I don't know how many GMC owners are using the Rostra cruise control instead of the factory one.
On our recent trip 'out west' I melted the short extension on my Rostra speedometer speed sensor. It goes inline with the speedometer cable (adding resistance to the governor gear) and luckily the cable broke instead of the governor gear.
We pulled out of the campground at Grand Tetons and I see the speedometer is not working. Hmm. Get up to 45 or so and try the cruise control, nope, no cruise. I stopped to investigate and the speed sensor speedometer cable extension was melted and broken. I deleted it and attached the speedometer cable directly to the transmission (actually to my speedometer calibration gearbox)
Having 2000 miles to drive home, with no cruise control, was not something I looked forward to and I wondered if the Rostra would accept the Tach signal from the HEI distributor as a VSS signal. There was some time to think about it, sitting there driving home with my right foot planted in one spot and my knee aching. Anyone else suffer from 'gas pedal knee' ? It's actually a thing.
About 3/4 of the way home, I had convinced myself that worst case scenario, it's not going to fry anything and leave me stranded. The tach signal harkens back to points and condensor distributor days, it's a 12v signal pulled to ground as the points close. I probed the connection to the Rostra and found one leg was Ground. And the other leg was not ground, must be the signal input. I crudely wired it to the Tach output on the HEI and DRUMROLL ...... it didn't work. Still no cruise control. But the Tach still worked so at least I didn't fry anything.
Drove the rest of the way home with it still connected that way and no cruise.
At home I read the Rostra universal cruise control manual and noted that as designed, it will accept a VSS signal from the vehicle ECU. Googling it, it seems like the VSS signal standard is 12v square wave.
Using the dipswitches on the Rostra, I changed the settings to 10,000 pulses per mile (2500rpm x 4 pulses per rev) , and the signal to Square wave. Took it for a test spin and BINGO! Cruise control worked!
So now I had temporary way to at least have engine speed cruise control, just until I can get a replacement cable right?
Some background on my experience with the Rostra.
I had worked with the Rostra settings but was never able to get the cruise to work the way I wanted. Best I could do was on its lowest 'sensitivity' On a drive it would typically start out below the set point at the bottom of a hill, then accelerate up the hill only to crest it at basically WOT and a speed higher than the setpoint. On the way down it would do the opposite, go slower and slower down the hill and end up actually under the setpoint just in time to accelerate up the next hill. It was doing exactly the opposite as I would if driving with my foot.
If I were driving without the cruise control, I would hit the bottom of the hill at a speed over the setpoint, then let the speed bleed off on the way up the hill, crest the hill under the setpoint, then roll down the hill at slightly over the setpoint. To achieve this using the cruise control I was having to fiddle with the 'coast' 'accel' buttons on the rostra while going up and down hills. That much attention sort of defeats the purpose of the cruise control but at least my leg wasn't required to be in one spot.
Well, last week I took it ~600 miles on a camping trip to a bluegrass festival, using the engine speed control. and I have to tell you, I like the way it controls the speed WAY better than vehicle speed control. It's maintaining the engine speed, not the vehicle speed. It drives the coach almost exactly as I would drive it with my foot. Going up hills the speed bleeds off, the throttle opens up a bit, the engine rpm stays put and we go up the hill gently. No more accelerating up the hill at WOT. On the way down, it rolls a little over my set speed but only ~2 mph. This is Western and Upstate NY btw, by hills I mean rolling swales compared to out west, holy cow you guys have some hills!
Aside from it behaving more like it should imo, there are two added bonuses to this idea.
1. No added load on the transmission governor gear.
2. No need to spend ~$100 on the VSS
This might be something to consider if someone's OEM cruise control dies and you're thinking about the Rostra.
On our recent trip 'out west' I melted the short extension on my Rostra speedometer speed sensor. It goes inline with the speedometer cable (adding resistance to the governor gear) and luckily the cable broke instead of the governor gear.
We pulled out of the campground at Grand Tetons and I see the speedometer is not working. Hmm. Get up to 45 or so and try the cruise control, nope, no cruise. I stopped to investigate and the speed sensor speedometer cable extension was melted and broken. I deleted it and attached the speedometer cable directly to the transmission (actually to my speedometer calibration gearbox)
Having 2000 miles to drive home, with no cruise control, was not something I looked forward to and I wondered if the Rostra would accept the Tach signal from the HEI distributor as a VSS signal. There was some time to think about it, sitting there driving home with my right foot planted in one spot and my knee aching. Anyone else suffer from 'gas pedal knee' ? It's actually a thing.
About 3/4 of the way home, I had convinced myself that worst case scenario, it's not going to fry anything and leave me stranded. The tach signal harkens back to points and condensor distributor days, it's a 12v signal pulled to ground as the points close. I probed the connection to the Rostra and found one leg was Ground. And the other leg was not ground, must be the signal input. I crudely wired it to the Tach output on the HEI and DRUMROLL ...... it didn't work. Still no cruise control. But the Tach still worked so at least I didn't fry anything.
Drove the rest of the way home with it still connected that way and no cruise.
At home I read the Rostra universal cruise control manual and noted that as designed, it will accept a VSS signal from the vehicle ECU. Googling it, it seems like the VSS signal standard is 12v square wave.
Using the dipswitches on the Rostra, I changed the settings to 10,000 pulses per mile (2500rpm x 4 pulses per rev) , and the signal to Square wave. Took it for a test spin and BINGO! Cruise control worked!
So now I had temporary way to at least have engine speed cruise control, just until I can get a replacement cable right?
Some background on my experience with the Rostra.
I had worked with the Rostra settings but was never able to get the cruise to work the way I wanted. Best I could do was on its lowest 'sensitivity' On a drive it would typically start out below the set point at the bottom of a hill, then accelerate up the hill only to crest it at basically WOT and a speed higher than the setpoint. On the way down it would do the opposite, go slower and slower down the hill and end up actually under the setpoint just in time to accelerate up the next hill. It was doing exactly the opposite as I would if driving with my foot.
If I were driving without the cruise control, I would hit the bottom of the hill at a speed over the setpoint, then let the speed bleed off on the way up the hill, crest the hill under the setpoint, then roll down the hill at slightly over the setpoint. To achieve this using the cruise control I was having to fiddle with the 'coast' 'accel' buttons on the rostra while going up and down hills. That much attention sort of defeats the purpose of the cruise control but at least my leg wasn't required to be in one spot.
Well, last week I took it ~600 miles on a camping trip to a bluegrass festival, using the engine speed control. and I have to tell you, I like the way it controls the speed WAY better than vehicle speed control. It's maintaining the engine speed, not the vehicle speed. It drives the coach almost exactly as I would drive it with my foot. Going up hills the speed bleeds off, the throttle opens up a bit, the engine rpm stays put and we go up the hill gently. No more accelerating up the hill at WOT. On the way down, it rolls a little over my set speed but only ~2 mph. This is Western and Upstate NY btw, by hills I mean rolling swales compared to out west, holy cow you guys have some hills!
Aside from it behaving more like it should imo, there are two added bonuses to this idea.
1. No added load on the transmission governor gear.
2. No need to spend ~$100 on the VSS
This might be something to consider if someone's OEM cruise control dies and you're thinking about the Rostra.
