rear end question for 65 skylark gran sport

Hello, I have a non stock bop 8.5 open rear end with bolt on axles I my 65 skylark gran sport I am having a posi installed. I know the stock rear end with my switch pitch 300 trans is 3:08. I have the option to build it to 3:23. Will I gain that much on launch with the larger gear? I have heard that the 3:08 doesn't take advantage of the horse power over 325 and I plan to dual quad the car. I just want a good cruiser that can move when I want to. Also, will a 3:23 over strain the two speed tranny? Any comments welcome.

 

I thought all the 65 GS's came with the 401 Nailhead??

 

It is a Real 65 gran sport with a 401. Cali one owner car. All matching except the rear end. Somewhere along the way the original rear end was replaced. The original electric switch does activate the stall feature but obviously not as peppy with the open rear end. Im told the 8.5 ten bolt is a good rear to build . Leaning toward 3:23 ratio. Thank you all.

 

Larry, the 65 had the ST300 mated to the Nailhead. A ST400 is a nice upgrade though.

I like the 3.23:1 gears. If you already have the 8.5 Rear, you are golden for posi upgrade.

 

Larry, The ST400 is a 3 Speed and came in the Riv and the Wildcat. I have a 425 and an ST 400 from a Wildcat that I'll drop in my GS. Someday.....Someday.

 

ST300 two speed was the only automatic offered in the Special/Skylark/GS intermediates in 1965 and 66.
The round bellhousing Nailhead version ST300 was ONLY installed in the 65-66 Skylark GS. No other Buicks got this trans!
I don't get it.....Buick already had the Nailhead version of the ST400 3 speed trans for the big series cars, but went out of their way to design/build a 2 speed for use in the Skylark GS! Apparently they thought it was the better trans for the car.
Buick did use the 3 speed ST400 trans in the '67 GS.....finally.

3.08 vs 3.23...... if you don't do a lot of higher-speed highway driving, I'd go with the 3.23's.

Swapping in a ST400 into a GS would require moving the crossmember back, shortening the driveshaft, and modifying the shifter. I did the swap on my blue car.

 

Hi Walt. How hard was the 3 Speed Swap. I plan on having the 400 overhauled and a 3:23 Posi installed. Did you have to get a new cross member or did just sliding the old One back do it? How much did you have to take out of the Drive Shaft? Sorry about all the questions but I want to be ready when the time comes. It might have to come sooner than later. I just cracked a Piston in the 401. I have the 425 that needs overhauling, so I might just have to start working on it. Thanks Man. :TU:

Jim

 

The fella i bought mine from started making mine a clone. I do not recall what the car was he grabbed the engine/tranny from but mine now has the 401/ST400 and a posi rear from what he said was a convertible. I can see where he slid the crossmember back. The driveshaft however is the 2 piece vulcanized hoo hah and i want it out ASAP. Not only am i afraid to tear the unit apart but i also found the yoke is right up against the tailshaft of the tranny. It doesnt make noise or wine nor does it leak yet but i know the slip yoke needs room to move. He also drilled out the pinion and used retainers from a 9" to hold in the rear u-joint.

 

Hey Ponch, The stock frame mount is too far forward on the 65-66 for the ST400. You can use the same crossmember, but for a GS with convertible-type frame, you need a frame mount to bolt it to... You can fab something and weld it to frame, or even use some big pieces of angle iron and bolt it to the frame.
For the 5 speed install I did, I tried something different... I took a non-GS crossmember, cut the ends off, and welded a forward extension to go to the stock GS frame mounts. Sort of a 'L' shaped extension.

I don't recall how much the driveshaft needs to be shortened, I did the swap in the 1980's!
I somewhat recall someone saying a Ford F-150 driveshaft will work. Maybe it was Brian. Maybe a late 80's truck IIRC.

Stock floor shifter will need mods for clearance. A better option is to get the cable conversion from Shiftworks.
http://www.shiftworks.com/buick.htm

Use the GS converter, it's smaller and will give a higher stall speed than a stock ST400 converter.

The 3 speed is more enjoyable to drive, but don't expect an ET improvement.

 

Hi Walt, Thanks for all the Tips. I spoke with the guy who's going to rebuild the 400 and install it for me. He told me he would probably have to get a new cross member. So now I can tell him to re-use it but just weld in some supports for it. He can figure out how much to take out of the driveshaft. I was going to go to 3:23 gears but if I can get a 400 trans with a lower First Gear, Forget it. Right now with the 3:08 I'm cranking 3 Grand at 70mph. That's pretty high. With the QJ I had on it , if I was doing 70 and gave it more gas I could hear the Secondaries opening up. That's a Lot of gas for just cruising down the expressway.

On another note, I ran into a guy who has a Brand New 425 bored out .030 and all new rings and bearings. A guy gave it to him to overhaul I don't know how many Years ago. Guy never came to pick it up and never gave him much money along the way. He's a well known engine builder around here. So he's selling it to me for a Grand. Not too shabby. Did I run into a Deal or what. Basically a new engine. It has a Big Kenne-Bell cam in it which I'll probably take out and put my TA-25 Cam in it. I'm not going to race it so I don't need a big cam. I'll probably have to take it apart to see if there's any rust in it. It's been sitting for Years in a plastic engine bag on a stand. I have a set of Stainless Valves I'll have to put in it too. Should be a good strong runner. I want to put the Dual Quad system on it for the WOW factor.

Anyway, Thanks again for all the tips.

Ponch