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[GMCnet] 3.21 to 1 Final Drive Pinion Seals [message #200295]

Fri, 01 March 2013 20:35

USAussie

Messages: 15912
Registered: July 2007
Location: Sydney, Australia

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Ken,

You can download the 3.21 to 1 manual here:

http://www.bdub.net/manuals/1967_Toronado_3.21_Planetary_Final_Drive.pdf

Turn to page 3EC-18 and check step:

19. Install seals into bearing housing as shown in Fig. 3EC-51.

The seal facing the tranny is installed with the spring towards the tranny and the seal facing the final drive is installed with the
spring facing the final drive.

There is no mention of any weep holes in the seals or the housing.

Figure 3EC-53 shows a "vent pin."

If you haven't already done so I would suggest giving John Biwersi a call before you re-install the final drive, I'm sure he'd
clarify anything you need to know about the 3.21. He walked JohnS and me through the inspection procedure step by step.

I'll send you his telephone number off net.

Regards,
Rob

From: Ken Henderson

Stick and I removed the 3.21 FD from his coach today to replace the back-to-back seals, which I thought was the source of his ATF
leak. It turned out that the top portion of the FD/Transmission gasket was in bad shape but the seal looked perfect (well centered,
resilient rubber, and no side play on pinion shaft). So I've decided against fixing sumthin' that ain't broke. We'll install with
the new gasket tomorrow and HOPE. I haven't yet found the weep hole for those back-to-back seals, so I really don't know where his
leak was from. We may have not accomplished anything.
:-(

Ken

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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: [GMCnet] 3.21 to 1 Final Drive Pinion Seals [message #200302 is a reply to message #200295]

Fri, 01 March 2013 21:47

Surbo

Messages: 213
Registered: February 2004

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Robert Mueller wrote on Fri, 01 March 2013 20:35

Ken

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Howdy Fella's;

There is a weep hole in the FD housing, just below and to the inside of where the fill tube enters the FD. There is suppose to be a "vent pin" in that vent hole, along with a seal between the FD and the tranny, to keep the vent hole clean. Most of the time the vent pin gets left out, probably because the rebuilder does not know what it is for.

The back to back shaft seals should straddle that vent hole, so if there is any FD fluid leaking pass the seal facing the FD, the fluid will vent out the weep hole and not enter into the tranny. Same for the seal facing the tranny, so any tranny fluid leaking pass that seal will not enter the FD, but exit out the vent hole.

Bob Drewes in SESD

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Re: [GMCnet] 3.21 to 1 Final Drive Pinion Seals [message #200305 is a reply to message #200302]

Fri, 01 March 2013 22:11

Ken Henderson

Messages: 8726
Registered: March 2004
Location: Americus, GA

Karma: 9

Senior Member

Bob,

Sounds like I've been looking in the wrong area for the weep hole -- on top
of the housing instead of near the fill tube. I'll look there tomorrow.

What do you think of my decision to leave the apparently good seals alone?
The final drive lube was Amzoil, so the red color there didn't raise any
suspicion about ATF having mixed with it. It was also very thick (and
cold) so there was no apparent thinning by ATF.

I find it hard to believe that the damaged-at-top FD-425 gasket could lose
4 qt. of ATF in 200 miles -- but no less hard to believe the seal and weep
hole could pass that much either. How could there be that much pressure in
the transmission in that area??? I'm beginning to fear a more serious
problem, involving a ruptured pressure seal somewhere, despite the nice,
normal, operation of the transmission.

Ken H.

On Fri, Mar 1, 2013 at 10:47 PM, Bob Drewes <bmdrewes@iw.net> wrote:

> There is a weep hole in the FD housing, just below and to the inside of
> where the fill tube enters the FD. There is suppose to be a "vent pin" in
> that vent hole, along with a seal between the FD and the tranny, to keep
> the vent hole clean. Most of the time the vent pin gets left out, probably
> because the rebuilder does not know what it is for.
>
> The back to back shaft seals should straddle that vent hole, so if there
> is any FD fluid leaking pass the seal facing the FD, the fluid will vent
> out the weep hole and not enter into the tranny. Same for the seal facing
> the tranny, so any tranny fluid leaking pass that seal will not enter the
> FD, but exit out the vent hole.
>
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Ken Henderson
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www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach

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Re: [GMCnet] 3.21 to 1 Final Drive Pinion Seals [message #200308 is a reply to message #200305]

Fri, 01 March 2013 23:17

roy1

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Registered: July 2004
Location: Minden nevada

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Ken if you are dealing with a 3:21 differential rather then a 3:08 you might consider adding a vent to the case cover rather then depend on the little vent hole in the seal. Fritz Slama convinced me to add one to my 3:21 back in the day. If you go this route I found the hole needs to be located at the top of the case then a short length of 3/16" copper tubing silver blazed and extended inside the case close to the ring gear but away from the slinging oil. Rubber on the outside then up and looped high too keep it clean of dirt. It took me 3 tries to get it right so it didn't leak.

Roy Keen Minden,NV 76 X Glenbrook

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Re: [GMCnet] 3.21 to 1 Final Drive Pinion Seals [message #200310 is a reply to message #200308]

Sat, 02 March 2013 06:27

Larry

Messages: 2875
Registered: January 2004
Location: Menomonie, WI

Karma: 10

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roy1 wrote on Fri, 01 March 2013 23:17

What John B and I have found about the 3.21 FD is that the filler hole in the FD is located about 1" to high on the cover. I use to loose FD oil out of my 3.21, a little through the weep hole, but mostly out of the vent which is a spring loaded vent in the center of the left hand drive plate. See this:
http://www.gmcmhphotos.com/photos/fd-visual-differences-3-07-vs-3-21/p16034.html
I would loose about 1" of oil and it would level off there. John and I talked extensively about this, and I started filling the 3.21 to a level that was 1" below the filler. I do not loose any oil now. As a result of this, John now brazes a filler hole into the cover of his rebuilds, 1" below the original, and instructs people buying his FD to fill using the original hole until the oil just starts coming out of the lower hole. For a while John was venting the 3.21 as described by Fritz, but he no longer does that. I have put on about 20K miles now...mostly long trips over the past 4 yrs and have not had to add oil to my FD. Just my experience with it.

Larry

78 Royale w/500 Caddy
Menomonie, WI.

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Re: [GMCnet] 3.21 to 1 Final Drive Pinion Seals [message #200313 is a reply to message #200310]

Sat, 02 March 2013 06:57

Ken Henderson

Messages: 8726
Registered: March 2004
Location: Americus, GA

Karma: 9

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Roy & Larry,

Thanks for the tips. Stick's leak was definitely ATF, not final drive
lube. Our schedule for this operation won't allow either of your
recommended modifications. But we can be careful to not overfill the case.
Which brings up the next question: What gear lube should we use? The '67
manual Rob pointed me to calls for a special lube with a GM number, which
means nothing to me. It came from Bill Telgen with THICK Amsoil, but we
didn't save it.

Re: The OEM vent: Are y'all now telling me that the vent through the left
axle is the only vent -- none on top of the case like (supposedly) on the
3.07? If so, the ATF leak definitely was not through the pinion seal, as I
now suspect. That still won't eliminate the FD-425 gasket which was
damaged at the top, but it will relieve my mind about my decision to not
change the pinion seal.

Thanks,

Ken H.

roy1 wrote on Fri, 01 March 2013 23:17
> > Ken if you are dealing with a 3:21 differential rather then a 3:08 you
> might consider adding a vent to the case cover rather then depend on the
> little vent hole in the seal.
>
...
>

On Sat, Mar 2, 2013 at 7:28 AM, Larry wrote:

> What John B and I have found about the 3.21 FD is that the filler hole in
> the FD is located about 1" to high on the cover. I use to loose FD oil out
> of my 3.21, a little through the weep hole, but mostly out of the vent
> which is a spring loaded vent in the center of the left hand drive plate.
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Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach

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Re: [GMCnet] 3.21 to 1 Final Drive Pinion Seals [message #200314 is a reply to message #200313]

Sat, 02 March 2013 07:19

USAussie

Messages: 15912
Registered: July 2007
Location: Sydney, Australia

Karma: 6

Senior Member

Ken,

I put 90W synthetic gear oil in Double Trouble's 3.21; unfortunately due to CRS I can't remember which brand. It may have been Mobil
1 or Valvoline or ?????.

Regards,
Rob M.
�

-----Original Message-----
From: Ken Henderson

Roy & Larry,

Thanks for the tips. Stick's leak was definitely ATF, not final drive
lube. Our schedule for this operation won't allow either of your
recommended modifications. But we can be careful to not overfill the case.
Which brings up the next question: What gear lube should we use? The '67
manual Rob pointed me to calls for a special lube with a GM number, which
means nothing to me. It came from Bill Telgen with THICK Amsoil, but we
didn't save it.

Re: The OEM vent: Are y'all now telling me that the vent through the left
axle is the only vent -- none on top of the case like (supposedly) on the
3.07? If so, the ATF leak definitely was not through the pinion seal, as I
now suspect. That still won't eliminate the FD-425 gasket which was
damaged at the top, but it will relieve my mind about my decision to not
change the pinion seal.

Thanks,

Ken H.

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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: [GMCnet] 3.21 to 1 Final Drive Pinion Seals [message #200316 is a reply to message #200313]

Sat, 02 March 2013 07:21

Larry

Messages: 2875
Registered: January 2004
Location: Menomonie, WI

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Ken Henderson wrote on Sat, 02 March 2013 06:57

Ken,
I've been using 75W90 Amsoil in my FD, and yes the only vent I have is the left axle vent, and IMO is all that is needed provided you do not overfill. (1" below the filler)

I don't know what to tell you RE the trans fluid leak. Wish I was there to help.

Larry

78 Royale w/500 Caddy
Menomonie, WI.

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Re: [GMCnet] 3.21 to 1 Final Drive Pinion Seals [message #200320 is a reply to message #200313]

Sat, 02 March 2013 07:50

Surbo

Messages: 213
Registered: February 2004

Karma: 0

Senior Member

Ken Henderson wrote on Sat, 02 March 2013 06:57

Ken;

If you are sure the leak is ATF, it has nothing to do with the vent system of the 3.21 FD

If the ATF is coming out of the weep hole, just above the flat horizonal casting that is near the filler pipe going into the FD, it is most likely the pinon shaft seal. The 3.21 had some peculiar leak problems with the pre-load items, but I won't get into that here.

If the leak is other than the weep hole, it could be the FD/tranny gasket, or several other places for leaks.

Another thing to check, is the tranny building up pressure and forcing a leak? The OEM tranny dip stick has a split "O" ring at the top for venting. The chain case has a vent for venting. If a long dipstick has been installed from the front engine cover, and no vent provisions, which most haven't, it may cause pressure build-up in the tranny. Is the chain case vent clear?

I would not install the FD without checking and/or replacing the shaft seals, just to easy to do now with the FD out on the bench. Pull the seals and do a pre-load check and see what that is. Remember, the pinon shaft is the support for the tranny output shaft, so things have to be up to spec's.

Bob Drewes in SESD

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