NAPA SKF-21771 rear bearing seal fails the 0.25" test

RF_Burns

RF_Burns

Super Moderator
Staff member
Sep 7, 2008
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Ontario Canada
So I went to NAPA thos morning to pick up the SKF-21771 rear bearing seals. I brought along a 1/4 hex bit to test the seal which actually measures
0.247". It fails the test as your can see in these photos.

http://www.gmcmhphotos.com/photos/g7044-skf-21771-rear-seal-fails-test.html

Any ideas?

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
Hubler 1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
> So I went to NAPA this morning to pick up the SKF-21771 rear bearing seals. I brought along a 1/4 hex bit to test the seal which actually
> measures 0.247". It fails the test as your can see in these photos.
>
> http://www.gmcmhphotos.com/photos/g7044-skf-21771-rear-seal-fails-test.html
>
> Any ideas?

Have them open every box in the store. Maybe one of them is right.
--
73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"Every day I become more convinced that I am the only person left on the planet that recognizes nonsense for what it is."
 
What exactly are you testing?

Pete
--
Cary, NC

No Coach yet but likely center kitchen, dry side bath Royale, 78, 403, hopefully with good original white Imron paint.
 
Pete,
Its the distance from the inner face of the metal ring of the seal, to the seal itself. It should be 0.26", below are some photos.

http://www.gmcmhphotos.com/photos/rear-axle-seals-skf21771/p36362-inside-measure.html

http://www.gmcmhphotos.com/photos/rear-axle-seals-skf21771/p36356-says-made-in-the-usa.html

http://www.gmcmhphotos.com/photos/rear-axle-seals-skf21771/p36367-stralian-test-must-slide-under-rubber-lip-rob.html

http://www.gmcmhphotos.com/photos/rear-axle-seals-skf21771/p36372-new-bad-timken-rear-wheel-bearing-seal.html

Apparently seals are being made in which the rubber of the seal is too close to the inner bearing and damages it... letting the grease out.
--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
Hubler 1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
Looking through my parts this morning I found 6 of the 21771 seals.
They're all OLD stock -- no less than 10 years old since I've had them in
my storage for that long.

All of the 6 are NAPA-labeled. 4 are relabled Chicago Rawhide; their outer
circumferences are Green. The other two are have only NAPA labeling; their
outer circumferences are Black.

Using a 1/4" screwdriver bit as the clearance gauge, I tested each of the 6
on a flat Formica surface. Here are the results:

Green #1 -- Rubber barely touched the gauge
Green #2 -- Rubber very slightly deformed by the gauge
Green #3 & #4 -- Rubber noticeable deformed by the gauge, WAG 0.003"
Black #1 & #2 -- Rubber very obviously deformed, WAG 0.010"

All of this has piqued my interest, CRS having taken care of most of my
memories from when this topic was originally broached some years ago.
Aside from the contention that the out-of-tolerance seals will allow the
seal to touch the bearing, I don't recall the details of the problem. I DO
recall, however, that somewhere (which I can't locate in any manual now)
there was a requirement that the seal be seated proud of the rear of the
hub. In fact, I still have an un-machined aluminum "seal seater" which
Duane Simmons had Ragusa cast. We were going to use those to make a
special tool for properly seating seals. The aluminum proved difficult to
machine, so we gave up that idea. I did, IIRC, make one from steel which
worked well. BUT, I can remember neither its dimensions nor its location.
:-( Could it be that the problems with at least some of the
out-of-tolerance seals are really caused by incorrect installation? Does
anyone know where the official instructions are for R&R of rear wheel
bearings and seals?

Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL,
Manny Brakes & 1-Ton, etc., etc., etc.
www.gmcwipersetc.com

> So I went to NAPA thos morning to pick up the SKF-21771 rear bearing
> seals. I brought along a 1/4 hex bit to test the seal which actually
> measures
> 0.247". It fails the test as your can see in these photos.
>
> http://www.gmcmhphotos.com/photos/g7044-skf-21771-rear-
> seal-fails-test.html
>
> Any ideas?
>
 
Ken, you are absolutely correct. Do not seat the seal below the outer part
of the hub casting. Leave it a bit "proud" meaning sticking out a bit for
insurance purposes. Jwid.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

> Looking through my parts this morning I found 6 of the 21771 seals.
> They're all OLD stock -- no less than 10 years old since I've had them in
> my storage for that long.
>
> All of the 6 are NAPA-labeled. 4 are relabled Chicago Rawhide; their outer
> circumferences are Green. The other two are have only NAPA labeling; their
> outer circumferences are Black.
>
> Using a 1/4" screwdriver bit as the clearance gauge, I tested each of the 6
> on a flat Formica surface. Here are the results:
>
> Green #1 -- Rubber barely touched the gauge
> Green #2 -- Rubber very slightly deformed by the gauge
> Green #3 & #4 -- Rubber noticeable deformed by the gauge, WAG 0.003"
> Black #1 & #2 -- Rubber very obviously deformed, WAG 0.010"
>
> All of this has piqued my interest, CRS having taken care of most of my
> memories from when this topic was originally broached some years ago.
> Aside from the contention that the out-of-tolerance seals will allow the
> seal to touch the bearing, I don't recall the details of the problem. I DO
> recall, however, that somewhere (which I can't locate in any manual now)
> there was a requirement that the seal be seated proud of the rear of the
> hub. In fact, I still have an un-machined aluminum "seal seater" which
> Duane Simmons had Ragusa cast. We were going to use those to make a
> special tool for properly seating seals. The aluminum proved difficult to
> machine, so we gave up that idea. I did, IIRC, make one from steel which
> worked well. BUT, I can remember neither its dimensions nor its location.
> :-( Could it be that the problems with at least some of the
> out-of-tolerance seals are really caused by incorrect installation? Does
> anyone know where the official instructions are for R&R of rear wheel
> bearings and seals?
>
> Ken H.
> Americus, GA
> '76 X-Birchaven w/Cad500/Howell EFI & EBL,
> Manny Brakes & 1-Ton, etc., etc., etc.
> www.gmcwipersetc.com
>
> On Mon, May 29, 2017 at 12:52 PM, Bruce Hislop

>
> > So I went to NAPA thos morning to pick up the SKF-21771 rear bearing
> > seals. I brought along a 1/4 hex bit to test the seal which actually
> > measures
> > 0.247". It fails the test as your can see in these photos.
> >
> > http://www.gmcmhphotos.com/photos/g7044-skf-21771-rear-
> > seal-fails-test.html
> >
> > Any ideas?
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Just checked the 4 old stock Chicago Rawhide 21771 seals I purchased on an online auto parts store and they failed the 1/4 test by about .014. Hard to
measure, had to use the plunger end of the caliper and try to keep it vertical, got about .236. Although I saw in the photos someone had used the
inside measuring side of the caliper but the large jaw interferes with the other side of the seal tipping the jaws slightly making the measure appear
to be .25 but the flat surface test with on exact 1/4 screwdriver bit fails. I assume the 1/4 requirement is exact and .236 will not do?
--
Eric & Ree '74 ex-Sequoia + '75 Eleganza Alexandria, Ontario, Canada
 
Well, Carl P. knew where to find the seal spec: Page 512 of the Assembly
Manual (bdub has it). Turns out the metal portion of the seal should be
left 0.025"-0.045" proud of the hub. Since we don't have a dimensioned
drawing of the seal nor of the assembly, we can't be sure of the
significance of that information. However, since I intend to make a seal
seating tool before I do them again, to be sure I observe that
specification, I'll be comfortable using the Chicago Rawhide seals I have:
If 0.26" is adequate clearance, then I must assume that's based on the
seal being seated with only 0.025" proud. So, I've got
0.045"-0.026"=0.019" tolerance available. That means that a 0.019"
deflection of the seal should be safe -- none of those I have deflect
anywhere near that much.

I will, of course, check the other features of the assembly to be sure this
hypothesis is correct.

There was another interesting bit of information in the reference: It's
specified that the wheel must be rotated at least 3 times during the
tightening and adjusting of the wheel bearing. That's a practice I've had
for 60+ years, but this is the first time I recall seeing it in any GMC
manual.

I've temporarily posted the relevant portion of the reference here:
https://drive.google.com/file/d/0B3XquSIYjDleenNDM1BHQlNHa1E/view?usp=sharing

My seal seating tool will simply be a steel disc slightly larger than the
outer diameter of the seal, with a recess in one side of 0.40" to receive
the seal. That means I'll be 0.005" shy of the minimum seating of the
seal, and have 0.014" of "safety factor".

Ken H.

> Ken, you are absolutely correct. Do not seat the seal below the outer part
> of the hub casting. Leave it a bit "proud" meaning sticking out a bit for
> insurance purposes. Jwid.
> Jim Hupy
> Salem, Or
> 78 GMC ROYALE 403
>
>
 
I will call SKF tomorrow and get a dim drawing. Pass it along to the group. It is possible that SKF changed their internal spacing, as all the information in their seal catalog describes only applications where the seal is treated as a stand alone assembly, and not as a part (of a larger assembly). I'll turn a few seal installation tools, this weekend.

----- Original Message -----

From: "Ken Henderson"
To: "gmclist"
Sent: Monday, May 29, 2017 7:47:35 PM
Subject: Re: [GMCnet] NAPA SKF-21771 rear bearing seal fails the 0.25" test

Well, Carl P. knew where to find the seal spec: Page 512 of the Assembly
Manual (bdub has it). Turns out the metal portion of the seal should be
left 0.025"-0.045" proud of the hub. Since we don't have a dimensioned
drawing of the seal nor of the assembly, we can't be sure of the
significance of that information. However, since I intend to make a seal
seating tool before I do them again, to be sure I observe that
specification, I'll be comfortable using the Chicago Rawhide seals I have:
If 0.26" is adequate clearance, then I must assume that's based on the
seal being seated with only 0.025" proud. So, I've got
0.045"-0.026"=0.019" tolerance available. That means that a 0.019"
deflection of the seal should be safe -- none of those I have deflect
anywhere near that much.

I will, of course, check the other features of the assembly to be sure this
hypothesis is correct.

There was another interesting bit of information in the reference: It's
specified that the wheel must be rotated at least 3 times during the
tightening and adjusting of the wheel bearing. That's a practice I've had
for 60+ years, but this is the first time I recall seeing it in any GMC
manual.

I've temporarily posted the relevant portion of the reference here:
https://drive.google.com/file/d/0B3XquSIYjDleenNDM1BHQlNHa1E/view?usp=sharing

My seal seating tool will simply be a steel disc slightly larger than the
outer diameter of the seal, with a recess in one side of 0.40" to receive
the seal. That means I'll be 0.005" shy of the minimum seating of the
seal, and have 0.014" of "safety factor".

Ken H.

> Ken, you are absolutely correct. Do not seat the seal below the outer part
> of the hub casting. Leave it a bit "proud" meaning sticking out a bit for
> insurance purposes. Jwid.
> Jim Hupy
> Salem, Or
> 78 GMC ROYALE 403
>
>
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I think I kept the box from the SFK seal from last year and will see if same number. IIRC the fail made is that the wrong one has the metal touching
the bearing resulting in metal particles in the rollers. If it were just the rubber wearing and not sealing that would almost be better.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
John,

IIRC, you're thinking of the front wheel bearing seal. From the drawing I
posted, it appears virtually impossible for the metal to touch the
bearing. But the rubber is separated from it only by about the distance
the seal should be left proud of the hub.

https://drive.google.com/file/d/0B3XquSIYjDleenNDM1BHQlNHa1E/
view?usp=sharing

Ken H.

On Tue, May 30, 2017 at 9:19 AM, John R. Lebetski
wrote:

> I think I kept the box from the SFK seal from last year and will see if
> same number. IIRC the fail made is that the wrong one has the metal touching
> ​ ​
> the bearing resulting in metal particles in the rollers. If it were just
> the rubber wearing and not sealing that would almost be better.
 
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