V belts sizes?

[Robert Holmes]

It looks like the original belts on my 68 were 3/8 wide. The current cross references give replacements as 7/16, but seem to be so short I can't get them over the pulleys.

Why the width change, and why don't the recommended sizes seem to fit?

Any reccommendations beyond trial and error?

Thanks,
Robert Holmes

[Duke W.]

Re: V belts sizes?

GM developed a nasty habit of consolodating service V-belts, and it was typical to service 3/8" OEM belts with 7/16" replacements and they were sometimes a bit longer. This cost me two lower radiator hoses on my Cosworth Vega as the longer 7/16" service belt for the alternator allowed the it to rub against the hose.

If you call GM Customer Service at 800-222-1020 and request a "Restoration Pakcage", it will include the AMA specifications for your car, which lists the actual dimensions for the OEM belts. You can then match them by size.

They'll want your VIN and there is no charge for the package.

Duke

[Duke W.]

Re: V belts sizes?

GM developed a nasty habit of consolodating service V-belts, and it was typical to service 3/8" OEM belts with 7/16" replacements and they were sometimes a bit longer. This cost me two lower radiator hoses on my Cosworth Vega as the longer 7/16" service belt for the alternator allowed the it to rub against the hose.

If you call GM Customer Service at 800-222-1020 and request a "Restoration Pakcage", it will include the AMA specifications for your car, which lists the actual dimensions for the OEM belts. You can then match them by size.

They'll want your VIN and there is no charge for the package.

Duke

[Joe L.]

Re: V belts sizes?

Robert------

Most original belts were of 3/8" width, although a few were of other "oddball" widths. In 1973, GM switched to 7/16" wide belts and these replaced the earlier width belts for GM SERVICE. Generally, the pullies did not change and GM used many of the same pullies in PRODUCTION with both the 3/8" and the 7/16" belts. However, the 7/16" wide belts ride higher in the pulley grooves than the 3/8" wide belts. So, a slightly longer belt may be needed when a 7/16" wide belt replaces a 3/8" wide belt for SERVICE. Belt length is critical in instances of a "captured" belt (e.g. the crank pulley-to-water pump pulley belt which has no adjustment). For other applications, the difference between the 3/8" and 7/16" belts can often be compensated in the available adjustment range of the pulley system. In any event, as a general rule, about a 1/2" greater length is required for a 7/16" belt which replaces a 3/8" belt.

You may be able to obtain 3/8" belts from aftermarket sources like Dayco, Gates, or Goodyear, although most of these have replaced the 3/8" belts with the 7/16", too. Reproduction belts of the original lengths and widths are DEFINITELY available. One thing to keep in mind, though: the original 3/8" belts were mostly of "wrapped" construction; the 7/16" belts are of "cut" construction. The "cut" construction produces a belt which is stronger and more durable than a "wrapped" type belt.

[Joe L.]

Re: V belts sizes?

Robert------

Most original belts were of 3/8" width, although a few were of other "oddball" widths. In 1973, GM switched to 7/16" wide belts and these replaced the earlier width belts for GM SERVICE. Generally, the pullies did not change and GM used many of the same pullies in PRODUCTION with both the 3/8" and the 7/16" belts. However, the 7/16" wide belts ride higher in the pulley grooves than the 3/8" wide belts. So, a slightly longer belt may be needed when a 7/16" wide belt replaces a 3/8" wide belt for SERVICE. Belt length is critical in instances of a "captured" belt (e.g. the crank pulley-to-water pump pulley belt which has no adjustment). For other applications, the difference between the 3/8" and 7/16" belts can often be compensated in the available adjustment range of the pulley system. In any event, as a general rule, about a 1/2" greater length is required for a 7/16" belt which replaces a 3/8" belt.

You may be able to obtain 3/8" belts from aftermarket sources like Dayco, Gates, or Goodyear, although most of these have replaced the 3/8" belts with the 7/16", too. Reproduction belts of the original lengths and widths are DEFINITELY available. One thing to keep in mind, though: the original 3/8" belts were mostly of "wrapped" construction; the 7/16" belts are of "cut" construction. The "cut" construction produces a belt which is stronger and more durable than a "wrapped" type belt.

[Wayne W.]

Re: V belts sizes?

I think that you will find that most aftermarket supliers are actually suppling metric belts and except in the restoration field 3/8 will be hard to find.

[Wayne W.]

Re: V belts sizes?

I think that you will find that most aftermarket supliers are actually suppling metric belts and except in the restoration field 3/8 will be hard to find.

[Duke W.]

Re: V belts sizes?

Modern belts are typically specified in metric sizes and the old 3/8" converts to 9.5 mm.

Duke

[Duke W.]

Re: V belts sizes?

Modern belts are typically specified in metric sizes and the old 3/8" converts to 9.5 mm.

Duke

[Robert Holmes]

Re: V belts sizes?

Thanks everyone for the info. I found that going one length above the "reccommended" 7/16 replacement size seems to fit well, solve the problem of getting the belt on, and isn't so long it can't be adjusted.

I don't think the cross references always allow enough extra length to get the thicker cross section belts over the sides of the pulleys during installation. Anyway, I finally have new quiet belts that fit!

Thanks,
Robert Holmes

[Robert Holmes]

Re: V belts sizes?

Thanks everyone for the info. I found that going one length above the "reccommended" 7/16 replacement size seems to fit well, solve the problem of getting the belt on, and isn't so long it can't be adjusted.

I don't think the cross references always allow enough extra length to get the thicker cross section belts over the sides of the pulleys during installation. Anyway, I finally have new quiet belts that fit!

Thanks,
Robert Holmes