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So the high side pressure hose on my '98 1500 Express 143,000 miles finally decided to spring a leak. Well it had been leaking for awhile, just got worse all of a sudden.


So I get a new hose and before installing it decided to see what line wrenches the fittings take. The small fitting that goes into the steering box (or rack?) was 5/8". Flip the wrench around to 11/16" and it won't fit the larger nut.


I get out my digital caliper and measure both nuts. The small nut comes to 15.9 mm, the bigger nut comes to 17.9 mm.


I thought perhaps it was just the new hose but the fittings on the factory hose are also 16 and 18mm.




I look through my toolbox and I have no 16/18 mm line wrenches. I go down to the autopart stores and they have none. Of course they had nothing as well. Do they even make a 16/18mm line wrench?


I go through both sets of my metric wrenches and I don't even have an 18mm wrench ! However I did have an 18mm stubby. I couldn't get enough torque on it so I placed an old jack handle I use as a cheater bar on the closed end and smacked it with a hammer to break it loose. I didn't care if I rounded it off or not.


So i resorted to using the 5/8" line wrench at the rack or steering box and the 18mm stubby on the larger nut going into the bottom of the pump.


My last resort was to use an adjustable wrench but luckily it didn't come to that.


My question is has anyone ever ran into this before? Why would GM use an 18mm fitting when an ordinary 18mm wrench is not even that common.




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  • 4 years later...

They did it so you would take it to them so they can charge you an arm and a leg to replace it. Harbor freight has a set of crows foot wrenches which they call flare nut 16mm and 18mm sizes you need for $35.00. You can pay for the wrenches by buying the hose from parts geek for $18.00 vs. Oreilly $69.00. Would be surprised if dealer would it for less than $500.00. You know you have to pay for their rags.

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gearwrench has a complete flair nut wrench set , used to have a sale , buy metric set and get sae set,  6  wrenches in each  set , it was about 70.00 for both sets

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