KB5 Hydrovac

Hey guys, I just pulled the Hydrovac (third series, single stage) from my KB5. I am wondering if anyone has any experience bypassing or not using a Hydrovac?

I am not sure if mine was working or not. I upgraded the master cylinder and am replacing all of the brake lines. I am looking at the Hydrovac on my garage floor wondering if I really need it or not. I am not that familiar with vacuum assist brakes so I am not sure how much a good working Hydrovac improves braking.

I would appreciate any advice.

Well, they sure are a nice option when they are working. So, did you make sure whether or not the old MC had a check valve in it? there were 2 configurations. Check valve in MC and NOT in the hydrovac. And the other was the opposite, no check valve in the MC, and one in the hydrovac. if both or neither have the check valve, the brakes won't work right.

Just my uninformed opinion, but if the truck was designed to have a hydro-vac, I think you would need it OR completely upgrade the whole brake system. The KB5 was designed to carry Weight, and the added assist of the hydro-vac was needed to bring that all to a halt.
Those are my thoughts, and other more knowledgeable folks will speak up.

No, do not bypass or delete the hydovac, they were made with them for a reason, that is a heavy truck to stop.

I have driven my KB 6 without a hydrovac , and then with the hydrovac . The difference is amazing , I don't know how they work other than real good . If yours is not working its worth it to get it fixed . When you look at the stuff in the manuals it seems pretty complicated but its not , clean it all up and take a good look at the diaphragm , I think it's usualy what is wrong with them , I have one soaking in anti-freeze to soften it up and keep it soft .

Thanks, guys.

Tom, I looked at my manual and it looks like the check valve is on the Hydrovac for the third series units. There is a "control valve" which I am guessing is the check valve. I need to take a closer look at the Hydrovac itself to make sure, but I think this is it.

Thanks for all of the additional input. Looks like I will add rebuilding the Hydrovac to my to-do list. Does anyone know of there are parts available for these? Especially the diaphragm?

The most common problem is on the brake fluid side, they can leak just like a wheel cyl or master cyl. The leak internal and brake fluid come in contact with the vacuum chamber.
haveing said that, I find the very reliable and Both mine work fine, I don't know if they have ever been off.
They get blamed for more then their share of problems because they aren't well understood by many.

What do you mean you "upgraded the master cylinder"?!?!?!?!?!?

The truck was built with a hydro-vac and there was a reason for it!!! A truck that size/weight with brakes the size it has it's almost a no brainer why they use hydro-vacs.

Also the stock MC is matched to the particular HV unit so they work as a "team",this should not be changed!!! They also correspond to the bore(s) of the wheel cylinders.

In some systems the HV has a residual check valve whilst the MC does not,in other's the MC has the RCV and the HV does not. They cannot be "mixed and matched",one or the other must have a RCV but never both.

The control valve is not a check valve,it controls the vacuum actuation,the RCV is located in the end cap on the slave cylinder (end cap is where the hydraulic output line connects).

I can't look up the HV or MC at GangstarIH because the section with them is missing. I have a list with many MC's I've crossed to aftermarket pn's plus the rebuild kits but not for the K/KB5. I'd like to add them if anyone can provide the IH's pn's or copies of the pages in the book.

Other things to know...
There should also be a vacuum check valve somewhere in the supply line from the intake manifold to the HV unit,usually mounted to the firewall.

If the vacuum system has any hose connecting the steel tubing,it is special hose and must be replaced with same.Not hard to find,all trucks with HV's used it in either 1/2" or 3/4" ID.

If you have the IH parts manual (MT-52D) for the truck you can find the illustrations for the HV unit,the vacuum hosing & piping in Group 12.

Forget about rebuilding it yourself,you won't find the parts,I've tried and they are NLA.

The piston type units also require periodic "lubrication" as they have leather seals inside that must be kept pliable,neatsfoot oil is the most popular.

This link has a lot of useful info.
http://www.bepco.biz/Catalogs/vacuums_&_hydraulics.htm

I use "Section III - Bendix Brake Boosters" all the time for reference and identification.

I also have a few links for rebuilders if needed. They usually go for around $300 w/exchange from what I've found.

Scottso, can you post the links to the rebuilders? My NOS one is acting up, and I may send the old one to be rebuilt as a backup.

I rebuilt my Hydrovac, and while it wasn't hard it was a PIA to find parts. There are about half a dozen different boosters, all called Hydrovac, of different sizes and configurations. I ended up getting a couple of kits off eBay, using the parts that fit and reusing some of the old ones that still looked good. I have yet to reinstall it, so I don't know for sure if it will work or not- the whole exercise may have been pointless and I may end up sending it to be rebuilt.

There was an a outfit in Germany that had rebuild kits for a C@ddy (same unit as in my A120). It ran $250 and shipping would have made it even more expensive. If I had to do it all over again, I would send it to a rebuilder just because finding the right parts was so hard. The cost would be similar to that.

These guys have some rebuilt units on the shelf and will trade in cores or rebuild yours. There are other good rebuilders as well and some can pipe up on who they are. Hydrovac is one of Remans specialties:

http://www.remaninc.com/