Brake booster, adjustment rod, or something else? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

zac · 07-31-2013, 12:53 PM

Went through brake system on my '70 K10 Burb, still having trouble. Truck was converted to front discs by a PO. Brakes never seemed to be very good, eventually got to where I couldn't ignore them anymore. Rears didn't seem to be working at all, in front pads were worn but everything else seemed OK. Some lines replaced, new MC and proportioning valve. Everything is properly bled. Truck stops, but doesn't seem to have enough authority. Pedal is hard, not at all spongy. Hammer the brakes and it just slows down. Back when I was driving 40's and 50's trucks with a single res MC that would tell me to lengthen the actuator rod. I think that's what I have here. Any opinions? The power brake system seems to be fine, so I doubt it's the booster, but you never know. Thanks.

68gmsee · 07-31-2013, 03:34 PM

I would first check to make sure rear breaks are adjusted properly -I adjust new brake shoes out until they lock the drum and then back off until they barely scrape the drum. On used ones I do the same but then back off until brake shoes are just off the drum.

Then take the truck out to a dirt road or gravel road and see if the brakes will lock on the soft surface. Stop and actually look at each side and front and back tire marks. This will at least let you know if all of them are braking.

If all that looks good and you're sure the booster is actually working okay go buy a good set of brake pads and shoes. Sometimes it's the material they're made of. I had a similar problem with some cheap brakes I bought some years ago.

Check this out: http://www.classicperform.com/TechBo...ot.htm#pushrod

Longhorn 70 · 07-31-2013, 03:51 PM

I had a similar feeling on my brakes after I did the disc in the front. The way I adjusted the rod in my booster, and I don't know if it's right procedure, was to

1. Steel some modeling clay from my 5 year old daughter
2. Place a pea sized blob on the M/C piston where the rod should meet
3. Tighten the M/C to booster (do not touch pedal)
4. Start the engine and let idle for 30 seconds or so
5. Remove M/C from booster and make sure I had about 32/nd of thickness with no breaks in the clay.

It worked for my brakes. I now feel they are much better than they were.

Also after you get it adjusted properly, fast idle for 30 seconds or so then shut down the engine. Wait 30 seconds and see how many assisted pedal presses you have... I have 2 and a half or so.

zac · 07-31-2013, 04:45 PM

Thanks for the input. I can't get the brakes to lock even on wet grass. I did a bunch of reverse rear brake adjust runs and they seem to be adjusted based on the fact that the parking brake works well now where it was kinda loose before.

I have a donor '72 parts truck that I know was working and had new parts on it. I know because I put them on. It appears adjusting the rod requires dropping the column a bit. Pedal has 1/2" to 5/8" play, book says 1/8". Think I'll swap on the booster from the '72 and use the rod or compare it to the one I have and see what happens.

Longhorn 70 · 07-31-2013, 08:19 PM

Quote:

Originally Posted by zac

Thanks for the input....... It appears adjusting the rod requires dropping the column a bit. Pedal has 1/2" to 5/8" play, book says 1/8". Think I'll swap on the booster from the '72 and use the rod or compare it to the one I have and see what happens.

I understood the pushrod between the booster and master cylinder. I apologize for the mistake. My brakes wouldn't lock either when I first installed the disk. I had to shorten the pushrod a bit and then it stopped faster.

zac · 07-31-2013, 09:40 PM

OK, better now. Lengthening the rod helped alot, the other booster was clearly better. Also, this is a converted system, and the guy who did it made some understandable compromises, especially with the lines since there was no such thing as '70 K10 disc brakes. Too many couplers for my taste, a couple were seeping just a little. Also, I didn't put new shoes on the back because they seemed to have quite a bit left. But when I was popping the drums back on I noticed the right rear shoes had cracks. Drums were much lighter than the finned '72s and seemed too thin. Should have put later drums on and new shoes, that's on me.

Still, the truck brakes as good as my '72 K10 burb ever did, which was never awesome, even with all new parts. I may be expecting better performance than it is capable of. These are the only 67-72s I've ever owned. My '79 K20 has a full floater with the big brakes, gets driven with an empty bed most of the time. Goes from 60 to zero in what seems like 50 feet. Not a good comparison.

07-31-2013, 12:53 PM	#1
zac Registered User Join Date: Jul 2008 Location: louisville, ky Posts: 502	Brake booster, adjustment rod, or something else? Went through brake system on my '70 K10 Burb, still having trouble. Truck was converted to front discs by a PO. Brakes never seemed to be very good, eventually got to where I couldn't ignore them anymore. Rears didn't seem to be working at all, in front pads were worn but everything else seemed OK. Some lines replaced, new MC and proportioning valve. Everything is properly bled. Truck stops, but doesn't seem to have enough authority. Pedal is hard, not at all spongy. Hammer the brakes and it just slows down. Back when I was driving 40's and 50's trucks with a single res MC that would tell me to lengthen the actuator rod. I think that's what I have here. Any opinions? The power brake system seems to be fine, so I doubt it's the booster, but you never know. Thanks.

07-31-2013, 03:34 PM	#2
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Brake booster, adjustment rod, or something else? I would first check to make sure rear breaks are adjusted properly -I adjust new brake shoes out until they lock the drum and then back off until they barely scrape the drum. On used ones I do the same but then back off until brake shoes are just off the drum. Then take the truck out to a dirt road or gravel road and see if the brakes will lock on the soft surface. Stop and actually look at each side and front and back tire marks. This will at least let you know if all of them are braking. If all that looks good and you're sure the booster is actually working okay go buy a good set of brake pads and shoes. Sometimes it's the material they're made of. I had a similar problem with some cheap brakes I bought some years ago. Check this out: http://www.classicperform.com/TechBo...ot.htm#pushrod __________________ 68 GMC 250/3 speed Saginaw p/b p/s 69 Chevy 350/350 currently in pieces still lookin for a cab 06 Trailblazer I just want a vehicle that I can work on, that won't talk to me, leave error msgs or keep track of how I drive... Last edited by 68gmsee; 07-31-2013 at 03:43 PM.

07-31-2013, 03:51 PM	#3
Longhorn 70 Registered User Join Date: Dec 2012 Location: Chandler AZ Posts: 1,149	Re: Brake booster, adjustment rod, or something else? I had a similar feeling on my brakes after I did the disc in the front. The way I adjusted the rod in my booster, and I don't know if it's right procedure, was to 1. Steel some modeling clay from my 5 year old daughter 2. Place a pea sized blob on the M/C piston where the rod should meet 3. Tighten the M/C to booster (do not touch pedal) 4. Start the engine and let idle for 30 seconds or so 5. Remove M/C from booster and make sure I had about 32/nd of thickness with no breaks in the clay. It worked for my brakes. I now feel they are much better than they were. Also after you get it adjusted properly, fast idle for 30 seconds or so then shut down the engine. Wait 30 seconds and see how many assisted pedal presses you have... I have 2 and a half or so. __________________ 1970 Longhorn, Front Disc, 350/4 bolt, 882 heads, HEI, Edelbrock, 700R4, HO-52/4.11. 1996 Corvette, Collector Roadster, LT4, 396, 450RWHP, 6sp, 4.11/Dana44/posi 5 point roll bar And let us not grow weary of doing good, for in due season we will reap, if we do not give up. Gal 6:9 Last edited by Longhorn 70; 07-31-2013 at 03:57 PM.

07-31-2013, 04:45 PM	#4
zac Registered User Join Date: Jul 2008 Location: louisville, ky Posts: 502	Re: Brake booster, adjustment rod, or something else? Thanks for the input. I can't get the brakes to lock even on wet grass. I did a bunch of reverse rear brake adjust runs and they seem to be adjusted based on the fact that the parking brake works well now where it was kinda loose before. I have a donor '72 parts truck that I know was working and had new parts on it. I know because I put them on. It appears adjusting the rod requires dropping the column a bit. Pedal has 1/2" to 5/8" play, book says 1/8". Think I'll swap on the booster from the '72 and use the rod or compare it to the one I have and see what happens.

07-31-2013, 09:40 PM	#6
zac Registered User Join Date: Jul 2008 Location: louisville, ky Posts: 502	Re: Brake booster, adjustment rod, or something else? OK, better now. Lengthening the rod helped alot, the other booster was clearly better. Also, this is a converted system, and the guy who did it made some understandable compromises, especially with the lines since there was no such thing as '70 K10 disc brakes. Too many couplers for my taste, a couple were seeping just a little. Also, I didn't put new shoes on the back because they seemed to have quite a bit left. But when I was popping the drums back on I noticed the right rear shoes had cracks. Drums were much lighter than the finned '72s and seemed too thin. Should have put later drums on and new shoes, that's on me. Still, the truck brakes as good as my '72 K10 burb ever did, which was never awesome, even with all new parts. I may be expecting better performance than it is capable of. These are the only 67-72s I've ever owned. My '79 K20 has a full floater with the big brakes, gets driven with an empty bed most of the time. Goes from 60 to zero in what seems like 50 feet. Not a good comparison.



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