Suburban Speedo, Need help!

[aggie91]

I swapped in a cluster from a 1990 Suburban into my '85 with an LS swap.

I had the PCM programmed for my gear ratio (3.73) and my tire size (315/35-20; 28.68" tall).

I have 2 issues, one of which bugs the piss out of me.

The Speedo reads slow. Speedo shows 25 mph, by my GPS I am doing 41-42mph. Has only one else had the speed read incorrectly when doing this swap?

Second is the turn indicator lamps come on when you turn on the headlights. This only bugs me at night...The signals work but when I turn on the emergency flasher, nothing flashes...

If I can get some help with the Speedo, I think I can track down the indicator light problem, I just need some time to think that one thru...

Anyone got any ideas on the Speedo?

[aknovaman]

Have someone with hptuners data log the truck and see if it is the dash cluster or the PCM file. If the scanner reads same as the gps, then it's the cluster. If the cluster is ioff you can change its input signal from the PCM without changing the trans tables. Both can be adjusted via hp tuners or tunercat.

[clinebarger]

The indicators lighting up with the headlights is generally a ground issue. Check the headlight grounds at the core support, The Core support has a ground from the right frame rail that needs to be there.

[ls1nova71]

Is the odometer accurate, or is it off too? If its slow by the same ammout then it has to be in the tune. If it is accurate and the speedo isnt, then you have a bad speedo.

[aggie91]

Thanks for the responses guys. I need to check the odometer, I really haven't paid that much attention to it...

[homemade87]

I did a burb cluster in my 82 and everything worked perfect . I did have to repin the cluster to match the 82 wiring for everything to work right . Also had to use hp tuners to get the speed right . Sounds like you have already got every set up correct . Must be the speedo is off .

[aggie91]

Well, I was able to spend some time checking the odometer against my gps on my phone. It is off too, by about the same percentage as the speedo.

Looks like I need to find someone with software to read my setting in my PCM to verify what I told the tuner to put in...

[BR3W CITY]

Doesn't the 90-91's electric speedo use the DRAC? The thing that takes the PPM signal from the trans? I don't know if you can avoid that thing with correct HPT programming, but I'd imagine that if you have one and its setup wacky, then no amount of good programming will change that.

The part itself is less than $20. If you search "DRAC" a bunch of speedo related threads in the model specific forums pop up.

[clinebarger]

Originally Posted by BR3W CITY

Doesn't the 90-91's electric speedo use the DRAC? The thing that takes the PPM signal from the trans? I don't know if you can avoid that thing with correct HPT programming, but I'd imagine that if you have one and its setup wacky, then no amount of good programming will change that.

The part itself is less than $20. If you search "DRAC" a bunch of speedo related threads in the model specific forums pop up.

The Drac is just a Signal Converter, It does the same thing that is built into Flash-Memory PCM's.

I "Think" his speedo takes a 4000 PPM DC signal, A DRAC & PCM can not share the same VSS sensor.

[MalibuSSwagon]

I had a similair issue with my cluster, the printed circuit on the cluster is junk. The input pins where the dash connector plugs in can come loose from the backing and cross paths.

[aggie91]

After we get past this weekend (HS graduation for Korbin, Conformation for Katie at church, whole lot of family in this weekend), I hope to pull the cluster out and recheck everything on it. I noticed today, that the odometer jumped from about 12 miles on the trip odometer to 122 miles...I found a replacement speedo unit so I may just order that and swap it into the original '85 cluster housing...

[68c10airstream]

If memory serves correctly when i went to GMC schooling in early 90's the training i had involving speedo reading wrong involved pulling the cluster, plugging in a special 2 wire harness and you touched 12 volts positive and negitive and burned the built in resistors in the cluster. Then the dealer purchased a package of 12?? gold plated bridging clips to be pushed into holes in the back side of the cluster after you looked up on a chart the tire size and gear ratio. I looked at the post twice before i remembered the pigtail harness i used once. This info is getting old (i think). Good luck on your quest with this info in your head now! Brian F.

[aggie91]

Thanks, Brian. That might be one method to fix it, but since the signal is controlled by the PCM now, I am not sure that would help since the tire/gear info in put into the program in the PCM.

Since the trip odometer skipped ahead, I am going to replace the speedo first since I found one for $60.

[68c10airstream]

Karl, I just checked on alldata pro and it is as I suspected. I looked up a 1990 5.7 gm 1500 truck and the VSS comes from the trans and the ratio adaptor is in the cluster along with a buffer and a programming clip. This is where gear ratio, tire size plays into the equation. From there a 2,000 pulse and a 4,000 pulse go to the various systems that need it, ecm, abs, cruise module, when it leaves the cluster. If I understand your new setup with a pcm being the central programming house than yes this would have to match the tire size and gear ratio for the output to leave correctly for the trans to work correctly. I believe unless you match the tire size and axle ratio from the new cluster you are going to get you will have a mismatch again. As a further thought if you "Y" off of the vss signal and one leg pair goes to pcm, and one leg pair goes to the cluster this could be the answer provided again the cluster matches your current tire and axle. Possible cluster repair center could help out on this because if a new printed circuit was needed than bridging clips would be needed. This is my interpretation at this time but I see a discrepancy between how the 2 systems do tire/ ratio changes. Good luck, Brian F.

[homemade87]

Aggie , What year system did you install . If it was 2000 and later you should be good to go for the speedo. In my 82 I have a 04 truck system and installed a 91 burb cluster . I had to do nothing but set the pcm with tire size and gear ratio . I think airstream is over thinking it . Many have done this swap with no issues and I am one of them. Also There is a couple places to change the gear and ratio in hp tuners . If not done in the proper place it will not take the changes and be correct. The place you need to change it is where the program ask to recalculate and it will do all the work for you to make the corrections . Ask me how I know this .

Of cource this is all base on if you are using all the oem wiring and trans and pcm with the cluster .

[68c10airstream]

Did a little more alldata searching and it seems that 90 and older used the bridging programming clip, and 91 and newer uses a DRAC or pcm programming, depending on the application.