Are speedometers different between models and years?

[DrJekl]

First my question, then some back ground:

Are speedometers different (function and calibration wise) between models of square body trucks? I know the old style 70s versus 80s is different so let's focus on speedometers that are the same 80s syle used in CUCV, C and K series trucks, blazers, and Subs.

Yes, I know that you must be running the right sleeve/gear combo for your application.

Yes, I know that tire size plays a role. Tires are rock stock so I should be close on the needle if everything else is right.

I installed a Gear Vendor OD unit in my M1031 truck. The speedo was bouncy before the install so I swapped the speedo for a similar mile unit from an 87 K5 Blazer that ran smooth. The GV has the right gear and sleeve in it for the 4.56 gears so I should be in the ball park on posted speed. My GPS has me about 2-3 MPH off before the install and before the needle would go crazy after 35MPH. Now, I am 10 MPH fast but the needle is steady (maybe I should ignore the speed and be happy the needle is steady?).

The GV unit should not be a consideration as the sleeve and gear is on the output just as with your trans or t-case would. The input to the cable is off the tail end of the drive live.

All that said, are all the speedos calibrated the same and in theory this should have been plug and play or is there a calibration difference between models other than your gear and sleeve in the trans/t-case/gear vendor overdrive unit?

Thanks!

 

[transman]

The Hollander interchange lists both speedos as beeing the same #3331f. You must be the victim of 80s manufacturing tolerance allowances.

 

[Wolf.Dose]

For the CUCV Series trucks the speedos are all the same, as said above. However, the acuracy of these mechanical devices is relatively poor, which is depending on the simple designe. and the big allowed toenance of the parts. If you have enough parts on hand, you can go for the best. If not, use what you get. And if you calibrate that with your GPS, you know where you are.
As long as the speedo reads more than your actual speed, you are on the legal side.
Wolf

 

[Bob H]

a bouncing needle is rarely due to the speedo itself. but the drive cable or a loose drive gear at the trans.
I'd suspect the the Gear vendors unit has the wrong # of teeth on the speedo drive gear.
also the speedo will be off by a percentage not a specific mph. i.e 2.5 off at 25mph would be 5 off at 50mph and 7.5 off at 75mph
There are sites that cover this, google it, but IIRC basically if your speedo is off 10% you need a gear with 10% less teeth on it.

 

[Jersey4x4]

Is there a gear change drive unit mounted on the output of the t-case just before the speedo cable? My M1008 has this and so did my 87 K5 civilian blazer and they are both listed in the parts book as optional(what ever that means) I think it is a reduction drive for transfercase ratio compared to dired drum ratio as in a 2wd vehicle and this could be the tollerence differential. 10mph sounds almost the exact difference I had when I ran my K5 without the gear box before the speedo cable. As far as I can see in the books the speedo is the same for all C/K trucks function wise but the font in the numbering and picture design is different for the 70s but they still fit and function all the way up to 1991 when the C/K series died

 

[ODdave]

C/K series didnt die till 2000. Sorry, that was just bothering me.

 

[Jersey4x4]

Wrong! The last C/K pickup was 1987 except for the club cabs up to 1991 and the suburban and blazers were built up to 1991 also. Just because they use a c or k in the vin does not make it a C/K series truck. The C/K series trucks were the same design as the CUCV and they sure did not make any trucks like that n 2000. The later trucks were all aerodynamic looking, had tortion bar front suspension and it was the end of GM Making a good heavy duty work truck. They were trying to compete with the socer mom trucks and make the ride better but the rough and tough truck Died in 1991. Maybe you can check google. History

C/K series didnt die till 2000. Sorry, that was just bothering me.

 

[Recovry4x4]

In 1988 the square body GM trucks were changed to R/V. The new body styles got the long running C/K clasifications. I have a 1991 V2500 Suburban. Before this I have a 94 K3500.

 

[ODdave]

Wrong! The last C/K pickup was 1987 except for the club cabs up to 1991 and the suburban and blazers were built up to 1991 also. Just because they use a c or k in the vin does not make it a C/K series truck. The C/K series trucks were the same design as the CUCV and they sure did not make any trucks like that n 2000. The later trucks were all aerodynamic looking, had tortion bar front suspension and it was the end of GM Making a good heavy duty work truck. They were trying to compete with the socer mom trucks and make the ride better but the rough and tough truck Died in 1991. Maybe you can check google. History

Sorry but C/K still means 2 or 4 wheel drive up till 2000. But thats not what this thread is about so belive what you want.

 

[Bob H]

Not that it matters for the speedo discussion

my 87 GMC is a V model & my 87 Chevy was a K model

 

[DrJekl]

As stated, the GV has the correct sleeve and the correct gear. Nothing was changed other than the speedo. The bounce is gone but is off my 10MPH, not 10%.

I have a speedo from an 88 with a trip meter in it and similar miles on the odometer. I'll give it a shot since the speedo is the same. My concern was that the CUCV may have had a different calibration in the speedo itself.

Thanks! Have fun with your C/K argument.

 

[Bob H]

all speedo heads are the same, function wise at 1000 revolutions per mile. which is why there are gears to calibrate the readings.
You can verify if the head is screwing up as well as the drive gear ratios by using the highway milemarkers
drive at least 10 mile markers and check the odometer, if it's exact the head is bad. If it is off it has the wrong drive gear.

 

[ODdave]

IIRC that spedo from the 88' is electronic. fwiw

 

[DrJekl]

They have an electronic sending unit on it for the computer. They are still manual units. The 87 is the same way.

 

[Jersey4x4]

Actually the 88 1500 and 2500 had a electronic dash that was totaly different the the 87 and did not use a cable because it is not a C/k Series truck. Yes they still use C & K to designate 2wd or 4wd but it is NOT A Square bodied C/K series and yes in the last few years of the C/K series truck they used R & V to designate 2wd and 4wd but it was still a C/K series truck. but what do I know, I have just had every C/K truck style through my shop and have every GM Factory book available for them, military and civilian. But I am sure someone will still argue semantics of a letter placed on a VIN tag equaling the type series of vehicle. Best info online for the C/K series CHUCK'S CHEVY TRUCK PAGES.COM - HOME PAGE - 1973 - 1987 Chevy Silverado, Chevy Blazer, Chevy Scottsdale, Chevy Cheyenne, Chevy Custom Deluxe, 73 - 87 Chevy Trucks. The BEST source for info on the web!

They have an electronic sending unit on it for the computer. They are still manual units. The 87 is the same way.

 

[Recovry4x4]

Actually the 88 1500 and 2500 had a electronic dash that was totaly different the the 87 and did not use a cable because it is not a C/k Series truck. Yes they still use C & K to designate 2wd or 4wd but it is NOT A Square bodied C/K series and yes in the last few years of the C/K series truck they used R & V to designate 2wd and 4wd but it was still a C/K series truck. but what do I know, I have just had every C/K truck style through my shop and have every GM Factory book available for them, military and civilian. But I am sure someone will still argue semantics of a letter placed on a VIN tag equaling the type series of vehicle. Best info online for the C/K series CHUCK'S CHEVY TRUCK PAGES.COM - HOME PAGE - 1973 - 1987 Chevy Silverado, Chevy Blazer, Chevy Scottsdale, Chevy Cheyenne, Chevy Custom Deluxe, 73 - 87 Chevy Trucks. The BEST source for info on the web!

To the original poster, I aologize for this short but necessary hijack.

Jersey4x4, I am growing weary of you providing obviously incorrect information to this forum. I have attached GM documentation which shows which truck is which. Speedos and square bodies do not denote which truck is which series. Just because you call all square bodies C/K is not relevant to the facts. Provide proof that GM was wrong. Provide proof that the R/V trucks are C/Ks. The semantics of the letter in the VIN is, GM put it there for a reason. It denotes the body style just as GM intended. Go to your parts manuals and provide part numbers for a door for a K3500 vs a V3500. Heck, I'm still waiting on the scan from your 10" manual showing a sheet metal coverter cover for a 4x4 700 R4. My GM parts illustration manual doesn't have it. Show me any relevant parts manual showing parts for a 1989 C/K series suburban. I will publically apologize if you can prove me wrong but don't think you can. I find that the best onfo on the trucks is from the manufacturer not the page you have listed. You are doing a disservice to the members providing false information. If it's your opinion that the R/V trucks are C/K thats fine but telling everyone that R/V trucks are in fact C/K trucks is just wrong.

 

[ODdave]

OP, just so we are on the right track, EVERY spedo you are talking about is from the "square body" style of chevy (like the cucv's) regardless of year or vin code, correct?

 

[Jersey4x4]

No problem. Call your GM dealer and use any CUCV VIN and ask for the part number for the door shell, Then use the VIN from a 1991 Suburban which has an R or V in the VIN and it is the same part number. Then try for a 92 and see what you get. Uh OH, not the same because it is a different body? How did that happen. By definition the C/K series trucks have and always been the 1973 to 1987 Chevy Trucks from K10 to K30 the 1500 to 3500 designation did not start until after 1987 except for suburban, Blazer and quad cab 1 ton trucks and the model was the number being " Chevy 1500" not K1500 because there is none. The GM Factory paper parts manual from the dealer is for 1973 to 1991 C/K series trucks. If you reference anywhere that is what they are. If I had more time I would love to scan (guessing)4500 pages of this book and post it because it is a great reference for the CUCV parts since most of the parts were from older design trucks but I just don't have the time. But do the parts search and you will see what I am talking about. and the 1988 body style was never marketed as a C/K series truck by GM and if it has I would love to see it. Just like the CUCV style trucks were never marketed as an R/V style because they had a V in the vin in the last few built, they just did not have enough VIN codes left to keep using the C/K codes. Look it up your self.

To the original poster, I aologize for this short but necessary hijack.

Jersey4x4, I am growing weary of you providing obviously incorrect information to this forum. I have attached GM documentation which shows which truck is which. Speedos and square bodies do not denote which truck is which series. Just because you call all square bodies C/K is not relevant to the facts. Provide proof that GM was wrong. Provide proof that the R/V trucks are C/Ks. The semantics of the letter in the VIN is, GM put it there for a reason. It denotes the body style just as GM intended. Go to your parts manuals and provide part numbers for a door for a K3500 vs a V3500. Heck, I'm still waiting on the scan from your 10" manual showing a sheet metal coverter cover for a 4x4 700 R4. My GM parts illustration manual doesn't have it. Show me any relevant parts manual showing parts for a 1989 C/K series suburban. I will publically apologize if you can prove me wrong but don't think you can. I find that the best onfo on the trucks is from the manufacturer not the page you have listed. You are doing a disservice to the members providing false information. If it's your opinion that the R/V trucks are C/K thats fine but telling everyone that R/V trucks are in fact C/K trucks is just wrong.

 

[doghead]

By definition the C/K series trucks have and always been the 1973 to 1987 Chevy Trucks from K10 to K30 the 1500 to 3500 designation did not start until after 1987 except for suburban, Blazer and quad cab 1 ton trucks and the model was the number being " Chevy 1500" not K1500 because there is none.

Chevrolet and GMC never called their 4 door cabs a "Quad cab", they called it a Crew cab.

Dodge used the name "Quad cab".

BTW, I am tired of your argumentative, and negative comments in the forums. If it continues, I will not hesitate to give you some time off, or put you on "moderation".

 

[DrJekl]

Is everyone on here a lawyer with the intent on being right? Why would I be concerned about a speedometer used in an 88 model truck? We're talking about the square body style trucks to 1987 and the same Blazer and Suburban to 91 using similar equipment as the CUCV? May as well include the Corvette because it has a C in it! The CUCV is based on a 84 style truck, not an 88 style truck so it would seem that an assumption could be made here. If I am talking CUCV with a GM diesel engine in it do I have to clarify I am not talking about a Duramax or a big arse Detroit Diesel tank pack or will I get bombarded with technical jargon? Or since you have one you built and put a MH-60M engine in it that runs on diesel then that makes it a possible option as well?

Really guys, this thread is amazing. Simple question with situation detail turned into a contest to see who is packing the biggest club. Sounds like Bill Clinton in here defining what "is, IS".

Thanks to the straight shooters, I appreciate your input as it has been helpful.