need trans info, which one to run???

[tucsonjwt]

I have had a 73 C20 2WD with a 454/TH400 and now have a 83 454/SM465 4spd granny and 4:10 rear with gear vendor. I never had a 4WD or monster tires, but the 454/TH400 was the best combo in a truck I have owned. I have never used the 83 to tow much, so I never really needed the gear vendor, but since you have a 4:56 rear end, I think that is going to restrict anything else you do to your truck. A 3:23 or 3:73 would seem like a better option to open up the top end speed. Gear vendor only advertises a 20% change in final drive ratio, and fuel economy, so most of your gain is in towing or performance.
The thing about the gear vendors is that they seem to hold their value very well - always seem to go quick and for a good price on Ebay, plus easy to ship because they are relative small and light, compared to a transmission. Once you get the driveshaft mod and adapter, I think you are into at least $2K used. There is a driveline place in Las Vegas that specializes is rebuilt gear vendors, but they are still pricey. I have seen a few old suburbans and pickups with an installed gear vendor for sale, so that might be an option for someone who wants one.

[68 TT]

Originally Posted by tucsonjwt

I have had a 73 C20 2WD with a 454/TH400 and now have a 83 454/SM465 4spd granny and 4:10 rear with gear vendor. I never had a 4WD or monster tires, but the 454/TH400 was the best combo in a truck I have owned. I have never used the 83 to tow much, so I never really needed the gear vendor, but since you have a 4:56 rear end, I think that is going to restrict anything else you do to your truck. A 3:23 or 3:73 would seem like a better option to open up the top end speed. Gear vendor only advertises a 20% change in final drive ratio, and fuel economy, so most of your gain is in towing or performance.
The thing about the gear vendors is that they seem to hold their value very well - always seem to go quick and for a good price on Ebay, plus easy to ship because they are relative small and light, compared to a transmission. Once you get the driveshaft mod and adapter, I think you are into at least $2K used. There is a driveline place in Las Vegas that specializes is rebuilt gear vendors, but they are still pricey. I have seen a few old suburbans and pickups with an installed gear vendor for sale, so that might be an option for someone who wants one.

Running the gear vendor as an underdrive of 20% would do what he needs without having to swap gears in the axles or go through the hassle of installing a 4L80E. You won't find many of them configured this way used so it would probably have to be a new unit to get it set up as an underdrive.

[southern gator]

i cant hit 75mph, im pushing the motor in 3rd gear sounds like it im gonna blow it up. so if i have another gear it would shift into 4th lowing the rpms, right???? if i change to 5.13 its gonna raise my rpm's. If i gear it lower say 3.73 its gonna start off slow but when i pick up speed ill be at a lower rpm at a higher speed, i think?

[68 TT]

Originally Posted by southern gator

i cant hit 75mph, im pushing the motor in 3rd gear sounds like it im gonna blow it up. so if i have another gear it would shift into 4th lowing the rpms, right???? if i change to 5.13 its gonna raise my rpm's. If i gear it lower say 3.73 its gonna start off slow but when i pick up speed ill be at a lower rpm at a higher speed, i think?

With the gears and tire size you have it should only be at a touch over 2600 rpm at 75 mph. If you can't hit 2600 rpm in 3rd gear you are down on power and may have a flat cam or other engine problems and if you are at much higher rpm's than that then you may have problems with the trans.

I am leaning toward bad trans or converter with the load of pushing 44's around. I went through several freshly rebuilt & upgraded T-400's and different torque converters only running 40's on my truck.

Are you sure it has 4.56's? Maybe you have much more gear than that.

[southern gator]

im sure its 4.56 gears, but the th400 thats in it now it 3 months old fresh everything. and the torque converter is new also. I guess ill double check my gears when i get home for the hell of it..

[68 TT]

Originally Posted by southern gator

im sure its 4.56 gears, but the th400 thats in it now it 3 months old fresh everything. and the torque converter is new also. I guess ill double check my gears when i get home for the hell of it..

How new it is doesn't matter. I broke one converter under 100 feet out of the garage after putting it in. I just coasted around the building on inertia alone and rolled it right back into the shop to yank it back out. Turned the guts into a bag of marbles.

Unless it is upgraded to handle the extreme loads of 44's even a well done rebuild on a T-400 will not last long. It needs to be rated for over 700 hp to have the right parts in it to live in your truck. Any less does not have any upgraded internals, most likely just a stock sprag and clutches.

Most torque converters under $500 won't last long either. You need parts designed for extreme abuse and power. Something made for a 3500 pound car with a 500 hp small block will last 30 seconds in your truck under power. Look for a rating over 600 hp on the converter and get anti-ballooning plates on it for sure.

[southern gator]

well i know the converter is a 1800-2200 stall i had built at one of the local tranmission shops, i told them i needed it for towing and handly my 44's with 1-tons so they built that to my need. And the th400 has heavy duty clutchs and a shift kit in it. I dont remeber what shift kit, the transmission shifts and drives to nice to be a bad transmission. I like all the info im getting on this topic giving me alot of different points of views

[68 TT]

Originally Posted by southern gator

well i know the converter is a 1800-2200 stall i had built at one of the local tranmission shops, i told them i needed it for towing and handly my 44's with 1-tons so they built that to my need. And the th400 has heavy duty clutchs and a shift kit in it. I dont remeber what shift kit, the transmission shifts and drives to nice to be a bad transmission. I like all the info im getting on this topic giving me alot of different points of views

From what you are saying it sounds like the 3rd gear clutches are burnt up. It will shift fine and move fine in 1st & 2nd and at low throttle in 3rd but under load the 3rd gear clutches start to slip and the RPM's go up without moving the truck much faster. It makes sense with the high RPM and inability to hit 75 mph.

Drop your trans pan and see how the fluid looks and how much metal is in the pan & filter.

[southern gator]

no metal in pan or transmission fluid is like new, still sound like a bad transmission???

[68 TT]

Originally Posted by southern gator

no metal in pan or transmission fluid is like new, still sound like a bad transmission???

You could still have a bad converter. Nothing else but the trans or converter would let the RPM climb but not move the truck down the road.

Nothing else can explain not being able to hit 75 mph unless you are in 4-low. Have you checked to make sure you have all the ranges in the transfer case? Maybe something in there let go and you are stuck in 4-low. That would be about right. 75 mph would be about 5300 rpm.

[southern gator]

yeah my shift rails are in the right spot. front shaft not moving while going down the road, i was thinking about opening up my np205 maybe a pin for the shift fork is broke and its not shifting..

[southern gator]

UPDATE: well i opened the rear axle and yes the gears are 4.56 i opened my pto cover on my np205 t-case nothing broken in the case, everything shifting good and ect... so, any other suggests???

[68 TT]

Originally Posted by southern gator

UPDATE: well i opened the rear axle and yes the gears are 4.56 i opened my pto cover on my np205 t-case nothing broken in the case, everything shifting good and ect... so, any other suggests???

The only thing left is the converter is bad or the trans is slipping in top gear.

[southern gator]

well i just swapped a brand new just built converter a week ago or two and no change. Had turner transmission build me a new one i swapped it out. no change. Does this sound like a bad th400 gear???

[68 TT]

Originally Posted by southern gator

well i just swapped a brand new just built converter a week ago or two and no change. Had turner transmission build me a new one i swapped it out. no change. Does this sound like a bad th400 gear???

You have eliminated everything else so all that is left is the trans itself.

[southern gator]

also i heard a whinning noise when i towing, found out that could be a gear slipping. so transmission time... thanks guys for the help