Home » Public Forums » GMCnet » Tranny fluid check via modulator question
| Tranny fluid check via modulator question [message #276261] |
Mon, 20 April 2015 07:39  |
Tilerpep
Messages: 404
Registered: June 2013
Location: Raleigh, NC
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I found an old post with the attached...but the second question I share and didn't see an answer. I don't want to crawl under while running, but it seems that would be necessary...
Also, I would assume moderator is threaded in...do I use a sealant or something going back in?
Start the engine and let it run until warm. Remove the vacuum modulator and
let the fluid run out until the level is as high as the bottom of the
modulator opening. Replace the modulator. Check for leaks. Calibrate
dipstick while you are at it. Should read full when fluid is at the bottom
of the modulator hole.
Jim Hupy
Salem, OR
78 GMC Royale 403
To do the modulator spill over test, how much time do we have after key off to get an accurate level before the converter drain down comes in to play and you end up under filled? Also is this test at full operating temp, like 20 min driving?
John Lebetski
Woodstock, IL
77 Eleganza II
Source America First
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
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| Re: Tranny fluid check via modulator question [message #276265 is a reply to message #276261] |
Mon, 20 April 2015 08:03  |
Tilerpep
Messages: 404
Registered: June 2013
Location: Raleigh, NC
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I think I found my answer in another post: two steps. 1) calibrate 2) level check
:
Yes, Temperature does effect fluid LEVEL. Just like the TC being drained down will effect the level. That is why when you are checking for fluid LEVEL you need to follow the procedure, level ground, hot (but not overly so), idling in park so the TC is full.
But, for this, you are NOT checking the fluid level, you are just seeing where on the dip stick is the level to the bottom of the modulator hole.
After this is known, and marked, fill and check the fluid LEVEL with your calibrated mark and the correct procedure.
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
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| Re: [GMCnet] Tranny fluid check via modulator question [message #276268 is a reply to message #276261] |
Mon, 20 April 2015 08:02 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
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Tyler,
Yes, the transmission should be at normal operating temperature, as after a
few miles of driving. If you can comfortably grip the dipstick near the
fluid, it's OK.
Do NOT remove the modulator with the engine running. The converter will
not drain down immediately. Draining down is not a planned event, and will
not happen immediately; you've got time to do the fluid level check.
The modulator is held in with a forked retainer clamp which is, in turn,
held to the transmission by a 1/4-20 cap screw (7/16" wrench). Remove the
screw and clamp and just pull the modulator straight out -- it's sealed
with an O-ring. If there's been leakage around the modulator, that O-ring
should be replaced; it's probably OK.
Be sure the clamp is around the modulator and holding it in place when you
replace it -- someone recently reported having somehow installed one
incorrectly, resulting in the modulator being blown out by hydraulic
pressure when the engine was started. Be sure to tighten the retainer bolt
to 12 ft-lb or so (tight).
HTH,
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL,
Manny Brakes & 1-Ton, etc., etc.
www.gmcwipersetc.com
On Mon, Apr 20, 2015 at 8:39 AM, Tyler wrote:
> I found an old post with the attached...but the second question I share
> and didn't see an answer. I don't want to crawl under while running, but it
> seems that would be necessary...
> Also, I would assume moderator is threaded in...do I use a sealant or
> something going back in?
>
>
> Start the engine and let it run until warm. Remove the vacuum modulator and
> let the fluid run out until the level is as high as the bottom of the
> modulator opening. Replace the modulator. Check for leaks. Calibrate
> dipstick while you are at it. Should read full when fluid is at the bottom
> of the modulator hole.
> Jim Hupy
> Salem, OR
> 78 GMC Royale 403
>
>
> To do the modulator spill over test, how much time do we have after key
> off to get an accurate level before the converter drain down comes in to
> play
> and you end up under filled? Also is this test at full operating temp,
> like 20 min driving?
>
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
> Source America First
>
> --
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Tranny fluid check via modulator question [message #276270 is a reply to message #276268] |
Mon, 20 April 2015 08:19 |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
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And a minor point, the "O" ring is actually not round in shape, but square. Low pressure at the "O" ring, so a round one will do. I understand that the square "O" rings are impossible to find.
Also, be careful when reinstalling the modulator and do not cut the "O" ring. You can dump a lot of transmission fluid if the ring is damaged. Unfortunate personal experience.
Tom, MS II
2012 Phoenix Cruiser model 2552
KA4CSG
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| Re: [GMCnet] Tranny fluid check via modulator question [message #276275 is a reply to message #276270] |
Mon, 20 April 2015 08:56 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
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Tom,
Depending on the size you need a quad ring might be found:
http://www.seals.ru/up-files/50558fcf1763c9e1c40e8936f3b5b805.pdf
Regards,
Rob M.
-----Original Message-----
From: Thomas Phipps
And a minor point, the "O" ring is actually not round in shape, but square. Low pressure at the "O" ring, so a round one will do.
I understand that the square "O" rings are impossible to find.
Also, be careful when reinstalling the modulator and do not cut the "O" ring. You can dump a lot of transmission fluid if the ring
is damaged.
Unfortunate personal experience.
Tom
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: Tranny fluid check via modulator question [message #276277 is a reply to message #276261] |
Mon, 20 April 2015 09:14 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
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So after the modulator spill over step, and reinstallation all with engine off, one would need to then start it to check and calibrate the stick reading? I don't see any step to restart, pull and wipe stick and recalibrate if needed. If you check level with engine off, it would read high on the stick, you would be tempted to lengthen the tube to get it to read right. Then the next time you checked with engine running in park it would read low and you would add Dexron creating an overfill condition. Is this the correct logic?
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Tranny fluid check via modulator question [message #276281 is a reply to message #276277] |
Mon, 20 April 2015 09:25 |
James Hupy
Messages: 6806
Registered: May 2010
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Don't over think what I said. When the dripping stops from the modulator
hole. Reinstall it. Then, wipe your hands off, get in the coach and pull
the dipstick without starting the engine. If it indicated full, you are
done. If not, mark the stick with a 3 square file or similar tool. Then,
go wash your hands, hug your significant other, have a cold one, pet the
dog. You are done with this job. On to the next one.
Jim Hupy
Salem, Or
78 GMC ROYALE 403
On Apr 20, 2015 7:16 AM, "John R. Lebetski"
wrote:
> So after the modulator spill over step, and reinstallation all with engine
> off, one would need to then start it to check and calibrate the stick
> reading? I don't see any step to restart, pull and wipe stick and
> recalibrate if needed. If you check level with engine off, it would read
> high on
> the stick, you would be tempted to lengthen the tube to get it to read
> right. Then the next time you checked with engine running in park it would
> read low and you would add Dexron creating an overfill condition. Is this
> the correct logic?
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
> Source America First
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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| Re: [GMCnet] Tranny fluid check via modulator question [message #276282 is a reply to message #276275] |
Mon, 20 April 2015 09:34 |
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thesmith
Messages: 589
Registered: February 2015
Location: Cary, NC
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USAussie wrote on Mon, 20 April 2015 08:56Tom,
Depending on the size you need a quad ring might be found:
http://www.seals.ru/up-files/50558fcf1763c9e1c40e8936f3b5b805.pdf
Regards,
Rob M.
-----Original Message-----
From: Thomas Phipps
And a minor point, the "O" ring is actually not round in shape, but square. Low pressure at the "O" ring, so a round one will do.
I understand that the square "O" rings are impossible to find.
McMaster has a LOT of sizes of square O-Rings...........
http://www.mcmaster.com/#o-rings/=wu22wi
Perhaps someone could measure an original and find a match.....
Pete
Also, be careful when reinstalling the modulator and do not cut the "O" ring. You can dump a lot of transmission fluid if the ring
is damaged.
Unfortunate personal experience.
Tom
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Cary, NC
1978 Center Kitchen Royale.
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| Re: [GMCnet] Tranny fluid check via modulator question [message #276284 is a reply to message #276270] |
Mon, 20 April 2015 09:38 |
emerystora
Messages: 4442
Registered: January 2004
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Tom
Just to pick on you 😃, they are round in shape but square in cross section.
Also not impossible to find.
A local hydraulic hose ship here stocks them.
You can also find them in many places on the Internet.
I did a Google search on the Net for "square o rings". Here is the first of many places I found.
http://theoringstore.com/index.php?main_page=index&cPath=367_98_97&zenid=d1aaa13f54cc0c1cab76c45a81a7f3e5
Emery Stora
> On Apr 20, 2015, at 7:19 AM, Thomas Phipps wrote:
>
> And a minor point, the "O" ring is actually not round in shape, but square. Low pressure at the "O" ring, so a round one will do. I understand that
> the square "O" rings are impossible to find.
> Also, be careful when reinstalling the modulator and do not cut the "O" ring. You can dump a lot of transmission fluid if the ring is damaged.
> Unfortunate personal experience.
> Tom, MS II
> --
> 1975 GMC Avion
> _______________________________________________
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| Re: Tranny fluid check via modulator question [message #276293 is a reply to message #276261] |
Mon, 20 April 2015 11:38 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
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""To do the modulator spill over test, how much time do we have after key off to get an accurate level before the converter drain down comes in to play and you end up under filled? Also is this test at full operating temp, like 20 min driving?
""
Unless something is dramatically wrong, you don't need to worry about converter drain back for days or even months.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: Tranny fluid check via modulator question [message #276337 is a reply to message #276261] |
Mon, 20 April 2015 21:05 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
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I still don't get it. THMs are always level checked running in park. How does a new scribe make you just made engine off, show accurate level with it running in the future?
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Tranny fluid check via modulator question [message #276356 is a reply to message #276337] |
Tue, 21 April 2015 07:25 |
Tilerpep
Messages: 404
Registered: June 2013
Location: Raleigh, NC
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I was missing it also until I saw the info in my second post - the engine off/modulator process is to calibrate the dipstick only. Then engine on, normal procedure to check fluid level.
Thanks for all the detailed "how to" everyone - down to the wrench sizes...love it!
T
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
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| Re: Tranny fluid check via modulator question [message #276357 is a reply to message #276337] |
Tue, 21 April 2015 07:36 |
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Matt Colie
Messages: 8547
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Location: S.E. Michigan
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JohnL455 wrote on Mon, 20 April 2015 22:05I still don't get it. THMs are always level checked running in park. How does a new scribe make you just made engine off, show accurate level with it running in the future?
John,
You are not the first to not understand this sort of thing.
The "Pull the Modulator" trick merely establishes the level for the purpose of marking the stick. Where the rest of the transmission fluid is at that time is of no interest. If one did this test on a cold transmission, he might get quite a bit of fluid. If his mark is right and the level was good, as soon as he restarts he will have to add exactly that much fluid. This is because the new stick mark does not include the fluid "hang up" everywhere in the transmission.
This method is much as we might be do on a bench during product development where we take a P1 (level of prototype)of something and make windows (holes) in it. Then fill it to level and decide what will determine both the "cold" and "hot" levels. This is usually some internal feature that either does or does not want to be sitting in the lubricant. Our "window" here is the modulator port.
So, once the desired level is established and the stick marked, then check should be done as a hot check.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: Tranny fluid check via modulator question [message #276360 is a reply to message #276261] |
Tue, 21 April 2015 08:58 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
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I understand all that Matt as we are trying to establish a benchmark cal on.the stick. The part that seems to be missing in the directions is, 'then start the vehicle and add fluid if necessary to reach the new mark'. A THM will drop in level running due to the fluid hang as you described. If dipped 'Off' it will show high leading you to bleed off fluid creating an underfill situation and possible slipping damage. If all the above is correct, then I 'get it'. Also once added to new mark running, you will get fluid out of the case if you pull the modulator again engine off but be back at the new scribe mark on the stick. I hope no one is running underfilled by not doing the running check after cal
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Tranny fluid check via modulator question [message #276361 is a reply to message #276360] |
Tue, 21 April 2015 09:11 |
James Hupy
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Registered: May 2010
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If there is a way to make a simple procedure more complicated, this group
is SURE to find it and maneuver far afield from the original topic. I am
perhaps one of the worst offenders in this regard. Hope all of us learn how
to calibrate a dipstick from this thread, but somehow I have a few doubts !
(Grin)
Jim Hupy
Salem, Oregon ( temporarily located in Abbotsford, B.C. working on GMC's)
On Apr 21, 2015 6:58 AM, "John R. Lebetski"
wrote:
> I understand all that Matt as we are trying to establish a benchmark cal
> on.the stick. The part that seems to be missing in the directions is, 'then
> start the vehicle and add fluid if necessary to reach the new mark'. A THM
> will drop in level running due to the fluid hang as you described. If
> dipped 'Off' it will show high leading you to bleed off fluid creating an
> underfill situation and possible slipping damage. If all the above is
> correct, then I 'get it'. Also once added to new mark running, you will
> get fluid out of the case if you pull the modulator again engine off but be
> back at the new scribe mark on the stick. I hope no one is running
> underfilled by not doing the running check after cal
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
> Source America First
> _______________________________________________
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| Re: [GMCnet] Tranny fluid check via modulator question [message #276384 is a reply to message #276361] |
Tue, 21 April 2015 12:45 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
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James Hupy wrote on Tue, 21 April 2015 08:11If there is a way to make a simple procedure more complicated, this group
is SURE to find it and maneuver far afield from the original topic. I am
perhaps one of the worst offenders in this regard. Hope all of us learn how
to calibrate a dipstick from this thread, but somehow I have a few doubts !
(Grin)
Jim Hupy
Salem, Oregon ( temporarily located in Abbotsford, B.C. working on GMC's)
On Apr 21, 2015 6:58 AM, "John R. Lebetski"
wrote:
> I understand all that Matt as we are trying to establish a benchmark cal
> on.the stick. The part that seems to be missing in the directions is, 'then
> start the vehicle and add fluid if necessary to reach the new mark'. A THM
> will drop in level running due to the fluid hang as you described. If
> dipped 'Off' it will show high leading you to bleed off fluid creating an
> underfill situation and possible slipping damage. If all the above is
> correct, then I 'get it'. Also once added to new mark running, you will
> get fluid out of the case if you pull the modulator again engine off but be
> back at the new scribe mark on the stick. I hope no one is running
> underfilled by not doing the running check after cal
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
> Source America First
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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Very good Jim !!
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] Tranny fluid check via modulator question [message #276412 is a reply to message #276361] |
Tue, 21 April 2015 17:02 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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G'day,
Below is an email I sent in on February 27, 2014 and asked people to review it. I have edited it taking into consideration comments
that were received.
Once again feel free to comment or criticize.
G'day,
I called Manny and ran this past him and he blessed it.
REMOTE TRANSMISSION dipstick CALIBRATION
NOTE: This procedure is written for vehicles with Left Hand Drive, if your GMC is Right Hand Drive the location of the transmission
modulator is on the driver side.
You will need the following items to perform this procedure:
1) Three ton jack stands - 4 ea.
2) Rags
3) Oil drain pan
4) Tool capable of removing existing marks on transmission dipstick
5) Tool capable of remarking transmission dipstick
6) Half inch (1/2") socket, extension, and ratchet to remove / reinstall modulator retainer
7) Transmission fluid
Procedure:
Comments: before you start this procedure look at the passenger side of the transmission and locate the modulator (Ref: Parts Book
78Z - TRANSMISSION - Pg. 17-2 Key 6 Modulator.
NOTE: You need to do the checking fairly quickly after stopping when the engine and transmission are HOT!
1) Park your GMC on a level surface
2) Set the parking brake
3) Set the suspension system to TRAVEL
4) Start the engine and allow coach to reach TRAVEL height
5) Depress the brake pedal
6) Cycle the transmission lever through all the positions back and forth several times slowly
7) Return the transmission to PARK
8) Leave the engine running and check the fluid level of the transmission
9) The fluid level should be at the "COLD" line if not slowly and carefully fill the transmission to that level
10) Get back in the coach and drive it long enough for the engine and transmission to come to normal operating temperature
11) Park the GMC on a level surface
12) Put the transmission in Park and set the parking brake
13) With the engine running check the fluid level of the transmission; if it's not on the HOT mark continue as below
14) Shut the engine off and place jack stands under the frame so that if a torsion bar were to fail you won't get crushed
Note: if you're girth is large you will probably have to jack the GMC up (front and rear) level to gain access to the
modulator
15) Be careful from this point onwards not to burn yourself on the HOT exhaust pipes
16) Place a drain pan under the modulator on the passenger side of the transmission
17) Remove the rubber vacuum line
18) Remove the bolt that holds the modulator retainer to the transmission using the half inch socket, extension, and ratchet
19) Remove the modulator (be careful it will be HOT)
20) Allow fluid to drain into the pan until it just drips (be careful, the fluid will be HOT!)
21) If fluid does not drip out add it slowly until it does
22) Re-install the modulator and retainer and hose
23) Remove the drain pan and jack stands
24) Get back in the GMC, start the engine and drive the GMC until the engine and transmission are at normal operating temperature
25) Park the GMC on a level surface
26) Set the hand brake and put the transmission in Park
27) Check the level on the dipstick, it should be at or near the "HOT" mark; if not note where it is
28) Remove the existing "HOT" mark on the dipstick and mark it at the correct level
29) Allow the transmission to cool overnight
30) Start the engine the next day and cycle the transmission lever through all the positions back and forth several times slowly
31) Check the level on the dipstick, it should be at or near the "COLD" mark; if not note where it is
32) Remove the existing "COLD" mark on the dipstick and mark it at the correct level
Maintenance Manual X-7525
SECTION 0 - GENERAL INFORMATION, PERIODIC MAINTENANCE AND LUBRICATION
Page 0-13 - TRANSMISSION
If I missed anything or what I've written isn't clear PLEASE let me know.
Regards,
Rob M.
-----Original Message-----
From: James Hupy
If there is a way to make a simple procedure more complicated, this group
is SURE to find it and maneuver far afield from the original topic. I am
perhaps one of the worst offenders in this regard. Hope all of us learn how
to calibrate a dipstick from this thread, but somehow I have a few doubts !
(Grin)
Jim Hupy
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: Tranny fluid check via modulator question [message #276455 is a reply to message #276261] |
Wed, 22 April 2015 08:29 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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Thanks for the full instructions Rob. I think my confusion is that in step 27 the engine must be running. The simple yet hard to fathom concept is that the spillover sets the high mark on the stick, then level is set hot to that mark engine running in park. You can't just spillover and call that the level or you will be underfilled. Thanks again.
John Lebetski
Woodstock, IL
77 Eleganza II
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