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Old 12-18-2018, 05:07 PM
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1979 gmc k25 gvwr

I recently purchased a 1979 GMC K25 and I'm trying to figure out the GVWR. There were 3 options for that model and year, which were 6800, 7200, and 8400. IIRC the 6800 was only available with the standard rear brakes and mine has the HD 13 inch rear drums. It also has 7 rear leaves which leads me to believe it might be 8400 but I want to make sure. It also has 3.73 gearing and a 14 bolt full floating rear with a Dana 44 front. Any help is appreciated.

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Old 12-18-2018, 08:02 PM
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Quote:
Originally Posted by EragonSuperH View Post
I recently purchased a 1979 GMC K25 and I'm trying to figure out the GVWR. There were 3 options for that model and year, which were 6800, 7200, and 8400. IIRC the 6800 was only available with the standard rear brakes and mine has the HD 13 inch rear drums. It also has 7 rear leaves which leads me to believe it might be 8400 but I want to make sure. It also has 3.73 gearing and a 14 bolt full floating rear with a Dana 44 front. Any help is appreciated.

If you have vacuum breaks then you have the 6800 rating.

If you have the "HD power breaks"= Hydroboost. Then you have the 7500 or 8400 rating.

Due to your rear axle ratio I would go with the 7500 rating.

I believe the 8400 rating was only offered with 4.10 or 4.56 gearing and a few extra codes.



This is for 78 but is a good reference for you.

https://www.gmheritagecenter.com/doc...olet-Truck.pdf

Page 13 and 14 for GVWR.
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Old 12-18-2018, 08:07 PM
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Quote:
Originally Posted by cerial View Post
If you have vacuum breaks then you have the 6800 rating.



If you have the "HD power breaks"= Hydroboost. Then you have the 7500 or 8400 rating.



Due to your rear axle ratio I would go with the 7500 rating.



I believe the 8400 rating was only offered with 4.10 or 4.56 gearing and a few extra codes.







This is for 78 but is a good reference for you.



https://www.gmheritagecenter.com/doc...olet-Truck.pdf



Page 13 and 14 for GVWR.
I have that whole PDF for the 79 models. It has vacuum brakes, and 13 inch drums (15.5" outside diameter). Are you absolutely sure that the HD power brakes means hydroboost? 3.73 gearing was the standard gearing at all gvwr levels for all 4x4 3/4 tons with a 350, other ratios were optional. This is based on the PDF

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Old 12-19-2018, 03:23 AM
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I know in the 2wd models the hydroboost moves up the rating up then the ratio moves it up more. Rims also play a part as well as motor.

Am I 100%? No. This is one of those things that is vague and you will get various weights. Best to be safe.

The gvwr is not the gvcw. You can still tow a good smount.
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