A stupid question about rear drum brake cylinders (1 Viewer)

[Cody Quesnelle]

Sooo little confused ...pulled the drums off my 1976 fj40 and noticed the brake cylinders are oriented front and back but when ordering cylinders for 76 fj40 they are labeled as top and bottom....most photos of rear drums are oriented top and bottom....yea not a drum brake guy any insight would help

 

[Racer65]

Sooo little confused ...pulled the drums off my 1976 fj40 and noticed the brake cylinders are oriented front and back but when ordering cylinders for 76 fj40 they are labeled as top and bottom....most photos of rear drums are oriented top and bottom....yea not a drum brake guy any insight would help

Same difference . It's just the nomenclature: "Front or upper", "Rear or lower".

 

[Cody Quesnelle]

Same difference . It's just the nomenclature: "Front or upper", "Rear or lower".

 

[BeerM3]

All 4 cylinders are identical, mechanically speaking. The reason they're listed separately is so the clockwise/counterclockwise adjustment is the same. Basically 2 of the pistons are left hand thread, and 2 are right hand. Properly installed, you tighten or loosen the shoes by clicking the adjuster toward or away from the axle whether you're adjusting the one in front of the axle or the one behind. I don't know where you're seeing the later top/bottom configuration, but a '76 has them vertical (which can be an air entrapment problem for aftermarkets). CruiserOutfitters can get you the right ones. So can Mark's Offroad.

Here's a great image for spring orientation as well as cylinder. Your '76 should have front disc so ignore the top diagram.

 

[Austinlejenkins]

Here's a picture of what the stock rear shoes and cylinders look like on my '72, hope it helps.

Untitled by austin jenkins, on Flickr

 

[Cody Quesnelle]

Nice thank you ....

Here's a picture of what the stock rear shoes and cylinders look like on my '72, hope it helps.

Untitled by austin jenkins, on Flickr

I doesn’t look like your cylinders are mounted on a slope hmmm any ideas why my rear cylinder is lower than the front

 

[Austinlejenkins]

Nice thank you ....

View attachment 1971104I doesn’t look like your cylinders are mounted on a slope hmmm any ideas why my rear cylinder is lower than the front

mine is 100% stock ride height, Do you have a lift? If you do, it would slightly spin the axle to accommodate for the pinion angle. or maybe your backing plate for the drum is installed wrong, Is the other side the same way?

 

[BeerM3]

any ideas why my rear cylinder is lower than the front

Do you have some tall lift shackles on the rear springs? Is it just an optical illusion because the front of the truck is jacked up higher than the rear and/or the driveway slopes? It definitely looks off in that photo.

 

[mike1978fj40]

I have a similar question I did not replace the wheel cylinders just rebuild the rear end and replaced exactly as they were, I noticed when the brake is applied only the lower shoe is being pushed.

 

[BeerM3]

I have a similar question I did not replace the wheel cylinders just rebuild the rear end and replaced exactly as they were, I noticed when the brake is applied only the lower shoe is being pushed.

View attachment 2108248

Probably just the path of least (hydraulic) resistance with nothing in place to push against. You bled both cylinders with no bubbles? It’s possible one is frozen, but tighten a bar clamp or big c clamp on the one that’s working and see if the other now moves. If so remove the clamp, put on pads & springs and test again.

 

[mike1978fj40]

Probably just the path of least (hydraulic) resistance with nothing in place to push against. You bled both cylinders with no bubbles? It’s possible one is frozen, but tighten a bar clamp or big c clamp on the one that’s working and see if the other now moves. If so remove the clamp, put on pads & springs and test again.

Probably just the path of least (hydraulic) resistance with nothing in place to push against. You bled both cylinders with no bubbles? It’s possible one is frozen, but tighten a bar clamp or big c clamp on the one that’s working and see if the other now moves. If so remove the clamp, put on pads & springs and test again.

I have the shoes and springs on, both cylinders work but it’s just the bottom of the cylinders that move on both

 

[73FJ40]

Did you really push the brake pedal with the drum off in order to witness this? If so, bold move!
@BeerM3 is correct - the cylinders are designed to push on both top and bottom pistons equally, so maybe gravity is helping the lower pistons move first?

 

[mike1978fj40]

Did you really push the brake pedal with the drum off in order to witness this? If so, bold move!
@BeerM3 is correct - the cylinders are designed to push on both top and bottom pistons equally, so maybe gravity is helping the lower pistons move first?

Yes but just enough to see what was happening, wasn’t going to rebuild the cylinders

 

[igotta40]

Sounds like you have air trapped in the upper part of your cylinders