71 Blazer 4X4 Speedometer - The 1947 - Present Chevrolet & GMC Truck Message Board Network

71NVBlazerK5 · 08-20-2009, 11:26 AM

I have just put 33's on my blazer and now want to get the speedometer to tell me the truth. Telling the Highway Patrol, Sir my speedometer said 55 probably wont get me out of a ticket.

So the 205 transfer case has the speedo hooked to it through some adapter looking thing. HOW do I calibrate it? I know tire size and gear ratio play into it but where do I find which adapter or speedo gear I need.

Also, is there any other good sources of NOS parts other than LMC? thanks

**71blksuper4x4** · 08-20-2009, 11:38 AM

I don't think LMC carries NOS parts. Do you mean reproduction parts? If so, there are many companies out there that sell parts for the 67-72 truck line. For NOS, try ebay or sometimes on here. Be willing to pay for NOS stuff though, it's not cheap, and there is a reason for that.

JimKshortstep4x4 · 08-20-2009, 12:39 PM

Here is a link for you.

Jim

http://chevelleengineer.home.comcast...eer/speedo.htm

**passthebuck** · 08-20-2009, 12:40 PM

I learned a lot here:

http://www.transmissioncenter.net/sp...n_______va.htm

http://www.bgsoflex.com/speedo1.html

I figured out what I had in there for gears/tires, plugged it in & it told me what I needed to get. It seems hard initially, but once you lay out the numbers, it all makes sense.

71NVBlazerK5 · 08-20-2009, 02:05 PM

Yeah, I meant reproduction, not NOS. sorry.

**'68OrangeSunshine** · 08-21-2009, 06:18 AM

I have a '71 Jimmy with 33x12.50x15s. I once got pulled over by the AZ DPS [Dept of Public Safety= Highway Patrol] on I-10. I had been going 75 MPH, the posted limit, so I waved at the bear in the median as I clipped by one Sunday morning. He started up -- chased me -- and pulled me over. I told him the story about the larger tires, etc and that I thought I was doing the legal limit... This guy pulled out some scratch paper and a pencil, and started cyphering Pi x R squared on the hood of his cruiser, and came up with a percentage formula that my speedo was out by so much. 7 to 10%, I think. He let me go with a verbal warning.
All those nice guys have long since retired. Now I use a GPS.

08-20-2009, 11:26 AM	#1
71NVBlazerK5 Registered User Join Date: Jul 2009 Location: Fallon, NV Posts: 4	71 Blazer 4X4 Speedometer I have just put 33's on my blazer and now want to get the speedometer to tell me the truth. Telling the Highway Patrol, Sir my speedometer said 55 probably wont get me out of a ticket. So the 205 transfer case has the speedo hooked to it through some adapter looking thing. HOW do I calibrate it? I know tire size and gear ratio play into it but where do I find which adapter or speedo gear I need. Also, is there any other good sources of NOS parts other than LMC? thanks

08-20-2009, 11:38 AM	#2
71blksuper4x4 SWB 4x4 Collector Join Date: Jun 2001 Location: Osage City, KS Posts: 5,156	Re: 71 Blazer 4X4 Speedometer I don't think LMC carries NOS parts. Do you mean reproduction parts? If so, there are many companies out there that sell parts for the 67-72 truck line. For NOS, try ebay or sometimes on here. Be willing to pay for NOS stuff though, it's not cheap, and there is a reason for that. __________________ TREVOR 1970 CST swb 4x4 (speedwarning,cruise,tilt,tach,8track, original red shoulder belts,tow hooks) 1972 Jimmy (soon to be Hickey cloned) 1971 Cheyenne Super 4x4 swb (tilt,tach,buckets, original blue shoulder belts,am/fm,cruise,tow hooks, dealer 8 track) 1972 Cheyenne Super K20 4x4 Custom Camper (tilt, tach, am/fm, tow hooks, bed toolbox, aux gas tank 1972 Cheyenne Super Crew Cab K30 4x4 Duramax, Allison, np205, buckets, tow hooks (CURRENT PROJECT) http://67-72chevytrucks.com/vboard/s...d.php?t=624819 1989 V3500 Crew Cab (454tbi, NV4500, np205) 1970 Chevelle SS (LS5 454,th400,8track,buckets,tach) :2004 Jeep Wrangler Rubicon (daily driver) WTB: 1968-70 Cruise Control Lever

08-20-2009, 12:39 PM	#3
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Re: 71 Blazer 4X4 Speedometer Here is a link for you. Jim http://chevelleengineer.home.comcast...eer/speedo.htm __________________ 1971 Shortbox step side 4x4, 350 sbc, 3:07 rear end 1965 Impala SS 400 sbc, Muncie rock crusher 1966 Impala SS 396 bbc, TH 400 1969 El Camino, 350 sbc, TH 350 1971 Snowplow built on a Blazer frame 1972 GMC Short bed, stepside, TH 400, 427 BBC

08-20-2009, 12:40 PM	#4
passthebuck Sisyphus was my mentor! Join Date: Sep 2002 Location: Carleton Place, Ontario CANADA Posts: 984	Re: 71 Blazer 4X4 Speedometer I learned a lot here: http://www.transmissioncenter.net/sp...n_______va.htm http://www.bgsoflex.com/speedo1.html I figured out what I had in there for gears/tires, plugged it in & it told me what I needed to get. It seems hard initially, but once you lay out the numbers, it all makes sense. __________________ passthebuck #5642 -TWO 1967 GMC 910's. One with L6/3-on-the tree and the other with 355 w/435hp & a 700r4. -a 2013 Honda Civic as my "sensible" car

08-20-2009, 02:05 PM	#5
71NVBlazerK5 Registered User Join Date: Jul 2009 Location: Fallon, NV Posts: 4	Re: 71 Blazer 4X4 Speedometer Yeah, I meant reproduction, not NOS. sorry. Last edited by 71NVBlazerK5; 08-20-2009 at 02:06 PM.

08-21-2009, 06:18 AM	#6
'68OrangeSunshine Senior Member Join Date: Feb 2002 Location: Tucson, AZ USA Posts: 7,504	Re: 71 Blazer 4X4 Speedometer I have a '71 Jimmy with 33x12.50x15s. I once got pulled over by the AZ DPS [Dept of Public Safety= Highway Patrol] on I-10. I had been going 75 MPH, the posted limit, so I waved at the bear in the median as I clipped by one Sunday morning. He started up -- chased me -- and pulled me over. I told him the story about the larger tires, etc and that I thought I was doing the legal limit... This guy pulled out some scratch paper and a pencil, and started cyphering Pi x R squared on the hood of his cruiser, and came up with a percentage formula that my speedo was out by so much. 7 to 10%, I think. He let me go with a verbal warning. All those nice guys have long since retired. Now I use a GPS. __________________ Every 25 years I like to rebuild that 292, whether it needs it or not. Last edited by '68OrangeSunshine; 08-21-2009 at 06:19 AM.

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