Identificatoin and open centre diff

[dmulally]

That it is pre 1950's helps my cause but I think I would have been ok as it is a follow on.

I have an sm 420 chev truck gearbox and the two top bolts go directly into the buick bellhousing. The bottom ones are a little too low though.

Seeing as my bellhousing is just grease, can anybody tell me if it is mild steel? If it is I could weld a couple of ears to the bottom to take the chev gearbox. Oooorrrr...

I could solid mount the engine and gearbox and just use the two top bolts. It is going into a racing car. The chev gearbox suits me as it is open drive, about 10 inches long and most important...I have one.

Cheers

Damo

[raycow]

IMO, there is a risk of cracking the gearbox lugs if you use only the top two holes.

The bellhousing is cast iron, and can be welded or brazed if you are good at this sort of thing. However, I would personally recommend a mechanical connection for a job like this. You can machine the bottom edge of the bellhousing if necessary and bolt a piece of steel angle to it. Then drill the other arm of the angle for the lower two mounting bolts.

If you are intending to race the car, you might not care for the shifting characteristics of the SM420. Fortunately, the same bolt pattern was also used on Chevrolet passenger cars from 1955 up, and on most other GM 3, 4, and 5 speed car gearboxes from the 1960s through the 1980s.

Ray

[dmulally]

Thanks Ray.

My constraints are that they must be of the same decade which in my case would be pre Dec 49. There are allowances for follow on design rules but I dont want to cause fuss. Also, it must all be American or English. No SU's on a buick for example. It will never be quick. I have all the steering and suspension. The sm420 is the worst for quick changes. The gaps between gears are a joke. 1st gear is unusable as it is 7:1. Im not bothered though. Old gearboxes are hard to find here unless its English.

I can take a pic and show you but there is a thick rib that comes off the port side of the buick bellhousing which could be drilled and tapped. Would that be an option? It looks rather meaty.

Cheers

Damian

[raycow]

Damian, that sounds like a good plan if the mounting bolts go into the bellhousing rather than pass below it as I wrongly thought. You could build up the low areas with brazing rod, which I think would be safer than trying to weld on cast iron. If it's not too much trouble, please post a pic of the bell, as I am not familiar with the rib you are talking about.

Good luck, and please keep us posted on how the project is coming along.

Ray

[dmulally]

Hi Ray

Here is how I did it just to show you.





Cheers

Damo

[raycow]

Hi Damian -

Thanks for posting the pic. That explains everything. It looks pretty close, but you should still be ok even if the holes break through the bottom edge of the bell.

In case the SM420 shifts so badly you can't race with it, you might want to keep an eye open for a Chevy truck 3 speed from 1948-up. These have the same bolt pattern as the 4 speed and shift as easily as a passenger car gearbox. Chevy used a torque tube through 54, but the torque tube connection is quite a bit different from Buick and is fairly easy to convert to open drive.

Ray

[dmulally]

Thanks Ray.

You are a genius.

I completely forgot that I have the entire running gear sans engine from a 48 1/2 ton Chev truck. It has the v8 bellhousing from a later truck so just dismissed it. I actually prefer a torque tube rear end as although I am limited in ratio sets, my *** is right on top of it so it just gives me some protection. I just have to chop it down to length which isnt so stressful.

As for those lower bolt holes, they may peep through but such is life.

Thanks Ray. Ill get my 3 speed box out of storage and line it up to take a pic. Next week when everything is open Ill get some steel to make the chassis so I can at least cart the engine round. It is a rather heavy thing.

Cheers and merry xmas

Damo

[dmulally]

Hi All

Silly question time. Please look away if it is annoying or tedious. I dont wish to offend.

Firstly, what is this little box in the middle of the pic?



Next. What screws into here?



Last of all. After giving the engine a good clean, turns out it was blue. Anyway, can anyone please tell me how to get the bellhousing off? I have taken the dust cover off the bottom and the four obvious bolts (two holes seen here in the pic) but it wont budge. I gave it a smack with a hammer and that didnt work. Any hints?



Cheers

Damo

[dmulally]

Is question two the clutch slave?

[suntreemcanic]

That "box" is a block vent.