2kturkey

Col, I have an old Rostra vacuum unit which I bought back in Canada in '94 and recently installed on my wife's Commodore - it performs very poorly, cuts in sharp and keeps cycling on and off (I suspect due to lack of sufficient vacuum pressure to hold a speed). I am ditching this as it is just useless - the only saving grace is that it only cost me $AUD99 back then (prices are much cheaper in North America).

Can you tell me how much you paid for your unit, what is an RF switch (radio frequency?) and what switches do you have inside the car to operate the unit.

Thanks,

AusS2000

Hi Col.

I realised we've discussed this before but A) I forgot the conclusion B) others may want to know. What is the difference between the Electronic and Vacuum versions and what are the PRO's and CON's.

kupe

Can someone tell me where the pickup for the VSS
is located ? I presume it's straight from a small
black piece of plastic hanging out of the gearbox ?

-CK.

Col

2kTurkey,

I also have an old Rosta vacuum unit (1991) on my wife's Turbo Laser and it works fine but it was a slow process to set the sensitivity to remove the all on / all off syndrome. Now it works perfectly with the only complaint that it does take a second or two to get the throttle open to hold the speed. The trick is not to hit "Set" then hold the throttle as it thinks it does not have to pull the cable. Instead if you hit "set" then lift off the throttle it pulls in quickly and then holds it nicely.

The electronic (stepper motor) version on the S2K cost about $550 from memory including the RF switch which has a switch unit that mounts on the steering wheel and looks for all the world like the OEM cruise plus the receiver unit under the dash. It has the standard two button but no on / off. The switches are "Set / Decelerate", "Reset / Accelerate", note the accelerate / deceleate are on the opposite switches to my old vacuum unit. I believe this RF type control unit can be used on both vacuum and electronic although they are different part numbers to account for the different wiring.

The switches come in a couple of versions to mount vertically, on top or on the bottom, (only the screen printing on the switches is different). I chose the vertical and mounted in exactly the same place as the OEM, in hindsight I think mounted on the top of the centre of the wheel would have been better and easier to see and use with either hand, but each to their own.

Kupe,

You are correct the VSS is mounted on the gearbox and the VSS feed is Blu/Wht. During the install I did investigation on the VSS and the results are not straightforward. If you use the straight VSS output on the Rosta you get a pulse rate of close to 90,000 / Km (50 pulses / 0.55m) or 145,000 / Mile (Note this is different to nearly 100% of all other cars, even all other Hondas...)and this is not within the Rosta input range. This then goes directly to the ECM and the instrument panel. From the instruments there is a divided feed (White/black) to the roof control, EPS (Electrical power Steering), plus some other items - the pulse rate on this is very close to 2,560 / Km (5 pulses / 1.95m) or 4,000 / Mile. Therefore you cannot use the direct VSS output into the Rosta only the divided output for the cruise control.

I eventually used the input to the roof control and this works well. Initially it was very severe in operation. I have the cable attached on the same cable pully as the pedal cable and Rosta said I had to use a bigger diameter pulley to effectively cut back the throttle application of the control unit. I didn't want to do this for two reasons, firsly to add an extra pulley was not straight forward and secondly it wouldn't have looked as neat. I then experimented with the settings for the pulses / Km on the Rosta control unit and fooled it into thinking the car is going faster then it really is and therefore it applies less throttle - exactly the effect I wanted..

Ideally it would be better to have a higher pulses / Km for fine accuracy but I was too lazy to build a divider circuit to cut down the initial VSS 90K / Km, and experimentation has the unit working nicely.

As to AusS2000's questions. The key differences between the two are price, the electronic version is much more costly and harder to find, secondly the vacuum version uses manifold vacuum to operate the cable pull for the throttle. All OEM units are electronic as they are more accurate and theoretically should be able to be easily "programmed" for and car. I haven't had a good look at the vacuum version but assume it would have the same settings as the electronic version. All the fitters I spoke to recommended the electronic version if cost was not a big factor.

If I get a chance I will post some photos over the next few days but unfortunately I will be away from tomorrow thru to Tuesday and not near the car.

Col.

2kturkey

Col, are you sure you've never been an auto electrician? You have fantastic knowledge here.

I'm interested in your comments re VSS takeoffs - not for the S2000 but for my bloody Commodore.

I cannot yet get my Rostra cruise control working with VSS input. I am using it in straight throttle position sensing mode. It states in the manual that it will accept only 2000, 4000 or 6000 pulse signal inputs whereas the VTII Commodore apparently outputs 10,000 pulses. Based on your comments how would I step this down - and how would I measure the # of pulses - is this something I can do with a multimeter or do I need special measuring instruments.

In addition, what is the impact of receiving 10,000 pulses instead of 6000 - does this mean the cruise control thinks the car is going twice (or half) as fast as it really is and therefore won't cut in?

You also talk about sensitivity settings - I know the newer Rostra units have a means of setting sensitivity but my old unit doesn't seem to have such a setting. I am assuming that as my unit is the same vintage as the one in your wife's Laser that there is a means of seeting sensitivity. Is there a hidden trim pot or similar I can use to achieve this?

Sorry for all the questions - you can PM me if you want to answer this offline.

Col

2kTurkey,
To measure the pulses per mile. Connect a voltmeter to the VSS output then turn on the ignition and slowly roll the car and the VSS output should go between earth and +5V, then after moving the car a few metres do an accurate count Vs distrance travelled and convert to pulses per mile (Km).

If the commodore is putting out 10K and you set the Rosta to 6000 it will just think you are going faster then actual, also because it will think the speed is changing quickly it may apply more throttle and be a bit on/off rather then smooth.

My old unit has a circular control portion that could be screwed onto the actuator or mounted remotely and it had a pot adjustment for sensitivity which I adjusted. It was beside the other DIP switch settings.