1970 hot water valve

[Jeffrey S.]

Hello all! This weekend we replaced the hot water valve on a fellow chapter member's 1970 A/C small block car. This car is a very low mile, very original example. Below are pictures of the valve we removed and we would like opinions as to whether this is an original part. What we found interesting is the stud next to the vacuum port that had a small round retainer on it that held the vacuum hose in place. The hose itself has a plastic fitting on the end that slipped over the stud. "Type H 25" and "Ranco" is stamped into the part. Thanks for your input.
Jeff

[Patrick H.]

Re: 1970 hot water valve

I like it. It looks similar to what I once removed from my 71.

[Jeffrey S.]

Re: 1970 hot water valve

Patrick,
Thanks for the response. We didn't have a '70 AIM to compare the part number with the '69 part # which we had with us. My '69 valve, when removed, was more like the replacement valve where the hose just pushes on. Can you give me the part number fro the '70 AIM for comparison?
Jeff

[Patrick H.]

Re: 1970 hot water valve

Patrick,
Thanks for the response. We didn't have a '70 AIM to compare the part number with the '69 part # which we had with us. My '69 valve, when removed, was more like the replacement valve where the hose just pushes on. Can you give me the part number fro the '70 AIM for comparison?
Jeff

Jeff,

I only have the 71 and 72 AIMs at home.

[Jeffrey S.]

Re: 1970 hot water valve

I have the '72 as well and by then the valve wasn't used (at least it doesn't appear in the AIM).
Jeff

[Joe L.]

Re: 1970 hot water valve

Patrick,
Thanks for the response. We didn't have a '70 AIM to compare the part number with the '69 part # which we had with us. My '69 valve, when removed, was more like the replacement valve where the hose just pushes on. Can you give me the part number fro the '70 AIM for comparison?
Jeff

Jeff------


1969 used valve GM #3949878. I can't find that this valve was ever available in SERVICE. For SERVICE, the valve was GM #3940250. I have no idea how they differed, if at all.

The early 1970 valve was also the GM #3949878. Later 1970 used valve GM #3984642. This valve also became SERVICE for 1969 when the 3940250 was discontinued in June, 1971.

GM #3984642 was later discontinued and replaced by GM #3984641. The latter was discontinued without supercession some time ago.

[Jeffrey S.]

Re: 1970 hot water valve

Joe,
Thanks for the part numbers. Is it possible that the service part was the same as the assembly line part except that the mounting screws were included generating a different part number?
Jeff

[Joe L.]

Re: 1970 hot water valve

Joe,
Thanks for the part numbers. Is it possible that the service part was the same as the assembly line part except that the mounting screws were included generating a different part number?
Jeff

Jeff-----

Yes, that's possible. In any event, I really don't think there was any difference, at all, in the 3949878 and the 3940250.

I think the only difference between these two and the later 3984642 is that the former have a straight vacuum nipple and, perhaps, some sort of mounting stud nearby while the 3984642 has a curved vacuum nipple and no mounting stud, at all.

[James B.]

Re: 1970 hot water valve

I have the '72 as well and by then the valve wasn't used (at least it doesn't appear in the AIM).
Jeff

Do we know why this type of valve wasn't installed beginning with the 1972 model?

[Joe L.]

Re: 1970 hot water valve

Do we know why this type of valve wasn't installed beginning with the 1972 model?

James------


I don't know but I expect GM figured that if they could get by without the valve for cars without air conditioning, then they could also get by for cars with air conditioning.

A valve came back for 1975 but only for Corvettes without air conditioning. For 1976-82, all Corvettes had a valve.

[Timothy B.]

Re: 1970 hot water valve

Joe,

I am helping my Brother with a low mile late produced 75 Corvette roadster with A/C.

I want to back flush the heater core but did not know if this car had a hot water valve. Am I correct to assume no valve and OK to back flush? the core.

[Joe L.]

Re: 1970 hot water valve

Joe,

I am helping my Brother with a low mile late produced 75 Corvette roadster with A/C.

I want to back flush the heater core but did not know if this car had a hot water valve. Am I correct to assume no valve and OK to back flush? the core.

Timothy------


If the 1975 had A/C, then it should have no valve. Is it OK to back flush? I would assume so.

[John V.]

Re: 1970 hot water valve

Jeff, Thank you for posting the thread and pictures.
Joe, Your insight is appreciated. Based upon what you identify as the "straight" vacuum nipple w/ stud...the valve pictured is a 3949878.
I am now reviewing my 1970 AIM -sheet D4. Note#2 dated 12-12-69, for (Sym #2) states: WAS 3949878 VALVE ASM.
It would appear there were still some 3949878 valves that made it into at least January 1970 production.
My VIN ...2127; built Jan. 28th, 1970.
Would you agree?

[Joe L.]

Re: 1970 hot water valve

Jeff, Thank you for posting the thread and pictures.
Joe, Your insight is appreciated. Based upon what you identify as the "straight" vacuum nipple w/ stud...the valve pictured is a 3949878.
I am now reviewing my 1970 AIM -sheet D4. Note#2 dated 12-12-69, for (Sym #2) states: WAS 3949878 VALVE ASM.
It would appear there were still some 3949878 valves that made it into at least January 1970 production.
My VIN ...2127; built Jan. 28th, 1970.
Would you agree?

John------


Definitely. I would expect the 3949878 at least through January, 1970 if not well beyond that time.

[Reba W.]

Re: 1970 hot water valve

It was not on my Sept. 24-built 1972 with AC.