Hydro boost master cylinder?

[max 02]

I`m swapping a hydro boost brake system into my 77k10 out of a 81 k20.

Will the master cylinder from the vacuum assisted 77 work on the 81 hydro boost system?

They look the same, I thought if I just use the master that I got hooked up already it could save me from bleeding the brakes.

The 77 was a two wheel drive converted to 4x4 with 1/2 ton axles, converted to 3/4 ton axles now. The master that I`m using seems to work good.

 

[diesel4me]

I'd say yes--I used a master cylinder off my old '77 GMC K2500 that had vacuum assist on my '82 GMC K2500 that has hydroboost with a 6.2..

All you need to do is ensure the push rod seat is the same depth as your original master cylinder had...

The ports on the '77 master cylinder did not match up though,I had to buy two brass adapters to make the lines fit,they were only 1.75 each at Autozone...

I recently had to replace that master cylinder because it leaked from the rear chamber--the replacement I got is the same one many GM full sized cars and trucks used in the early to late 70's (Impala,Caddilacs,etc) and the ports were the correct sizes for the lines to screw in without the adaptors....the part number was 10-1521 if I remember right,it came from autozone.."Fenton" brand I think--A-1 Cardone uses the same number I think also...has a 1-1/8" bore...

 

[max 02]

I'd say yes--I used a master cylinder off my old '77 GMC K2500 that had vacuum assist on my '82 GMC K2500 that has hydroboost with a 6.2..

All you need to do is ensure the push rod seat is the same depth as your original master cylinder had...

The ports on the '77 master cylinder did not match up though,I had to buy two brass adapters to make the lines fit,they were only 1.75 each at Autozone...

I recently had to replace that master cylinder because it leaked from the rear chamber--the replacement I got is the same one many GM full sized cars and trucks used in the early to late 70's (Impala,Caddilacs,etc) and the ports were the correct sizes for the lines to screw in without the adaptors....the part number was 10-1521 if I remember right,it came from autozone.."Fenton" brand I think--A-1 Cardone uses the same number I think also...has a 1-1/8" bore...

Thanks Robert! I guess I`ll giver a try then.

 

[dremu]

The pushrod down the center should be a different length. I forget which is which, so ll either the pedal won't press the master at all or it'll pop the seals

Note that a hydroboost master generally switches the front and rear outputs from a vacuum type, so expect to swap the lines around (easy to do, just confusing if you're not expecting it.)

And remember the hydroboost rod mounts to the pedal in a different place than the vacuum.

Aw heck, we've done this all before... see

http://coloradok5.com/forums/showthread.php?t=306221

-- A

 

[diesel4me]

There are 2 types of push rod seats in the master cylinders,one is "deep" and I'd guess it goes in a good inch or more--the other is just a shallow "cup" that looks like a drill was used to make a 1/4" or so depression in the piston..some masters also may differ in the bolt pattern or size of the piston housing where it goes in the booster,but I'd say all the ones used in the 70's till they went with aluminum ones are the same there..and even some of the aluminum ones still fit and work,just look different..

Be aware the brake lines will screw into the master cylinder ports on a vacuum boosted master,but they would have to be swapped front to rear!--dont do that!--I learned the hard way the front chamber is for the front brakes,the rear one for the rears..when I tried swapping the lines so they fit "directly" ,I had practically NO front brakes,and the rears locked up instantly with a feather touch on the pedal.and I'd SKID ,while the truck barely slowed down at all...
---and just my good luck,my first test ride after I put the master on,I had a COP walk out in front of me who was working a traffic detail,and he put his hand up as if to say "STOP",and I skidded about 150 feet,going only 30 mph..stopped about 6" from him,he didn't even MOVE!...I was lucky not to have gotten a nice ticket for that --luckily he believed me when I said "My brakes suddenly didn't work right"--told him I thought a line popped when I hit the pedal.....after I went and bought the adapters and put the lines in the right ports,all was fine again...

 

[76zimmer]

I would give it a shot as well Dean...I had to make a custom length pedal pushrod for my setup...I used a Hydro boost from a 82 Diesel K5 and a m/c from a 78 C30 with JB8 brake option and hydroboost (all 1 tons have hydro) That gave me the biggest bore m/c for my 4 wheel disc setup...If your keeping the 3/4t calipers on the front and the big drums in the rear, I think it will work ok.
You can do a search on Rockauto or Oreilly auto parts to get a pretty good desciption of each master cylinder application(s)
My set up works awesome when its not leaking!

 

[max 02]

Thanks for that link Dremu!
I was looking for that! Now my comp is not conecting to the net and my phone is just to small! Lol!
Got some reading to do... thanks For the info Guys!

I ll let you all know how it goes in a few days. I'll be busy with feild work for a bit.

 

[max 02]

I got the hydro boost and the pedals for my standard swap in yesterday.

Now after a bunch of reading and thinking, I need to swap the power steering box with the one I got out of the hydro boost donor truck so that the lines will match up.

Stupidly! I went and scraped the frame and the brake lines off that truck.

So I am going to get some from another diesel truck that is sitting in a field close to me.

 

[diesel4me]

Far as I know the steering boxes are all the same--the pump might have more output,a larger "can" and an extra return line nipple for the hydroboost,but a regular pump will work too,you can tee the return lines together...

 

[76zimmer]

I think he needs the later model steering box for the oring lines instead of the flared lines on his 77box.
good luck Dean!

 

[diesel4me]

OH !--I thought he was thinking Hydroboost steering boxes were different...that makes sense...he could have some adapters made up at a hydraulic hose shop so he wont have to replace the box,but seeing he has a parts truck nearby,swapping the boxes would be easier..

 

[max 02]

I got the box in my garage on the floor.

 

[max 02]

Finished it yesterday... turns out the steering box in the truck "1980 frame" has o ring fittings. The 81 stuff I had was standard style.

Anyway the 86 parts truck up the road from me had the parts I needed to hook it all up.

So now it has all the proper factory hydro system on it.
Hope I did it right!