Converting '68 120 mph Rallye Speedo to 150 mph

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jbc426

jbc426

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I called Precision Graphics about updating and restoring my dash and possibly changing my speedo over to the 150 mph version, as the car will soon be much faster than it is currently. He referred me over to Thomas at Instrumen-Specialties over on the right coast.

Thomas told me it was no problem at all to convert the 120 speedo to a 150 speedo, but that it just wouldn't have the trip meter or reset mechanism in it. I don't care about that detail.

I also want my amp gauge converted to a volt meter. They can do that as well with either the stock amp gauge face or a volt gauge face. I'll go for the volt gauge face, and have him test and update my remaining factory gauges. I had the clock done years ago and it still keeps perfect time.

I'll also have him restore the entire plastic gauge panels and polish the lens, glove box panel etc. I have a dash cap in the top pad now and my lower is still in great condition.

Those real 150 mph speedos or complete Rallye gauge sets for the '68's are very hard to find!
 
I don't think you understand. He's going to re silk screen my 120 mph core speedo to the 150 mph unit that's all rebuilt and re magnetized internally to be adjusted to work correctly. It just won't have the trip meter, but it's lots cheaper than an original that needs restored.
 
if you want google Mr Heater Box. They do that as well as upgrade tach to electronic . Dad n I have 1st hand knowledge with them. They do great work.
 
My rallye gauges came with a clock. I never use a tach on this car or any other really, I just rev it until it sounds like it should go into the next higher gear, but thanks for the reference!
 
jbc426 said:
I don't think you understand. He's going to re silk screen my 120 mph core speedo to the 150 mph unit that's all rebuilt and re magnetized internally to be adjusted to work correctly. It just won't have the trip meter, but it's lots cheaper than an original that needs restored.
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www.redlinegaugeworks.com will do this same conversion. He can also convert your amps to volts. And convert your temp gauge to show actual numbers in original type script with a calibrated temp sender (new replacements have the wrong resistance).
 
They are not that uncommon why not just find a 150 speedo for 68 up? The only difference between the 68 and 69-71 is the direction of the numbers, change the face decal and none would know and you can also retain your tripometer. What were you quoted to do the 120 conversion?
The 67 is a one year only has the same face as a 68 but it has a screw on cable where all the others uses the push on type.
 
60 on the 120 is in the same place as the 75 reading on a 150.

How exactly is the odometer going to be correct. The same number of revolutions is going to give an entirely different MPH reading on each speedo. Are they changing the odometer gearing?
 
Rocky_JS said:
They are not that uncommon why not just find a 150 speedo for 68 up? The only difference between the 68 and 69-71 is the direction of the numbers, change the face decal and none would know and you can also retain your tripometer. What were you quoted to do the 120 conversion?
The 67 is a one year only has the same face as a 68 but it has a screw on cable where all the others uses the push on type.
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There is not one for sale anywhere and I've been looking for a while. I was told the speedos were from 68 to 71. You would have to use the screw on spedo cable for the 678. I also can't find a very nice 68 grill.
 
crackedback said:
60 on the 120 is in the same place as the 75 reading on a 150.

How exactly is the odometer going to be correct. The same number of revolutions is going to give an entirely different MPH reading on each speedo. Are they changing the odometer gearing?
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The change the magnetic something or another in there and it works out correctly.
 
autoxcuda said:
www.redlinegaugeworks.com will do this same conversion. He can also convert your amps to volts. And convert your temp gauge to show actual numbers in original type script with a calibrated temp sender (new replacements have the wrong resistance).
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I will also be running a set of aftermarket oil pressure, water and trans temp gauges just under the dash next to the underdash A/C vents.. The factory amp gauge is being converter to volts. Redline did my 70 gauges. My trip meter still doesn't work right. I don't think its a problem specific to Redline though. I believe its some kind of a factory issue....maybe. My buddy posted about his '70 doing the same thing. Everything else they did was nice! Here's a shot of the '70's interior. Tee blue tint is the windshield factory tint with aftermarket tint over it.
 

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I sent you a PM. Also which side 68 grille do you need? Or do you need surrounds and headlight bezels?


jbc426 said:
There is not one for sale anywhere and I've been looking for a while. I was told the speedos were from 68 to 71. You would have to use the screw on spedo cable for the 678. I also can't find a very nice 68 grill.
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The speedometers needle is carried by a magnetic gyro. If not for the odometer being inside it wouldn't need or contain a single gear. Changing the speed displayed has no effect on miles clocked.
From my experience with the trip odometers I have to think they are deleting you trip clock because either they don't want to deal with it or they are actually exchanging your instrument for one they have on hand that doesn't have that feature.
Accuracy in a speedometer is great for avoiding speeding tickets. If it shows anywhere near 70 mph , don't look at it again. Watch where you're going.
I can put a 150 mph decal on a 120 mph speedo head, then adjust its calibration just a tad, and its fine up to about 70 mph. The faster you go, the more inaccurate a cable to magnet driven speedometer reports. The inaccuracy is increased a little by the shifted scale on the alternate screen. To repeat, none of this is relevant to odometer and miles recorded. That should be considered a separate instrument for all practical purposes.
Electronic accuracy is found only in those instruments.
 
Rocky_JS said:
I sent you a PM. Also which side 68 grille do you need? Or do you need surrounds and headlight bezels?
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Thanks for the PM. I'm looking for a nice set, both sides with good headlight buckets, and the outer-most aluminum trim. Mine has been crushed almost flat over the years.

The rest of my grills, the inside trim parts are in good shape except the parking/turn light lenses, which are all crazed. I assume those are still are currently available.
 
RedFish said:
The speedometers needle is carried by a magnetic gyro. If not for the odometer being inside it wouldn't need or contain a single gear. Changing the speed displayed has no effect on miles clocked.
From my experience with the trip odometers I have to think they are deleting you trip clock because either they don't want to deal with it or they are actually exchanging your instrument for one they have on hand that doesn't have that feature.
Accuracy in a speedometer is great for avoiding speeding tickets. If it shows anywhere near 70 mph , don't look at it again. Watch where you're going.
I can put a 150 mph decal on a 120 mph speedo head, then adjust its calibration just a tad, and its fine up to about 70 mph. The faster you go, the more inaccurate a cable to magnet driven speedometer reports. The inaccuracy is increased a little by the shifted scale on the alternate screen. To repeat, none of this is relevant to odometer and miles recorded. That should be considered a separate instrument for all practical purposes.
Electronic accuracy is found only in those instruments.
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Darn, I use and enjoy an accurate odometer and love an accurate speedometer. I'll place a post in the wanted section as per a suggestion from fellow member Rocky_JS and look for a real one, get it calibrated and go that route.

Thanks guys!
 
crackedback said:
60 on the 120 is in the same place as the 75 reading on a 150.

How exactly is the odometer going to be correct. The same number of revolutions is going to give an entirely different MPH reading on each speedo. Are they changing the odometer gearing?
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As it turns out, I don't think they can....good call!
 
jbc426 said:
As it turns out, I don't think they can....good call!
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Yall still don't quite understand that these are 2 instruments in the same house.
The odometer is direct drive and only way to change its calibration is in gear ratios. The speedometer is a magnetic and indirect drive. If this carried the odometer it couldn't possibly record millage correctly.
 
jbc426 said:
My rallye gauges came with a clock. I never use a tach on this car or any other really, I just rev it until it sounds like it should go into the next higher gear, but thanks for the reference!
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I was referencing the tach as an fyi that they do that as well. Dad had both his tach AND his 150 speedo with trip odo calibrated by them. They can do what you are asking, here is their link. They have a TON of parts speedos etc to help

http://www.mrheaterbox.com/
 
It sounded as though only an overlay was being done to convert it. Apparently not the case.

If they change the magnetic force to calibrate the correct MPH for rotations, then it would be OK.
 
crackedback said:
It sounded as though only an overlay was being done to convert it. Apparently not the case.

If they change the magnetic force to calibrate the correct MPH for rotations, then it would be OK.
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I was trying to state that it could be done with a decal/overlay. A needle return spring and a counter weight provide some adjustment. No it wont be dead on accurate but then they never were and surely aren't now at 40+ yrs old.
 
RedFish said:
I was trying to state that it could be done with a decal/overlay. A needle return spring and a counter weight provide some adjustment. No it wont be dead on accurate but then they never were and surely aren't now at 40+ yrs old.
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I swapped out my 120 MPH speedo for a 150 MPH in my '69 Barracuda. I bought the 150 MPH speedo on ebay for $75 and paid $165 to get it refurbished (I think I sent it to Redline). Anyway, the 120 speedo didn't have the trip odometer but the 150 did. I removed the 120 speedo and located the trip odometer shaft on the dash. Then I drilled a very small hole in the black spot (depression) on the instrument panel where the trip shaft would normally be. It came out perfect and worked flawlessly. I don't know what you're going to pay for the guy to redo your speedo face and recalibrate but I didn't think I paid too much for what I ended up with...it came out nice. I even had the speedo guy set the mileage to where my old one was!!
He also repainted the needle for free!! One thing that did throw a monkey wrench into the gears was the fact that I had a push on plastic speedo cable/speedo connection and the 150 MPH speedo was the screw on type so I did have to replace the cable. But as it turns out, I was installing a 2004R in the Cuda around the same time and had to buy a longer cable anyway so I just bought one the correct length with the proper ends . Turns out the majority of Mopar transmissions have the same speedo cable connection on the transmission as many other cars (GM, Ford, etc).
All I had to do is make a trip to O'rielly's and buy a GM speedo cable for $7 and it solved the problem.

Of course with the 2004R my top speed is now over 190 miles an hour so the 150 MPH speedo doesn't quite cut the mustard!!! Where's the nearest salt lake????

Treblig
 

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