Seat belt attachment bolt size

The P.O. of my car had removed the two rear seat belt buckles that bolt under the rear seat cushion and the attaching nuts are nowhere to be found. Does anyone know what size those nuts are?
Thanks

Nuts are (supposed to be) welded into the floor pan. GM does not have much variation on parts such as this, suggest you ask a dealer parts counter *or* consider just going to a pick & pull and pull bolts from a different G body that isn't wrecked, like an Aurora, Bonneville, Lucerne, Park Ave.

Yeah I figured I would have to end up doing that.
Thanks

Cliff96 wrote:

Yeah I figured I would have to end up doing that.
Thanks

It's far from a disaster.  You're right to reinstall the buckles and righteous bolts to hold them. In many if not most 2 door coupes, including Riviera, the back seats don't even get used much, thus there shouldn't be a concern with re-using good OE bolts.  Use your judgment.

I think your only headache will be the nuts welded into the floor pan.  Check them from underneath the car.  If you have a wire battery terminal brush, clean the nuts out/off if they need it before you install the replacement bolts, and consider spraying undercoating on the underside after you install the belts to slow down/stop any corrosion.  They don't get hit by road splash but if you drive at freeway speeds on salty slushy highways the salt fog will get to them.

Albertj

Yeah, I don't know why they were removed in the first place. I know they may not get used but I like to keep everything in place and working on a car if I can.

Some people have a 'thing' about the rear seat belts. For instance, they may rattle - although that is fixable, some would just as soon dispense with the buckles. Some remove them and the rear seat for autocrossing or other rallye purposes (although, the Riv as a rallye car is a bit tough on the imagination).

Upon further inspection I see what was done. When the P.O. installed a boom boom stereo system he removed the back seat and he took off the buckle sections of the belt and tossed the nuts. He also cut off the left side shoulder belt at the floor attachment and at the upper portion where it comes out of the reel. He didn't cut the other side though. The buckle sections are secured by nuts to the studs that stick up. The shoulder belts are secured to the floor by torx bolts. I'm gradually fixing things that the P.O. destroyed. Good news is there's no rust and the engine and transmission are sound. I'm am going to have to replace the coupler in the supercharger though, it's noisy at idle

Cliff96 wrote:

Upon further inspection I see what was done. When the P.O. installed a boom boom stereo system he removed the back seat and he took off the buckle sections of the belt and tossed the nuts. He also cut off the left side shoulder belt at the floor attachment and at the upper portion where it comes  out of the reel. He didn't cut the other side though. The buckle sections are secured by nuts  to the studs that stick up. The shoulder belts are secured to the floor by  torx bolts. I'm gradually fixing things that the P.O. destroyed. Good news is there's no rust and the engine and transmission are sound. I'm am going to have to replace the coupler in the supercharger though, it's noisy at idle

Replacement seat belts are not that bad... RockAuto has the fronts, they are listed under "Air Bag Switch" (go figure). The rears are pretty easy, inertia reel jobs, see the link:

https://www.wescoperformance.com/3-point-seat-belt-enb-retr.html

If the buckles fit (they probably do) then in the rear you can use the old floor straps and just replace the inertial reel and anchor.

Also, good used/refurb seat belts from another GM G-body same vintage may be available.

It'll work out.

Yeah I'm going to try and pull one from a salvage car

https://www.ebay.com/itm/Buick-GM-OEM-97-99-Riviera-Rear-Seat-Belt-Rear-Belt-Assembly-12534940/164326281330

Ones for the 96 can not be far away...

https://www.ebay.com/itm/OE-GM-12530956-Rear-Seat-Belt-Retractor-Side-For-95-96-Riviera-Apps-RED/333526929204

Thanks. Not a bad price on the second one.

Do you happen to know if a 1998 Buick Lesabre rear shoulder belt will work in the Riviera? The LKQ I go to has one with the correct color interior.

Cliff96 wrote:

Do you happen to know if a 1998 Buick Lesabre rear shoulder belt will work in the Riviera? The LKQ I go to has one with the correct color interior.

I do not know.

The LKQ will have access to a Hollander cross-reference guide that will tell you, though. However, they may fit but not cross-reference if for instance the difference was the buckles.  In that case the set might fit if you transferred both buckles and belts all.  

The insight is that for mandatory stuff like seat belts, other than decoration any variation in style does not actually buy you much.  For GM in general there were a couple styles of seat belt webbing - one for the corvette and one for everything else.   Buckles varied some years but not all.  Length appeared to vary depending largely on attachment points. So I'd really expect interchangeability between Aurora/Park Avenue/Seville/Riviera. Maybe but not necessarily LeSabre, because it's a cousin of the Olds 88/Regency/LSS/Bonneville for 1992 - 1999 pretty much.

You can also get an idea by browsing the eBay listings.