VSSB calibration

[millsroger]

Don't know where this should go but since it comes down to electrical I put it here as a start. Mods feel free to put it wherever you think it would help the most.

This info is from several sites plus notes I made when I did it for my sig truck.

Different tire sizes make the Speedo wrong, duh, we all know that. On ODB1 '91-95 with the DRAC or VSSB the proper division of the Speed sensor is programmable. What the programming is depends on the tire size that the vehicle "originally" came with, unless re-programmed by a dealer or ???

To do this yourself you start with a basic decision, do you want to change it whenever you want or are you going to do it ONLY one time.

My suggestion is to install DIP switches in place of the wired in jumpers. You can get them online or any electronics supply store. They are 7 position 14 pin DIP switches, rocker or slide type work. There are four pics of the DRAC and VSSB boards showing the jumpers and then with DIP switches installed. The DIP's shown were shelf items, I suggest getting the ones mentioned above. You will need one or two depending on the board. About $5 bucks should cover it.

These boards are static sensitive and should be handled by people who know what they are doing, ie a computer repair shop. You can take the info and the board to them and get it done pretty safely.

I am including WHAT needs to be done, who and how is up to you.

What you do is remove the module and then remove the board from the module. Per the pics you can identify the jumper locations. Write down the existing jumper locations. Using solder wick clean the solder from the jumpers and pads, then using a tweezer or ? heat the back side and pull the jumpers, then blow out the holes and make sure there is no solder spatter between any of the traces. Install the DIP switches and solder them in place. Close the switches that match the original jumper locations. You can re-install the board and module for testing at this point--it should work as before.

You will need to know two things, the axle ratio and the circumference of the tire in inches. A hand calculator is all you need to figure this out. I included an XL spread sheet that has the RPO codes for various ratio's, and a table showing the ratio from a tooth count of the gear set you have. You can get circumference several ways, pi (3.1416) x diameter, mark and roll, tape measure, etc.

Once you have the ratio and circumference, do the math per the formula shown in the spreadsheet and look up the answer in the chart. That will tell you what the jumpers should be to calibrate the Speedo, Cruise control and ABS. One note here---the VSSB has two DIP switches, looking at the pics you can see that they are reverse mirror images of each other, make sure you do that with the new setting. By this I mean--if # one on the right has a jumper then # one on the left does not.

A double check can be done by using the original tire size and original ratio, it should come out with the jumper configuration already there. (plus or minus one position since this assumes that the speedo was reading right to begin with). This is probably a good idea before you remove any jumpers, the presumption is that the vehicle is using a speed sensor that generates 40 pulses per driveline revolution--it is my understanding that a few do not have the same pulse count, but, no one has confirmed that.
Please note: the DRAC pic may show the pin sequence reversed. It is not my pic, as can be seen from the chart the #1 position alway has a jumper, the pic shows that as #7. My truck has the VSSB so I have no way to verify the pic.
View attachment Tire size calibration of VSSB.xls

 

[someotherguy]

I recognize those pics from the TBICHIPS website.

Just FYI those modules are used in more GM vehicles than just our trucks - but in our trucks, 1991 does not use this type of setup. It's built into the dash cluster itself. The GM fullsize trucks that use this setup are only 1992-1995.

The 1988-1991 GMT400 series trucks can be done in a very similar fashion but the settings are different and the circuit you're modifying is different, too. Example:

The white diamond-shaped socket is where I just removed the speedometer from a 1988 unit; the row of green devices just to the right of the socket are "micro-fuses" that the factory selectively blows out in order to calibrate the speedometer. They serve the same purpose as the hardwired jumpers in the 1992-1995 unit. To reprogram them later if needed, a kit was used to blow all of them out so they're all open circuits (just as if you removed them completely), then a "programming clip" is used where you break pins out of a row and plug it into the socket next to the fuses (note maroon single row socket) which jumps the necessary circuits. Instead of messing with all that, you can remove the fuses and replace with a DIP switch, just as you would with the hardwire jumpers on the 1992-1995 units:

The settings table differs for 1988-1991 as well:

Back to the 1992-1995 trucks, I used to modify the modules all the time, to the point that I made a little hack to my '94 extended cab in order to easily test/configure modules for my customers - a little slit cut in the glovebox liner allowed me to poke the harness through and keep the module inside the glovebox for easy access.

Richard

 

[millsroger]

Thanks for the added info Richard, I found that my speedo was low by one position on the chart. Flipped the switches and now it reads the same as my GPS. Tires are original size with 3/4 tread and spec pressure so I figure it was right with brand new tires. Now it will be a bit low on new ones and a bit high when worn down.

 

[danner]

I have seen pictures of the 91 DRAC with jumpers going from 1 to 7 and the opposite.. from 7 to 1.. which is correct?

Also wondering if my high miles 93 1500 I bought still has the original tranny... My 93 has the DRAC from the 91 picture with just one set of jumpers 1-7, not the double set. The guy I bought it from also stated it had the 700 transmission.. which was earlier than my year of truck in most cases... any know how to tell the difference by looking?

Thank you for the information.

Dan

 

[someotherguy]

You have to be careful following the years indicated on those pictures from TBIChips because he got DRACs/info from apparently several vehicles, not just fullsize trucks; in 1991 the fullsize truck did not even use a DRAC like that - it was built into the cluster, like the picture I posted.

It doesn't really matter which way you install the DIP switch as the numbering doesn't affect how you set the switches, you just have to remember when setting them that the jumpers and table w/corresponding info assume you are choosing the far left position as #1.

Many '93 trucks came with the single bank DRAC. I have worked on several that were bone stock original, and equipped with the 4L60E transmission.

As far as telling the difference by looking - do you mean the transmission? The 700R4/4L60 and 4L60E are similar but have definite obvious differences. Do keep in mind 700R4 and 4L60 are the same transmission, just different names, as GM converted to the new naming convention. The 4L60E (key difference being "E") is the electronically controlled version that hit the scene in '93. It won't have a throttle valve (TV) cable going into the case, would be one big giveaway. The other which is much harder to see, is on the passenger side there's a large round harness connector going into the lower part of the case on the top side of the valve body area. This is hidden by a heat shield bolted to the side of the trans which protects the harness from the catalytic converter.

Richard

 

[danner]

Richard, thank you for your reply. I have a 6 postion dip switch to install.. the number one jumper is always (almost judgeing by the table) connected so I want to install it in postions 2-7 but would need to know which side the 1 is on to get it in the right place. My current set up was not helpful because it has a jumper on 1 and 7 so it did not give it away for me.

I was wondering about the transmission. Thank you for the tips of what to look for there. This throttle valve cable you refer to.. is it like an old time spedometer cable? Would it go all the way to the instrument panel?

Thank you for the help.

Daniel

 

[someotherguy]

Yep, #1 jumper is always on, which means in the case of the 2 bank DRACs, the #1 position is always open on the 2nd bank. I've done many with just 6 position DIPs as they're fairly easy to find.

Throttle valve cable on the 700R4/4L60 goes in at the upper side of the valve body area, and looks similar to the detent ("kickdown") cable on an old 3 speed TH350 transmission. Here's a pic of a 700R4/4L60 with the cable installed:

Note this is the same area of the case that the 4L60E's large round harness connector would be at.


An easier-to-spot difference between the two is the driver's side of the 700R4/4L60 has a governor behind a domed metal cover just ahead of the tailshaft housing; the 4L60E will not have this. Black metal cover in this pic:

Richard

 

[danner]

Thank you for the pictures there. I won't have any trouble telling which transmission I have.

I still am not sure which side of my 7 jumpers is the number one side?

Thank you,
Daniel

 

[someotherguy]

In that picture up top from TBIchips that he has labeled "1991 DRAC" his numbering scheme is correct for the single bank design.

Richard

 

[danner]

Thank you Richard, I was not sure which picture to believe, the one on this thread or the one on another thread which had them the other way. I'll get my DIP soldered in to the right side and get it dialed in for my tires.

Thank you very much and have a great day!

Daniel

 

[Eli]

I need info on setting dip switches. I have 20”Rims 4:11 gears. and I am doing the cluster upgrade. I have a 90 and upgrading to a 93. Does ay if this matter?

 

[Will L.]

Welcome Eli. Rim size does not matter. Tire height (aspect ratio) does. You could have 28” tall tires or 44” tall tires on a 20” rim, and that is what counts. Although your new here, I am a old grey haired guy and have to bust your chops on 20s a little- change them before someone notices your underwear showing too, haha. JK

If you get lost figuring how to do this and would rather buy a set up unit that’s adjustable, talk to John at uniquediesel.com he makes them, and is a descent guy.

 

[Eli]

LOL! Thanks Will. I was up late last night. I plan on getting a DRAC and installing dip switches soon. I am going from a 90 cluster to a 93. Does the DRAC have to be from a 93 or can I use anyone?

 

[ak diesel driver]

Are you gasser or diesel?

 

[Eli]

Gas

 

[ak diesel driver]

Might be better to go to gmt400 site.

 

[Eli]

Ok. Thanks I’ll look into it.

 

[Lloyd Ray]

Don't know where this should go but since it comes down to electrical I put it here as a start. Mods feel free to put it wherever you think it would help the most.

This info is from several sites plus notes I made when I did it for my sig truck.

Different tire sizes make the Speedo wrong, duh, we all know that. On ODB1 '91-95 with the DRAC or VSSB the proper division of the Speed sensor is programmable. What the programming is depends on the tire size that the vehicle "originally" came with, unless re-programmed by a dealer or ???

To do this yourself you start with a basic decision, do you want to change it whenever you want or are you going to do it ONLY one time.

My suggestion is to install DIP switches in place of the wired in jumpers. You can get them online or any electronics supply store. They are 7 position 14 pin DIP switches, rocker or slide type work. There are four pics of the DRAC and VSSB boards showing the jumpers and then with DIP switches installed. The DIP's shown were shelf items, I suggest getting the ones mentioned above. You will need one or two depending on the board. About $5 bucks should cover it.

These boards are static sensitive and should be handled by people who know what they are doing, ie a computer repair shop. You can take the info and the board to them and get it done pretty safely.

I am including WHAT needs to be done, who and how is up to you.

What you do is remove the module and then remove the board from the module. Per the pics you can identify the jumper locations. Write down the existing jumper locations. Using solder wick clean the solder from the jumpers and pads, then using a tweezer or ? heat the back side and pull the jumpers, then blow out the holes and make sure there is no solder spatter between any of the traces. Install the DIP switches and solder them in place. Close the switches that match the original jumper locations. You can re-install the board and module for testing at this point--it should work as before.

You will need to know two things, the axle ratio and the circumference of the tire in inches. A hand calculator is all you need to figure this out. I included an XL spread sheet that has the RPO codes for various ratio's, and a table showing the ratio from a tooth count of the gear set you have. You can get circumference several ways, pi (3.1416) x diameter, mark and roll, tape measure, etc.

Once you have the ratio and circumference, do the math per the formula shown in the spreadsheet and look up the answer in the chart. That will tell you what the jumpers should be to calibrate the Speedo, Cruise control and ABS. One note here---the VSSB has two DIP switches, looking at the pics you can see that they are reverse mirror images of each other, make sure you do that with the new setting. By this I mean--if # one on the right has a jumper then # one on the left does not.

A double check can be done by using the original tire size and original ratio, it should come out with the jumper configuration already there. (plus or minus one position since this assumes that the speedo was reading right to begin with). This is probably a good idea before you remove any jumpers, the presumption is that the vehicle is using a speed sensor that generates 40 pulses per driveline revolution--it is my understanding that a few do not have the same pulse count, but, no one has confirmed that.
Please note: the DRAC pic may show the pin sequence reversed. It is not my pic, as can be seen from the chart the #1 position alway has a jumper, the pic shows that as #7. My truck has the VSSB so I have no way to verify the pic.
View attachment 34015View attachment 34016View attachment 34017View attachment 34018View attachment 34019

Hey bud I'm getting ready too modify my vssb tomorrow I have all the numbers I need I am curious if you can help me figure out the start point and how too insert the sequence into the dipswitches?