71 TH400 Modulator O-Ring?
Thread Starter
Melting Slicks
Joined: Jul 2005
Posts: 3,389
Likes: 83
From: Norfolk Virginia
71 TH400 Modulator O-Ring?
My modulator doesn't seat all the way to tranny casing, and is leaking. The body is still off of the chassis so everything is acessable. I took the modulator out when I cleaned the tranny, but I don't recall an O-Ring. I read many of the threads in the search and everyone keeps reffering to the "Modulator O-ring". Is there supposed to be an O-ring around the neck of the modulator. If so can someone please post a pic.?
Thanks folks,
Dean
Thanks folks,
Dean
Safety Car
Joined: Oct 2004
Posts: 3,921
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From: Youngstown Ohio
See the pics of modulators in this link.....the o-ring is on the neck going into the trans;
http://www.thefind.com/cars/info-vacuum-modulator
http://www.thefind.com/cars/info-vacuum-modulator
Thread Starter
Melting Slicks
Joined: Jul 2005
Posts: 3,389
Likes: 83
From: Norfolk Virginia
See the pics of modulators in this link.....the o-ring is on the neck going into the trans;
http://www.thefind.com/cars/info-vacuum-modulator
http://www.thefind.com/cars/info-vacuum-modulator
By the way.....I grew up in Youngstown/Hubbard.
Dean
Last edited by dprinter1; Mar 28, 2011 at 05:51 AM. Reason: Typo
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
The retainer strap should pull the modulator completely down to the tranny surface when the bolt is installed. If it doesn't, there is something amiss. Are you sure the modulator pin is engaging with the modulator when you install it?
Thread Starter
Melting Slicks
Joined: Jul 2005
Posts: 3,389
Likes: 83
From: Norfolk Virginia
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,114
From: Crossville TN
That looks similar to the original unit. The factory one was painted black, I believe, and the dimensions look to be a bit different...but it's very close. The important aspects are that it doesn't leak and it operates like it is supposed to.
If the unit now seals [since you've installed the O-ring and the tranny shifts correctly at very light throttle and also WOT, then it is doing what it is supposed to do.
UPDATE: I did a web search and that modulator is for Cadillacs up to 1977. It may be a bit different dimensionally, but if it works OK, so what....
Further UPDATE: The FRAM #2329 unit is [apparently] a correct replacement for the THM 400 transmission. It is available at Amazon.com for less than $20.
If the unit now seals [since you've installed the O-ring and the tranny shifts correctly at very light throttle and also WOT, then it is doing what it is supposed to do.
UPDATE: I did a web search and that modulator is for Cadillacs up to 1977. It may be a bit different dimensionally, but if it works OK, so what....
Further UPDATE: The FRAM #2329 unit is [apparently] a correct replacement for the THM 400 transmission. It is available at Amazon.com for less than $20.
Last edited by 7T1vette; Mar 28, 2011 at 11:31 AM.
Thread Starter
Melting Slicks
Joined: Jul 2005
Posts: 3,389
Likes: 83
From: Norfolk Virginia
That looks similar to the original unit. The factory one was painted black, I believe, and the dimensions look to be a bit different...but it's very close. The important aspects are that it doesn't leak and it operates like it is supposed to.
If the unit now seals [since you've installed the O-ring and the tranny shifts correctly at very light throttle and also WOT, then it is doing what it is supposed to do.
UPDATE: I did a web search and that modulator is for Cadillacs up to 1977. It may be a bit different dimensionally, but if it works OK, so what....
Further UPDATE: The FRAM #2329 unit is [apparently] a correct replacement for the THM 400 transmission. It is available at Amazon.com for less than $20.
If the unit now seals [since you've installed the O-ring and the tranny shifts correctly at very light throttle and also WOT, then it is doing what it is supposed to do.
UPDATE: I did a web search and that modulator is for Cadillacs up to 1977. It may be a bit different dimensionally, but if it works OK, so what....
Further UPDATE: The FRAM #2329 unit is [apparently] a correct replacement for the THM 400 transmission. It is available at Amazon.com for less than $20.
My problem is that mine is not seating all the way back to the trans casing, and i cannot figure out why. The car is not driveable, as the body is not yet back on the frame.
Any suggestions on how to get this modulator seated will be appreciated.
Dean
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It looks like you have it installed correctly with the tabs pointing the right way. The bolt is supposed to be a real short one...any chance it's bottoming out in the case before pulling the clamp plate down all the way?
JIM
JIM
Thread Starter
Melting Slicks
Joined: Jul 2005
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From: Norfolk Virginia
Thanks, Jim
Dean
Burning Brakes
Joined: Nov 2006
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From: Orange Park Florida
The end of the modulator that fits into the tranny has a hole. Inside the tranny, I believe, is a pin, or plunger that is operated by the modulator. Look inside the tranny to see if the pin is centered so that the modulator slides over it. I have a '72 with a TH400, and your modulator looks different than mine. Mine only has one vacuum hose port, and you definitely need an o-ring.
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
JimT... That modulator only has one vacuum port, also. The other "thing" on the end is the adjustment screw for fine-tuning of the shift speeds.
BTW, I've been looking for a vacuum modulator that has the same/similar external design as the original unit. After seeing the pic and model numbers of this one, I've ordered one from Amazon. Thanks for the info!
Also, if the tranny shifts OK [early shifts around 2000 rpm at light throttle setting; later shifts around 5000 rpm for WOT shifts], then it is working as expected. If it doesn't leak since you put on the O-ring, drive away...all is good.
BTW, I've been looking for a vacuum modulator that has the same/similar external design as the original unit. After seeing the pic and model numbers of this one, I've ordered one from Amazon. Thanks for the info!
Also, if the tranny shifts OK [early shifts around 2000 rpm at light throttle setting; later shifts around 5000 rpm for WOT shifts], then it is working as expected. If it doesn't leak since you put on the O-ring, drive away...all is good.
Last edited by 7T1vette; Mar 29, 2011 at 10:54 AM.
Thread Starter
Melting Slicks
Joined: Jul 2005
Posts: 3,389
Likes: 83
From: Norfolk Virginia
JimT... That modulator only has one vacuum port, also. The other "thing" on the end is the adjustment screw for fine-tuning of the shift speeds.
BTW, I've been looking for a vacuum modulator that has the same/similar external design as the original unit. After seeing the pic and model numbers of this one, I've ordered one from Amazon. Thanks for the info!
Also, if the tranny shifts OK [early shifts around 2000 rpm at light throttle setting; later shifts around 5000 rpm for WOT shifts], then it is working as expected. If it doesn't leak since you put on the O-ring, drive away...all is good.
BTW, I've been looking for a vacuum modulator that has the same/similar external design as the original unit. After seeing the pic and model numbers of this one, I've ordered one from Amazon. Thanks for the info!
Also, if the tranny shifts OK [early shifts around 2000 rpm at light throttle setting; later shifts around 5000 rpm for WOT shifts], then it is working as expected. If it doesn't leak since you put on the O-ring, drive away...all is good.
Thanks for all suggestions,
Dean
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
Feedback for those who are interested: The Fram 2329 modulator I ordered from Amazon was delivered today... Bad news...same unit that you get as a replacement for the original modulator. It looks nothing like the original unit. Nice try, I guess.
