Topic: Caliper guide pin thread size

[81Turbo TA]

I have an 81 and I'm trying to find the thread of the rear  caliper guide pin.  I think gm used a metric caliper so I'm unsure if the hardware was changed.
The reason, while installing the rear caliper, the lower guide pin hole in the mounting bracket is stripped and the bolt spins.  Since I can't find the bracket for sale I figured I'd have to helicoil it.   

[81Turbo TA]

I found that there is a guide pin with a slightly larger thread for fixing this exact problem.  I still have no clue what the thread size is though

[Wallington]

Part # 18004418. Sorry, no details.

[81Turbo TA]

Part # 18004418. Sorry, no details.

Thanks.  The part someone referred me to was from Dorman, 13897.   The funny thing was I emailed ac delco and another company asking for the thread size and neither gave me any info. I'd rather not screw in a larger size, I'd rather fix it so that it doesn't throw me or another owner off if a future repair is needed. "Why doesn't this new bolt fit?"  I can see it now. Lol.   I keep forgetting to take a guide pin to the hardware store and use their thread gauge.

[Wallington]

What you need is someone with a disc rear end to respond, there's plenty of them but they offer up nothing to others. I'll search some more manuals. I know some of those parts are Metric, not sure on that pin and doesn't say where it is mentioned. But if it was Metric, the oversized imperial Dorman wouldn't be suitable for a repair either. Maybe that's why it's stripped, people trying to make incorrect threads fit.

[Wallington]

The 1979 Service Manual has a list of Metric brake parts, there is no mention of the caliper pins. Not conclusive, just info. A lot of fittings are, booster mount, steering column mount, trans mount, etc.

[81Turbo TA]

Thanks for trying.
I most likely will go with using the dorman pin. The description says for stripped out holes..but I like options

[Angelo]

Reach out to one of the brake specialist companies. By me is Right Stuff but all of them, CPP, SSBC, Inline tube, etc... sell the 79-81 rear disc brake conversion kits for non disc brake 70-81 cars, they also use the Cadillac Eldorado/Seville rear calipers for rear axles that do not require the staggered shocks.  When looking make sure you get the ones for "staggered shocks". Though it will be a pain to take the rear diff cover off and pull the axle to replace the bracket, it would be better to get new bracket than to mess with a new thread size in my opinion. Right Stuff has helped me a few times on some oddball custom made lines and such, I suspect if you ask for a specific side of the staggered brackets I bet they sell it to you. The next best option I just found is a bracket kit from Inline Tube: https://www.ebay.com/itm/201541813332 .

Before you buy anything reach out to Scarebird he may sell just the brackets. I got a set of the parking brake lever brackets for my 81 rear disc calipers, they are out of this world high quality strong steel and plated, highly suggest replacing them while you are in there: https://scarebird.com/index.php?route=product/product&product_id=95 If Scarebird makes them they will be top shelf quality, you will most likely be able to just buy the bracket you need without a full kit.

[81Turbo TA]

The axle has to come out if I want to change  that piece??

    

[Angelo]

I think so. There may be a way to unbolt the factory bracket then cut it in 2 spots to slide it out. The factory bracket has a ring that goes all the way around unlike the aftermarket brackets. The replacement only use 3 bolts but do not hold me to that until you get the directions for the bracket you get. Others may be able to chime in who have swapped in the aftermarket rear brackets with how they made the change leaving or removing the rear axle shaft.

Taking the diff cover off, removing the center pin and c-clip then sliding the axle shaft out is not too difficult. If you haven't changed the diff oil in a few years then you would knock off 2 birds with one stone sort of speak.

[81Turbo TA]

It's been a while since I last tackled this  brake problem I have but I figured I'd give an update, it helps me remember also.

Trying to fix the right rear lower caliper guide pin hole, I ordered the dorman pin that is oversized and designed to cut new threads. That didn't work well. It went in and started spinning. As I took a look I noticed that the threaded hole in the caliper bracket is now an oval shape, it seems the top one is almost the same.  I'm not sure if rust caused this or a previous owner did.
As far as thread sizes go, im still a bit confused. The new oversized dorman  package says it is 7/16-20.  I can not thread a 7/16-20 die on that pin at all.
Using a die on the normal ac delco pin ,18k92, I can nicely fit a 1/2-13.  This does not make sense to me.  So I believe the pin is a metric thread. 
My next course of action is to remove the axle  then the caliper bracket and take it to a welder to weld plug the holes and start over. Hopefully he lines them up right.   The caliper brackets used are very, very expensive.