79 C70 with hard brakes - bad hydro-vac? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

hkopp · 09-05-2018, 05:49 PM

I've been a member for a while, but usually hang out in the 60-66 k10 area. I have a 79 C70 with hydro-vac that I recently acquired. Its brakes are nearly non existent and hard, and require pumping of the peddle then pressing VERY hard to make the truck stop. I'm assuming its a bad hydro-vac unit under the side step, has anyone experienced this before? I see reman units for around $160 with a core, but would rather hear some feedback before I start throwing parts at it. I've had a C70 in the past and when working correctly the hydro-vac brakes nearly throw you thru the windshield, even with a full load.

Any troubleshooting procedures or pages dedicated to this, or is this a common symptom of a bad h-vac? Thanks!

sweetk30 · 09-05-2018, 06:22 PM

had one that some one took out the check valve inline to the booster from the engine vac port . brakes only half worked good after a doo hard pull and decel building vac .

put a new valve inline and all was good .

5Tractorguy · 09-05-2018, 08:42 PM

My '61 5000 has a Midland Hydro-vac. Same symptoms with yours when I first got it. I used to have to pump the pedal twice to get good brakes, then a couple, then I took it for a drive one day and no amount of pumping would stop it.

Sent it to DS Parts Co. in Bluefield VA for a rebuild, now I can stomp on the pedal and leave dually skid marks on the road.

On those re-manned units.... make sure you call before you order! I have an uncommon Midland unit and Summit just so happened to show one on their site. After 3 weeks of not receiving it I called and apparently there was 0 in stock. They had to wait for a rebuildable core to come in (who knows when) to the Cardone Co. so it could be rebuilt and sent to me. DS had a 7-8day turnaround on the rebuild, ran about $260 with shipping.

hkopp · 09-05-2018, 09:55 PM

Thanks for the replies. Good to hear someone had the same issue and a booster fixed it. I'll check to make sure everything is there, but since I have zero boosted brakes ever, I'm pretty sure no vac is being stored. Time to remove it and see if it'll hold vacuum on its own or if it has brake fluid in it.

09-05-2018, 05:49 PM	#1
hkopp Registered User Join Date: Feb 2014 Location: Nampa Idaho Posts: 68	79 C70 with hard brakes - bad hydro-vac? I've been a member for a while, but usually hang out in the 60-66 k10 area. I have a 79 C70 with hydro-vac that I recently acquired. Its brakes are nearly non existent and hard, and require pumping of the peddle then pressing VERY hard to make the truck stop. I'm assuming its a bad hydro-vac unit under the side step, has anyone experienced this before? I see reman units for around $160 with a core, but would rather hear some feedback before I start throwing parts at it. I've had a C70 in the past and when working correctly the hydro-vac brakes nearly throw you thru the windshield, even with a full load. Any troubleshooting procedures or pages dedicated to this, or is this a common symptom of a bad h-vac? Thanks!

09-05-2018, 06:22 PM	#2
sweetk30 Registered User Join Date: May 2012 Location: horseheads,ny rust belt Posts: 2,794	Re: 79 C70 with hard brakes - bad hydro-vac? had one that some one took out the check valve inline to the booster from the engine vac port . brakes only half worked good after a doo hard pull and decel building vac . put a new valve inline and all was good . __________________ 77-k30lb BIG truck build . 87-k30lb budget beater build . 85-k30lb the plow machine build . 85-c10sb summer fun toy . ----------------------------- HOLLEY SNIPER efi = worst case of p.i.t.a i ever had . EDELBROCK pro flo 4 = best deal going so far . love my setup works great.

09-05-2018, 08:42 PM	#3
5Tractorguy Registered User Join Date: May 2015 Location: Central Massachusetts Posts: 496	Re: 79 C70 with hard brakes - bad hydro-vac? My '61 5000 has a Midland Hydro-vac. Same symptoms with yours when I first got it. I used to have to pump the pedal twice to get good brakes, then a couple, then I took it for a drive one day and no amount of pumping would stop it. Sent it to DS Parts Co. in Bluefield VA for a rebuild, now I can stomp on the pedal and leave dually skid marks on the road. On those re-manned units.... make sure you call before you order! I have an uncommon Midland unit and Summit just so happened to show one on their site. After 3 weeks of not receiving it I called and apparently there was 0 in stock. They had to wait for a rebuildable core to come in (who knows when) to the Cardone Co. so it could be rebuilt and sent to me. DS had a 7-8day turnaround on the rebuild, ran about $260 with shipping. __________________ Jake 5Tractorguy on Youtube

09-05-2018, 09:55 PM	#4
hkopp Registered User Join Date: Feb 2014 Location: Nampa Idaho Posts: 68	Re: 79 C70 with hard brakes - bad hydro-vac? Thanks for the replies. Good to hear someone had the same issue and a booster fixed it. I'll check to make sure everything is there, but since I have zero boosted brakes ever, I'm pretty sure no vac is being stored. Time to remove it and see if it'll hold vacuum on its own or if it has brake fluid in it.



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