86 or 87 Gauge Cluster

[Cody the Roady]

The gauge cluster on my 1987 R10 LWB is needing to be replaced. The circuit board is fried, gauges not working, etc. I found a cluster on E-Bay, listed as 1973-1987, used, and in very good condition. I bought it, BUT I did so even after knowing the following: E-Bay has a mechanism that allows you to check if the item for sale will fit your vehicle. The cluster would fit a 1986, but it said it would not fit a 1987. The only thing I could think of was because of the 1987 being the first year for the TBI. I bought it anyway, thinking that E-Bay is full of...they don't know what they're talking about. Am I right to doubt them? It looks exactly like my old one. Somebody put my mind at ease.

[Irish_Alley]

there is a difference in the 81-87. other older gauges might be maniacal (oil) or different layout. think the only problem with the newer ones is dealing with the electric speedo but this wont be till 89 or so

[Cody the Roady]

Yep, that's kind of what I was thinking. I knew of the differences in the gauge clusters for the earlier years, but for the life of me I could NOT understand why there would be a difference between a 1986 and 1987 cluster. Thank you for the clarification.

[bd]

For use with TBI, the IP cluster will need to have facility for the VSS optical sensor integrated into the back of the speedometer head.

[hatzie]

For use with TBI, the IP cluster will need to have facility for the VSS optical sensor integrated into the back of the speedometer head.

82-86 with cruise control has optical VSS on the speedometer as well. 
Are you sure the VSS for the ECM is on the 87 speedometer and not on the transmission like the Jags That Run VSS boxes?

From orbit on my Android.

[DnStClr]

As I understand it, the vss optical sensor in the speedometer is connected to the cruise control system. Somehow, thru an LED, it supplies an optical speed signal to a buffer which amplifies the signal and then sends it to the controller, a light green module mounted near the accelerator pedal, that operates the cruise control vacuum servo.  That's just a layman's explanation, but it's the best I can do.    

[Irish_Alley]

Thought the dracs box sends the signal for the cruise ? The dracs box get the vss sensor signal and then breaks that down into other signals abs, speedo, ecm and rwal

[bd]

Thought the dracs box sends the signal for the cruise ? The dracs box get the vss sensor signal and then breaks that down into other signals abs, speedo, ecm and rwal

In general, the DRAC (Dynamic Ratio Adapter Controller) is post-1988 truck production.  the DRAC receives its input signal from a permanent magnet pulse generator (VSS) mounted on the transmission (2WD) or transfer case (4WD) to register output shaft rotation in pulses per mile.  DRAC output is used by the engine/transmission PCM, air core speedometer, Custom Cruise III and later iterations of cruise control, and the rear wheel anti-lock brakes (RWAL) ECU for vehicle speed reference.  The DRAC approach is virtually all electronic, relying on a stationary pulse generator.

Optical VSS was used on 1988 TBI and prior truck applications to as early as 1982, in conjunction with a vehicle speed buffer module that provided output to the engine ECM and Custom Cruise III module.  Optical VSS is electro-mechanical, relying on a rotating split-window optical reflector in the back of the speedo head that is driven by the speedometer cable.  It was an interim design between full mechanical and full electronic systems.

[Irish_Alley]

Thanks bd. Didn't know the dracs started in 88