Missing a part on my Oldsmobile's engine

TheBrisbyMouse

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May 1, 2021
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I went to a junkyard a few months ago for a speedometer cable when I noticed something, the car I was getting parts from(Olds 98) had a part that my engine didn't. It's some electrical doodad mounted in front of and off to the driver's side of the carb, more than halfway to the front of the engine. When I got home, I found a pair of electrical connectors tucked away that I hadn't noticed before, as well as a u-shaped mount for whatever that thing is. I also assume that a vacuum line goes to it, because when I redid them, there was a dead end approximately where this thing would be. I went back to the junkyard a couple weeks ago to get the part in question, but the car had been scrapped.

Could anyone tell me what it is and how to get my hands one one of them? My car is a 1984 Oldsmobile Delta 88 Royale with the 307/2004r. It runs fine without it, but I'd prefer to have it, since the random electrical connectors bug me.

 
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GoodOldsGuy

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Oct 20, 2020
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the picture's a little hard to make out, but my first guess is its for the cruise control diaphragm, that's about where it lives on the Olds engines. I could be wrong tho, I can't recall (or find a decent pic) of what the connectors look like.
I’m siding with GP403 on this. Every Olds I’ve had has the cruise servo in that spot however, mine have all been (and are) older than 84 and utilized the plain servo (non computer controlled) with only a vacuum line to the transducer on the drivers side fender well. Incidentally, the transducer on the fender is exactly where you should have had to connect the speedometer cable from the transmission, and then another cable to the meter itself in the dash.
 

GoodOldsGuy

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Oct 20, 2020
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Texas
That connector and the bracket are certainly parts of the cruise control module system. You'll need other parts such as the linkage and a vacuum tank to make it work.
Since the car uses a speedometer cable, it certainly does not have an electric speedometer, so there definitely should be a cruise transducer between the cable coming from the transmission and the meter itself. That’s how the cruise control “knows” what speed to maintain via applied vacuum to the servo (the rubber diaphragm thingy that pulls the throttle open). So I agree with MarkClark that you probably need the linkage from the servo to the throttle control as well. The speedometer probably wouldn’t work at all if you didn’t have a transducer in-line with the speedo cable. (Unless your Speedo cable goes from the transmission tail shaft directly to the meter-then I don’t know what you have). My experience with Olds cruise is they all worked directly off of manifold vacuum directed by the transducer to the servo. My guess is someone replaced the carb on that car with a non Olds application without the cruise connections or they couldn’t figure out how to connect the servo linkage to the carb, but I’m further guessing that you have everything you need except the servo and carb linkage. Those systems used a vacuum dump switch and an electrical disconnect switch on the brake pedal, make sure you have those as well. Again, my experience is with older cars, but cable driven mechanical speedometers don’t normally produce an electrical signal to indicate vehicle speed to the servo (unless the transducer is generating that signal for the servo). I don’t remember the TH200-4R ever having an electric speed signal. So the transducer should be at the end of the Speedo cable coming from the transmission, from there, it should have vacuum lines and wiring to the servo. I’m going on memory here, and those are old memories. Lol
 
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GoodOldsGuy

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Oct 20, 2020
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Since the car uses a speedometer cable, it certainly does not have an electric speedometer, so there definitely should be a cruise transducer between the cable coming from the transmission and the meter itself. That’s how the cruise control “knows” what speed to maintain via applied vacuum to the servo (the rubber diaphragm thingy that pulls the throttle open). So I agree with MarkClark that you probably need the linkage from the servo to the throttle control as well. The speedometer probably wouldn’t work at all if you didn’t have a transducer in-line with the speedo cable. (Unless your Speedo cable goes from the transmission tail shaft directly to the meter-then I don’t know what you have). My experience with Olds cruise is they all worked directly off of manifold vacuum directed by the transducer to the servo. My guess is someone replaced the carb on that car with a non Olds application without the cruise connections or they couldn’t figure out how to connect the servo linkage to the carb, but I’m further guessing that you have everything you need except the servo and carb linkage. Those systems used a vacuum dump switch and an electrical disconnect switch on the brake pedal, make sure you have those as well. Again, my experience is with older cars, but cable driven mechanical speedometers don’t normally produce an electrical signal to indicate vehicle speed to the servo (unless the transducer is generating that signal for the servo). I don’t remember the TH200-4R ever having an electric speed signal. So the transducer should be at the end of the Speedo cable coming from the transmission, from there, it should have vacuum lines and wiring to the servo. I’m going on memory here, and those are old memories. Lol
One further note, if you’re looking for those parts at junkyards, remember a lot of RWD GM’s (82-90) used the 307/200-4R combo and would have similar systems if not the exact same system. So don’t limit your search to Olds only. Many Buick, Olds, Pontiac wagons used that system as well as RWD Cadillacs. My dads 1988 Fleetwood Brougham had that exact same setup. Also, just about any RWD GM car with an Olds Diesel would likely have the same 200-4R and cruise control setup that you have. The diesels had a vacuum pump supplying vacuum instead on using manifold vacuum but the rest would be nearly the same, if not identical.
 
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markclark

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May 2, 2021
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Also, get a complete copy of the GM factory service manual with the Electrical service manual. Don't use Chilton's or those other junk manuals. Aftermarket manuals are woefully inadequate for these cars. These cars are very technical and you need the diagnostic charts and repair information only found in the factory manual.

If your going to keep the car then buy the GM parts manual off e-bay. Many parts sellers improperly describe or misstate correct parts fitment, and though two parts appear to be identical, they in fact have different specifications.

Good luck.
 

TheBrisbyMouse

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May 1, 2021
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Thank you all for the replies. I finally got a chance to work on the car today, and you guys seem exactly right on it being the cruise control servo. I already had a suspicion that my car had some sort of cruise control because there's a third wiring connector heading down near the brake switch. But then it gets weird. There's a second hole in the brake switch bracket for what I know is part of the cruise control due to a diagram I got from the local GM dealership, but nothing is there. In addition, the turn signal stalk, which is used to activate and modulate the cruise control, is non-cruise control.

It appears that a previous owner deleted the cruise control for whatever reason. This doesn't make much sense, because they left the smog stuff intact. So at the very least I know that I need the servo, servo bracket, servo linkage, brake pedal cruise control thingy, turn signal stalk, and potentially a few other parts.

Regarding the speedometer cable, it goes straight from the transmission to the gauge.

I know about the GM badge engineering stuff and parts commonality, but I'm relatively new to car stuff and don't know which exact ones will have it. Does anyone know where to find this information?

I need to finish putting in the new transmission(and financially recovering from said transmission -.-) and verifying that it works before getting involved with anything else, so it'll be quite some time before I can get to installing the deleted cruise control components, I'm pretty stoked about getting it put back together, because I've never had a car with working cruise control before.
 
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GoodOldsGuy

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Oct 20, 2020
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Thank you all for the replies. I finally got a chance to work on the car today, and you guys seem exactly right on it being the cruise control servo. I already had a suspicion that my car had some sort of cruise control because there's a third wiring connector heading down near the brake switch. But then it gets weird. There's a second hole in the brake switch bracket for what I know is part of the cruise control due to a diagram I got from the local GM dealership, but nothing is there. In addition, the turn signal stalk, which is used to activate and modulate the cruise control, is non-cruise control.

It appears that a previous owner deleted the cruise control for whatever reason. This doesn't make much sense, because they left the smog stuff intact. So at the very least I know that I need the servo, servo bracket, servo linkage, brake pedal cruise control thingy, turn signal stalk, and potentially a few other parts.

Regarding the speedometer cable, it goes straight from the transmission to the gauge.

I know about the GM badge engineering stuff and parts commonality, but I'm relatively new to car stuff and don't know which exact ones will have it. Does anyone know where to find this information?

I need to finish putting in the new transmission(and financially recovering from said transmission -.-) and verifying that it works before getting involved with anything else, so it'll be quite some time before I can get to installing the deleted cruise control components, I'm pretty stoked about getting it put back together, because I've never had a car with working cruise control before.
Hey, I did just a little bit of digging around and I’m coming to the conclusion that the last year the fender well mounted cruise transducer system (for Oldsmobile) was 1983. My old time GM friends that had access to every bit of GM production parts info have all retired, so instead of just being told by someone I’ve known for 30 years, I’m struggling to find out what they went to in 84. Since the one piece Speedo cable off the 98 worked and connected the same way on your car, I’m assuming it was a 1984 as well. There simply has to be a speed signal generator of some sort (somewhere) so the cruise control will ‘know’ what speed to maintain. I’ve never seen or heard of a 200-4R with an electric Speedo drive, and as far as I know they all had mechanically driven meters so I have no guess where the speed info comes from for the cruise, but I’m quite certain that it didn’t work on magic. Lol I will say that the older non resume/accel systems are very straight forward, are extremely common across a very wide range of GM cars, and would be fairly easy to add to your car. Just make sure that you have an Olds application carburetor (with the right linkage to connect to the throttle butterfly link). If you tell me the carb numbers I can look it up for you. Non Olds carb applications had somewhat different cruise linkage connections, and I can’t think of a better reason to delete cruise control than it couldn’t be hooked up to a replacement carb. Also, the fella in North Carolina that said he might have what you need would be a good place to start looking for stuff too. Good luck! I can’t believe that I got so old that all the guys I worked with retired, but I’ll keep snooping around for answers.
 

markclark

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May 2, 2021
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The car has a VSS - Vehicle Speed Sensor system that calculates the vehicle speed. The control module is mounted behind the dash on the driver's side. You don't need to bother with it, just know that's how the ECC - computer - knows the vehicle speed which is used for many functions including the cruise control. It sounds like the vacuum break switch for the cruise control has been removed from the brake pedal assembly. You'll need a new switch and hopefully the vacuum lines are still present and in good shape. I'm going to post some images from the factory service manual.
 
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markclark

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May 2, 2021
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Here's copies from the Factory Service Manual . You'll need to print the pdf because some copies are upside down. Make sure the diagram applies to your car as several models are covered by the manual. Your Car should be a B body with a 5.0 liter "Y" type VIN.

I believe the VSS gets it input from the transmission sensor.
 

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