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Master cylinder kits problems


MarcDeSoto

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I'm working on my 48 DeSoto's brakes and I ordered this master cylinder kit:   http://www.ebay.com/itm/Brake-Master-Cylinder-Repair-Kit-Professional-Grade-Raybestos-MK143/252631329239?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

I thought the plunger in this kit looked a little wide, but I thought that is just the photography.  When I got the kit today, I check to see if the plunger would go in my master cylinder and it was about 1/8" too wide!  So I called my local NAPA store and they said they had the kit in stock, so I went there with my old plunger to compare.  The NAPA kit looked identical to the Ebay kit in that the plunger was too wide.  I have a repair kit I bought in the 80s, but decided not to use it due to the O ring on the plunger had some age cracks.  Has anyone ordered a master cylinder kit lately and did yours fit?  Thanks.  Marc.

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My cylinder has a 1" bore.  I checked the DeSoto Parts List and they don't say what the bore is.  The kit sellers don't say what the bore is on their kits.  I think my master cylinder is original.  Are you saying the original master cylinders for these cars were 1 1/8" bore?  Also how do you remove the plunger from the cylinder.  There is nothing a grab hold of.  I could unscrew the back end of the cylinder and push it out, if that is the way you do it. 

Edited by MarcDeSoto
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thanks for that info!  So you just taught me something.  I have a 1950-55 master cylinder!  So I should buy a 1950 master cylinder kit.  I have a 1946 Motor Manual that goes back to 1935.  According to my book, the 1941 models also had a 1 1/8" bore.  I wonder if I should buy a new master cylinder with a 1 1/8" bore, or maybe it doesn't matter? 

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My '41 Dodge had a 1-1/8" bore MC when I first started driving it. I swapped it with a 1" bore with no ill effects. I think the 1" will require more pedal travel to move the same amount of fluid, but the affect I saw was minimal if any. I was told the smaller bore creates more hydraulic pressure with the same foot pedal pressure, but I don't know if that is a tested fact or a law of physics or something. Should you swap to 1-1/8"? It is my "opinion" that it doesn't matter, but that is a choice only you should make. I am only relating my personal experience with each MC bore size. I have been known to do some things that others feel are, shall we say, abnormal. :cool:

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1948-53 Trucks (hyd) are 1-1/4".... air brakes 1-3/4" and 1949-52 Chrysler Disc brakes use a 1" bore  M-cyl.:D

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1949-52 Dodge's use a 1-1/8"  ( factory shop manual...)

1949-50 DeSoto 1-1/8"              ( factory Shop manual...)

1949-52 Chrysler'ss 1" or 1-1/8"   depends on model and if PB used

1946-54 Plymouth's 1-3/8" see attached pic.............I .don't think so!:D

Generally Isee 1-1/8" bore in most cars except brake boosted  wagons and big Chryslers which are 1" bores cars.

Pull the master cylinder apart first before ordering as already mentioned.

M Cyl.JPG

Edited by Dodgeb4ya
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Both my reference books say the same for the 42-54 Plymouth being 1 3/8's and while I do not have a  master or old parts from the master on hand, I can assure you the rear wheel cylinders are 1 1/8   (could not locate my old front kits) While it is good to use the book, once in a while you will hit a snag...the repair procedure will be the same either size, you should always check specifics prior to ordering parts when possible or be prepared for returning them on the odd chance they wrong...I can never state often enough that over the years one never knows who changed what to keep the vehicle in operation.  

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I'm not the "most experienced" person on this forum but I remember taking master and wheel cylinders apart, walking to the nearest service station and buying rubber cups for a dime apiece, your choice on size. Pretty much everything else was re-usable after a good cleaning and a light sanding with emery cloth.

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The cylinders can  rust pit right where the rubber cup lip sits and behind it. That can cause leaks.

When these cars were driven everyday moisture was boiled out of the brake fluid minimising pitting in the cylinder bores.

These old cars today sit 80% of the time absorbing water into DOT 3,4 and 5.1 fluids damaging wheel cylinder bores that usually cannot be 100% properly cleaned up..

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@Dodgeb4ya Yeah, I know. I just kinda miss the old days; or at least the prices.:) I just bought a set of front wheel cylinders and shoes for my '47. I also recently went through the front brakes on a 1999 GMC pickup. I know it's apples to oranges but rotors, calipers, pads, and hardware cost less than wheel cylinders and shoes for the Plymouth. With good brake drums for these old cars being nearly non-existent and parts availability it's easy to see why so many convert to discs. 

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Gyro activated rear thrusters sound good to me.. Let me know when you get 'em in production..:) I'd had a little problem with a spongy brake pedal. While bleeding the brakes the right upper wheel cylinder shot craps.   Looks like the previous owner replaced all the brake parts with the exception of the right front wheel cylinders and hose. 

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I kind of gave up on the idea of rebuilding my master and wheel cylinders.  They have been sitting a rusting too long.  I was able to knock the pedal pin out of the master cylinder with a drift.  It's only a bit rusty on the end.  I'm going to try to reuse it.  Or if I can't, they sell new ones on Ebay for $46.  So I ordered a new master and six new wheel cylinders from Rock Auto and saved about $140 over the Ebay prices.  I get to send back my old master cylinder for a $25 core refund. 

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