So i went to my engine shop last week, and things went in my favor. Turns out that we're supposed to work on my Nailhead this Friday, and get the heads decked and finish the valve job. If time allows for Friday we'll also check piston to valve clearance and see how much the pistons need to be fly cut, because they got a little too close w/o decking the heads. I also got an update on my Trans. I had purchased the 66 Nailhead St trans used for 150 bucks knowing it was probably cooked/roached, but it was getting a full rebuild. Turns out that everything was recked except the case and output shaft, so i'm basically getting a brand new trans for around 500 bucks, manual/auto valve body, Th400 pump, etc. It wont be a switch pitch anymore but it'll be way easier and cheaper for a nice converter. Got a B&M quicksilver ratchet shifter from a friend, brand new w/ cable, mounting hardware and cover for dirt cheap, bought a T handle for it and its all set. Also, with light modification, it will fit in the original dynaflow cover/indicator plate :grin:, but i will have to cut the Centerconsole storage box by about an inch to make everything fit right. Sorry if i rambled, but i thought you guys might enjoy an update on my car.
I would not go that far into a trans without making a switch pitch out of it... or keeping it a switch pitch..... the switch pitch is far better than just a plain th400.... I have both ,,, a sp in my 65 and a plain th4 in the riv.... huge difference in the power going to the ground.... your trans man is selling you a bill of goods.... a th4 can be made to be a sw pitch by swapping in the right parts.... and vice versa.... dont settle for a plain th 4......
Old post but the switch pitch is the best combo package for a 65 riviera. Heres food for thought. A ST 400 VP w/ a converter from a 300 ( higher stall) 3.23 posi gears good for highway cruise and off the get go with a switch pitch toggle or timer box, 28'' tires and a big q-jet. Heres my take on a smart mans OD. the math goes like this 65 mph x gear ratio x 336 divided by tire dia. = 2546 RPMs this basically what the OD trans is going to get but with no lugging. Plus added a trans go premium shift kit. with the q-jet running on primaries but has the option to step on it and open up coupled with the switch pitch keeping it within the sweet spot driving no need for a OD trans, has the option to race if need be or economy for the long trips, hopefully looking at 20 mpg with this stock set up. 425 nailhead and ST400 VP was the best set up buick came up with, in my opinion way ahead of there times. The Hot Rod Homepage Keepin it Hot Rod [HR][/HR] The Switch Pitch TH-400 Share Summary: The reasoning behind installing an overdrive transmission is running a low rear gearing to get off the line, but still retain manageable RPMs at freeway cruising speeds. This seems like the best of both worlds, but this article will examine some reasons why an overdrive transmission is not always be the best solution. Traditionally GM overdrive transmissions such as the 700-r4 and the 200-4r were viewed as anemic pieces for gas sipping transportation appliances. The last several years have revealed that these transmissions can be modified to handle significantly more power then in base configurations. A well-built and properly adjusted overdrive transmission should be able to handle around 450 ft/lbs of torque. Is that enough for the engine combinations that people run in their hot rods? In many cases the answer is no and I for one, have been through enough built 700-r4s for a lifetime. So what then is the solution? The solution is the tried and true TH-400, more specifically the variable-pitch version of the TH-400. The variable-pitch, or switch-pitch TH-400 is nothing new as it has been around since 1965. Originally found in Buick, Olds, and Cadillac the switch-pitch offers two stall speeds, a low stall and a high stall. Applying a positive 12-volt signal to the appropriate terminal on the transmission case makes the selection of low or high stall. The high stall gives you the advantages of torque multiplication to get off the line with a taller rearend gear and the low stall decreases slippage for cruising or on the big end of the track. The variable-pitch stator is not the only advantage that the TH-400 holds over its more modern overdrive counterparts. A TH-400 will generally cost less then an overdrive and it can be built to handle some serious horsepower numbers. The TH-700 and TH-200 also require a T.V. cable to be installed and adjusted correctly or serious damage and shifting problems will result, and getting it correct is often harder then it seems at first glance. Another advantage of the TH-400 is a small spread between gears. First lets put some gearing numbers out there for reference: Gear Ratio Comparisons: [TABLE="class: cms_table_cms_table"] <TBODY>[TR] [TD][/TD] [TD]1st[/TD] [TD]2nd[/TD] [TD]3rd[/TD] [TD]4th[/TD] [/TR] [TR] [TD]TH 400[/TD] [TD]2.48[/TD] [TD]1.48[/TD] [TD]1.00[/TD] [TD][/TD] [/TR] [TR] [TD]TH 700[/TD] [TD]3.06[/TD] [TD]1.63[/TD] [TD]1.00[/TD] [TD]0.70[/TD] [/TR] [TR] [TD]TH 200[/TD] [TD]2.74[/TD] [TD]1.57[/TD] [TD]1.0[/TD] [TD]0.67[/TD] [/TR] </TBODY>[/TABLE] It is clear that the two overdrive transmissions in the comparison chart have lower first gear ratios as well as have the advantage of overdrive, but let us look at the numbers that are hidden between these ratios. Between Gear Gap Comparisons: [TABLE="class: cms_table_cms_table"] <TBODY>[TR] [TD][/TD] [TD]1st-2nd[/TD] [TD]2nd-3rd[/TD] [TD]3rd-4th[/TD] [/TR] [TR] [TD]TH 400[/TD] [TD]1.00[/TD] [TD]0.48[/TD] [TD][/TD] [/TR] [TR] [TD]TH 700[/TD] [TD]1.43[/TD] [TD]0.63[/TD] [TD]0.30[/TD] [/TR] [TR] [TD]TH 200[/TD] [TD]1.17[/TD] [TD]0.57[/TD] [TD]0.33[/TD] [/TR] </TBODY>[/TABLE] Notice the large gaps between gear ratios. The TH-700 has a particularly nasty gap between 1st and 2nd. In fact if you combine the 1st-2nd and 2nd-3rd gaps on the TH-400 you get roughly the same gap as the 1st-2nd on the 700-r4. The result of this is that your first gear in the TH-700 may launch you like a rocket, but the huge gap is going to lug your engine and drop RPMs, hurting performance. The TH-200 has a more favorable gear separation then the TH-700, but the TH-400 still has a slight edge. Now to address the flaw in my argument that I am sure many of you are thinking about. The TH-400 does not have an overdrive gear and if you dont run an overdrive then how can you possibly expect to have a respectable freeway cruising RPM? The solution to this is easy, run a taller rearend gear. I argue that the many hotrods rarely, if ever, see the drag strip and spend a lot more of their time on the road. So why then do we put in a low rearend gear that makes freeway driving unpleasant and limits out terminal velocity to 115 miles per hour. An overdrive transmission will make up for our low rear gearing, but this introduces several problems. Overdrive was never intended to be an acceleration gear, which it is being forced to become if you are running a deep rearend. High drive shaft speeds Running a 4.11 gear with a TH-700 sounds like a good idea until you consider that with a 275/40R17 tire at 100 mph your drive shaft is spinning at somewhere in the neighborhood of 5383 RPM for comparison a TH-400 with the same tire and a 3.08 rearend gearing will turn 4034 RPM. The same comparison at 150 mph yields 8075 for the overdrive versus 6051 for the TH-400. Spinning the drive shaft that fast takes horsepower and can have other problems like magnifying the effects of driveline alignment problems, drive shaft imbalance, and driveline component wear. With the right setup, a switch-pitch TH-400 provides a viable alternative to the modern overdrive. Controlling the converter: There is a multitude of possible methods for controlling when and how the converter changes from high to low stall. Use a delay box to have the converter go to low stall after you leave the starting line. An RPM switch could have the converter lock up once your car is into its power band. Wiring a relay to the brake switch would allow you to put the converter in high stall for stoplights in a car with a radical camshaft. A simple switch can be used to allow full driver control of the system. For most those who want to have the most control of their driving experience this probably the best option. [article on wiring a switch pitch transmission] Where do I get my hands on a switch pitch TH-400? I purchased the unit in my 1966 Malibu from PAE Enterprises in Texas. They offer both Chevy and BOP cases for a resonable price. PAE also sells conversion kits so those of you that already have a TH-400 are in luck. PAEs contact information can be found in the sources section of this article. Sources: How to Work with and Modify the Turbo Hydra-Matic 400 Transmission by Ron Sessions ISBN: 0-87938-267-8 P.A.E Enterprises, Inc. 4401 Turf Rd. Bldg E El Paso, TX. 79938 915.855.6009 915.857.4727 -> Tech Line 8-10am and 4-5pm MST M-F www.paeenterprises.com
Just a quick addendum to the above post by Snake: I trashed a THM-350 with a slightly built-up sbc 400. I then bought Ron Sessions book on the THM-350. I had never done any kind of automatic transmission modification or performance build-up before - only stock overhauls. The THM-350 that I was able to put together on fairly short money was bulletproof. I found his book to be complete, well-written, easy to follow, and accurate. I assume that the same is true of his THM-400 book.
We used that book to build a TH400 with a 4000 stall behind a 455 running low 11s in a 4000 Lb Skylark. After a few years, we had ATI rebuild the transmission to see of there was anything else to be gained. It continued to run the same numbers. That says a lot for Ron and his book. Cheryl
Don't get me wrong,I love my ST400 in my 64 skylark,but the above article is flawed. This article assumes an overdrive is installed because the rear gear is street un-friendly,and to just change the rear gear and live with the slower off the line accelleration with an non-overdrive,instead of matching the trans with the rear gear,a cam change would also be in order that wasn't mentioned to make the combo match. If you run a 4.11 gear with a 700R4,the 1st gear multiplication ratio would be,4.11 X 3.06 = 12.576:1,which with a street car's rear suspension would be useless(dry pavement would be like driving on the ice when the pedal is to the metal in first gear). I have a 700R4 in my 65 Impala with a 3.07:1 gear in it,and first gear is traction limited even with the drag radials on it in first gear. To turn that article upside down,if you use the street/strip first gear multipliction ratio of 9.5:1 for first gear is used,the the 700 only needs a 3.10:1 rear gear,and a TH400 would need a 3.83:1 rear gear ratio to be at 9.5 first gear multiplication ratio. So the closest gear for the 700 would be 3.08:1,which would be 9.4248:1 first gear multiplication ratio,and for the TH400 a 3.73:1 rear gear ratio,which would be a lesser 9.2503:1 first gear multiplication ratio,which would destroy highway cruising for the TH400. The 200R4 rear gear needed to get a 9.5,the closest would be a 3.42:1 rear gear.(actual 9.3708:1) For these three examples without doing the rpm math(don't have that much time)the final drive ratios would be for the 700R4 = 2.156:1 final drive ratio. 200R4 = 2.291:1 final drive ratio. TH400 = 3.73:1 final drive ratio.:Smarty: To add,both overdrive transmissions have come futher than when that article has be written,the 200R4 can be had to handle 800 + HP,and the 700R4 over 1,000 HP.:Brow: With a lock-up converter,not as good as a switch pitch converter,but you can have a high stahl speed and lock-up,with overdrive.(lock the coverter towards the end of the track):TU: And taking a ST400,and coverting it to a regular TH400 is just plain makes me sad.:ballone of the,if not,the best non-overdrive transmissions ever made)
OD transmissions have come along way no doubt, However what the article is stating is why get the 700-r4 or 200-r4 if you already have a TH400, with a few parts can be converted to a switch pitch and run a taller gear and tire with minimal fees almost under $400. To switch to an OD would cost alot more and modifications to accomplish the exact same thing ei. poor mans OD, I call it the smart mans OD. Talked to a few old tranny guys they love these things, the would set these up to tow motorhomes or towing trailers or even racing. Very strong tranny, and as Doc is stating best set up for a 401 or 425 nailhead with a big buick car Rivi or skylark that originally came stock with the car, no spending money there. Ask Kenne Bell, Pheonix and TCI, they recommend a better converter for race or street. Greg Ducato from Pheonix trans told me to just install a converter from a ST300VP for my set up. Hell! this can be set up to be a 6 speed automatic if you choose, I see why Doc is saying stay with switch pitch, alot more bang for the buck. Just my .02 cents!
I wasn't bashing the switch pitch,I was pointing out how the article you posted is flawed. You just can't go from a "Hot Rod" engine that was cammed for a 4.11:1 rear gear and a 3,500 stahl and just through a 3.08 gear in it without it turning into a dog,even with a switch pitch converter,without changing the cam to match the rear gear.(unless the engine is a Nail Head,hard to kill the low end torque on one of those :Brow:,not a high RPM HP engine to start with,not so much with a big cam either) I love my ST400,wouldn't change it for anything,its a Nail Head in front of it so I don't have to worry about having enough torque to take off with a 3.23:1 rear gear,plenty of low end torque.Gas mileage is decent also,because its in a 64 Skylark which is a light car to start with,I think its 20 mpg +. The only thing I would change would be to put a Gear Vendors unit behind it,if I hit the lotto.LOL:TU:
300 sbb overkill, Yes, I catch that now! but since I have the 65 425 with ST400 It dosnt cross my mind to think about that with a cam that goes 270 int dur , 280 ex dur .469 int lift and .496 ex lift on a 110 lobe center. Tell me 300 sbb overkill, how is 3.23 posi . I have 3.08 peg leg and going to a 3.23 posi.
You should feel a difference for sure!:Brow: My little 401 takes off like a freight train without a load with that combo,love it! I think you have a Riv am I correct? If so,it is a heavier platform than the A-body Skylark,but you still should feel the difference(especially with a posi),and your gas mileage shouldn't change much,its only a 5% change in gear size,so I would think(if you can keep your foot out of it,:Browyour mileage shouldn't go down more than 5%,I would guess less than that.:TU: What is the duration @ .050" on your cam? At .050" is more informing than the advertised.(to me anyway) Sounds like a heathly cam though. I like overdrive transmissions more with a small block cars,to exspendsive to make them handle big block torque. Give me a ST400 any day behind a big block! The gearing in an O/D helps make up for less torque with a sb vs a bb.(unless its a really big small block :eek2 GL,and enjoy your classic Buick! :beer Derek
I went from an open 3.08 to a posi 3.23 on my 65....knocked off .17 from my 60 ft, but for whatever reason I expected more...I love the gear and am glad I did it, but it wasnt the earth shaking difference I thought it would be. I know I had the open diff jacked around to where it would launch pretty good, but I figured two wheels would be twice as quick! Not quite! Turns out, 3.08 is not a bad gear after all!
Put that ST400 in,that would of made a bigger difference than a gear change:Brow:,I know,you want to run stock class. But still,.17 off your 60 ft times isn't to shabby,did it help your 1/4 mile times? Is .17 5% better? And yes,the gear change is only 5%,so not that big of a difference(can't expect twice as quick with only 5% :grin,but with a heavy Riv,5% should help to get it moving with traction. If he wanted to he could just bolt the 3.08 ring gear to the posi unit and keep the 3.08,a much easier install than removing and replacing the pinion gear,and save some $$.o No: I appologize to the OP for going off topic.
What is the duration @ .050" on your cam? At .050" is more informing than the advertised.(to me anyway) Sounds like a heathly cam though. Its a custom Isky grind I had done with a stock Isky billet cam , Adv. @ .050 int 214 and ex 220. I also have a peg leg 3.08 diff on the Rivi car now , should I just get those gears and put them into the third member pumkin 3.23 posi sitting on the garage floor.
Like Derek mentioned, the 3.23's won't be a huge difference over the 3.08's, but they should still offer additional gains. In terms of running a switch pitch setup, I can't say that I've found it vastly beneficial, as I usually just run in high stall all the time. With the factory ST400 converter, low stall was practically unusable. Even with a V6 ST300 converter (which flashes to about 2300/2900), the only time I ever run in low stall is when I'm on the highway for more than 10 minutes or so. Maybe this is all because of my relatively large cam, or because I only actuate the switch pitch with a toggle switch. With that said though, I don't know that I'd go through the work of converting a switch pitch trans to a fixed stall setup. It's too cool to get rid of. Plus, with a properly built switch pitch converter from someone like TSP, I'm sure the low stall characteristics could be tweaked to actually make it usable.
Is that a billet roller cam? Or did you mean a cam blank ready to grind? If you change the gears from 3.08 to 3.23 you will need to replace the pinion seal and crush sleeve,among other things,and is more involved than taking out the open diff and removing the ring gear and remove the ring gear from the posi and put the 3.08 ring gear on the posi unit and install into the rear. Its up to you,and you ability level,and available tools,you'll still need to re-center the "new" posi unit to get a good wear pattern on the ring gear.(dealers choice,the 3.23 will give you 5% more gear,and take your first gear multiplication from 7.638:1 to 8.01:1 which is a little more substantial than having ST300 first gear gearing. (a ST300 has a 1.76 first gear) So with a ST300 going from a 3.08 to a 3.23,the first gear multiplication would be from,5.421:1 to a 5.685:1.(this is for Rhett) not as big a difference with the 1.76 first gear than a 2.48 first gear,the larger number first gear,the more of a difference. As you can see,the 1.76 first gear 5% difference is a lesser difference than the 2.48 first gear, .264:1 difference with the ST300,and a .372:1 difference with a ST400(not that big of a difference,but not nothing).:TU: Its been a while since I did my 12 bolt chevy in my Impala,had a open diff with 3.07 gears,I removed the diff,and removed the ring gear from the open diff and bolted it on the posi to the 3.07 ring gear(being out of the car at the time made it much easier on jackstands when I upgraded from the original 10 bolt chevy). Then I installed the unit back in,had to change the shim paks to get a good pattern,and backlash.(I used an old Motors Auto Repair Manual to help me get things right)After that the cover went back on and filled with lube and posi-additive,in the car,and I was down the road making duel stripe pattern burnouts.:Brow: Its up to you,perhaps you can sell the 3.23 gear set and look for a 3.42 gear set instead,for a close to 10% increase? And for now run the 3.08 with the posi?o No:
As much as I love the 3.23's, if I had thought about the option to not mess with the pinion and keep the 3.08s while installing the ltd slip, I might have done it just to keep it simple and get through the job..if he's got the 3.23's on the shelf then go the whole route like I did... It's hard to say what the 3.23's were worth as I made a few changes all about that time, but I'd guess at least a 10th.. I was running 15.1-15.3, and it was around then I started to get into the 14's pretty often but I had also done the distributor and that was a big one.. I will say I do like my switch pitch, and can run low stall all the time if I want to - even at idle. 300sbb - The ST400 is still on the agenda, but I had them build the ST300 core back up, I actually went to see it today. Still waiting for my converter to come back. I'll post all the details when it goes back in under the ST300 Hop Up thread..
300 sbb_overkill, So your saying go with the 3.08 on the peg leg and install them on the 3.23 pumkin posi correct.
I thinnk thats what he's saying. If you've got the tools and the experience to read gear patterns, then definitely do the 3.23's. If not, save the 3.23's for another day and use the posi underneath the 3.08's - much simpler and 3.08's are not a bad gear. That said, for the rear end experts, do you have to re-shim when changing carriers only? 'Cause if you do, then go all the way and do the 3.23's
I think that you do have to reshim... because no 2 carriers will machine out exactly to the same dementions... only if you reuse the same carrier and bearings/races can you get away with not reshiming... or you are lucky....
You'll most likely have to reshim the side carrier bearings to get the correct preload and gear backlash. It's easy to do, but you'll need a dial indicator to measure backlash. Preload is usually close with a 'tap the shims into place with a little effort', and not a slip fit. The pinion gear depth and preload would only need to be setup if you change the ring and pinion gears. That'll take more knowledge, tools, and patience to do properly.
