Hydroboost Saginaw pump? (a little off topic..)

[Cubey]

This is a little off topic, due to it being for the 94 GMC G3500 RV I'm switching to, but.. I figure it this is the best site to ask on.

The van has a Saginaw pump, with a remote reservoir. And when poking around on rockauto, I found a hydroboost "booster" for $30 on closeout. (the last available closeout is $68 now) and it's a direct fit, just made for dually variation of Chevy/GMC G series 1 ton van. I also ordered the two directly compatible pressure hoses for dirt cheap on closeout too for ($5 each). i don't know if it actually requires a different master cylinder, but it calls for a different one vs vacuum booster version master cylinder. I'll have to ask on GM sites about that, I guess.

But regarding the Saginaw pump, does a stock pump work well enough for power steering plus hydroboost, or are there special high flow pumps? It's a bit on topic for here, since IDI vans got Saginaw through 91, and I know some people convert to Saginaw because it's better or something.

Having a remote reservoir metal can via hose, I can probably just put a tee in the gravity feed hose to add an extra return line, and use the common power steering pump for the van, since there doesn't seem available a hydroboost specific PS pump for van (anymore).

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[Clb]

If Irc
The master is different from the vacuum version in either port size or pushrod....
Pump flows are higher for h.b., but you're probably going to experience a slight lag in panick braking pressure due to volume of flow available.
My 93 v3500 quad cab weighs @9k
Factory brakes will lockup the rears with a light trailer tagged on...

 

[Cubey]

If Irc
The master is different from the vacuum version in either port size or pushrod....
Pump flows are higher for h.b., but you're probably going to experience a slight lag in panick braking pressure due to volume of flow available.
My 93 v3500 quad cab weighs @9k
Factory brakes will lockup the rears with a light trailer tagged on...

The plumbing is supposed to go from the pump to HB first, then to the steering gear, so HB should get the primary flow.

The hoses I ordered state pump to hb, and hb to (steering) gear.

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I did read that it might be good to add a small oil cooler for the PS system to help with the extra load on the fluid. Dunno if it's needed or not though.

It's possible to buy a pump with the dual returns for an ok price, but it would delete the remote reservoir. Not a big deal, I'm used to IDI Econolines with the standard Saginaw buried down in the same spot on the engine as it is on the 350. But I'm guessing I can just tie in the extra return to the gravity feed to the pump from the remote reservoir.

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[Cubey]

If Irc
The master is different from the vacuum version in either port size or pushrod....
Pump flows are higher for h.b., but you're probably going to experience a slight lag in panick braking pressure due to volume of flow available.

Oh and the port sizes are reversed on the proper MC for HB. The MC bore is smaller (34mm) vs vacuum booster (40mm). Easy enough to get adapter fittings to change the line ends for HB

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[Clb]

My point was
The gpm of the h.b. pump is greater...

 

[Cubey]

My point was
The gpm of the h.b. pump is greater...

Gotcha.

This one says 3.0-3.5gpm: https://www.borgeson.com/p-s-pump-f...kd1zFJQa9iUNrWOrg-8GWIP0xc3zmY0B0y9hpFfBgjT2D

For some reason, some sites like Amazon claim 3.5-4gpm for that same pump, but I'll trust the maker's site that says 3-3.5

This source online says "Typical Saginaw power steering pump in a GM car or truck is 1.3 GPM at 500 RPM, and 3.1 GPM at 1500 RPM".

Another person elsewhere said: "The problem you run into with a Hydroboost is that it wants 2.5 to 3 GPM and most performance steering boxes and racks want 2 gpm. You have to pick." I don't know if stock gears have that issue or not.


Rockauto only has the vac booster system pumps with reservoirs. The bare pumps don't specify gpm or if they are for hydroboost.

Furthermore, Rockauto doesn't even list any power steering pumps at all for 94 C/K 3500 that was only hydroboost. Presumably they were Saginaw pumps with higher flow. (edit: yes they do. headache today so my brain is foggy, i was looking for the power steering pump in brakes. 1983 GMC G3500 van PS pump with dual is also available on rockauto, but not 1994)

But a quick search for "1994 K3500 power steering pump" pulled this up: https://a-premium.com/product/Power...994-Chevrolet-K3500-XHZB6uHj4p?variant=595887

I also spotted one for 94 C/K3500 on ebay for $106 with dual return, so they do exist out there.


I suppose I can try it out with the existing Saginaw pump first, and if it's crap, I can go back and upgrade the pump later. If I didn't get the hydrobooster so cheap, I doubt I'd be going down this route, at least not right now. And depending on if the current MC is leaking at the booster or not (haven't checked yet) I might put off doing the conversion entirely until later. I haven't dug into why the brakes are crappy yet, but I am intending to at least replace the pads, shoes, hoses, and of course do a good fluid flush, regardless of what the problem is... hence why I was on rockauto looking at brake parts.

I only have ~$40 in the hydroboost parts right now, if they sit on a shelf for a while and get used (or resold) later, that's fine.

 

[u2slow]

T-ing the return line is normally sufficient. I did that on my F350 swap, based on reading numerous hydroboost threads. Keep the tee close to the reservoir though.

Chevy masters often swap between vac and hydroboost. Have done it before ('91 V3500 crewcab). Piston size might be slightly different, because calipers and wheel cyls tend to be bigger on the hydroboost trucks.

 

[Cubey]

T-ing the return line is normally sufficient. I did that on my F350 swap, based on reading numerous hydroboost threads. Keep the tee close to the reservoir though.

Chevy masters often swap between vac and hydroboost. Have done it before ('91 V3500 crewcab). Piston size might be slightly different, because calipers and wheel cyls tend to be bigger on the hydroboost trucks.

The master cylinder bore is smaller for hydroboost, dunno about the cylinders/calipers, I haven't looked it up.

The front calipers for heavy duty (9200lbs) are totally different, and cannot mount up to the lighter duty (8400lbs) setup this has, so there's no point looking up info about the bores. Since that can't be changed, no point messing with the rear wheel cylinder sizes either.

So I don't care about upgrading the brakes at the wheels, since you can't do anything there anyway, other than using heavy duty pads/shoes, which I will do.

In that case, I don't know if it even needs the different master cylinder for hydroboost, unless the vac one can't bolt up to it, but I think it can.

I will have to buy a universal push rod kit ($20ish) and carefully cut it down to the size needed, and also file it down for a tapered end. Just a bit of extra work to retrofit, since you can't just buy the pushrods for hydroboost, and they often don't/never come with hydroboosters.

 

[u2slow]

The master cylinder bore is smaller for hydroboost, dunno about the cylinders/calipers, I haven't looked it up.
...

In that case, I don't know if it even needs the different master cylinder for hydroboost, unless the vac one can't bolt up to it, but I think it can.

Going from memory only, I believe the hydroboost master cylinder bores were larger.

I bolted up a '93 vacuum master to my '91 chevy (factory hydroboost) so i know the physical fit was right. Brakes felt fine.

 

[Cubey]

Going from memory only, I believe the hydroboost master cylinder bores were larger.

I bolted up a '93 vacuum master to my '91 chevy (factory hydroboost) so i know the physical fit was right. Brakes felt fine.

This reply shows screenshots from rockauto. https://www.oilburners.net/threads/hydroboost-saginaw-pump-a-little-off-topic.94268/post-1155078

Unless the data is wrong. That is possible. The Bendix pads are listed incorrectly. the 153 pads for 8400 say they are for 3.5 rear systems, and 149 says it's for 2.5 systems The photos are correct but the details are wrong. Other brands using the 153/149 numbers say things right and also show the right pictures. Every site online lists the bendix wrong, so it's info coming out of the company.

They list a wrong A/C line too claiming it fits these vans, despite the right hose being straight at one end, and the wrong for trucks is 90 degrees, and has an extra service port fitting that puts it under the doghouse cover instead of under the hood.

So parts, database info is very broken.

 

[u2slow]

MC39309 lists for hydroboost w/rear disc elsewhere. May be bad listing.

MC39435 is what I'm used to seeing on the 9200# GVWR. 1.313" bore. This is one i had swapped with a '93 vacuum master, most likely a MC39649 (1.25" bore) with no noticable difference in braking.

 

[Cubey]

MC39309 lists for hydroboost w/rear disc elsewhere. May be bad listing.

MC39435 is what I'm used to seeing on the 9200# GVWR. 1.313" bore. This is one i had swapped with a '93 vacuum master, most likely a MC39649 (1.25" bore) with no noticable difference in braking.

The only two styles they show for these vans are the two separate lids plastic reservoir one for 2.5" rear drums (JB7, 8400lb system) or the metal lid one like MC39309 for 3.5" or DRW (which would be 9000+).

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It has the plastic type of MC right now since it's all the stock 8400 vac booster systm. No point changing to the metal one if I can't change the calipers/cylinders, correct? It might still brake better with HB instead of vac? Maybe it's a lost cause to convert if i can't upgrade calipers/cylinders?

 

[u2slow]

Theres no lost cause. Hydroboost will brake harder with existing master and calipers/cylinders (my f350 was a prime example).

I don't trust the parts listing for the 90's chevy vans.

 

[Cubey]

Theres no lost cause. Hydroboost will brake harder with existing master and calipers/cylinders (my f350 was a prime example).

I don't trust the parts listing for the 90's chevy vans.

O'Reilly shows the same 2 style and lists the bores in inches. Again, it shows the HB one having a smaller bore. JB8 comes up as "BRAKE SYSTEM,HYDRAULIC POWER DISC,DRUM"

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[Cubey]

Regarding the wheel cylinders, it's the same one for both width shoes (2.5 & 3.5) if SRW, but different for DRW. I think maybe only DRW got HB, but I could be wrong. Bigger bore for DRW only.

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