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

[u2slow]

My JB8 braked '91 v3500 (hydroboost, SRW) shows a 1.31" bore. The '93 JB7 master (vacuum) i used was 1.25" bore.

The NMC11318 and MC39309 masters are for rear disc - check the other things it fits. I believe the G-van application for them (rear drum) is incorrect.

Edit: SRW can be 2.5 or 3.5" shoes. DRW is always 3.5".

 

[Cubey]

My JB8 braked '91 v3500 (hydroboost, SRW) shows a 1.31" bore. The '93 JB7 master (vacuum) i used was 1.25" bore.

The NMC11318 and MC39309 masters are for rear disc - check the other things it fits. I believe the G-van application for them (rear drum) is incorrect.

Edit: SRW can be 2.5 or 3.5" shoes. DRW is always 3.5".

M39435 (1.31) is shown for C/K/P/V but doesn't specify HB, only says "power" brakes. They don't do a good job with details, do they?

Dorman Products - Aftermarket Auto Parts & OE Solutions - M39435

Brake Master Cylinder

www.dormanproducts.com

M39309 (1.25/34mm) is showing disc for some and drum for others. Yeah could be wrong.

ShieldSquare Captcha

Sucks trying to find parts for 30-40 year old trucks when they get the data wrong.

 

[Cubey]

The ACDelco one that looks M39435 on the lid says it's for JB7 or JB8 depending on the vehicle but not for G series.

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[u2slow]

The master you posted for the van with dual bore sizes and dual reservoirs seems van-appropriate. Never seen one of those on a pickup.

1ton C/K series always got hydroboost in my experience, plus diesels, plus some military-spec K20's. Vans are funny because 10-20 series are both 5lug, and the base 30 series starts with 20 series truck brakes/axle/suspension.

Something has changed in the listing. Seems to me the van brake parts roster was massive - and was combined with P-van (includes A class motorhome) and some had rear disc. Now it's been split up and G30/3500 stuff seems off.

 

[IDIBOBS]

Gonna be a no help jerk here but if you put it all back to stock and adjust and bleed correctly you won’t need all this other stuff. My 1990 with vacuum and drums stops just as good as my 2001 super duty with 4w disc or my 2010 super duty or my 2005 suburban. And yes even when hauling in the mountains. As for towing all my trailers have proper brakes so they actually stop better while towing then not. If you put everything back to stock you won’t have all this head ache.

 

[Cubey]

The master you posted for the van with dual bore sizes and dual reservoirs seems van-appropriate. Never seen one of those on a pickup

That's the lower weight one (8400/8600)

 

[u2slow]

That's the lower weight one (8400/8600)

It would not surprise me if that was used on both vac and h-boost; and the listing is wrong.

We parted out a lot of 1ton Chevy vans back in my wrecking yard days (church vans and dually cube vans) - all rear drum. None used the MC39309 master... It's an easy one to spot.

 

[Cubey]

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

Hm, make of this what you will. It's from my 94 G series FSM. The drawing is clearly a MC39309 style, with the nuts holding on the reservoir from underneath. It also shows HB return being dumped back into the top portion of the remote PS reservoir, so it didn't use a different pump, I guess. Dunno what that #6 "Switch, flow" is on the PS pump return line coming from the PS gear.

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The various brake systems:

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Notice how for diesels, it's HB including for 2.5" rear drums under JD7.

Looking up MCs for a 94 G3500 diesel, rockauto shows this. it's for JB8 and JD7. So it seems yes that MC is right for all HB uses, based on the FSM and parts listings online. Unless GM had the drawing done wrong and has wrong info in the FSM table for brake systems.

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[Cubey]

Someone went crazy tightening down the two nuts for the MC to booster, so I had to use some wd40 and a small breaker bar to get them loose. The booster has signs of a leaking MC: rust/corrosion on the booster below the MC. It's rusty on the booster push rod too, but I don't see or feel any moisture from the MC, like I did on Smurf with it's leaking MC, so the leaking MC might have been replaced at some point, but not the booster. So maybe I won't have to mess with that right now, since the pedal isn't hard. Could be as simple as needing rear shoe adjustments.

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[u2slow]

Hm, make of this what you will. It's from my 94 G series FSM. The drawing is clearly a MC39309 style, with the nuts holding on the reservoir from underneath. It also shows HB return being dumped back into the top portion of the remote PS reservoir, so it didn't use a different pump, I guess. Dunno what that #6 "Switch, flow" is on the PS pump return line coming from the PS gear.

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The various brake systems:

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Notice how for diesels, it's HB including for 2.5" rear drums under JD7.

Looking up MCs for a 94 G3500 diesel, rockauto shows this. it's for JB8 and JD7. So it seems yes that MC is right for all HB uses, based on the FSM and parts listings online. Unless GM had the drawing done wrong and has wrong info in the FSM table for brake systems.

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'94-95 are tough year examples because they made the G30HD with rear disc, tilt nose, and 19.5" wheels. Is that in your FSM too?

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Also with GM, diesels always got hydroboost.

Here is the mc39309's application list.
Each of these had rear disc in a specific configuration, except the H1 (default).

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Edit: lots of different masters fit the GM hydroboosts. I have two different iron ones on mid-80 GM pickup hydroboost. I have also tried a '94 Dodge one (aluminum) and a MC39309. All fit identically. I even checked a 95 F450 master!

 

[Cubey]

'94-95 are tough year examples because they made the G30HD with rear disc, tilt nose, and 19.5" wheels. Is that in your FSM too?

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Also with GM, diesels always got hydroboost.

Here is the mc39309's application list.
Each of these had rear disc in a specific configuration, except the H1 (default).

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Edit: lots of different masters fit the GM hydroboosts. I have two different iron ones on mid-80 GM pickup hydroboost. I have also tried a '94 Dodge one (aluminum) and a MC39309. All fit identically

Yeah but if there are errors in some parts fitment data, couldn't it be that's an error too? I wish I could find a PDF of the parts/part number book, like I found for 3rd gen Econoline.

The FSM only seems to cover the regular van body. The cover says "G VAN" (and 1994). Here's a picture of the model/body types page found in the book under general information.

G30HD is probably considered a medium duty truck, despite being called "G". The cab appears to be larger/taller, so it's likely not the same class of vehicle.

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[u2slow]

Yeah but if there are errors in some parts fitment data, couldn't it be that's an error too? I wish I could find a PDF of the parts/part number book, like I found for 3rd gen Econoline.

G30HD is probably considered a medium duty truck, despite being called "G". The cab appears to be larger/taller, so it's likely not the same class of vehicle.

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Anything is possible i guess. I've had the mc39309 master on my radar for probably 20 years for running a disc brake rear axle, as it fits the otherwise common 'rear drum' hydroboosts. There is a revision to an even larger master piston size (92+? 96+?) but then the stud spacing increases and pilot is larger.

The G30HD would fall under the cutaway or 'magnavan' model. It's built with the same recipe as the 3500HD C-series truck with 19.5" wheels made from '91-02.

 

[Cubey]

The G30HD would fall under the cutaway or 'magnavan' model. It's built with the same recipe as the 3500HD C-series truck with 19.5" wheels made from '91-02.

G30HD is unibody too?

 

[u2slow]

G30HD is unibody too?

Full frame as far as I know.

 

[Cubey]

It would not surprise me if that was used on both vac and h-boost; and the listing is wrong.

We parted out a lot of 1ton Chevy vans back in my wrecking yard days (church vans and dually cube vans) - all rear drum. None used the MC39309 master... It's an easy one to spot.

Looking through my 1994 G-series official GM factory service manual for some torque specs, I ran across this. It clearly shows a MC39309 for JB8/JD7. Make of that what you will.

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