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700R4 Speedometer Drive
#1310928 Thu May 16 2019 06:23 PM
Joined: Oct 2005
Posts: 3,304
MNSmith Offline OP
"Hey! I sound like Darth Vader!!
So, I got around to fixing my speedo driive some time back. Got the correct gear with matching drive. The OEM gear had popped off before I got the transmission. New speedo head. Speedo operated fine and correctly for a little while. Then the needle started pulsing. Then no speedo. Figured the drive gear popped off again. It did. I put the gear back on but this time, left the cable disconnected. Oh, I had put a new cable in some time ago. Chassis Engineering trans cross member. My own bracketry to use the '86 'Vette trans. I have a VSS driven directly off the trans. See pic. That put the cable end and housing in to the cross member a bit. I figured that and the curve to head up front created enough of a bind to make the drive gear pop off. My current fix. I'm waiting for a 90* drive that I'll put on the VSS, then the cable to give the cable a more direct route and, hopefully, take all bottom end bind out. Thoughts?

Attached Files
1952suburban302.jpg (61.02 KB, 142 downloads)
speedometerdrive.jpg (17.67 KB, 134 downloads)
Re: 700R4 Speedometer Drive
MNSmith #1310935 Thu May 16 2019 07:05 PM
Joined: Feb 2004
Posts: 23,004
H
'Bolter
Looks good to me- - - -cable routing is something some people don't consider, and it can create problems. The cable-drive tachometers we used to use on Mallory dual point distributors had a bad habit of lagging in response time just enough to let the engine run past redline if we weren't very careful about the radius of the loop the cable made from the engine compartment to the dash.
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: 700R4 Speedometer Drive
MNSmith #1310948 Thu May 16 2019 08:52 PM
Joined: Apr 2005
Posts: 2,837
C
'Bolter
You may not be interested but we have gone to gps speedometers on nearly all the rods we build and some of the restorations. No cables, gears, or ratios to worry about and you can switch to any tires or or rear gear and they stay dead accurate. They are starting to make some that fit the factory instrument cluster on popular models. There are virtually no "dead spots" for gps units anymore. Just a potential option to consider.


Evan
Re: 700R4 Speedometer Drive
MNSmith #1310966 Thu May 16 2019 11:17 PM
Joined: Oct 2005
Posts: 3,304
MNSmith Offline OP
"Hey! I sound like Darth Vader!!
Thanks Jerry!


Evan, you never know what the future will hold! I've used my old Garmin on long trips to help verify my speed.

Re: 700R4 Speedometer Drive
coilover #1310968 Thu May 16 2019 11:50 PM
Joined: Sep 2001
Posts: 31,205
Bubba
Originally Posted by coilover
There are virtually no "dead spots" for gps units anymore.

I wondered about this when I went through the Chesapeake Bay Bridge-Tunnel twice this week?

[I was using Apple Maps routing - Verizon Cellular - there was no lost signal.]
[I’ll also use a GPS next time - to see if the two devices behave the same.]

Last edited by tclederman; Fri May 17 2019 06:37 PM. Reason: Added bracket comments.

Tim
1954Advance-Design.com [1954advance-design.com]
1954 3106 Carryall Suburban [stovebolt.com] - part of the family for 49 years
1954 3104 5-window pickup w/Hydra-Matic [1954advance-design.com] - part of the family for 15 years
- If you have to stomp on your foot-pedal starter, either you, or your starter, or your engine, has a problem.
- The 216 and early 235 engines are not "splash oilers" - this is a splash oiler. [chevy.oldcarmanualproject.com]
Re: 700R4 Speedometer Drive
tclederman #1311021 Fri May 17 2019 06:52 PM
Joined: Mar 2004
Posts: 206
F
'Bolter
MNSmith: back in the early days of the 700R4, like thru 87, the output shaft of that trans had two holes drilled in it to locate the retaining clip for the speedo drive gear. Corvette was the only odd-ball, having a specific extension housing which used the rearward locating hole, meaning the positioning of the driven gear in the extension housing was different also. You said Corvette 1986, but does it really have a Corvette extension housing? Does the output shaft have one or two holes drilled back there for the drive gear? Was the output shaft maybe changed out for one with a single hole? You can mix and match a lot of parts in that tranny, but it doesn’t always work out. Sounds like the drive and driven gear aren’t lined up correctly. Just a few things to consider. Good luck, Dave


1948 5-window 3100 Chevy
327 V-8 TBI 700R4 Posi 3.73
"Old Blue"
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Re: 700R4 Speedometer Drive
MNSmith #1311040 Sat May 18 2019 02:44 AM
Joined: Jun 2004
Posts: 8,420
W
'Bolter
Does a GPS speedometer have an odometer also?


They say money can't buy happiness. It can buy old Chevy trucks though. Same thing.

1972 Chevy c10 Cheyenne Super
Re: 700R4 Speedometer Drive
MNSmith #1311043 Sat May 18 2019 03:13 AM
Joined: Apr 2016
Posts: 650
M
'Bolter
I have the Dakota VHX gauges with GPS, cruise, 1/8 and 1/4 mile time. also 0-60 time. It has odometer. The cruise is just the turn signal handle that fits my 57 turn signal switch. I have a Frankland quick change rear end with about 124 gear ratios available from about 212 to 840 so I didn't want to have to mess with calibrating. The speedo also has memory in case you lose signal.


Old enough to know better, too young to resist.
Re: 700R4 Speedometer Drive
Flatblu4748 #1311046 Sat May 18 2019 04:10 AM
Joined: Oct 2005
Posts: 3,304
MNSmith Offline OP
"Hey! I sound like Darth Vader!!
Originally Posted by Flatblu4748
MNSmith: back in the early days of the 700R4, like thru 87, the output shaft of that trans had two holes drilled in it to locate the retaining clip for the speedo drive gear. Corvette was the only odd-ball, having a specific extension housing which used the rearward locating hole, meaning the positioning of the driven gear in the extension housing was different also. You said Corvette 1986, but does it really have a Corvette extension housing? Does the output shaft have one or two holes drilled back there for the drive gear? Was the output shaft maybe changed out for one with a single hole? You can mix and match a lot of parts in that tranny, but it doesn’t always work out. Sounds like the drive and driven gear aren’t lined up correctly. Just a few things to consider. Good luck, Dave



Thanks Dave! My output shaft has two holes. I believe I put the clip in the forward hole.

Better shots of my tail shaft housing. I might have done some mixing and matching? It's been a while.

Attached Files
1952suburban32.jpg (33.13 KB, 69 downloads)
1952suburban35.jpg (32.07 KB, 66 downloads)

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