3 Speed to SBC Options (1 Viewer)

[New Trucker]

I just pulled the Chevy 350 that the PO put in the truck and found a big surprise. Apparently when he mated the old J30 3 Speed to the Chevy bellhousing he used an old Downey adaptor plate but used the original front bearing retainer so the trans is not aligned to the bellhousing by anything but the mounting bolts!

I think I will have to have a machine shop fabricate some sort of adaptor ring to center the bearing retainer in the bellhousing opening, and I know the ID of the bellhousing opening is 5.125in but does anyone know (or could measure) the outer diameter of the 3 speed front bearing retainer?
Thanks

 

[bikersmurf]

I'd ditch the marginal J30 in favor of an Sm465/420.

 

[Leaping Deer]

I agree on the 420 or 465. Better suited to be behind the 350

 

[reddingcruiser]

Yeah, what these two ^^^ guys said. Or look in the classified for someone getting rid of a complete 3 speed to SBC adapter.

 

[New Trucker]

I'm curious why everyone always seems so negative about the 3 speed? I will probably never wheel the truck, the 3 speed has the same 1:1 top gear as the rest and I would assume the 350 will have more than enough torque to pull the higher first gear. Plus everything is already set up for the 3 speed (engine mounts, trans mount, clutch slave, driveshafts etc).
Is there a really good reason to undo all that to go with the 4 speed?

 

[lcwizard]

if you never wheel I guess you can live with the 3 speed's shortcomings, all or most of them being off road
related. i don't understand why the adapter wasn't fitted to the 3 speed bearing retainer. All it should be is a spacer since the 3 speed has the same bolt pattern as the early ( sm420 era ) gm bellhousing. The spacers I've seen are simply laser or cnc plasma cut flat plate , the center hole matching the 3 speed bearing retainer plus the four mounting holes

 

[shelfboy1]

there were several adapters made one style had the to bearing retainer bolted to the front of it for alignment and the others were just spacers .i have seen similar setups to yours run for 30 years or more with no problems.my first 4 or 5 fj40s were 3 speeds never new there were short comings .good luck

 

[New Trucker]

there were several adapters made one style had the to bearing retainer bolted to the front of it for alignment and the others were just spacers .i have seen similar setups to yours run for 30 years or more with no problems.my first 4 or 5 fj40s were 3 speeds never new there were short comings .good luck

Thanks, I think I'm starting to get a handle on my options. I'm not sure which adapter i have but I think it might be an early Downey plate adapter that was supposed to be used with the spacer ring between the original bearing retainer and the bellhousing. Do you know of anyone that has run one without the spacer? Because then I could just bolt it back up and get back on the road. Otherwise I think my options are:
1) get an early SBC bellhousing that should accept the 3 speed directly.
2) buy a new adapter kit and have the "custom" trans mount welded to the adaptor plate.
3) fabricate or buy a spacer ring to adapt the 3 speed to the later SBC bellhousing.
I have been leaning twords #3 and found Advance Adaptors part #716041, http://www.advanceadapters.com/categories/bellhousing-index-reducers/223/ which is a spacer ring with an OD of 5.125 and an ID of 4.686, but since I wont have access to my truck for a while I am trying to find out if that will fit the stock 3 speed bearing retainer?

This is what I have

 

[New Trucker]

Just in case anyone runs into this in the future I thought I would post the measurements I took. The outside diameter of the 3 speed bearing retainer looks like it is about 5.039" and the retainer extends about 0.360" out from the far of the transmission. The opening in the adaptor plate I have measures about 5.350" in diameter and my bellhousing opening is 5.125" diameter.

Those numbers eliminate options one and three for me and it looks like I have to either buy a new adaptor kit or think about some sort of 4 speed conversion.

 

[reddingcruiser]

Am I missing something??? This picture would have helped in the beginning. That's a 4 speed adapter plate. No wonder the 3 speed won't fit. Maybe you should consider going the four speed route after all.

 

[jakek2525]

Post a pic of your transmission

 

[lcwizard]

Reddingcruiser is right. The 4speed bearing retainer is in that Figure 8 shape that matches the adapter. A 3 speed is just round .

 

[pbgbottle]

That is a 4sp adapter plate for sure.
I had one like that but it had dowel pins in it for alignment.

Sent from iPhone

 

[New Trucker]

That is a 4sp adapter plate for sure.
I had one like that but it had dowel pins in it for alignment.

Sent from iPhone

Yeah it looks like the PO just drilled out the bottom two holes and used it as a spacer plate. The 3 speed was just floating free in the adaptor and the bellhousing with nothing to index it but the pilot bushing in the crank.

 

[Tancruiser]

Put a 4 speed in it the3 speed is a non syncro 1st gear and it will eventually fail

 

[pbgbottle]

see this thread showing what downey offered to align/index the tranny .

https://forum.ih8mud.com/40-55-series-tech/387214-help-id-bellhousing-adapter.html


,,,

 

[blake bowerman]

All I do is wheel with my 40 and it has a 3 speed dose just fine but if you want to crawl just put on a crawl box.