'66 with a 2.73 in the rear?

[C10Slim]

Is it possible for a 66 to have a 2.73 gear in the rear? My 700r4 is setup for a 3.73 gear because that's what I want to run and that's what I thought was in there. Any whoo, after finally getting it on the road the speedo is way off. So I jack up the rear and do the ol' turn the shaft and count the tire rotations and comes out to about 2.75 turns. Is that possible? Also seems to be a weak or open diff? You can spin one wheel and both will spin but you can stop one wheel and the other will keep going. Is that right?

[Captainfab]

These trucks did not come from the factory with 2.73's. As far as I know the gears available were 3.07, 3.73, and 4.10's. I've never had good luck tyring to calculate the gear ratio by spinning the tires and counting the driveshaft rotation. The best way to see what gears you have is to pull the rear cover. The rear end is one of the most neglected parts of a vehicle, so I would imaging the oil could stand to be changed. Just get a couple quarts of 85W90 gear oil and a cover gasket, and open it up. The gear tooth count will be stamped on the edge of the ring gear, as well as the date and the part number. The numbers 11 41 will be a 3.73 gear....41/11 = 3.73.

Also, your speedometer is not going to be correct since you changed the transmission. The speedo gears in that trans are setup for the gear ratio and tire diameter in it's original application. To have you speedo to be accurate, you will need to change one or both gears in the trans. Of course you will first need to know your gear ratio for sure, and also your tire diameter.

Originally Posted by C10Slim

Is it possible for a 66 to have a 2.73 gear in the rear? My 700r4 is setup for a 3.73 gear because that's what I want to run and that's what I thought was in there. Any whoo, after finally getting it on the road the speedo is way off. So I jack up the rear and do the ol' turn the shaft and count the tire rotations and comes out to about 2.75 turns. Is that possible? Also seems to be a weak or open diff? You can spin one wheel and both will spin but you can stop one wheel and the other will keep going. Is that right?

[C10Slim]

Thanks Captain I will pull the cover off tomorrow and see what's really in there. Your right who knows when the fluid was last touched.

The tranny is new monster trans and it's supposed to have the 3.73 speedo gear in it. But either it doesn't or the gears are not 3.73's. Its also kind of a dog to get rollin, but with 430hp under the hood it should be pretty peppy. That's why I also think I have low gear in there. Maybe its the 3.08.

Guess we will see tomorrow. Thanks again for the infor and advice!
Posted via Mobile Device

[Captainfab]

Do you have the TV cable properly adjusted? That is very inportant with the 700R4's

So you have a monster trans?.........hopefully you have better luck than some other members have had with them. Do a search in the 'Engine and Drivetrain' section

[C10Slim]

I am pretty sure I have the tv cable right now. After several attempts to use the monster cable and POS bracket I finally broke down and bought a tv made easy kit. It was much easier to set up. It seems to run ok and shift well. Just a dog to get rolling. Once your crusing it will down shift and run.

I have not been trilled with the monster trans to be honest. It leaks. Got a leak coming from the front pump seal or somewhere under the converter cover. The pan gasket is leaking although that might have been my bad. I called monster about the front pump seal to see if the would send me another to have installed and they told me no I would have to send the trans back. What??? You want me to pull and ship the entire trans for what's probably a $5 part? Forget it. So the warranty is really no good unless you granade it and then they would proably find some way out of it. Oh well live and learn.

I have since met a really good trans shop through my GN club. Their main focus is on 200r4s but they have done them all. Once I get the truck running good enough where I feel safe running across town I am going to take it to them to replace the seal and double check everything.
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[summerj]

Yes I would remove that cover clean out that old grease and oil and add some fresh gear oil.


I am getting ready to upgrade my powerglide to something else. If I were a betting man I would say I have the stock 373;s in my stock 65 rear. Some say this was the most common stock gear set up back then .

Q: If you had to do over what route would you take with your transmission? I was thinking 30 spline 700R 4 with heavy duty 3rd and 4th gear kit.

[LT1 Burb]

I have 308 gears in the rear of mine with a 700R4 and at 65 MPH I am turning about 1600 RPM with a 30" tire. My speedo is around 8 MPH off also. I would be interested in knowing what your RPM's are now at 65 and after you change to 373's as that is what ratio I am thinking.

[Chevy Fleetside]

I have 3.08s in my 65 and I had no doggin going one except going slow on the freeway. Off the line was not a problem. 2.73's came in cars with smaller tires. it is posible someone swapped one in at one time.

[C10Slim]

Ok just pulled the cover and I do have 3.73's! Sure doesn't feel like it. The speedo is still way off. I called monster and confirmed gear and tire size and they confirm that what is in there "should be close" but when he did his calculation he got 2 different sized gears. I don't recall the exact numbers but was something like 15/45 vs 17/44. So I ordered the 15/45 that his calculation came up with. We'll see if that gets the speedo closer.

So anyway, I am happy that the 3.73's are in there, but that throws a wrench in my theory about gears being the reason it's a dog out of the hole. Do you guys think could be because I am still running open headers? I need to drive it up to the muffler shop and have them fab up the rest of the exhaust. Maybe the motor needs a little back pressure to build tq? It engine dynoed at 436HP and 460TQ so should have plenty get up and go in that truck. Right now it's pretty dissapointing. It's loud as hell, but just not going anywhere.

Any other thoughts or suggestions? got a 2200-2500 stall in it, but that should be a good setup for the power and weight of the truck.

@Summerj: You'll have to ask me that question again in another month or so. The whole reason I got the 700 was for the more aggresive 1st gear and the 4th. I am hoping to be able to curise to Austin or Dallas just humming along and getting good mileage. But for now it's just been one big PITA getting eveything installed and set up right.

[C10Slim]

PS... any tips on buttoning the rear back up? I have new gasket and gear oil. Should I put some RTV on the cover side?

Oh and how the hell do you fill it?

[chevyrestoguy]

Are you sure the trans is starting out in 1st gear from a stop? 700r4s have a lower first gear than a th350 or th400, and coupled with a 430 horsepower and a 3.73 rear gear, it should be peppy. It should be blowing the tires off. What carb are you running? If it's a mechanical secondary carb, that might be part of the problem. What distributor are you running? The vacuum advance might not be working. Having an open exhaust is not the problem, and in theory, it should run better now than when you get the exhaust installed.

From what you describe, it sounds like it's not starting out in low gear. Post up your combination, and maybe we can pin-point a culprit. I've been in the same boat as you before, and it's frustrating.

[Clyde65]

Have you put the tranny in lo and started off? ran it like a standard tranny?

[C10Slim]

WTH!! I go to O'rielly and Advanced looking for the diff cover gasket and all they have listed is the 10 bolt. I try telling them no I have a 12 bolt and they look at me like I am stupid! Anybody have like a felpro part number?

Chevyrestoguy: I assume so but don't know for sure. I just put it in Drive and go. I am pretty sure it is though because one click up and it goes in to neutral. It's a Blueprint 383 dressed engine so came with Edelbrock 1406 carb on performer intake and with MSD ignition.

Clyde: I tried it a few times still didn't seem to pull as hard as it should.

[C10Slim]

Ok. Looked up a 67 truck and got the 12 bolt gasket I needed.

[Rich 5150 69]

You do have other issues. as restoguy says with 3.73 rear gears, 306 tranny first gear, and a 2500 stall, you should be blowing the tires off...

[C10Slim]

Ok I am a Dee. Found the probable cause for my speedo being off you have to calibrate it. It's an autometer electronic speedo and I found a write up on their web site, so I will try that tomorrow.

As for the lack of power down low, I dunno. I took another drive today dropped it down to first and punched it from a roll down the drive way and left a 30 foot stripe down the street so the power is there.

The problem seems to be when hitting the gas off idle like from a stop sign or tuning a sharp corner. It kinda of sputters (one time it almost died) and then all of a sudden it will fire and take off. So I got something off. Either the carb or the timing. This is my first carbed vehicle so I really have no idea how to tune it. Any suggestions on what might cause this sputter and what I might do to adjust it? Again Edelbrock 1406 carb.

I am going to retime it tomorrow and see if that makes a difference. Thanks for the posts everyone!

[Rich 5150 69]

Is that a new elde carb or used...only asking for the reason of float adjustment...the only other thing I can think of is vaccum advance, you running HEI with an adjustable vaccum advance,... is it hooked up on full manifold vaccum or ported vaccum at the carb.

[C10Slim]

It's new carb. Came installed on the motor from blueprint. I assume they dynoed it with the carb and distributor on it so should ihave been set up properly. Although I did remove the dist to prime the motor. I didn't touch the carb accept to connect fuel line and brackets.

It is HEI w adjustable advance.I am pulling vacuum off one of the carb ports and have the other blocked off.
Posted via Mobile Device

[Rich 5150 69]

Sounds as if timing is off a tad. Retime it...you may have to re-adjust the vaccum dashpot.

[losthope]

make sure the vacuum your hooked up two is the right one!!

this may help..

Edelbrock Carburetor Installation and...

[Rich 5150 69]

Good video Losthope, the problem arises on how they had setup the dizzy, either way is right, it just depends on how they set it up, my HEI is hooked up to full manifold vaccum, and adusted for it. Low end is phenomenal.

[Rich 5150 69]

Here is an interesting link for HEI, he`s aleady got a adjustable vaccum advance, maybe something here will help...or confuse..
http://www.73-87.com/7387garage/drivetrain/hei.htm

[C10Slim]

Originally Posted by losthope

make sure the vacuum your hooked up two is the right one!!

this may help..
Edelbrock Carburetor Installation and Troubleshooting Part 3 - Installation 2 - YouTube

Well I got that part right I will verify what port BP did the inital setup with.

The more I think about it, the more I think timing is the issue. Is it possible to put the plug wires in the right order but all shifted one post off? I had to turn the dist like a 1/3 a counter clock wise rotation to get it started and timmed. The vacuum advance port is almost against the manifold. Would this matter? Should I bring it back to TDC and reset everything? Or it it ok as long as I can get the 34 degree timing they recommend?
Posted via Mobile Device

[C10Slim]

Originally Posted by Rich 5150 69

Here is an interesting link for HEI, he`s aleady got a adjustable vaccum advance, maybe something here will help...or confuse..
http://www.73-87.com/7387garage/drivetrain/hei.htm

Guess he answered my question about the wires being one off: "Number 1 plug wire should be at the front of the distributor just to the driver's side of centerline.* If that's not your #1 plug wire then you have the distributor installed off by a few teeth.* It won't hurt performance if timing is still set correctly but plug wire routing gets a bit messy."

I will have to read that a few times to grasp it.
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[C10Slim]

Progress! So I was reading up on vacuum advance last night and came across an interesting ported vs manifold vacuum post on a hot rodder forum:
http://www.hotrodders.com/forum/vacu...bad-47495.html

A lot of the issues they were describing sounded like my issue, so I thought what the hell I'll give it a shot. Switched to manifold vacuum and what a difference at least on start up. Before the change if you choked the motor at all it would never start. Always had to start with no choke and part throttle. You had to hold it at 2000-2500 rpm to keep it running until it got warmed up. Then it would idle down with out killing it.

With manifold vac, it tried to fire with the first click of the key (never happens). So this time I gave it about half choke, no gas other than a pump or two before turning the key and it fired right up! Couple more blips of the throttle and it settled down right on idle. WOW! (again never happens). I let it run for a few seconds and then slowly backed out the choke. Again perfect idle and seems to run a bit smoother.

The only catch is now when I put it in to gear it kills it. Before the change it would (again after holding the revs up for several min) it would finally idle down to about 1000-1100 before you put in gear. Then once you put in drive it would idle down to about 800, but keep running.

With the change right off start it idles down to 1000-1100 in park , but just falls flat when you put it in gear. What would cause that? Should I raise the idle?

One more thing, I understand why the idle drops when I put it in to gear, but when I put it back in park it doesn't come back up unless I blip the throttle. Is this because the trans is still somewhat engadged and then the blip basically forces it to disengadge?