Help ! Identify brake master/booster

[oldusafmsgt]

I need help identifying this booster/master in my 63 C10, It's mounted flat on the firewall, no bracket. GM metric g body maybe ? Front discs/calipers appear to be GM metric. Thanks !

[lolife99]

S10 maybe?
Anyone know?

[67c10rustbuket]

That booster could be an S10 but the master cylinder is definately not.

I have attached some pics the first is a late square body S10 9" dual diaphragm booster that I have which looks the same but the master cylinder tank on yours has a serious rake.

the second pic shows the ID decal to identify the booster (I cant read yours but the sticker is there) YC = 9" dual diaphragm. Take a look and see what the code is. There is also an ID decal on the front of the booster tank that will identify it, if it is still on there.

S10s had a few different options for boosters but the YC is the preferred for swaps due to its small size and dual diaphragm, they had to use this on 4.3 V6 S10s but the 4 cyl S10s had a larger diameter single diaphragm model.

After a quick "shot in the dark" search this is my guess 1986 Monte Carlo 5.0 HO. It has the 9" booster and raked master cylinder tank. (pic 3) I found this at autozone.com

[67c10rustbuket]

I think the only real difference between the '90 S10 4.3 V6 and the '86 Monte 5.0 HO is the fluid tank on the master. So I wonder how level is that brake fluid tank on your truck?

[oldusafmsgt]

It doesn't feel like I have any power assist at all, I'm suspecting the booster is bad. Probably replace both, get rid of the master rake. Does the S10 booster/master work well ?

[67c10rustbuket]

Originally Posted by oldusafmsgt

It doesn't feel like I have any power assist at all, I'm suspecting the booster is bad. Probably replace both, get rid of the master rake. Does the S10 booster/master work well ?

Sounds like that could be the problem but you may want to take a look at your prop valve first. Hopefully the PO used a disk/drum prop valve. If they left the original drum/drum prop valve it will feel stiff with minimal braking (my experience anyway). As far as "does it work well" in my S10 it worked well but I really have no idea if it works any better than one from the '70s. All I know is they are small and popular for swaps due to their size. Maybe someone else can compare the functionality of old school vs new 9" dual diaphragm for you.