Larger Wheel Cylinder than stock?

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   Okay, this may be a very dumb question.

So, here's my situation.  My Gremlin has 4-wheel, 9-inch non-powered drum brakes.  I have only been able to source rear wheel cylinders for Front-Disc cars. Now, according to my TSM, my car's rear WC's should have a 13/16" bore, whereas the Disc Brake model's WC's should have 7/8" bore.

Now, that's a difference of a 1/16th of an inch.  Can I use the ever-so-slightly-larger wheel cylinders on my car without any detrimental effects on braking?

Logic would say that the smaller bore (as in OEM standard size of 13/16") would give me more hydraulic pressure, thus more "oomph" against the shoes, but I'm not sure.

I look forward to seeing where this goes.

Thanks,
Peter

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ArdsleyTank Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: May/05/2017 Location: Dickson, TN Status: Offline Points: 95	Post Options Post Reply Quote ArdsleyTank Report Post Thanks(0) Quote Reply Topic: Larger Wheel Cylinder than stock? Posted: Feb/15/2019 at 9:00am
	Okay, this may be a very dumb question. So, here's my situation. My Gremlin has 4-wheel, 9-inch non-powered drum brakes. I have only been able to source rear wheel cylinders for Front-Disc cars. Now, according to my TSM, my car's rear WC's should have a 13/16" bore, whereas the Disc Brake model's WC's should have 7/8" bore. Now, that's a difference of a 1/16th of an inch. Can I use the ever-so-slightly-larger wheel cylinders on my car without any detrimental effects on braking? Logic would say that the smaller bore (as in OEM standard size of 13/16") would give me more hydraulic pressure, thus more "oomph" against the shoes, but I'm not sure. I look forward to seeing where this goes. Thanks, Peter
	1973 Gremlin Factory V8 Base--Trans-Am Red with Gold Pinstripes--304 2BBL Bone Stock

73Gremlin401 Members Profile Send Private Message Find Members Posts Add to Buddy List Supporter of TheAMCForum Joined: Mar/02/2013 Location: Stmbt Sprgs CO Status: Offline Points: 946	Post Options Post Reply Quote 73Gremlin401 Report Post Thanks(0) Quote Reply Posted: Feb/15/2019 at 10:18am
	AMC managed the majority of the brake proportioning with wheel cylinder volume, rather than proportioning valves, which is really clever, and in the AMC tradition, cheap. If you go to the 7/8" wheel cylinders in the rear, and keep the fronts as they are now, you will be able to lock up the rears quicker, which is not a good thing on any car, and a really, really not good thing on a Gremlin. The other thing that will happen is the drum brake master cylinder, which has roughly equal sized reservoirs on both sides, will cause a minor volume imbalance, which so long as you keep the MC full, won't be an issue, but if you don't keep an eye on it, will cause problems eventually.
	73 Gremlin 401/5-spd. 77 Matador Wagon 360/727. 81 Jeep J10 LWB 360/4-spd 83 Concord DL 4-dr 258/auto

ramblinrev Members Profile Send Private Message Find Members Posts Add to Buddy List Moderator Group Joined: Dec/28/2008 Location: Wisconsin Status: Offline Points: 11537	Post Options Post Reply Quote ramblinrev Report Post Thanks(0) Quote Reply Posted: Feb/15/2019 at 10:27am
	There should be no trouble finding the correct rear wheel cylinders for your drum brake Gremlin. RockAuto lists several...$5! Read the fine print and you should be fine. They are sized the way they are for a reason. I wouldn't mess with the size.
	74 Hornet Hatchback X twins (since 1977) 62 American Convertible (still worth the $50 I spent in 1973!) AMCRC #513, AMO #384 70 AMX 360 4-speed (since 1981)

ArdsleyTank Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: May/05/2017 Location: Dickson, TN Status: Offline Points: 95	Post Options Post Reply Quote ArdsleyTank Report Post Thanks(0) Quote Reply Posted: Feb/15/2019 at 10:44am
	Okaysies, Right after I posted this question I went to RockAuto's website, as I've been ordering from them lately. Sure enough, I could get a pair of CORRECT wheel cylinders for my car shipped and with tax for around $18. Compare that to the $12 a piece for the wrong ones at Oreilly's. So needless to say, I bought them. Also, for those contemplating this "mod" like I was, it appears that the larger cylinders do not have the correct brake line orientation for this to be a bolt in solution, also, as others have mentioned it probably isn't a good idea to do this anyway. So yeah, that answers my question. The correct ones are on the way, and I'll be returning the ones I bought at Oreilly's. I appreciate it guys, you're the best. Thanks again, Peter
	1973 Gremlin Factory V8 Base--Trans-Am Red with Gold Pinstripes--304 2BBL Bone Stock