rear diff - different rear bearing set-up - Alfa Romeo Bulletin Board & Forums
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post #1 of 7 (permalink) Old 09-10-2019, 10:11 AM Thread Starter
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rear diff - different rear bearing set-up

I'm rebuilding the rear end of a '69 GTV, to include later axles and a lovely new Quaife LSD. Finally got the service parts from Alfaholics who have been very helpful. I have a couple of questions related to dimensional differences in the front pinion bearing, originally a FAG 506578 and replaced by a Timken HM88638 / HM88611 set in Alfaholics' kit. Wondering if anyone here has run across the same issue.

While the ID and OD of the old and new bearings are the same, 32.0 x 72.0, their width (axial length) is different: 27.30 mm for the 506578 and 27.00 mm for the HM88638 / HM88611. My understanding is that this will require increasing the S1 (front pinion bearing) shim to match: by 0.30 mm. (I don’t have the factory tools for Alfas. My experience with other marques and with Gretrag transmissions in particular has been that pinion depth is stable over time.) Do I have this correct? And is there a source for the S1 shims for the front pinion bearing? They are a 61.0 x 70.8 mm shim that I do not have and am unable to locate.

The other issue is the width of the HM88638 inner race. The 506578 has a 26.00 mm inner race width (axial dimension), the HM88638 is 23.00 mm, a 3.00 mm difference. I certainly need to set bearing preload with the S2 shims next to the rear pinion bearing. But it appears I would be well off to first put a 3.00 mm spacer between the bearing spacer (tube) and the front pinion bearing. The reason for this, rather than adding more shim thickness to S2 is that, with the 3.00 mm difference in the front bearing inner race width, the fillet in the extra 3 mm of the pinion shaft otherwise exposed would not let the S2 shim sit correctly:

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Again, do I have this correct? To match the bearing spacer, I believe the additional spacer would be 31.9 x 40.0 x 3.0 mm. Anyone done this? Cheers,

Kevin
Catellus Engineering, Inc. - http://catellusengineering.com/
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post #2 of 7 (permalink) Old 09-10-2019, 10:24 AM
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for shims I use mitsumi USA .

https://us.misumi-ec.com/vona2/mech_...0/M1801030000/

The standard shims are 'good enough' and cheap. Do a search for rear diff shims and you will find the exact ones
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74 GTV with 10548's and Ingram pump
71 Spider 1750 BOMBER ; 1995 LS 78K tight fast car
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post #3 of 7 (permalink) Old 09-10-2019, 03:59 PM Thread Starter
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for shims I use mitsumi USA .

https://us.misumi-ec.com/vona2/mech_...0/M1801030000/

The standard shims are 'good enough' and cheap. Do a search for rear diff shims and you will find the exact ones
Goats, thanks, but I am not having any luck searching Misumi's site for "rear diff" or "rear differential." Can you point me in the right direction? The CIMR35-42-xx you mention on an earlier thread is close to what is needed for the rear bearing, altho I think CIMR28-40-xx with a little radius'ing the ID will be a better fit for the 28.5 x 40.0 original size. I am not having much luck finding something close to the 61.0 x 70.8 dimensions for the front (pinion end) bearing, setting the pinion depth.

Kevin
Catellus Engineering, Inc. - http://catellusengineering.com/

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post #4 of 7 (permalink) Old 09-10-2019, 04:01 PM
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sorry Kevin. Do a search on this forum on the BB for Mitsumi nd/or shims and you will find it here with the order number

74 GTV with 10548's and Ingram pump
71 Spider 1750 BOMBER ; 1995 LS 78K tight fast car
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post #5 of 7 (permalink) Old 09-11-2019, 07:03 AM Thread Starter
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Just got a note from Alfaholics. Max tells me they are having the pinion height (depth) shims made at the moment, and hope to have in stock in the next 2 weeks.

In the interim, I've found 56x72 mm shims available from another source, will be ordering some up to confirm fit.

Kevin
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post #6 of 7 (permalink) Old 09-11-2019, 07:47 AM
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Kevin, I thought about relieving the ID a little bit but then gave up -- I suppose it can be done with a pair of scissors in some cases (really thin shims) but I see no way to chuck up anything and change the ID on a lathe. Maybe can do on a mill but would need to secure the shim down.
I think I had custom shims made at Matsumi for the pinion depth. Its been a while...

Please post a list of sources for shims that you find as this has become an issue over time here -- BTW the Dana kit I posted works great on crown wheel position and preload and its only 10 bucks or so

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post #7 of 7 (permalink) Old 09-11-2019, 07:58 AM Thread Starter
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Please post a list of sources for shims that you find as this has become an issue over time here -- BTW the Dana kit I posted works great on crown wheel position and preload and its only 10 bucks or so
Happy to share once I have the parts in hand and can confirm they fit. I can share at the moment these 65 x 75 mm (approx.) shims that work for the differential carrier bearings. They can be ordered from either Porsche or VW/Audi, but they are much less expensive from Porsche.

012.409.387.AK 0.45 mm
012.409.387.AL 0.49 mm
012.409.387.AM 0.53 mm
012.409.387.AN 0.57 mm
012.409.387.AP 0.61 mm
012.409.387.AQ 0.65 mm
012.409.387.AR 0.69 mm
012.409.387.AS 0.73 mm
012.409.387.AT 0.77 mm
012.409.387.BA 0.81 mm
012.409.387.BB 0.85 mm

Porsche also used a slightly wider shim, about 65 x 76 mm, in the late 944 series cars. It drops right into the diff carrier and would be an alternative to the above. Available as:

0.24 mm 016.311.393.AP
0.27 mm 016.311.393.AQ
0.30 mm 016.311.393.AR
0.33 mm 016.311.393.AS
0.36 mm 016.311.393.M
0.39 mm 016.311.393.N
0.42 mm 016.311.393.P
0.45 mm 016.311.393.Q
0.69 mm 016.311.393.R
0.93 mm 016.311.393.S
1.17 mm 016.311.393.T
1.41 mm 016.311.393.AA

I've ordered what I hope is a usable 2mm spacer that should address the fillet issue, this part from McMaster-Carr.

Kevin
Catellus Engineering, Inc. - http://catellusengineering.com/
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