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Posted By: Phak1 Slave Cylinder Doesn’t Fit Backing Plate - Thu Sep 12 2019 10:53 PM
During reassembly of the front brakes on my 52’Chevy 1/2 ton, my new wheel cylinders I ordered (AC Delco from RockAuto) are too wide to fit. When I removed the installed cylinders I noticed that both dust boots were damaged and leaking, thus the reason for ordering new ones. Looking at the old cylinders its apparent that they didn’t fit either. Although they were narrower than the new AC Delco, when installed the rubber boots are getting pinched by a bracket that is attached to the backing plate. I ordered cylinders for a 52’ Chevy half ton and judging by the old cylinders the PO also ordered the same.

The second picture shows how the old cylinder boot was being pinched by the backing plate bracket.

The third shows how wide the new AC Delco is. Note that it’s still not even close to being seated.

Now I suspect the backing plate or maybe the whole axle is not from a 52’.

Any help sorting out this issue will be greatly appreciated.

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Posted By: 52Carl Re: Slave Cylinder Doesn’t Fit Backing Plate - Fri Sep 13 2019 01:38 AM
As far as I know, that is how they are supposed to be. Every one that I have worked on were like that. Those rubber parts are not seals to keep fluid in. They are dust covers to keep dirt out. BTW, the Factory Repair Manual states that it is normal to find a small amount of brake fluid on the inside of those rubber parts. If it pours out when you peel them back for inspection, then you need to replace them.
Posted By: Phak1 Re: Slave Cylinder Doesn’t Fit Backing Plate - Fri Sep 13 2019 02:05 AM
The old cylinders can be installed by slightly depressing the boots. The reason I questioned if its correct, is because the removed cylinders had holes in both dust boots and were weeping where the damage was. This damage is consistent on both sides.
The new AC Delco slave cylinders are just way too big to fit so they are not made for this backing plate.
Posted By: 52Carl Re: Slave Cylinder Doesn’t Fit Backing Plate - Fri Sep 13 2019 05:45 AM
Do the cylinders have a casting number on them? Someone on here may be able find out if they sold you the wrong parts.
Posted By: Phak1 Re: Slave Cylinder Doesn’t Fit Backing Plate - Fri Sep 13 2019 11:52 AM
I looked at the new AC Delco cylinders again and discovered that all I needed to do was to compress the boots and cylinders to get them to fit in between the bracket. If your saying that all of the cylinders you’ve installed look like that, they are probably correct.

I’m still wonder why the removed cylinder boots were cut by the bracket. I wonder if a PO pressed on the pedal when the drum was not installed crushing the boots between the pistons and the bracket. Another possibility is the pins that press against the shoes have been replaced and are too short.

Thanks 52CARL for your help.
Posted By: Hotrod Lincoln Re: Slave Cylinder Doesn’t Fit Backing Plate - Fri Sep 13 2019 04:55 PM
If you're concerned about the interference, just take an angle grinder to the bracket and widen the space a little. That bracket is only there to prevent the pistons from exiting the cylinder in case somebody has a stupid attack and doesn't adjust their brakes regularly. Some brake systems don't have them at all.
Jerry
Posted By: Phak1 Re: Slave Cylinder Doesn’t Fit Backing Plate - Fri Sep 13 2019 08:51 PM
No need the cut the brackets. I just finished installing the wheel cylinders and the brake shoes. Once I understood how they actually are installed, all went well.

My concern was the how the old boots got cut. I didn’t want to install new cylinders and have the same thing happen.

I try to be very through reassembling so I don’t have to do it again. I have found some pretty shoddy work on this truck so I am suspect of everything.

Thanks again Jerry and 52CARL for your support.
Posted By: bartamos Re: Slave Cylinder Doesn’t Fit Backing Plate - Fri Sep 13 2019 10:54 PM
The rubber got cut due to many years of vibration. The sharp corner and edges of the stamped keeper can be "softened" with a file. Chinese "rubber" will last much less time.
Posted By: Phak1 Re: Slave Cylinder Doesn’t Fit Backing Plate - Fri Sep 13 2019 11:26 PM
Good suggestion! Thanks! Unfortunately, they are already installed.
Posted By: 52Carl Re: Slave Cylinder Doesn’t Fit Backing Plate - Sat Sep 14 2019 02:33 AM
Sleep tight at night. If they get cut over time, nothing bad will happen. They are just dust caps. The cuts will be on the sides. If the pistons leak enough to ever reach as high as the cuts, the cylinders have gone bad and will need to come off anyway.
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