acheaving overdrive [Archive] - XtremeSystems Forums

Rukee

05-21-2006, 04:44 AM

I`ve got an old '65 GTO Muscle car with 5:81 gears, making cruzzing down the highway nearly impossable(3,000RPMs@55mph) I have realy big back tires(290/50/15) and don`t wanna increase the rear axle ratio cause I`ll loose all my bottom end launching power. I`ve been looking at theRichmand's 6-speed overdrive trannys ( http://www.jegs.com/webapp/wcs/stores/servlet/CategoryDisplay?storeId=10001&catalogId=10002&catalogIdentifier=&categoryId=15523&parentCategoryId=10561) and\or just an overdrive unit (http://www.gearvendors.com/aghr4sm.html) that mounts to the back of my existing tranny.
Anyone have any experience with either unit that could clue me in??
I`m leaning towards the Richmand as they are nearly the same price, and then the original tranny will be intact sitting on a shelf.

Soulburner

05-21-2006, 07:17 AM

For the price of that GV unit you could buy a whole new built transmission. I would just go with a 700R4 or 200R4 or something similar, or a good 6 speed like you stated.

5.81 gears...thats insane. I had 3.73's in my Monte Carlo and I turned 2300 @ 45mph.

Check out www.finishlinetrans.com though. Mine was built by them and i'd recommend them to anyone. The price of their built 6 speeds would be cheaper than one of the units you linked to.

Rukee

05-21-2006, 07:40 AM

Looks like they just deal in late model stuff, the 6 speeds they list are all one piece bell housing/tranny w/integrated internal shifter whereas the early stuff has a bolt on bell housing and a bolt on the side hurst shifter. Not sure how tha`d work out.

Soulburner

05-21-2006, 08:04 AM

Yeah i'm not sure if theres some sort of conversion or work you could do to fit it but it would be nice. It was a thought at least.

I'm curious about those gears though...did you put them in or did you buy it like that?

Rukee

05-21-2006, 08:48 AM

The car had them in there when I bought it. They had been replaced from stock as 5:81s are not avable from Pontiac. I use to have 14s on all 4 corners and man, it really screamed then, there was no way in hell to drive it down the highway. Now with the taller tires it`s alot better, but just not enough to be comfortable with those sustained RPMs.
Here are a couple photos of the car....
http://img.photobucket.com/albums/v675/Rukee/P1010068.jpg
http://img.photobucket.com/albums/v675/Rukee/P1010067.jpg
http://img.photobucket.com/albums/v675/Rukee/P1010066.jpg
http://img.photobucket.com/albums/v675/Rukee/P1010065.jpg

koensa

05-21-2006, 08:55 AM

3000RPM isnt that much?

or are those engines something different?

i drive my peugot always 3K a 4K before i swtich to higher gear

enlighten me,plz ;)

Rukee

05-21-2006, 09:13 AM

Underload 3k is fine, hell I`ll buzz 5 grand before I shift if I`m racing, but for just no load running at a constant RPM, I`d like to see abit lower for this ole Pontiac Big Block.

Soulburner

05-21-2006, 12:34 PM

I would think your RPMs would be higher as my 3.73 car did around 2500 @ 50mph with a 15" wheel though I don't remember the tire. It was something like 60 series though which is pretty tall.

Rukee

05-22-2006, 03:01 AM

Was your car an automatic or manual tranny???

Soulburner

05-22-2006, 01:15 PM

3 speed auto...3rd gear was 1:1.

Rukee

05-23-2006, 06:04 AM

Gawd never listen to the town moron. A local shop here had the rear cover off about 12 years ago and told me it was 5:81s, well I just pulled the cover off myself and allthough there is a 11 64 stamped onto the ring gear, the teeth count comes out as a 3:90 rear gear. I can also grab the carrier and move it left to right at least a quarter inch!!! :eek:
Know of any tire size/gear axle/rpm conversion charts so I can calculate which rear gear kit I should buy??

*edit* also the tires are 295/50/15s in back, not 290 like I originally posted. Circumference is 85 inches.

RyderOCZ

05-23-2006, 06:43 AM

Rukee

05-23-2006, 07:28 AM

Thanks Ryder!!
Looking for as close to 2000RMPs @ 60mph as I can get. Prolly looking at like a 3:09 or somethin huh?

RyderOCZ

05-23-2006, 07:39 AM

Thanks Ryder!!
Looking for as close to 2000RMPs @ 60mph as I can get. Prolly looking at like a 3:09 or somethin huh?With 85 inch Circumference at 60 MPH you need 2.68:1 gears to get 2000 RPM.....Unless you get overdrive...if you found an overdrive of 0.90 you could run 2.98:1.....0.85 overdrive you could go to 3.16:1

Hope that helps.

Rukee

05-23-2006, 09:57 AM

Yes it does. Thanks!
1 more...they are telling me that I can go down to 3:55s without changeing the carrier, can you tell me what rpm`s would be with those plz?

Soulburner

05-23-2006, 01:42 PM

That clears up a lot of confusion...I couldn't believe you had 5.81's...:cool:

RyderOCZ

05-23-2006, 01:50 PM

3.55:1 would mean 2645 rpm at 60 MPH.

Rukee

05-23-2006, 02:11 PM

Thank you very much!!
Ryder for MOTM!!!

...again!! :D

RyderOCZ

05-23-2006, 02:22 PM

YGPM at BE too :D

wdrzal

05-23-2006, 06:13 PM

3.36:1 is a good street grear. if you want to know your gear and don;t want to take the the cover off put on stands and put a chalk mark on top off the rear tire and one one drive shaft. turn tire 1 turn while you count drive shaft turns. 1 tire revaloution the drive shaft will turn 3.36 times. drive shaft will make 3 turns and end up at 4 o'clock position.you can figure your current gear . people always over estimate gear rations.

with a big block even 290:1 and you'll have good driveability and some semblance of gas millage.

Soulburner

05-24-2006, 01:22 AM

I have 3.23s and its a good gear. Compromise between mild and wild, I turn ~2200rpm at 75. I have an OD of .7ish though.

Rukee

05-24-2006, 03:01 AM

if you want to know your gear and don;t want to take the the cover off put on stands and put a chalk mark on top off the rear tire and one one drive shaft. turn tire 1 turn while you count drive shaft turns. 1 tire revaloution the drive shaft will turn 3.36 times. drive shaft will make 3 turns and end up at 4 o'clock position.you can figure your current gear .

That only works if you have a posi unit, if you have an open rear end and only one tire is turning, you`ll need to turn that 1 tire over twice while counting the driveshaft turns. Doing this and coming up with less then 4 revolutions of the driveshaft is what promted me to remove the cover to count the teeth.

wdrzal

05-24-2006, 10:49 PM

Either way, with 2 chalk marks you can pretty well tell.

Must be a 10 bolt??? What tranny is in their?

Nice car by the way!!!!

Rukee

05-25-2006, 03:00 AM

`65 was the first year for the 12 bolt posi, however, this car was built in 12/`64 so it still has the 10 bolt, as well as the battery on the wrong side too. It has a 4-speed fully synced tranny.

Soulburner

05-25-2006, 02:11 PM

`65 was the first year for the 12 bolt posi, however, this car was built in 12/`64 so it still has the 10 bolt, as well as the battery on the wrong side too. It has a 4-speed fully synced tranny.
Yeah, and I love how GM still used that piece of crap in my 2001...

(10 bolt)

Rukee

05-26-2006, 09:36 AM

The only things they have in common is they are both rear axles assemblies and they both use 10 bolts to hold the cover on, other then that, it`s not the same at all. Different size carriers, different ring and pinion gears, the 2001 uses 'C' clips to hold the axles in, this one doesn`t, etc. GM had about 4-5 versions of the "10-bolt" rear end.

Soulburner

05-26-2006, 05:54 PM

And none of them were made for much abuse :(

Oh well, I see a Moser 12 bolt in my future.

Rukee

05-27-2006, 02:47 AM

Actually the 10 bolt posi unit in the older cars (pre `65) is pretty stout. The 10 bolts in the intermediates into the early `70s was alright too, but I had an `82 Firebird I put fuel injection 454 in bored 60 over would turn 11.98 quarters and every time you floored the car it took the rear wheel bearings out of that 10 bolt.

Rippthrough

05-27-2006, 03:38 AM

Rukee

05-27-2006, 04:42 AM

Most all trannys, with the exception of overdrive trannys have a 1:1 finial ratio. I`d have to go with a Richmond 6-speed overdrive tranny like what I linked in the first post to acheave the gear change I`m looking for with just the tranny.

Soulburner

05-27-2006, 05:35 AM

Can you not just change the ratio of your last gear? I've haven't got a clue when it comes to your gearbox, but it seems that that would be the ideal solution here?
You can probably get new gearsets of the shelf over there can't you?
You can but then you sacrifice acceleration and that torquey feel in your other lower gears. Having an OD trans would only affect the last gear which is what you want.

Rukee

05-27-2006, 06:56 AM

No, you can`t really. 4th gear connects the input shaft with the output shaft turning them both together 1:1. You`d have to rearrange all the gears and use your overdrive gear in the 3rd gear place, use 4th for 3rd and then change the shift pattern between the two. Going from 1st to 3rd and have it be 1:1 already in 3rd would be a pretty steep gearing.

Soulburner

05-27-2006, 07:01 AM

My bad I thought that by "last gear" he meant the rear gears...

Rukee

05-27-2006, 07:05 AM

Possably I`m wrong then, I assumed he was talking tranny when he said 'gearbox'.

Rippthrough

05-28-2006, 02:20 PM

Yeah, I meant the last gear ratio, not the final drive.

Rukee

05-28-2006, 02:33 PM

So I`m still confused, are you talking the rear axle gear ratio?? Or transmission 4th gear finial ratio??

Soulburner

05-28-2006, 05:55 PM

He is talking about the actual transmission overdrive gear.

Sorry for the confusion.

Rippthrough

05-29-2006, 04:31 AM

So I`m still confused, are you talking the rear axle gear ratio?? Or transmission 4th gear finial ratio??

THe rear axle ratio is what I know as the final drive ratio.

Whereas 4th gear (in this case) is what I was wondering about.
I didn't say 4th because I was unsure how many ratios you have.

Rukee

06-09-2006, 04:15 AM

I ended up going with the original 3:55 gears and it put my speedo back to reading the right speed again. It`s got lots more legs between the gears now too, don`t really know why they dropped it to 3:90s.
I have a slight howl under load and no installation kit, anyone know which way the carrier needs to be shimmed to get rid of it??
Thanks.

wdrzal

06-09-2006, 04:50 AM

did you replace the the crush sleeve on the pinion?

IIRK you should shim the for around .005 to.008 of backlash on the carrier
.

Rukee

06-09-2006, 05:10 AM

Yes I did, but I had to tighten the pinion nut to extremes to get the play out of the bearings. I don`t have a dial indicator. :(
I adjusted to just the point I had a little play between the pinion and ring gear so I could turn the pinion just slightly before moving the ring. I have about 20 miles on it now and the howl is worse in 3rd and 4th of course. I just don`t wanna waist any gear lube shimming it the wrong dirrection if I can help it, I use Lucas oil stabiliser too, so don`t wanna do it twice if I can help it.

wdrzal

06-09-2006, 01:26 PM

To decrease backlash, increase the thickness on the left side while reducing the thickness an equal amount on the right side. To increase backlash, do the opposite.
you also need to check the contact patch by applying grease to the ring gear, I always used a special purple grease made by permatex,can't remember its name, it changed from dark purple to light where the gears mesh. There a certain contact pattern that occurs when the gears are set properly. theres no way I can describe that to you,in fact its different for hypoid(sprial cut) gears and straight cut gears.

To save a lot of headache and a ruined gear set find someone with experience to help you set them up correctly.Its not hard after you know what to look for. You will need a dial indicator.