The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - Need 1972 C30 rear brake shoe and seal data

71Dually · 04-28-2014, 07:58 AM

Thank you for the information on your truck. That will help. A stock or modified system will determine the manner to use to determine your brake size.

Stock methods. Check your SPID and ID tag on the driver door sill post. Check the Bendix number stamped on the backing plates. Are your wheels original? If they are original, what size tires / wheels are they? The answers to these questions will help determine your brake size.

I have an unmolested, 10,000 lb. as manufactured GVW rated, model CE31403 truck. As previously stated in post #3 it's a 1971, 157" WB, C30 cab chassis with a factory DRW HO72 with 13" X 2-1/2" rear brakes. The motorhome picture in post #8 of this thread is indeed my truck. The motorhome has since been removed and a flat bed has been installed.

I know all the above information because of the information on my door sill data tag and SPID. My truck has a 10,000 lb. GVW (as manufactured) stamped on the door sill tag and RPO codes F60 Heavy Front Springs, R05 DR Wheel Conversion and S76 16X550 F Wheel along with the model # and wheel base on the SPID. In comparison an HO110 axle would have an 11,000 lb. or 14,000 lb. GVW (as manufactured) stamped on the door sill tag. The SPID would have an RPO code of H22 in place of both F60 Front Springs and R05 DRW codes and would list one of the following RPO wheel codes of R90, R97, R98 or R99 in place of the S76 code for the 16" wheels.

A pic of my door sill tag:

The "*Maximum Capability" seen on the tag above does not necessarily reflect how a truck is actually equipped. Instead it is the capability obtainable with optional equipment specified in the owners manual. Per my owners manual for my truck to achieve it's maximum GVW capability it would need the RPO H22 axle (an HO110) and 19.5" 10 lug wheels / tires (RPO R97, R98 or R99) to attain this maximum 14,000 lb. GVW rating. With the HO110 axle and 18" 10 lug wheels / tires (RPO R90) the truck would have an 11,000 lb. GVW rating. Since my truck has a 10,000 lb. GVW (as manufactured) rating on the door sill tag according to the factory literature it is equipped with the HO72 and 16" 8 lug wheels from the factory. My trucks SPID coincides with this factory literature.

From the factory an unmodified HO72 axle will have 13" X 2-1/2" brakes, 8 wheel studs and 16" or 16.5" wheels and tires. The numbers stamped on my factory 13" X 2-1/2" backing plates are "Bendix 324636-L" & "Bendix 324636-R."

Pics of the number stamped on an original 13" X 2-1/2" HO72 backing plate. The backing plate was pulled by me from an original 71-72 axle and the arrow shows where the number is stamped:

Closer detail of the number on the same 13" X 2.5" HO72 backing plate pictured above. The number is actually stamped upside down when the backing plate is installed on the truck. Note the position of the star wheel brake adjuster hole in the two pics:

Since I do not have an HO110 axle I can only speculate what it has from the information available to me. This available information is the Master Parts Catalogue available on GMpartswiki, the factory truck specification literature from the GM Heritage Center (Link Here), Google search and the internet. According to this information in stock configuration the HO110 axle should have 15" X 4" brakes, 10 wheel studs and 18" or 19.5" wheels and tires. I do not know the number stamped on the backing plates.

All of the items on my door sill tag, SPID and the actual parts installed on my truck point to my truck and rear axle being unmolested. I know the history of my truck back to the early 80's. I have the two PO's documentation and receipts to support that history. The truck had 38,615 miles on the odometer when I purchased it last October. According to the documentation in my possession the truck had just under 1,000 miles logged on the odometer in the 11 years prior to my purchase. The overall condition of all the factory high wear items in the interior of the truck indicate the odometer has not turned over. This indicates it is a genuinely low mileage vehicle and very likely unmodified.

The only owner modification I'm aware of in the rear axle area of my truck was a rear leaf spring upgrade with the addition of 4 additional leafs per side in 1984. I have the receipt for the parts and the truck has evidence of this alteration in place with the added springs and a modified factory spacer block. The modification basically consists of doubling up the four inner springs and a cut and weld job to shorten the spacer block. There are modifications on other areas of the truck but these were mostly done by the original motorhome manufacturer and do not effect the rear axle.

If the RPO codes F60, R05 and S76 on my truck's SPID and the 10,000 lb. GVW on the door sill tag pictured above match the information on your trucks tags then I would say it is very likely you have an HO72 and 13" X 2-1/2" brakes if everything on your motorhome is intact as it came from the factory.

A modified truck is a whole different animal. If it is modified then other steps to identify the modification is in order. The following will also help in the event that your SPID and/or door sill data tag information is not available.

You don't need to pull the hub / drum to find out your brake size (but without question that is the most accurate method). Some things will point you to your brake size.

Pull the rear wheel. The drum should have a maximum diameter specification cast into it. What is this specification? My 13" X 2-1/2" HO72 brake brake drums say "Max Dia 13.09 In."

Measure everything with a tape measure, approximate measurements should suffice as there is a 2" difference between the two diameters. Measure the drum, if it's a 15" drum it will measure about 16" on the diameter of the exterior drum surfaces which coincides with the inner shoe contact area. A 13" drum will measure about 14". Measure the backing plates best you can. With 13" brakes the backing plates should measure about 14" on the diameter. The 15" brakes should measure about 16". Measure the width of the shoes contact area on the drum. This can be approximated on the outside. There will definitely be a big difference between 2-1/2" and 4" wide brakes. If your measurement is 3" to 3-1/2" then it won't accept a 4" wide shoe.

You really don't need a tape, eyeball the distance between the drum and the wheels. With 16" wheels the distance will be just under an inch for 13" brakes. 16" wheels will not fit on 15" X 4" brake drums. The distance of the 18" or 19.5" wheels should be about 1" to 2" I figure depending on the wheel. But the 15" brakes have 10 lug nuts and thats an easy check too.

As you can see from the picture in post #3 the Eaton HO72 axles will accept the later model 14 Bolt full float hub axle (14BFF) brakes. The stock Eaton drum is different from the 14BFF drums. The Eaton drums are smooth, the 14BFF drums have cooling fins to dissipate heat.

Here is a pic of the two different drums, the Eaton 13" X 2-1/2" drum is on the top and a 13" X 3-1/2" 14BFF drum is on the bottom.

I've located pictures of an HO110 axle and it has 10 wheel studs. It does have obvious differences from an HO72. Heres a link to those pictures: http://www.pirate4x4.com/forum/chevy...10-thread.html

Do you have a picture of your SPID and the door post tag? Do you have pictures of your rear end? Do you have pictures of your brake drums? Is it possible to post pictures of these items? That will help identify what you have. Without pictures its a little difficult to identify the rear end and brakes. Kind of like watching a silent movie with a blindfold on.

If pictures are unavailable then posting the SPID's RPO codes, the data tags GVW's and the stamped backing plate numbers are likely necessary to get closer to an ID of your brakes thru this topic. It's still best to post pics so we can see what you have to assist in identifying it and it's brake size.

A measuring tape will definitely tell the tale of the brake size. The measuring tape will also verify the information on the data tag and SPID.

This post contains a lot of details, information and methodology. I do hope it is not to convoluted or difficult to understand.

Hopefully this all helps, please keep us posted.

04-28-2014, 07:58 AM	#13
71Dually Registered User Join Date: Oct 2013 Location: San Fernando Valley, CA Posts: 84	Re: Need 1972 C30 rear brake shoe and seal data Thank you for the information on your truck. That will help. A stock or modified system will determine the manner to use to determine your brake size. Stock methods. Check your SPID and ID tag on the driver door sill post. Check the Bendix number stamped on the backing plates. Are your wheels original? If they are original, what size tires / wheels are they? The answers to these questions will help determine your brake size. I have an unmolested, 10,000 lb. as manufactured GVW rated, model CE31403 truck. As previously stated in post #3 it's a 1971, 157" WB, C30 cab chassis with a factory DRW HO72 with 13" X 2-1/2" rear brakes. The motorhome picture in post #8 of this thread is indeed my truck. The motorhome has since been removed and a flat bed has been installed. I know all the above information because of the information on my door sill data tag and SPID. My truck has a 10,000 lb. GVW (as manufactured) stamped on the door sill tag and RPO codes F60 Heavy Front Springs, R05 DR Wheel Conversion and S76 16X550 F Wheel along with the model # and wheel base on the SPID. In comparison an HO110 axle would have an 11,000 lb. or 14,000 lb. GVW (as manufactured) stamped on the door sill tag. The SPID would have an RPO code of H22 in place of both F60 Front Springs and R05 DRW codes and would list one of the following RPO wheel codes of R90, R97, R98 or R99 in place of the S76 code for the 16" wheels. A pic of my door sill tag: The "Maximum Capability" seen on the tag above does not necessarily reflect how a truck is actually equipped. Instead it is the capability obtainable with optional equipment specified in the owners manual. Per my owners manual for my truck to achieve it's maximum GVW capability it would need the RPO H22 axle (an HO110) and 19.5" 10 lug wheels / tires (RPO R97, R98 or R99) to attain this maximum 14,000 lb. GVW rating. With the HO110 axle and 18" 10 lug wheels / tires (RPO R90) the truck would have an 11,000 lb. GVW rating. Since my truck has a 10,000 lb. GVW (as manufactured) rating on the door sill tag according to the factory literature it is equipped with the HO72 and 16" 8 lug wheels from the factory. My trucks SPID coincides with this factory literature. From the factory an unmodified HO72 axle will have 13" X 2-1/2" brakes, 8 wheel studs and 16" or 16.5" wheels and tires. The numbers stamped on my factory 13" X 2-1/2" backing plates are "Bendix 324636-L" & "Bendix 324636-R." Pics of the number stamped on an original 13" X 2-1/2" HO72 backing plate. The backing plate was pulled by me from an original 71-72 axle and the arrow shows where the number is stamped:* Closer detail of the number on the same 13" X 2.5" HO72 backing plate pictured above. The number is actually stamped upside down when the backing plate is installed on the truck. Note the position of the star wheel brake adjuster hole in the two pics: Since I do not have an HO110 axle I can only speculate what it has from the information available to me. This available information is the Master Parts Catalogue available on GMpartswiki, the factory truck specification literature from the GM Heritage Center (Link Here), Google search and the internet. According to this information in stock configuration the HO110 axle should have 15" X 4" brakes, 10 wheel studs and 18" or 19.5" wheels and tires. I do not know the number stamped on the backing plates. All of the items on my door sill tag, SPID and the actual parts installed on my truck point to my truck and rear axle being unmolested. I know the history of my truck back to the early 80's. I have the two PO's documentation and receipts to support that history. The truck had 38,615 miles on the odometer when I purchased it last October. According to the documentation in my possession the truck had just under 1,000 miles logged on the odometer in the 11 years prior to my purchase. The overall condition of all the factory high wear items in the interior of the truck indicate the odometer has not turned over. This indicates it is a genuinely low mileage vehicle and very likely unmodified. The only owner modification I'm aware of in the rear axle area of my truck was a rear leaf spring upgrade with the addition of 4 additional leafs per side in 1984. I have the receipt for the parts and the truck has evidence of this alteration in place with the added springs and a modified factory spacer block. The modification basically consists of doubling up the four inner springs and a cut and weld job to shorten the spacer block. There are modifications on other areas of the truck but these were mostly done by the original motorhome manufacturer and do not effect the rear axle. If the RPO codes F60, R05 and S76 on my truck's SPID and the 10,000 lb. GVW on the door sill tag pictured above match the information on your trucks tags then I would say it is very likely you have an HO72 and 13" X 2-1/2" brakes if everything on your motorhome is intact as it came from the factory. A modified truck is a whole different animal. If it is modified then other steps to identify the modification is in order. The following will also help in the event that your SPID and/or door sill data tag information is not available. You don't need to pull the hub / drum to find out your brake size (but without question that is the most accurate method). Some things will point you to your brake size. Pull the rear wheel. The drum should have a maximum diameter specification cast into it. What is this specification? My 13" X 2-1/2" HO72 brake brake drums say "Max Dia 13.09 In." Measure everything with a tape measure, approximate measurements should suffice as there is a 2" difference between the two diameters. Measure the drum, if it's a 15" drum it will measure about 16" on the diameter of the exterior drum surfaces which coincides with the inner shoe contact area. A 13" drum will measure about 14". Measure the backing plates best you can. With 13" brakes the backing plates should measure about 14" on the diameter. The 15" brakes should measure about 16". Measure the width of the shoes contact area on the drum. This can be approximated on the outside. There will definitely be a big difference between 2-1/2" and 4" wide brakes. If your measurement is 3" to 3-1/2" then it won't accept a 4" wide shoe. You really don't need a tape, eyeball the distance between the drum and the wheels. With 16" wheels the distance will be just under an inch for 13" brakes. 16" wheels will not fit on 15" X 4" brake drums. The distance of the 18" or 19.5" wheels should be about 1" to 2" I figure depending on the wheel. But the 15" brakes have 10 lug nuts and thats an easy check too. As you can see from the picture in post #3 the Eaton HO72 axles will accept the later model 14 Bolt full float hub axle (14BFF) brakes. The stock Eaton drum is different from the 14BFF drums. The Eaton drums are smooth, the 14BFF drums have cooling fins to dissipate heat. Here is a pic of the two different drums, the Eaton 13" X 2-1/2" drum is on the top and a 13" X 3-1/2" 14BFF drum is on the bottom. I've located pictures of an HO110 axle and it has 10 wheel studs. It does have obvious differences from an HO72. Heres a link to those pictures: http://www.pirate4x4.com/forum/chevy...10-thread.html Do you have a picture of your SPID and the door post tag? Do you have pictures of your rear end? Do you have pictures of your brake drums? Is it possible to post pictures of these items? That will help identify what you have. Without pictures its a little difficult to identify the rear end and brakes. Kind of like watching a silent movie with a blindfold on. If pictures are unavailable then posting the SPID's RPO codes, the data tags GVW's and the stamped backing plate numbers are likely necessary to get closer to an ID of your brakes thru this topic. It's still best to post pics so we can see what you have to assist in identifying it and it's brake size. A measuring tape will definitely tell the tale of the brake size. The measuring tape will also verify the information on the data tag and SPID. This post contains a lot of details, information and methodology. I do hope it is not to convoluted or difficult to understand. Hopefully this all helps, please keep us posted. __________________ 1971 Chevy C30 Custom Camper Cab Chassis Dually 402 TH400 4.10:1 Eaton HO72 1969 Ford Mustang "Mach 1" 428CJ 4 speed "R Code" 1970 Mercury Cougar "Eliminator" 351C-4V C6 1972 Ford Ranchero GT 351C-2V C6 1974 Honda XL-350 Member of the "6 C's and a D" 1-Ton Fun Club!