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Discussion Starter #1
Bleeding brakes on a SBU, I assume it wont matter but this is on a 8 lug axle with the bigger calipers then a 6 lug.

I have to bleed my brakes tomorrow on a completely dry system. All new lines, rebuilt rear calipers and have a few Q’s

Questions
Do I need to bleed the master cylinder? First or Last? It has 1 bolt looking bleed screw on top in between the reservoirs. Any idea what kind of seal maybe used at this location. I’m tempted to leave it alone as I have not broken this connection open yet.
Should I bleed some of the air out of all 6 calipers before actually bleeding them?
Having never rebuilt lines before, how tight should the connection points be? They are pretty snug but I assume the flare will shape itself some to the new connection.
Any way to test for leaks before?
Front calipers only had the lines removed and replaced, Would it be worth the trouble of pushing them back in?


State of items.
Rear pistons are still In with the exception of the pads being set for clearance for the parking brake.
Parking brake is released.

My plan is as follows,

Fill both reservoirs
Open bleed screws to see fluid start to flow at each location.
Use a motive power bleeder starting on the front axle front calipers starting with passenger then drivers side.
Move over to the larger reservoir.
Bleed the front axle rear caliper, drivers side, passenger side rear, then drivers side rear.


I’m sure I’m putting too much thought into all of this but I’m just a little nervous as I just realized I made 40 new connections points thinking that I may end up with a shower of oil everywhere. I just need to relax..
 

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Hi Dave, I don,t know if this will apply to a Unimog, but an older mechanic who used to work on Bedfords with a similar air over hydraulic system told me that if you,ve got time, the best way is to keep the reservoirs topped up, open the bleed screws on the calipers and let gravity do the work for you, it will fill up all the corners and drive out the air and leave no air locks in the system (it fills so slowly the air doesn,t get trapped, it can just slip out ahead of the flow).
 

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I was little disappointed with Movit power bleeder.
I could only get 10psi on it and the thing was leaking fluid at the hose end by the tank.
I added new clamp after, it may work better now.
It did the job though, but then one of the flexi brake lines,
turned to be worn out, and I lost all the fluid in small circuit.
I'm waiting for new brake line now.
Eurotruck have them cheap, $17 a piece.

I did it in the same order you described.
Buy at least 2 litres of brake fluid.
I got Preston synthetic DOT4.
 

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I'd recommend gravity bleeding. By far the most relaxing method, although I'd only do one wheel at a time. Start with the wheel furthest away from the master cylinder and work towards it. That will end up with clean fluid in all the pipes and no air in the system.
 

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I have done 3 methods on my truck

1. Homebuilt brake bleeder - worked very well

2. gravity method, also worked well, less mess, and less bubbles (pumping the brakes can brake big bubbles into smaller bubbles which can be more of a PITA) but I'd still use the homebuilt since I have it now.

3. Front brake assist, only applicable if you have the 4 wheel park brake, set the front park brake, crack the bleeders, and holy man that's the best way to bleed the front brakes on my truck! Its like having someone apply constant pressure to just the front brakes without having to let up on the brake pedal. Very efficient.
 

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I made a pressure bleeder out of 2 Gunson Eezibleeds(£30 all in) that fits over both reservoirs at once. I can bleed up the whole truck in about 10 minutes. Previously documented on here so I won't bore you again. Gravity bleeding has never worked for me on anything, but I may just be a dullard.
Good luck.
 

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Dave, I hope you're doing better than me with the last minute brakes!

NWMF is just around the corner, and I too just started my brake job on the
U1200 a bit late.

I thought I was done, 3 of the 4 calipers I rebuilt myself are working. Caliper #4 had a sheared bleeder that somebody had attempted to remove and broke an ez-out in. I took it to a machine shop, and they got it out, but they also messed up the seat and slightly oversized the threads. It won't hold pressure:(

I'm hoping that Eurotruck has front calipers in stock and that he can overnight them to me.

BTW, the gravity bleed works great, except when you hit the brake the first time with a bad bleeder and you shoot brake fluid across the driveway.

Hope you make it, as do I.

Eric
 

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Lol I now tend to put on my 'Polish Head' and think what would my local mechanic do??? Why he would just tap out the hole and put in a bigger bleed nipple!!!!!!
 

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Discussion Starter #10
I apologize to the group for not getting back. But in regards to bleeding, I did the master cylinder, then worked my way around. No Issus in the bleeding dept.

Now in terms of calipers, I did have a bad seal in one of them and it caused me to panic for a while but I was able to get a new seal kit last Saturday which allowed me to get back on the road. 

Now the down side I still have the front calipers to do. I have to admit these calipers are too expensive I figure by the time I’m done I could how purchased a 404… oh well. I have to admit with the new lines, and rebuilt rear calipers my SBU stops, and stops Quick.
 

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Discussion Starter #11
Dave, I hope you're doing better than me with the last minute brakes!

NWMF is just around the corner, and I too just started my brake job on the
U1200 a bit late.

I thought I was done, 3 of the 4 calipers I rebuilt myself are working. Caliper #4 had a sheared bleeder that somebody had attempted to remove and broke an ez-out in. I took it to a machine shop, and they got it out, but they also messed up the seat and slightly oversized the threads. It won't hold pressure:(

I'm hoping that Eurotruck has front calipers in stock and that he can overnight them to me.

BTW, the gravity bleed works great, except when you hit the brake the first time with a bad bleeder and you shoot brake fluid across the driveway.

Hope you make it, as do I.

Eric
That is a really good Q what can be done when the threads and seat have be changed. I was thinking helicoil myself but will it hold liquid as the seat is supposed to do that but what do you do when both are messed up?
Does anyone make oversized bleed screws?
I guess you could have the thread oversized with a flat spot milled on top, and install some sort of head sealing bleed screw or bolt. Maybe a banjo bolt of sorts with a small bleed screw on top. Would look strange but it would work and be safe, if your caliper is anything like mine you have plenty of meat to the caliper to tap the next size larger.

In terms of new caliper costs… hope your sitting down. I’m afraid my front calipers maybe worse off than the rears were.
 

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What you guys don't know...

My original calipers were really rusty, beyond saving. A friend of mine had a used set of mixed front claipers from other projects. 3 of them are from a SEE, and the other who knows. The bad one is the "who knows", it's a bit different, the caliper pistons are opposite from the other 3. Meaning that the dish of the piston is on the exterior rather than the interior.

You guys are correct, a helicoil would easily do the trick,then fab up some bleeder. I would still be in a bad place with the missed matched calipers.

I figure it's money well spent. I need to stop.
 

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You wanna play, you gotta pay. I didn't find the price of the front calipers unreasonable from Eurotruck, I checked with a buddy whom has a Dodge 3500 and did nearly the exact brake job I did, same price. he bought direct from the dealership though, so perhaps he overpaid.
 

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Can someone tell me what size hose i should get to fit it over bleeding valve tightly (to see how dirty is brake fluid while bleeding it out of the system)
 

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An upgrade to gravity bleeding (which I like too) is to run the truck up a bank first. I had a 404 'bleed out' last week with pedal to the floor. Ran it up a steep bank, filled the reservoir, kept it topped up for about half an hour, and next morning it was ready to drive (after final top-up). This might not work in the case of a completely dry system though.

Related question: is there a brake fluid thief alien? Where does that fluid go sometimes?

Bob
 
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