think it may have had something to do with the torque convertor lock up on the vehicles with an ECM. once i got the DRAC to where the speedo was within a few percent of actual speed, it ran down the highway like a dream. not sure it matters, but i have a 700r4 with factory stock 10 bolt rear with 3.73 gears.

 

[Shaun Neubert]

my 1990 v1500 did not like the highway with the speedo off after a lift and going to 33s. i think it may have had something to do with the torque convertor lock up on the vehicles with an ECM. once i got the DRAC to where the speedo was within a few percent of actual speed, it ran down the highway like a dream. not sure it matters, but i have a 700r4 with factory stock 10 bolt rear with 3.73 gears.

I have the same setup. Except for the 35's and a new tranny. It is the 700R4 with 3.73 ratio. The ratio is going to change though. The rear diff grenaded soon after the tranny change.

 

[gmbellew]

I have the same setup. Except for the 35's and a new tranny. It is the 700R4 with 3.73 ratio. The ratio is going to change though. The rear diff grenaded soon after the tranny change.

i feel like 33s are pushing it with 3.73 and OD on the highway. 4.10 would probably be a better set up, but i dont plan to make a change until something blows up. for 35s, i think the advice you got above is good for gear ratio with OD and for where to look to adjust the DRAC. the DRAC is behind the dash under the radio, held in place by 2 hex head screws with heads you can see on the front of the metal dash.