Rear brake lock up question? M1009

[RickTheEngineer]

Hello folks! So I have this question regarding the M1009's brakes. When it it raining outside and the roads are slick, or maybe you are on a dirt hill or something, if you hit the brakes, harder and harder, do your rear wheels lock up first? I noticed that the the rear passenger, some sometimes the driver will be the first to lock up, much before the front ever do. This has not been an issue really on dry pavement. I was more curious about the instance when one might brake under lower traction situations. My parking brake light works, which leads me to believe that the proportioning valve should be okay, but obviously that is only a speculation. Thanks!

 

[BKubu]

I believe there is gear lube on your brake pads, which means that you have a bad seal. I had this same problem.

 

[RickTheEngineer]

I actually recently serviced the brakes, everything was perfect in there in that regard. I recall I may have made the rear brake shoes snug but not dragging after my adjustment, but nothing that I haven't done on all the truck I owned.

 

[cucvrus]

I think that to properly service the brakes on this old of a vehicle. You should pull the front and rear axles and replace the axle seals and bearings while you are in there. Also at the inexpensive cost of the wheel cylinders and hardware kit. Replace them also. Many of the older vehicles have bell shaped drums and new shoes do not conform to that shape and will cause lock up. I go over every CUCV I own when I first buy it. I change all brake components. Master cylinder., calipers, wheel cylinders, axle seals, I have the drums cut or replaced, same as rotors cut or replaced. I prefer having them cut and most times that works. I have a ton of OEM brake drums and rotors. And after rebuilding the entire brake system with new brake shoes and pads. I have about $200. in the entire job and a couple hours labor. That has also lasted for many years and provided many mile of driving in all conditions with no problems. Do it once. Do it right the first time and drive away. It's a simple task.

 

[o1951]

Post deleted. CUCVrus posted what I was typing.

 

[RickTheEngineer]

I actually did just service the entire brake system. Newaster, calipers, wheel cylinders, brake hardware, pads. The seals look new, like they were replaced at one point, and I cleaned everything front and rear, and it was truly spotless. I just wanted to know if the rear locking up first was normal behavior for a M1009/K5

 

[cucvrus]

NO. Why would it be normal? I did mention the bell shape of the drums and the new shoes not conforming to the shape. Did you replace or have the drums cut/trued? Not many people know how to cut rotors and drums anymore. Everyone just replaces parts and never gives the reusable parts a second chance. I wish they had ABS on the old CUCV's.

 

[RickTheEngineer]

Its just that every truck I ever had will lock up the rear before the front does. Maybe that is a bad thing haha. My mistake on my last post, I did not replace the shoes (I'll edit that out). Drums are in great shape too and are well within spec. They fit perfectly with the drum, and they had lots of meat on them. I wonder if maybe my adjustment made them too snug or something. It is not like the rears lock up all the time, just under hard braking with low traction.

 

[3jumpjeep]

I actually recently serviced the brakes, everything was perfect in there in that regard. I recall I may have made the rear brake shoes snug but not dragging after my adjustment, but nothing that I haven't done on all the truck I owned.

Recently serviced? New shoes? Have they worn in to the drum?

Sent from my SCH-I545 using Tapatalk

 

[o1951]

CUCVrus is telling it right. Drums get bell mouthed and out of round if overheated from hard braking. They only have support on 1 side. Quick check for out of round - in an open area, like an empty parking lot, go about 15 MPH and gradually apply parking brake. If you feel pulsating, drums are way out of round.

If you have drums turned, clean where brake lathe will clamp thoroughly, so drum seats on metal. Watch operator and make sure drum is centered on brake lathe, obviously if off center, it will be cut off center and lock. If he does not tighten clamp properly, can get a bad cut on drum, which will cause problems. If rear axle is bent, or bearing bad, will cause problems. I used to remove everything from axle, check bearings, replace seals, rebuild or replace wheel cylinders....... I would mount the drum before reinstalling the backing plate, and use a dial indicator to check that drum was turned true and did not have taper.

I always thoroughly cleaned braking surface with brakeclean to remove any rust proofing on new drums, or any residue on refinished drums.

 

[RickTheEngineer]

None of those problems have ever presented themselves, and the drums look great. I want to emphasize that this problem did not exist, until I did a brake shoe adjustment. I adjusted them so they dont drag but had tight tolerances. I do not know if it is possible to make it too tight or something. Everything was perfect, and still is just fine, just when traction is low it feels like the back will lock before the front. But not to any point of being unsafe.

 

[snowtrac nome]

I've chased this situation several times. the problem is in your parking brake cable its corroded and not fully releasing. you can check this by having some one pull the brake release, while you use a prybar to push back on the levers on each shoe my guess is they will release a little more one each side.

 

[RickTheEngineer]

I actually checked that out before, and they are in awesome shape for the year. I did read on another forum that tight brake shoes can cause this to happen on a 2 chamber master where the front and rear have their own plungers?

 

[o1951]

I actually checked that out before, and they are in awesome shape for the year. I did read on another forum that tight brake shoes can cause this to happen on a 2 chamber master where the front and rear have their own plungers?

That is called a dual circuit brake system. You say brake shoes are adjusted properly, so that should not be an issue.

 

[RickTheEngineer]

I believe I adjusted them right, considering I have done it about a dozen times to my trucks or friend's trucks. However, I never used a dual circuit brake system before, so I do not know if I adjusted the rear too tight. I might loosen it up ever so slightly

 

[NovacaineFix]

Rick, how long have you had this M1009?

You mentioned all the service work done and that is good, but have you flushed out the brake fluid?

This may or may not be the culprit, but it is worth mentioning since everyone else has mentioned good ideas and it seems that you have taken care of it in one form or another. If this is a newer recovery from an auction, it may still have some residual silicone brake fluid in the system, you know that DOT 5 stuff.
Why do I mention this, 'cause mine had the same thing and did the same exact thing as well.
Sometimes instead of locking up, the pass rear drum would stutter to a stop.

Flushed the fluid and out came a gelatinous goo, DOT 5 and DOT 3 mixed together after being mixed for quite some time.

The auction site I got mine from was a University and they didn't have experience with MV's [that mostly contain DOT 5] and they told me that they put in DOT 3.

I did the same when it came to replace a master cylinder about a year later, no problems up until then, probably should have used CUCVRUS's maintenance routine, but didn't. A few months later after no problems, while backing up my driveway, pass rear tire locks up at the slightest touch. The following weekend, checked everything, nothing really out of whack. Checked and flushed the fluid, and that's when I found the goo.

Why it seems to act on the pass rear drum, not sure why, but worth a look and doesn't cost anything but a little time and maybe some fluid.

 

[RickTheEngineer]

That was exactly what happened to me actually... I flushed out ALL the fluid, and cleaned every single line with denatured alcohol until you could use those lines as drinking straws. I used compressed air and let the alcohol flash off, replaced ANYTHING rubber, and just straight up overhauled the darn thing. Only thing that is original (that I tried flushing out as best I could) was the proportioning valve. But that always worked well. The only variable I changed was that when I did the brake drum it was nice and tight, and I do not know if that could be messing with the brake system, since that was never a problem with the more typical Master Cylinders setups out there (single circuit brakes). Currently I swapped everything out for DOT4, and it is clean as a whistle with NO trace of DOT5 anywhere

 

[rustystud]

OK, just to be clear. You had the drums turned correct ? I don't care if they "Look" good they can still be warped. So did you have them turned ? Since you "adjusted" the brakes that means they are closer to the drums then they where. So if the drums are warped they can lock-up that wheel. Also, did you replace the wheel cylinders ? They should always be replaced (if using DOT 3) or at least taken apart and cleaned if your using DOT 5. Did you ? As far as rebuilding a dual master cylinder, unless your my age you probably have never seen a single master cylinder as they all where changed by law in 1967. So unless you only work on really old vehicles they all have had dual master cylinders. Now there is a "rear limiting valve" used on the 1 tons that can get stuck but you have the "Blazer" so it should not have that. You also fully checked out the parking cable and it is working fine correct ? Did you install the parking brake "push bar" and springs correctly ? Did you use a shop manual to make sure the springs and bars where all installed correctly or did you install them by memory ? I still use the manual whenever I'm working on small vehicle brakes. Install the springs or levers wrong and "presto" no brakes. Now trucks "S" cam brakes I can do all day long by memory. Let use know what is happening and be honest with us. We cannot help you if you "fudge" the truth.

 

[RickTheEngineer]

No fudging here. I said I replaced the wheel cylinders earlier, all brake components were replaced except for the proportioning valve and lines (which were all cleaned individually as I said) the only think I did was adjust the brake shoes after putting it all back together as I thought there could have had a little better tolerance. Everything about that parking brake was for sure installed correctly. I took pictures before and after to make sure too. It scouts Honor was installed exactly correctly. I did not get the drums turned or replaced. If I have time I can try to use a dial indicator on it to see if it's out of round. I want to be clear that it's more or less the rear just locks up a little earlier than before. Nothing unsafe per se. The front pads are clean as a whistle, no oil, no nothing. I used a shop manual for everything with pictures just to make sure. I do not mean to come off as hard headed but I am 100% sure of the work I did. There are only two things that changed. Whether or not the proportioning valve is the culprit, or the tight brake shoes adjustment. I can see if I can get the rear drums turned or replaced, although it would be shocking that it would suddenly change what's been happening. You know what I mean?

 

[dougco1]

No fudging here. I said I replaced the wheel cylinders earlier, all brake components were replaced except for the proportioning valve and lines (which were all cleaned individually as I said) the only think I did was adjust the brake shoes after putting it all back together as I thought there could have had a little better tolerance. Everything about that parking brake was for sure installed correctly. I took pictures before and after to make sure too. It scouts Honor was installed exactly correctly. I did not get the drums turned or replaced. If I have time I can try to use a dial indicator on it to see if it's out of round. I want to be clear that it's more or less the rear just locks up a little earlier than before. Nothing unsafe per se. The front pads are clean as a whistle, no oil, no nothing. I used a shop manual for everything with pictures just to make sure. I do not mean to come off as hard headed but I am 100% sure of the work I did. There are only two things that changed. Whether or not the proportioning valve is the culprit, or the tight brake shoes adjustment. I can see if I can get the rear drums turned or replaced, although it would be shocking that it would suddenly change what's been happening. You know what I mean?

The horse is dead already.