Brake woes

[Lou Boffa]

Gentlemen (and Ladies) I'm stumped. Me and a bunch of old mechanics can not figure out why my 70 C10 brakes (drum all around) will suddenly lock after I've been driving for a while. I can go back the next day, and she is fine-for a while, then they will lock again.
About the brake system. I added a brake booster years ago. has braked well-as well as drum brakes do--for years. Then the locking brake thing started about a 5 months ago. Had a shop work on it and we have been through replacing brake lines, several boosters and actually had the old booster rebuilt. The last suggestion was to do a disc brake conversion on the front, which isnt a bad suggestions, but I am attached to my steelies and 10" dog dish hub caps. Its my understanding that I would not be able to use my old wheels after the disc conversion.
So, all this is to say, Help! Whats the best way to get her back on the road and stopping --reasonably well?
Lou

[HeloCrewChief]

Have you replaced all the brake hoses?

[Lou Boffa]

yes, all around

[Richard Jensen]

Hello,
Is there a proportioning valve by the master cylinder? Is the brake linkage from the pedal to the master cylinder loose and free? Pictures of the master cylinder might help. Are all wheels locked up? I don't know why you wouldn't be able to use your old wheels after a conversion to disk.

Thanks!
Richard

[cj847]

if it is always the same wheel, i would check to see if a wheel cylinder has leaked onto your friction material.

As to disk brakes, a couple of companies make a disk brake kit for 60-70 models with 6 lugs.

[jocko]

Lou, if your wheels are original to your truck, then you are correct, they will not fit with disk brakes. How many cap retaining nubs do they have, 3?
71+ K5/10 wheels will look identical, have the same 6 lug pattern and 4 nubs to retain your stock cap, and will clear a 71-72 style disk brake caliper. The 4 nubs are usually the most common indication that they are likely disk brake wheels, although not exactly sure that's gospel. The pre-71 wheels have a taper on the inner profile that interferes with the caliper.

As for the brake problem, the master cylinder or distribution block would seem to be likely culprits if all wheels are locking. If only one wheel is locking, then it seems it would have to be an individual wheel cylinder, or line that leads to it.

[68Gold/white]

Ok, which wheel(s) is locking up?

What is condition of drums? New? Machined originals? Machined new drums?

[Wrenchbender Ret]

The rod between the booster & the master cyl. needs adjustment. It is not letting the master cyl. piston return all the way.
George

[1971Stepside]

The rod between the booster & the master cyl. needs adjustment. It is not letting the master cyl. piston return all the way.
George

I have disc at all four corners with Hydroboost, but had the same exact symptoms you are having. It was as George suggested. Adjust the pushrod length between the booster and MC and it works great now.

[Reddeye]

I had the same issue over the last year or so and finally fixed it last month by replacing the booster and master. I bought them as one complete unit so I didn't have to adjust anything.

[firedemon]

https://www.ebay.com/itm/12376903988...53.m1438.l2649

this is a great tool for checking the rod between the booster and master but you should be able to make one cheaper

[Lou Boffa]

they are 16" wheels. I've decided to go ahead and do a disc conversion on the front, The last mechanic I spoke to (today) said the issue was between the drum and the hub. Ive driven it for years with drum all around, so an improved system seems like a good upgrade. Thanks guys.

[68Gold/white]

Originally Posted by Lou Boffa

they are 16" wheels. I've decided to go ahead and do a disc conversion on the front, The last mechanic I spoke to (today) said the issue was between the drum and the hub. Ive driven it for years with drum all around, so an improved system seems like a good upgrade. Thanks guys.

If you want to try a quick potential fix, get the drums machined......

[Steeveedee]

Originally Posted by 1971Stepside

I have disc at all four corners with Hydroboost, but had the same exact symptoms you are having. It was as George suggested. Adjust the pushrod length between the booster and MC and it works great now.

X3. If the problem is "between the hub and drum", how are disc brakes going to help keep the rear brakes from locking up? I am in the camp that holds that front disc brakes are better, but putting disc brakes on at this point is throwing parts at a problem hoping it clears up.

[RichardJ]

X2 Find the problem first.
You never answered any of the questions other than about the hoses. One wheel? Front or back wheels only or all wheels?

If all wheels, firedemon could be correct about the booster pin length. The special tool would be nice, but a couple of washers can be used to check if you are on the right track and then simple measuring tools can be used to check the correct pin adjustment.

[HO455]

let's take a minute to clarify the symptom. You say the the brake will suddenly lock after driving for a while. Does this mean while driving at a steady speed the brakes lock up as if you had slammed the pedal down?
Or do the brakes start dragging after being used and as the drums get hotter the friction increases until they lockup?
Does this only happen on rough roads?
When the brakes are cold can you push the truck on level pavement? How about after driving a while?
After driving for a bit do you find that when stopped in drive that no braking is needed to keep the truck from moving in drive (Automatic transmission only)
I recommend getting a infrared heat sensor and taking temperatures on all four drums every mile or so on typical drive where you would expect the problem to occur.
Have you checked the adjusters in side the drum for proper operation?
Any other observations would be helpful.