Parking brake won't let me back off (1 Viewer)

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flx

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Hi,

Background :
My 1974 FJ40 saw some good offroad actions in a 40 series meetup, then came back home normally, was parked (parking brake on) and sat for a month without being used (not planned but that's life...).
So after 1 month I start back my FJ40 and drive directly forward, I actually go to the local city and back without issue. But when I want to reverse it I notice a strong resistance, like a wall. Even being in a slope where normally the parking brake can't hold the vehicle I had to really force my way back for the truck to reverse. And it would reverse with the feeling of escalading big obstacles and regular "clongs" noise, not like something dragging.
At first I was very afraid that it was a gear somewhere... but after some dismantling and testing diff, transfer case and transmission seem fine. Issue comes from the parking brake.

I tried to play with the adjustment bolt of the parking brake and then set it back following manual, it unlocked the parking brake in both direction but as soon as I used the parking brake it stayed blocked again in reverse direction.
If I let the adjustment bolt untighten to the maximum it does not block again, but obviously something is wrong inside my parking brake so I opened it.

Drum looks fine:
1639945446223.png


parking brake untighten:
1639945485118.png


Parking brake tighten:
1639945543947.png



I tried to compare to the manual and part schematics but the only thing I can see missing is the dust cover for the adjustment bolt. But I don't think this can be the issue?
All springs are there and look ok. Brake pads looks good.

The bottom part can move freely but from the schematics I don't understand how it's supposed to be held in place ??


And when using the hand brake you can clearly see the movement is almost only on the left part and when untightening it does not come back completely in place. So it explains why it only catch in reverse but not why it's doing that ?


I couldn't find a video of the parking brake internals to see how it's supposed to function. So any help appreciated if you know how it's supposed to work or if you can spot what is the issue with mine.

Thanks!
 
How about you pull thoes shoes off and look at the linkage in back, where those 2 top rivets are.
There are a couple clips which could have come off...
 
How about you pull thoes shoes off and look at the linkage in back, where those 2 top rivets are.
There are a couple clips which could have come off...
Yes that's definitely my next move but I believe if one those C-clip was missing it would not move as it does.

The bottom play (1st video) feels very weird but looking at the schematics there is nothing to hold the bottom in place so I guess it's normal it moves around the hole of the adjustment bolt 🤔

The FSM indicates some grease points on the back plate, I could see that as a reason the brake pad not coming back to the center when released. But as this only some greased put on a plate I have difficulties to see how it could stay in place for long...
1639995737524.png
 
Oh and if it may serve someone one day, for the 40s built before 01/1974, the castle nut that hold the drum in place is a 29mm socket size and M19 thread size.
It's not a ISO size and this size is completely extinct, you will not find a right socket at your local store.
1639999273428.png


I post that because searching on this forum I saw multiple time the information that the socket size was 27mm. Someone at some point tried to jam a 27mm socket on the nut and the damage can be seen. Maybe going for a SAE size somewhere between 27 and 30 would work better.

1639999477540.png

Judging by the part number that goes from 90171-19035 to 90179-20061 I would think the post 01/74 nut is a M20 with a 30mm head. I saw some vendors that recommends to supersede the first one by the second, I'm not convinced it will work well.
 
Ok everything is out... one of the spring gave a good bit of resistance before accepting to be removed.
1640013104539.png


1640013083104.png


1640013140685.png


Everything seems ok, all C-clips are there.
Only thing I notice is there is a good bit more of brake pad debris on top of the left one but that may be from a few time forgetting to remove the e-brake for starting.


(And yes I'm on my way buying some brake cleaner)
 
Ok one thing I noticed while cleaning everything :
1640095498957.png

The 2 lower elevated part, that need to be greased and support the brake pad, are marked by the brake pads. And the right one is a lot more marked than the left one.
Could this explain the unequal movement of the pads and why the left one may stay too much to the left and block on the drum (if the right one is not moving correctly) ?
Is-it normal wear of the backing plate or an issue to fix ?



Anyway I need to reinstall everything for now to let a truck in running condition for the holidays. So my hack for the moment is to chamfer the upper angle of both pads:
1640095849954.png
1640095896837.png


I also tried to slightly squeeze the part of the right pad support that let the mark on the backing plate, not sure if it will help.
Will also put abundant grease on the 2 lower plates.
 
From your install pics, it looks like the unit is off center, with one side just about rubbing, and the other a good ways from the edge. I think Pigheads thought is a good one.
 
I don't know maybe I'm off, but I feel like it looks much like what I've seen in my experience. Everything looks "right" even the movement or play when everything is assembled from your videos. I experienced the same behavior as you did after rebuilding my ebrake and installing. Then I figured it needed to be adjusted. So adjusted the ebrake to all the way untightened like you said, then I pulled the brake pull lever thingy all the way or mostly out, then tightened the ebrake adjustment bolt a couple clicks until there was pressure then reversed that bolt a turn or 2 can't remember. Then went back in the truck and released the pull and put it in reverse and no more problems.

My guess is from sitting with brake pulled for so long it naturally "adjusted" the brake due to the springs that hold it tight. So it may just need to be readjusted and cleaning wouldn't hurt either. But I think it looks pretty correct imo.
 
From your install pics, it looks like the unit is off center, with one side just about rubbing, and the other a good ways from the edge. I think Pigheads thought is a good one.
As it can move freely at the bottom I can re-center it but if I pull the handbrake and release it is stays a bit more to the left. But I don't have the drum on so the left pad as nothing to push on, if I put something to block it the right pad start to move but still end-up a bit off center at the end.
I dismantled everything and it seems fine at the exception of the marks on the back plate as shown in the photo in my previous post but I don't know if it's enough to have an impact (because the right pad moves so it's not completely stuck in it).

I don't know maybe I'm off, but I feel like it looks much like what I've seen in my experience. Everything looks "right" even the movement or play when everything is assembled from your videos. I experienced the same behavior as you did after rebuilding my ebrake and installing. Then I figured it needed to be adjusted. So adjusted the ebrake to all the way untightened like you said, then I pulled the brake pull lever thingy all the way or mostly out, then tightened the ebrake adjustment bolt a couple clicks until there was pressure then reversed that bolt a turn or 2 can't remember. Then went back in the truck and released the pull and put it in reverse and no more problems.

My guess is from sitting with brake pulled for so long it naturally "adjusted" the brake due to the springs that hold it tight. So it may just need to be readjusted and cleaning wouldn't hurt either. But I think it looks pretty correct imo.
Yes at first the play at the bottom felt very weird and I thought something was missing or broken but obviously it's normal and how this is made...
It's an interesting method to set the the adjustment, it's kind of backward of the one from the FSM but I may try.

Currently I have reinstalled everything after cleaning, I heavily greased the 5 points and I adjusted it 3 clicks back from blocking (with hand brake not pulled) otherwise it catchs in one way. I still feel a little drag whatever the setting I use but maybe it's normal for a drum brake.

1640171418204.png


1640171556622.png


I had to put back the truck together for now but I will order the parts missing or the need to be replaced (dust cover, main C-clip, springs, cotter pin) and I may do this again properly in a few month in a better season to work outside.
Maybe even trying to find another back plate to replace this one...
 

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