85 GMC 2500 brakes question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

treetop_73 · 09-30-2011, 01:17 AM

Can someone help? Does my truck have 11" or 13" brakes? Depending on what I read, it says it can have either. Short of taken off the wheels, how can I tell?

TIA!

LONGHAIR · 09-30-2011, 05:54 AM

Crawl under it with a tape measure. It should be easy enough to tell. You may not be able to get an exact measurement, but telling the difference between 11 and 13 shouldn't be a problem.

As a "guess", I would say that it is probably tied to which rear end you have. The light duty semi floating axle would likely have the smaller brakes....but I wouldn't bet on it.
Do you have the trailer towing package? or any other options that would indicate heavy duty?

donut · 09-30-2011, 06:00 AM

Grab a tape measure and crawl under the truck. You can measure from the backside, (iirc you're looking for drum id).
Or pick up both sets and return the one not used.

Edit, need to hit "submit post" before I refill coffee...

treetop_73 · 09-30-2011, 06:37 PM

I'll crawl under. Thanks. I can't buy both sets as I never return the items. I have enough parts for things I don't have a use for. Trying to minimize that now.

It has the tow package, and seems to be a true HD from what I can tell. PO didn't do much before I got it.

Your41Plague12 · 10-02-2011, 04:44 PM

I'm betting you have the 13" brakes. My 83 did, and it has the 14 bolt semi-floating rear axle. If you have a serious stack of springs, you probably got the 8600 GVW model. I want to say mine has 8 leaf springs plus an overload. I could be wrong on the number of springs though, the truck is 140 miles from me.

clinebarger · 10-02-2011, 08:04 PM

A REAL 3/4 ton with 8 lug axles will have 13" drums doesnt matter if it has a 9.5" semi floater or a 10.5 full floater rear end.

WarBeard · 10-02-2011, 08:37 PM

STOLEN FROM WIKI!!!!

Design

The first design was produced from 1973 to 1985. The first design remained unchanged until 1986. This design had drums that were held on by the wheel studs and had a smaller diameter pinion bearing than the second design. The second design was produced from 1986 to present. One change that occurred in the second design was that on some models the brake drum could be removed without having to remove the hub and axle shaft. Additionally, the pinion received a larger diameter bearing while the pinion stayed the same diameter, which increased the durability of the pinion. All these axle are full floating.
[edit] Brakes

All of the 14 bolt differentials typically have drum brakes except for the newest models which have disc brakes. The first design of this differential had three different diameter brake drums. At first the differential was released with drums small enough to fit 15” wheels. Then after a few years a larger drum was standard on the ¾ ton along with the even larger drum on the 1 ton. This is an area of the axle assembly that is commonly converted by the enthusiast to disc brakes for added braking performance and lower cost of maintenance.[1]

treetop_73 · 10-03-2011, 10:35 AM

Thanks guys. I have 13

09-30-2011, 01:17 AM	#1
treetop_73 Registered User Join Date: Feb 2010 Location: Victorville, CA Posts: 98	85 GMC 2500 brakes question Can someone help? Does my truck have 11" or 13" brakes? Depending on what I read, it says it can have either. Short of taken off the wheels, how can I tell? TIA! __________________ '85 GMC High Sierra 2500

09-30-2011, 06:00 AM	#3
donut Registered User Join Date: Aug 2009 Location: S.C. Posts: 1,593	Re: 85 GMC 2500 brakes question Grab a tape measure and crawl under the truck. You can measure from the backside, (iirc you're looking for drum id). Or pick up both sets and return the one not used. Edit, need to hit "submit post" before I refill coffee... __________________ '86 C-30 dually, 454/tbh400 '73 K-20 350/350/205 (sold ) I'm kinda like duct tape- no real purpose, but handy to have around. Last edited by donut; 09-30-2011 at 06:02 AM. Reason: too slow

09-30-2011, 06:37 PM	#4
treetop_73 Registered User Join Date: Feb 2010 Location: Victorville, CA Posts: 98	Re: 85 GMC 2500 brakes question I'll crawl under. Thanks. I can't buy both sets as I never return the items. I have enough parts for things I don't have a use for. Trying to minimize that now. It has the tow package, and seems to be a true HD from what I can tell. PO didn't do much before I got it. __________________ '85 GMC High Sierra 2500

10-02-2011, 04:44 PM	#5
Your41Plague12 Registered User Join Date: Dec 2010 Location: Pittsburgh, PA Posts: 1,009	Re: 85 GMC 2500 brakes question I'm betting you have the 13" brakes. My 83 did, and it has the 14 bolt semi-floating rear axle. If you have a serious stack of springs, you probably got the 8600 GVW model. I want to say mine has 8 leaf springs plus an overload. I could be wrong on the number of springs though, the truck is 140 miles from me. __________________ Steve Member of the Foot Pedal Club '83 Chevy K20: 6" Rough Country, 3" Performance Accessories BL, Bushwacker Cutouts, 38x15.50 Mickey Thompson Baja Claws, 350 HP 350 crate engine from Jegs, Turbo 400

10-02-2011, 08:04 PM	#6
clinebarger Senior Member Join Date: May 2009 Location: Fort Worth, TX Posts: 6,370	Re: 85 GMC 2500 brakes question A REAL 3/4 ton with 8 lug axles will have 13" drums doesnt matter if it has a 9.5" semi floater or a 10.5 full floater rear end.

10-02-2011, 08:37 PM	#7
WarBeard Registered User Join Date: Jul 2008 Location: Show low,az Posts: 808	Re: 85 GMC 2500 brakes question STOLEN FROM WIKI!!!! Design The first design was produced from 1973 to 1985. The first design remained unchanged until 1986. This design had drums that were held on by the wheel studs and had a smaller diameter pinion bearing than the second design. The second design was produced from 1986 to present. One change that occurred in the second design was that on some models the brake drum could be removed without having to remove the hub and axle shaft. Additionally, the pinion received a larger diameter bearing while the pinion stayed the same diameter, which increased the durability of the pinion. All these axle are full floating. [edit] Brakes All of the 14 bolt differentials typically have drum brakes except for the newest models which have disc brakes. The first design of this differential had three different diameter brake drums. At first the differential was released with drums small enough to fit 15” wheels. Then after a few years a larger drum was standard on the ¾ ton along with the even larger drum on the 1 ton. This is an area of the axle assembly that is commonly converted by the enthusiast to disc brakes for added braking performance and lower cost of maintenance.[1] __________________ 1978 C10 Silverado Big 10 350/350.. play toy 1990 V1500 Suburban 350/700r4..Daily driver 1987 K10 Silverado 383/400.. Wife's rig WRECKED! 1989 V2500 Suburban 350/400.. SOLD! 1974 C10 Custom10 LWB 350/350.. SOLD! 1974 C10 Custom10 SWB 350/400.. SOLD! 1999 Silverado Z71 LS1.. Wife's rig WRECKED! On the hunt for a new project....... I'm a Chevy guy.....I'm just not a "NEW" Chevy guy.

10-03-2011, 10:35 AM	#8
treetop_73 Registered User Join Date: Feb 2010 Location: Victorville, CA Posts: 98	Re: 85 GMC 2500 brakes question Thanks guys. I have 13 __________________ '85 GMC High Sierra 2500



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