Astro Van Hydro Boost help....

[904Bronco]

Installing another Chevy Astro Van HB unit in my 1970 project, bought the exact same parts that I did a HB conversion on my 67 Bronco a few yrs ago.

"1995 Cardone Rebuilt Astro van HB unit #52-7333, Raybestos #MC39961 new master cyl"

I had the little connector shaft that the rebuilt unit does not have, you are supposed to transfer it from your core, in my parts collection for the 67 conversion.
I didn't have a second one, so Todd Z. was selling one in the parts section a while back and I picked it up at a great price. Put it in the spare parts collection for this project.
Everything is mounted up, plumbed up, PS lines all bleed, but the shaft sticking out from the HB unit is too long? It collapses the Master cylinder pretty far in just to get it bolted up to the HB unit. See pictures.
I don't have the 67 Bronco anymore to check if something is different. I suppose the master Cylinder could be boxed wrong? Kind of hard to check that with the auto parts store on a Sunday. Was wondering if there were different shaft lengths for other years, maybe that what I got from Todd Z. I could shorten it, but would prefer to do that as a last resort.

Anyone have any experience in this, maybe a 1995 unit they could take a measurement of the little connecting shaft?
I can't bleed the brakes until I resolve this...
Thx. Doug.
Pics - Back of the new Master, shaft sticks out 11/16" while the engine is running, as far as the master can go on before making contact with the shaft.

 

[904Bronco]

Master Cylinder appears to be correct...

After reviewing too many on line pictures, I sent a PM to Todd Z to ask if he remembers what his source was for the HB connector shaft, Spring, and washer. I am thinking it is not from an Astro/Safari van...?

 

[toddz69]

I checked my inventory and I have another pushrod in stock. It's about 3.75" long - probably from an Astro booster. The SD pushrod is about 4.3" long. If the 3.75" one would work, let me know and I'll drop it in the mail for you.

Todd Z.

 

[thegreatjustino]

There were different lengths of rods depending on the hole depth in the piston of the MC.

At Todd points out, you seem to have a Ford rod in the GM booster.

 

[catfan]

The astro Van rod is 3.2 " long.

 

[catfan]

I have an extra one Doug if you need it.

 

[904Bronco]

Thanks all for the replies, I will pop out the rod today and get a measurement.

 

[Madgyver]

cut rod to fit... that's what i do...

 

[904Bronco]

Rod is 3.75" long... .55" longer than it should be according to Cat Fan. (Thanks for that)
Mad your right, looked around on line at the local Pick-n-Pull and no one has a Safari or Astro van of the 95 Vintage. There are later models, one would think they would be the same rod, but I know the HB units changed... Then there is the drive there and back, diesel fuel for the truck, and my time.
The retainer looks the same, the spring might be a little longer, going to use what I got.

I do appreciate everyone's comments and info. Doug.

 

[El Kabong]

cut rod to fit... that's what i do...

I've done that on a master cylinder swap. Then ground the end round to resemble the original. Worked well.

 

[lars]

Thanks all for the replies, I will pop out the rod today and get a measurement.

Doug, with all due respect, that sentence could be twisted in so many ways.

 

[904Bronco]

Doug, with all due respect, that sentence could be twisted in so many ways.

Yeap, I stepped on something there...

 

[904Bronco]

So I removed the connecting rod and shortened it. All good there.
Got the new master cylinder bled on the bench and once installed I could not get the brakes bleed at all.
No fluid to the rears? After a little gravity feed, I got the front Disc calipers bleed. Still nothing to the rear.
Confirmed HB is working, I have brake fluid going through the manual brake proportioner valve from Summit at the master.
Ran out of time to see if it is getting through the H-block (Which I rebuilt). Tomorrow I will try again.

Sorry about my choice of words there Lars...

 

[904Bronco]

Still struggling, fluid getting to the H-block and coming out the other side on Brake petal pumping.

Broke the line on the out side of the manual proportioning line and cracked one the rear brake wheel cylinders open, put about 20 psi of air in the line and I can hear to escaping. Not sure what is going on...

 

[lars]

Still struggling, fluid getting to the H-block and coming out the other side on Brake petal pumping.

Broke the line on the out side of the manual proportioning line and cracked one the rear brake wheel cylinders open, put about 20 psi of air in the line and I can hear to escaping. Not sure what is going on...

How are you bleeding the brakes? The good old 2 person method with someone stomping the pedal and the other opening/closing the bleed screw? Or pressure bleed, or...?

I'm wondering if the h-boost pushrod is slightly preloading the master cylinder piston and blocking the port to the back brakes. First thought: loosen the bolts retaining the master cylinder to the h-boost, far enough that you can slide the master away say, 3/16-1/4 inch. Then by hand, try bottoming the master against the h-boost. If the booster pushrod is contacting the master piston before the mounting faces are in contact, you will feel it.

I recall some discussion once about this, long ago (like almost 20 years). Somewhere I recall reading that there should actually be some slight interference and that the h-boost pushrod retracts slightly (yeah, I know, don't go there) when the engine is started and it gets hydraulic pressure. But that could be a myth. Maybe Todd Z, who is more current on this stuff than I, will chime in. In any case, in the operational state there should be a slight clearance.

 

[toddz69]

This is a summary that I copied from an eBay listing from a guy who makes a lot of hydroboost kits:

***Typical booster input rod to MC piston gap is 0.0", some Fords run with 0-0.0150" pre-load, while some OEM Ford hydroboosted MCs had 0.038" pre-load and others had zero. The '03 Chevy 2500 runs about 0.0580" pre-load and some earlier trucks use 0.0650". Check your MC specs prior to shortening the input rod so that you accomplish the same gap or pre-load if required as there is a lot of variance among different master cylinders as far as how to set up the booster input rod adjustment. Some master cylinders will be less tolerant of pre-load due to the location of the compensation ports which could be blocked and lead to brakes that drag. Know the specifcations for the master cylinder you are using.

I used to have a lot of conversations with Paul at Hydratech years ago about this and I think my best advice is to always try and have zero preload on the master cylinder piston. You really can’t go wrong.

Todd Z.

 

[904Bronco]

Lars to answer your questions... 2 person - pump 3 and hold. Tried it last night with the engine running, open exhaust , no change.
I won this fancy power bleeder kit at a raffle a couple of years ago and non of the adapters will work with the Astro van master cylinder. There seems to be an option for a GM one I don't have, for a minor $40 plus shipping.

I know from assembly there is some minor preload on the master cylinder. I can zero that out with some shims. I will give that a try. H-block shuttle shaft has shifted over to where the brake light is on now...

 

[pcf_mark]

If you need or want to adjust the pushrod w/o taking it apart you can put a washer on the stud between the m/c flange and h/b flange. You can "tune" the preload with washers so the brakes do not drag. Then you can go back and shorten the pushrod the thickness of the washers. Or be like me and drive around with a washer in there for 5-6 years.

 

[904Bronco]

And the answer is... Brakes are bleed.
There was pre-load on the master cylinder, shimmed it out about 1/8" with Washers (pfc_mark). Started pumping the pedal from inside and saw fluid movement in the front MC chamber. Got my son to come out to do two person method as Lars says and we have fluid movement! Bleed all four wheels again. There are brakes! Had to pull one of the rear tires and take it back to the tire shop to have it rebalanced, the smallest amount of brake fluid will destroy the adhesive characteristics of the glue for stick on weights. I had a shim I made for a previous project that I think I can repurpose? First hydro boost I did (15 yrs ago) with the Camaro MC that always leaked no matter what I did... I am reluctant to cut down the rod again, if the master fails in the future, it would be easier to remove the shim with the replacement MC than it would be to add material to the rod. Now to see if the brake light on the dash is out after the bleeding?

Thank you all for you guidance and input... Doug.

 

[pcf_mark]

That is awesome! I use the washers until a test drive proves you have the right thickness. Mine front brakes had drag until I hit the thickness just. I bet you could 3D print a shim all the load it going outward on the studs not compressing the shim.

That is one CLEAN engine compartment. Mine looks every day of 54 years old.