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C4 Modulator

F

Fred C

New Member
I was advised to place my post here in a specific forum that may address my problem better.

Hello All, I'm looking for some infor. I purchased a Used 72 C4 for my 200ci six cyl engine and discovered after the fact that the modulator valve was not with the Transmission. Now I am asking which push in colored stripe modulator valve do I need and also what length pin do I need? I assume the pin would be shorter since it is attached to the six cylinder.
Thanks for any inputs.
 
I don't "know" the answer but I have several C4's laying around. I'll see if I can gather some info for ya... and by the way, welcome to the Fix.
 
Here is what I found. Factory length on modulator pin is 1.620", that may vary 0.010" or 0.015". A longer pin (0.030" - 0.045") will firm up shifts and the shift will be slightly later. A shorter pin does the opposite.

Push-In or Bracket Mounted Modulators:
1) Red-stripe with two vacuum inputs. (large & small) Usually found on earlier (73-74) vehicles where EGR Devices were first introduced. This can in most cases be replaced with the green stripe version and get better results for the shift characteristics. The red-stripe dual diaphragm equipped C-4s use a different modulator retaining clip. This retaining clip is held in place by an extension housing bolt that is located just above the modulator. When changing the modulator to a single diaphragm type, you need to get the correct retainer from the dealer or the boneyard. C-5s also use the same C-4 retainer made for the single diaphragm modulator. The dual diaphragm retainer will cover access to the hose connection on the single diaphragm modulator. The retainers are made of spring steel.

2) Yellow stripe, with one single hose connection for High Vac lower altitude driving. Usually found on larger engines with strong vacuum signals, and trucks with earlier governor shift point calibration. Usually found on 72-81

3) Blue stripe, with one single hose connection for engines that generate slightly higher than average vacuum signals. These fit a small variety of applications of the C-4 & C-5. This version seems to be very uncommon but finds its performance levels between that of the yellow and green paint stripe codes. Usually found on 79-83

4) Green stripe, with one single hose connection for average settings that fit the widest variety of applications of the C-4 and C-5. This version seems to be the most popular and widely used of them all. Usually found on 72-83

5) White stripe, with one single hose connection for average settings that fit the widest variety of applications of the C-5. This version seems to be popular in C-5 with the V-6 engine but can also be used on the C-4 and seems to work well with them when operating at altitudes above 3000 ft. Usually found on 81-83

Thread Mounted Modulators:
1) They can have either a White or Green stripe, with one single hose connection. These are
the only modulators available for C-4s built before 1972 and work well on engines that have little or no emission control devices. Usually found on 64-71. This same modulator works on C-6’s that use Thread Mounted modulators.
 
tarafied1 said:
Here is what I found. Factory length on modulator pin is 1.620", that may vary 0.010" or 0.015". A longer pin (0.030" - 0.045") will firm up shifts and the shift will be slightly later. A shorter pin does the opposite.

Push-In or Bracket Mounted Modulators:
1) Red-stripe with two vacuum inputs. (large & small) Usually found on earlier (73-74) vehicles where EGR Devices were first introduced. This can in most cases be replaced with the green stripe version and get better results for the shift characteristics. The red-stripe dual diaphragm equipped C-4s use a different modulator retaining clip. This retaining clip is held in place by an extension housing bolt that is located just above the modulator. When changing the modulator to a single diaphragm type, you need to get the correct retainer from the dealer or the boneyard. C-5s also use the same C-4 retainer made for the single diaphragm modulator. The dual diaphragm retainer will cover access to the hose connection on the single diaphragm modulator. The retainers are made of spring steel.

2) Yellow stripe, with one single hose connection for High Vac lower altitude driving. Usually found on larger engines with strong vacuum signals, and trucks with earlier governor shift point calibration. Usually found on 72-81

3) Blue stripe, with one single hose connection for engines that generate slightly higher than average vacuum signals. These fit a small variety of applications of the C-4 & C-5. This version seems to be very uncommon but finds its performance levels between that of the yellow and green paint stripe codes. Usually found on 79-83

4) Green stripe, with one single hose connection for average settings that fit the widest variety of applications of the C-4 and C-5. This version seems to be the most popular and widely used of them all. Usually found on 72-83

5) White stripe, with one single hose connection for average settings that fit the widest variety of applications of the C-5. This version seems to be popular in C-5 with the V-6 engine but can also be used on the C-4 and seems to work well with them when operating at altitudes above 3000 ft. Usually found on 81-83

Thread Mounted Modulators:
1) They can have either a White or Green stripe, with one single hose connection. These are
the only modulators available for C-4s built before 1972 and work well on engines that have little or no emission control devices. Usually found on 64-71. This same modulator works on C-6’s that use Thread Mounted modulators.
Click to expand...
Thank you so much Craig- This is what I've been looking for.

Fred C
 
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