[Zooguy]

I have a 1966 Pontiac Bonneville I'm wanting to get ready for Hot rod Power Tour this year.

I believe it has the factory 2.41 rear gear ratio but I would like to swap some 3.42 or 3:55 ish gears to have a little bit more get up and go.

Instead of trying to find another rear axle with gear ratio I want I figured it would be easiest to change the gears and differential carrier all at the same time. Possibly even adding a limited slip diff.

Does anybody have any recommendations on who carries all that for the Pontiac rear axles I'm not having much luck on Google and I'm not seeing very much interchangeability between the other models.

[TXSTARFIRE]

I don't think there is any aftermarket support for this differential. You would need to find a rear end from a manual transmission car, not many of those around. Someone with more info will probably chime in. Back in the day I ordered a set of 4.33 gears and a posi case from Pontiac for my 67 Catalina 4 door but that is not an option today.

[misterp266]

TXSTARFIRE is correct. There is no longer any support for these rear ends. Yes, they are a good strong unit but you will have a very hard time finding anything for parts. Fabcraft used to sell a bit but don’t think they do anymore. They are in full size Pontiacs only.

[steve25]

You have a 65 thru 70 big car rear as long as you’re not talking about a 66 Grand Prix.

Axles from any other 10 bolt rear will not work.

These rears when they had Posi where one piece cases.

Gear ratios were from 2.29 to 4.33.

In terms of using the same case and other gears your limited to 2.29 to 2.56.
2.93 to 3.23, or 3.42 to 4.33.

I am not 100% sure but I think your best hope is to find another big car 65 thru 70 rear with the gears you want in it, a Posi would be a plus, but here again II think they are not rebuildable.

[TXSTARFIRE]

Why would a 66 GP be different?

[Scarebird]

Wanting lower gears is nice, but wouldn't you want to wait till after the Power Tour to swap axles?

[stevep]

Originally Posted by TXSTARFIRE

Why would a 66 GP be different?

It's not different.

[64gp4spd]

65-70 B body are the same. Bonneville Catalina, Grand Prix 65-68, Star Chief
Fabcraft Metalworks makes 3.55 gears for these. 71-76B body are the same as well Not 69-76 GP
They show currently out of stock but looking to make another run with interest.
Phone 307-672-5454

[TXSTARFIRE]

"You have a 65 thru 70 big car rear as long as you’re not talking about a 66 Grand Prix."

My question about the 66 GP was because of this statement. My understanding is that a 66 GP would be the same unless there is something I am not aware of.

[rustyrelic]

If you are looking at swapping the entire rear axle assembly, be advised that the pickup points for the control arms are not the same year to year. Someone else will know for certain, but I "think" 65 and 66 are the same, but dont take my word for it and compare carefully.

[694.1]

You would likely be rather pleased with a 3.08.
A 3.23 carrier & gears in a limited slip these days runs around 400-700 before the rebuild.
A rear assy needing a re freshening will be even more.
I do like your plan.

[mgarblik]

I have a complete Limited slip differential for the 1965-1970 big Pontiacs. It's been in storage for decades. Should probably be taken apart and cleaned but I think it's NOS. It's for the higher numerical gear ratios that your considering. PM me if your interested.

[Carl S]

I will be selling the 3.08 posi from a 66 Bonneville station wagon that I just pulled tonight but I'm likely too far away to make a sale practical (Central Canada, 400 miles northwest of Minneapolis).

[MPKind]

The elusive P-Series Saf-T-Track. 3.42 will help with acceleration. It's great on short trips, but on long trips if you're going to cruise at 70 with 14" wheels, the engine will run around 2700-2800. 15" wheels help some.

[b-man]

If this is the same car you narrowed the rear end and installed enormous tubs and rear tires in you missed your chance to install either a Chevy 12-bolt or a Ford 9-inch.

You have very limited ability to find parts for your current rear end, if it were my car I’d be going back to that shop and getting a Ford 9” in there.

If you don’t swap rears then take up one of the offers from members who have responded here, these parts are rare and nobody who has anything good is giving them away.

[imposter]

how about changing the gears in the transmission i have a 2.75 first and 1.78 2nd gear in my Th350 with 3.31 rear end in the 66 tempest that goes great out the gate, and Th400 with 2.93 in my bonneville i haven't finished the bonne yet both cars with healthy/stealthy 455's and 10" converters

[rustyrelic]

It may of have been another OP, but wasn't someone recently posting about looking at going with a 4L80E?

[lust4speed]

Almost everything is available to rebuild the big car rearend. I just received $340 worth of parts from Dave at Fab Craft which included new bearings, seals, gaskets and other parts for building a spare '65 big car limited slip rear. Anyway, Fab Craft is alive and well and they have become my only source for the big car rearend parts. No worries when ordering from them because everything will be correct for the big Pontiac. Summit, Jegs, Rock Auto and other retailers will try and sell you either BOP 8.2 parts or Chevy 12-bolt parts. Even Yukon and US Gear don't seem to have a clue that their catalogs are totally wrong. Dave's prices are decent and you won't be receiving a bunch of parts that don't fit. He hasn't made another batch of the 3.55 gears, but is compiling a list of interested people. I have a set from the first run in the '65 Cat wagon and they are excellent.

I think the GP confusion might be because of the 1969 and later Grand Prix's dropped down to the A-body chassis and share underpinnings with the GTO. I mix suspension parts and rear ends between the '65 & 66 Catalina, Bonneville, Grand Prix, and Vista models. I've also used carriers, axles, and other pieces from the 1967/1969 big cars. I can't comment on the brackets because the '67 and later use a different diameter spring perch and haven't had the need to experiment with the later stuff in the 65's.

The rear is quite similar to a Chevy 12-bolt with some of the internal parts being the same, and some just slightly different. Both have a 8.875" ring gear diameter (but different) and share the same clutch packs. Pontiac axles are a little beefier with 32 splines.

[mgarblik]

Originally Posted by lust4speed

Almost everything is available to rebuild the big car rearend. I just received $340 worth of parts from Dave at Fab Craft which included new bearings, seals, gaskets and other parts for building a spare '65 big car limited slip rear. Anyway, Fab Craft is alive and well and they have become my only source for the big car rearend parts. No worries when ordering from them because everything will be correct for the big Pontiac. Summit, Jegs, Rock Auto and other retailers will try and sell you either BOP 8.2 parts or Chevy 12-bolt parts. Even Yukon and US Gear don't seem to have a clue that their catalogs are totally wrong. Dave's prices are decent and you won't be receiving a bunch of parts that don't fit. He hasn't made another batch of the 3.55 gears, but is compiling a list of interested people. I have a set from the first run in the '65 Cat wagon and they are excellent.

I think the GP confusion might be because of the 1969 and later Grand Prix's dropped down to the A-body chassis and share underpinnings with the GTO. I mix suspension parts and rear ends between the '65 & 66 Catalina, Bonneville, Grand Prix, and Vista models. I've also used carriers, axles, and other pieces from the 1967/1969 big cars. I can't comment on the brackets because the '67 and later use a different diameter spring perch and haven't had the need to experiment with the later stuff in the 65's.

The rear is quite similar to a Chevy 12-bolt with some of the internal parts being the same, and some just slightly different. Both have a 8.875" ring gear diameter (but different) and share the same clutch packs. Pontiac axles are a little beefier with 32 splines.

That axle in the pic looks fantastic.! I raced a 66 2+2 with a 3.73:1 gear ratio and a 4-speed for years. Other than axle bearings and seals, never had to service anything on it. Ran those old 7" wide slicks that were available back in those days. It never failed me.

[Zooguy]

Forgive me for the slow response everybody and I do appreciate all of your comments.

Just to clarify a few things no, this isn't MY big tire big motor star chief executive project. this is my wife's 1966 Pontiac Bonneville four-door hardtop.

CURRENTLY her cars has a 1970 400 short block that is worn out with a gratuitous amount of crankcase pressure that could pass as a steam locomotive.

So, what I'm wanting to do is clean up and refresh MY 389 out of the Star Chief with a little bigger camshaft (comp cams XE250H) and put it into her Bonnie, restoring it back to an original 389 motor that doesn't resemble Thomas the train.

So with keeping the motor relatively stock but trying to improve acceleration slightly I figure the best bang for my buck is going to be gear ratio.

A few of y'all mentioned you might have something coming up for sale that would benefit me. As long as you're within about 300 mi of me (OKC) I'd be willing to come pick it up from you. If you're willing to meet me partway that could extend the range even further.

I don't necessarily NEED a limited slip differential but if that's what you have that would a POSI-tive.

I've got a fairly big laundry list of items that I need to get done with her car. Different rear gears would be nice but they're not essential ...... And if there was somebody with the desire for the factory 2.41 rear gears who has something numerically higher and wants to trade that could be arranged as well.