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LM 2nd Design Front Spindle & Backing Plate Identification
Posted by: Lane66m ()
Date: October 13, 2020 05:26PM

I had a recent request to determine how someone could tell a 1st design front brake backing plate from a second design.

The second design changed the axle spindle, brake backing plate, brake pivot bolt and the pivot bolt washer.

Without removing the drum, there is no way to tell unless yo can find the axle spindle part number on it. I did not look for the part number on one. Maybe I will tomorrow.

Removing the drum, you can determine the second design by the hex plats on the brake pivot bolt. The 1st design has a wide flats on its bolt. The second design has thin flats on its bolts.

Once removed you will see the major changes. The bolt shoulder is not as large. It is 0.616. 1st design is 0.750. The 1st design will thread into the second design axle spindle hole. But it will damage the the 1st design backing plate. (VOE)

I found out about this change the hard way on my More Door when I did all the rework on the front suspension part. I grabbed the 2 best axle spindles and put them on. Then I found the bolt shoulder bending the backing plate when I started tightening. I thought I had not centered the plate. Lower bolts weren't in yet. Took it apart and found the smaller hole on plate and noticed the axle spindles fit the bolts. I grabbed 2 more axle spindles of the 2nd design and swapped them in with the right bolts and the matching plates. These 2nd design plates were the best I had.

Al
Georgia

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Re: LM 2nd Design Front Spindle & Backing Plate Identification
Posted by: jjohnsonjo ()
Date: October 13, 2020 06:07PM

Thanks Al, I was going to suggest you post that PIC to the group, but you beat me to it. I was thinking the ones without the shoulder on the pin side for the retainer plates may be from the rear. Maybe you can confirm.

J.O.

65 Corsa Turbo Vert
79 Honda XL 500S
69 Honda CL 160 D
2010 BMW F 650 GS
2003 Bounder 36D
2013 KIA Optima SX turbo-AKA ZIPPY (wife,s car)
69 Newport Holiday Sailboat
Baja 150 dune buggy cart
Coleman HS 500 UTV
2016 KIA Sorento SXL Turbo

Bethlehem,Pa


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Re: LM 2nd Design Front Spindle & Backing Plate Identification
Posted by: Lane66m ()
Date: October 13, 2020 06:13PM

J.O.

The other set of pins I have have a shoulder of 0.646. I thought those were rear bake pivot bolts. I will look again tomorrow and post better photos of all 3 styles.

Al
Georgia

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Re: LM 2nd Design Front Spindle & Backing Plate Identification
Posted by: Lane66m ()
Date: October 29, 2020 04:30PM

I finally got all pivot bolts together. This is the update I promised weeks back. This should close out anymore work on this subject.

More info that is correct.

1st design backing plate hole average is 0.750. Average bolt above threads is 0.746. Thread size is 7/16-20, I believe.

2nd design backing plate hole average is 0.656. Average bolt shank above threads is 0.648. Thread size is 1/2-20.

Info on possible GM cut in.

My 66 More Door has a 11A Willow Run Trim Plate and had the 1st design spindles. It now has 2nd design after suspension rebuild.

My 66 Coupe has a 05B Willow Run Trim Plate and has the 2nd design spindles.


Now is there any way you can tell the designs apart without removing the pivot bolts. The answer is NO. I checked the pivot bole and spindles for Identification numbers and there are none.

I made a mistake in the first post with statement on the thin wrenching flat bolts. They are not Vair parts. I have no idea where the came from or how got mixed in with my Vair suspension parts. I don't even think they are Camaro parts as I found the 4 bolts that I took off my Camaro. Rechecking all the backing plate holes and bolts shank dimensions brought this error to light tonight.

J.O.: If I sent you the incorrect plate, let me know and I will send you a second design plate. My apologies for the incorrect info,

Al
Georgia

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Re: LM 2nd Design Front Spindle & Backing Plate Identification
Posted by: cnicol ()
Date: October 30, 2020 07:51AM

I looked in the parts book, group 5.055, to see what GM had to say. GM thinks it's an early/late '65 split (I believe Al that it's a '66 split).

The smaller 1st Design threads are listed as 1/2-20 and the 2nd design threads are listed as 5/8-18.

I wonder why GM changed the design?

Craig N. Coeur d'Alene ID.
66 Black Monza 4dr, 4.2L V8 49k
61 Seamist Jade Rampside 140 PG
60 Monza coupe (sold, sniff sniff)
66 Sprint Corsa convt - First car! Re-purchased 43 years later
2+2 gnatsuM 5691

+17 Tons of parts

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Re: LM 2nd Design Front Spindle & Backing Plate Identification
Posted by: RobertC ()
Date: October 30, 2020 09:38AM

cnicol Wrote:
-------------------------------------------------------
>
> I wonder why GM changed the design?

Shared with other GM cars.


Found a parts book on gmpartswiki that listed 3885913:

66 - 69 Chevelle, Camaro
70 - 72 Chevelle, Nova
73 - 74 Nova

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Re: LM 2nd Design Front Spindle & Backing Plate Identification
Posted by: joelsplace ()
Date: October 30, 2020 09:38AM

Thanks for all the great info!
You know they changed it due to all the brake pin failures on the earlier design.

Joel
Northlake, TX
5 Ultravans, 113 Corvairs and counting...

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Re: LM 2nd Design Front Spindle & Backing Plate Identification
Posted by: jjohnsonjo ()
Date: October 30, 2020 10:09AM

Thanks Al, I already cleaned it up some more and painted the one you sent me. I went by the hex to shoulder length comparison, so that may no be valid. If its wrong it may be easier to make a spacer in my lathe. Mine is 03E Willow run. Hard to tell with this stuff. The YH jeting on is the later size. It also is a 65 with an EM turbo muffler and hanger from the factory. I don't know when or how many of these exist, but I know there are others. I once had a Chevy parts counter guy tell me I was nuts. Either way my shoulder is still too messed up to work on it.

J.O.

65 Corsa Turbo Vert
79 Honda XL 500S
69 Honda CL 160 D
2010 BMW F 650 GS
2003 Bounder 36D
2013 KIA Optima SX turbo-AKA ZIPPY (wife,s car)
69 Newport Holiday Sailboat
Baja 150 dune buggy cart
Coleman HS 500 UTV
2016 KIA Sorento SXL Turbo

Bethlehem,Pa


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