This was the culprit on my trip. New one was 75% smaller.
Bad tranny modulator
- Thread starter Richard Vyse
- Start date
Unfortunatly due to the filters here at work I can't view the photo, but I can probably help from memory. Just a assumption form your description.
The original modulator's can was approximately 3 1/2 inches long, with the vacuum nipple at 90 degrees to the end, on the side of the cannister. Also cannister diameter is about 1/2 size of original.
The replacement is probably 2" long or less, with the nipple on the end in the center of the cannister.
It will work, but IMO it will give a softer shift feel than the original one.
That smaller type was originally used on the TH350 trasnmission, the larger type was used on the TH400. You probably will not know the difference unless you thrash on it hard, the upshifts will not be as crisp.
The last Chevy "hot rod" I had was a El Camino, 77 m/y that was upgraded from the 305 to a 350, 327/350 cam, headers, Edelbrock intake, and a B&M shift kit. While in Michigan at the low altitude here, it regularly chirped the tires going into second. When I moved to the southwest, at 4600 feet above sea level, the shift got "mushy". I fixed that by changing to a TH400 modulator.
While I don't have the correct GM parts catalog for the pre '75 Cadillacs, but using the truck catalog it appears GM dropped the large can modulators, superceeding them to the smaller TH350 style. I seem to remember this from a few years back this same question came up at work.
I am working on acquiring a pre '75 catalog, if successful I should have one in a couple of weeks.
Some aftermarket source should have the large can available if this becomes a issue. I may be able to locate one too if needed.
P.S., saw your Lifeliner at Flint last Saturday. I introduced myself to Paul as we have communicated online and on the phone in the past.
The original modulator's can was approximately 3 1/2 inches long, with the vacuum nipple at 90 degrees to the end, on the side of the cannister. Also cannister diameter is about 1/2 size of original.
The replacement is probably 2" long or less, with the nipple on the end in the center of the cannister.
It will work, but IMO it will give a softer shift feel than the original one.
That smaller type was originally used on the TH350 trasnmission, the larger type was used on the TH400. You probably will not know the difference unless you thrash on it hard, the upshifts will not be as crisp.
The last Chevy "hot rod" I had was a El Camino, 77 m/y that was upgraded from the 305 to a 350, 327/350 cam, headers, Edelbrock intake, and a B&M shift kit. While in Michigan at the low altitude here, it regularly chirped the tires going into second. When I moved to the southwest, at 4600 feet above sea level, the shift got "mushy". I fixed that by changing to a TH400 modulator.
While I don't have the correct GM parts catalog for the pre '75 Cadillacs, but using the truck catalog it appears GM dropped the large can modulators, superceeding them to the smaller TH350 style. I seem to remember this from a few years back this same question came up at work.
I am working on acquiring a pre '75 catalog, if successful I should have one in a couple of weeks.
Some aftermarket source should have the large can available if this becomes a issue. I may be able to locate one too if needed.
P.S., saw your Lifeliner at Flint last Saturday. I introduced myself to Paul as we have communicated online and on the phone in the past.
Damn, you are good. Too bad we did not meet up for I'm always excited about meeting PCS people.
Jeremy D. Ledford
PCS Volunteer Chapter President
Looks like the one I took of my 73 and yep, the replacement I got was smaller to.
Not bragging, but I am a GM dealership parts consultant at present, ex volunteer firefighter/EMT (1981-1989). Also one of the parts people that actually know how to look up parts for GM and Isuzu Medium Duty trucks, did that on and off from 79-01, and exclusively 01-08.
I have been in GM dealership parts deparments since 1970 (yeah older than dirt), part time Harley Davidson parts person on and off since 1999 and a gearhead since 1966. Have never owned a pro-car, hopefully in the future though.
I'll try to answer questions and assist in procuring parts through GM if needed.
If you need to contact me, PM me for a company e-mail or phone number, as I don't want to use the forum as a advertisement .
I have been in GM dealership parts deparments since 1970 (yeah older than dirt), part time Harley Davidson parts person on and off since 1999 and a gearhead since 1966. Have never owned a pro-car, hopefully in the future though.
I'll try to answer questions and assist in procuring parts through GM if needed.
If you need to contact me, PM me for a company e-mail or phone number, as I don't want to use the forum as a advertisement .
I've known Joe for a long while, and first met him through the old website, but lost contact until this past week in Flint. He is one of the many good friends that I made over the years. He is very modest about his knowledge base. He is one of those rare people that knows where to look for that elusive part that no one else can find because they don't have a clue as to what grouping it is located in. Between his knowledge and the parts books that I have, together we can figure out most of the part numbers. He also is the owner of a beautiful 1967 Pontiac 2 + 2. A true motor head from the old school... :thumbsup: :thumbsup: :thumbsup:
Richard,
The Era Correct Part Number for your Vacuum Modulator is GM #3027842. It was later superceded to #8629939 after 1982, which is the smaller type modulator which GM offered as a replacment. I've been dealing in GM parts for many years. I have a full library of GM parts master books for all GM Divisions from 1940's -1990's. Let me know if you need any other part numbers.
Aaron
The Era Correct Part Number for your Vacuum Modulator is GM #3027842. It was later superceded to #8629939 after 1982, which is the smaller type modulator which GM offered as a replacment. I've been dealing in GM parts for many years. I have a full library of GM parts master books for all GM Divisions from 1940's -1990's. Let me know if you need any other part numbers.
Aaron