Rostra Cruise Control

[jaustinmd]

I initially tried to revive the OEM cruise control on my '82 911SC and never was successful - I've been told they don't work very well anyway with the vacuum servo! After finding some successful reports of installing a Rostra "Globalcruise" universal cruise control (#250-1233), I decided to install one. I'm told Rostra has made these for a long time and is an OEM supplier to many of the automakers and it is a quality unit. It works great and holds the cruise speed about +/- 1 mph and automatically disengages with clutch or brake application. It also has the typical "tap up" and "tap down" feature to increase the set cruise speed about 1 mph with each tap of the buttons. You have to buy the control switch stalk separately and they have a right-hand switch (#250-3743) that can be mounted in the original cruise control switch location on the steering column.
To mount the switch, I removed the OEM switch and made an aluminum plate with a 3/8" hole to bolt to the bracket that held the original switch:


Here's a pic of the mounted switch:


The cruise module/servo mounts in the engine compartment. A mounting bracket is included that can be used to attach the module/servo to the OEM vacuum servo mounting bracket. The throttle cable can be attached in a number of ways but included a black square plastic snap-in cable anchor that fit the original throttle bracket perfectly! The throttle arm moves 55mm and by coincidence, the Rostra servo has exactly 55 mm of travel, so it fit perfectly and didn't require a bead chain extension, etc.

The harness will have to be extended from the engine compartment to the frunk to access the remainder of the wiring. There is a 2-pin and a 4-pin connector that attaches to the cruise switch stalk on the steering column. I was able to pull the original cruise switch harness and route the new harness through the same grommeted hole under the dash to run the wiring into the frunk.

I have LED brake lights and had to add a brake light relay so the cruise could "see" a reliable ground until the brake lights activate. I was able to use the OEM clutch switch by accessing some of the clutch switch relay wiring and by shunting the vacuum servos connector terminals in the engine compartment to make a ground and relay to put in series with the brake light relay. I used a number of the OEM pins in the original cruise module socket to access some of the circuits and get +12V power, etc. I found some 2.5 mm pins that I could solder to my wiring and plug into the original pin sockets so as to not have to cut them off for some other connector - I removed the sockets from the large connector, plugged my wiring in, and covered with heat shrink so ensure they stay connected and could not short against another connector. Here's a diagram of the wiring:


I'm very pleased with the results! As stated earlier, the set cruise speed is tightly maintained, plus there is no surge or lag when the cruise is engaged. One person told me they installed one in their 911 in 2004 and it still works perfectly, so I feel the components must be of high quality and the total cost was approximately $215 plus some 18 AWG wire to extend the harness.

There are a number of dip switches that have to be set to configure the cruise module. Here's the settings for my 82 911SC:
#1 OFF
#2 ON
#3 ON
#4 OFF
#5 OFF
#6 ON
#7 OFF
#8 ON
#9 OFF
#10 ON
#11 OFF
#12 OFF
You can look these settings up in the installation manual, but this configures for mid-range gain, 6400 PPM (pulses per mile VSS), 6 cylinder/low set-up timer, square wave VSS input, manual transmission, and an open circuit control switch.

I had to do a lot of research and got a lot of help from other Pelicans - I hope by putting all this information in one thread it might help someone else down the road ... pun intended!

[dicklague]

I have installed this unit in one of my vehicles and it is a really good unit.

Very well built and very reliable. I like it a lot.

[Tippy]

Very nice install

[Brorag]

I've got the same analog system (and the same problems) on my '87--are you still satisfied with the unit? Would you do anything different?

[jaustinmd]

Originally Posted by Brorag

I've got the same analog system (and the same problems) on my '87--are you still satisfied with the unit? Would you do anything different?

Wouldn't change a thing! The stalk's position tends to hide the green power LED behind a spoke of my steering wheel, but that's OK since that is one less light to have distract me at night! However, since I used the original cruise stalk's location and did not have to add any more holes in the shroud, that's a plus, too!

I'm amazed at how well it works - engagement is very smooth and speed control is very tight - about what you would expect from a modern-day "factory" cruise control. I'm told the original vacuum servo's never worked that well, anyway!

All in all, a very satisfying upgrade for a fairly modest cost!

[Brorag]

well, here goes......................

[mysocal911]

An overly time consuming mod with little benefit in the end compared to a properly rebuilt Porsche CC. Just do a search on Pelican Parts of those who have had their Porsche CCs rebuilt.

[Brorag]

I respectfully disagree. I've been down that road and the expense of restoring the original unit to it's original spec, and enjoyed it while it lasted. The down-side is that it's still an old analog unit and stopped working after a period of time, as designed.
I'm getting too old to crawl around this thing any more--maybe if I was still a young pup I'd fix it again. I'll keep the original stuff in-place for the next person.

[jaustinmd]

It's all a matter of perspective and practicality.

I, too, had my cc computer professionally rebuilt and still never got the system working correctly - not surprising, it's a fairly complex system and the car is 34 years old - and the fact the servo is vacuum powered doesn't help!

I come from a background in experimental aircraft and actually enjoy "consuming" some time developing new and different approaches to problems. Further, my car is sort of a "restomod" with mods done where appropriate for definite improvements in function - for instance, I installed a Griffith's A/C system that is far better in performance vs the obsolete R-12 system that, even when new, never worked that great anyway.

The 911SC's are pretty common, so I'm not concerned about keeping it original for investment purposes (it wasn't in original condition when I bought it, anyway) - I bought it to drive, and if I can make it a bit more comfortable and functional, that's a plus for me!

[mysocal911]

Originally Posted by Brorag

The down-side is that it's still an old analog unit and stopped working after a period of time, as designed.

1. It was not designed to fail. Its mounting bracket contributed to its unreliability.
2. Obviously, your unit, "restored to its original spec" had not been properly rebuilt.
3. The effort to remove and replace (have rebuilt) the original CC takes about 5 minutes.

Bottom line: The time, effort and cost to install another complete CC system hardly justifies not having
the original CC properly rebuilt.

[Brorag]

same here--redid A/C also--car had factory installed spoiler kit, so I uppped the cooling capacity a good bit by installing snowmobile engine fans in the real spoiler to force air over the main condenser coils.--made a significant difference.

[mysocal911]

Originally Posted by jaustinmd

I, too, had my cc computer professionally rebuilt and still never got the system working correctly - not surprising, it's a fairly complex system and the car is 34 years old - and the fact the servo is vacuum powered doesn't help!

Actually, the Porsche CC system is fairly simple!

[Brorag]

Dave, went back and reviewed many of your 647 posts since 2014--I'm totally unworthy...I'll try to do better

[dicklague]

I installed a Rostra in my pickup truck and really like it. I can imagine that it is more modern than an Bosch unit.

I can't comment on 911 install but I feel is is good tech and very reliable.

Some people will always argue that the stock 45 year old CDI is just fine and the same for the 40 year old CC.

My 1973 911 runs much much better with Pertronix points and good [Dsytona-Sensors CD1] aftermarket CDI.

[Uwon]

Nice write up, John. Thanks. Tempting to instal one in my build as my OEM one is caput. Have you got any pics of your setup at the throttle body?
Cheers,
Johan

[Brorag]

John, how did you get the vehicle speed for the Rostra unit off of speedo--did you need an adapter from Rostra?

[larrym]

excellent tips - notwithstanding the "keep it oem" alt-perspective

- also great encouragement for adding a CC to older car that never had one - like my 914-6/3.2

only downside i see to adding one to old car is no VSS - so ya have to attach a magnetic sender to an axle shaft

anybody done that, and care to share?

[Brorag]

I installed one on an early Audi--worked fine.

[Uwon]

Originally Posted by larrym

excellent tips - notwithstanding the "keep it oem" alt-perspective

- also great encouragement for adding a CC to older car that never had one - like my 914-6/3.2

only downside i see to adding one to old car is no VSS - so ya have to attach a magnetic sender to an axle shaft

anybody done that, and care to share?

Years ago when I went rallying, we put magnets on the half shaft and and pickup L-braket attached to the trans. Maybe try a rally forum/web site.
Johan

[Brorag]

Rostra Universal kit (250-1223) and Wireless RF (Radio Frequency) Cruise Control Switch (250-1483)
rcv'd.



I just had engine rebuilt and need to put 1K mi so mechanic can check for smooth running and leaks. Odometer not working, so it's out and off to odometer dr--tried to get into speedo myself to change gears, but chickened out at bending flange phase. It's due back in abt 1 week--good to know one's limits.

The wipers chose to quit now also--paid $108 dumb tax for mechanic to confirm switch bad and motor good--switch ordered and I'll do the grunt work.

BTW, so far, this guy is good, albeit a little slow:maybe because he chose to do the work on my 911 himself--trained in Germany on 911's, honest, with a photographic memory--If you are looking for a mechanic in the western Carolinas, I would recommend him (Home).

Replaced all gauge lights with LEDs while R&R of speedo--helps to have access thru gauge holes for install of cruise and wiper switch.

The Rostra instructions do not address installation in a 911, so one has to be a little knowledgeable and intuitive--will let you know how it goes...this page by jaustinmd is the best guide I've found so far.

One thing I've noticed between jaustinmd's install and this one is the difference in location of the original cruise control module--his ('82) was located in the frunk, mine ('87) is located under the dash. My original unit is the old analog type also. On to plan B.