The Stovebolt Site Forums The Parking Lot Big Bolts 1958 Chevy Viking Vacuum Shifter Parts

Hello-

I have a 1958 Chevy Viking 6400 with two-speed rear axle. Anyone know where I can get the internal seals for the vacuum shift assembly that bolts onto the two-speed rear axle? I bought a new diaphragm already. Need the felt packing, and top and bottom seals. Underside of diaphragm has oil in it. I have a book at home with the part numbers. My wife works at a GM dealership, and is having her parts guys check on them. But I wanted to see if any fellow Big Bolt owners have went through this yet. Thanks in advance!

This might be very helpful , i think there is also a diaphragm on the back side of the speedometer too.

I think Ii will be in need for gaskets, or seals, for both.

So please distribute if you can get the part numbers.

These are the part numbers for the two speed chevrolet vacuum shift assembly on 2 speed axles for 1956-1958 in order to rebuild it:

Diaphragm- 3847058 GM#
374451 Bendix#

Whole assembly- 3874330 GM#
2504299 Bendix#
Cylinder and Boss assembly- 3847055 GM#
374460 Bendix#
Shell and seal assembly- 3721330 GM#
377271 Bendix #

Piston rod seal- 3721328 GM#
374534 Bendix#
Diaphragm seal- 31/32 I.D.x1.5 O.D.x 7/32 Thick
GM# 3705847

Diaphragm assembly gasket- 3705848 GM#

Diaphragm felt packing- 3705845 GM#

Packing retainer- 3705846 GM#

Piston rod seal gasket- 3723038 GM#
377416 Bendix#

Piston rod- 3721350 GM#
377274 Bendix#

Many of these parts are still sitting in GM dealerships. I had my wife check with her parts guy, and the parts I needed were available, but scattered throughout the US. I would have to pay the shipping to get them to her GM dealership, so cost will be pricey. Hope this helps.

Turns out my diaphram was bad, so I just replaced that. Shifts much quicker now and easy.

Any idea if these parts can fit my '54 GMC 350 vacuum 2 speed too? Mine drops out of High if I try to cruise it at road speed,from losing it's vacuum. Back out of the throttle or downshift one gear,all's well. I suspect it's just a couple of hose leaks,but might be worth having some parts on hand,just in case.
Speed

If any leaks or mafunction, is the rear gear defaulting on LOW or HIGH ?

I'm also curious about the answer to this question. I'm assuming that it pertains to whatever is in my '55.2 frankentruck, of course.

The rear normally stays in which ever range you leave it in, but if there is a default it would be LO range as that's the down position on the actuator plunger.

Mike B

I had assumed it was a vacuum actuated/spring return type unit. Good to know that's not the case.

There is no return spring involved...

Mike B

Do you know if any of these part numbers were used in a 1953 two ton vacuum shift?

Exactly what parts do you need? The Diaphragm is the same, but that might be about all...

Group 5.635

Mike B