Gear Vendors

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I just read some stuff from some of the T-bucket guys (early Ford Model T roadsters). Some of them are running shafts as short as 6" from center of joint to center of joint. Note that these are very LIGHT WEIGHT cars and have very little rear suspension travel. If my trans and rear axle aligned perfectly I wouldn't need a u joint at all -- but I have that Jaguar independent rear suspension -- the differential doesn't move. Well, mine is rubber mounted and the trailing arms do cause it to move a little, but you get the idea. 

In yours a 24" or so driveshaft would work, and you might have that much even with a GV unit. If it's too short it will bind when the rear axle moves and cause vibration, as noted. You can use a double cardan (two u-joints back to back, not shaft between them, but a special coupler) constant velocity (CV) joint to help since they will work at a higher angle, and are more flexible. One of the T-bucket guys stated they used TWO such joints and only 2" of tube between them, with a total length (end joint to end joint) or 6-7". Other just used two joints with the same length though -- as I said, not much rear suspension travel. The pinion angle of the rear axle and transmission are much more critical as the shaft gets shorter also.

The only time the $2600+ GV unit makes economical sense if you 1) just have to keep the stock trans for some reason or 2) have a really high power engine. GV states that you will break a typical high power built four speed (like a T-10, Muncie, or A833 -- not stock but built for drag racing) before you break the GV unit. The GV unit is stronger than the Laycock-DeNormanville unit AMC used... at least the current ones are. GV got their start by buying left over LD units from AMC after AMC stopped using them in the late 70s. GV converted them to divorced units at first, then started making adapters. Not long after they purchased manufacturing rights and started making a stronger unit. I wouldn't be surprised if any divorced unit you found in a truck or bus was actually manufactured by GV.

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farna Members Profile Send Private Message Find Members Posts Add to Buddy List Supporter of TheAMCForum Moderator Lost Dealership Project Joined: Jul/08/2007 Location: South Carolina Status: Offline Points: 19686	Post Options Post Reply Quote farna Report Post Thanks(0) Quote Reply Topic: Gear Vendors Posted: Sep/17/2018 at 5:59am
	I just read some stuff from some of the T-bucket guys (early Ford Model T roadsters). Some of them are running shafts as short as 6" from center of joint to center of joint. Note that these are very LIGHT WEIGHT cars and have very little rear suspension travel. If my trans and rear axle aligned perfectly I wouldn't need a u joint at all -- but I have that Jaguar independent rear suspension -- the differential doesn't move. Well, mine is rubber mounted and the trailing arms do cause it to move a little, but you get the idea. In yours a 24" or so driveshaft would work, and you might have that much even with a GV unit. If it's too short it will bind when the rear axle moves and cause vibration, as noted. You can use a double cardan (two u-joints back to back, not shaft between them, but a special coupler) constant velocity (CV) joint to help since they will work at a higher angle, and are more flexible. One of the T-bucket guys stated they used TWO such joints and only 2" of tube between them, with a total length (end joint to end joint) or 6-7". Other just used two joints with the same length though -- as I said, not much rear suspension travel. The pinion angle of the rear axle and transmission are much more critical as the shaft gets shorter also. The only time the $2600+ GV unit makes economical sense if you 1) just have to keep the stock trans for some reason or 2) have a really high power engine. GV states that you will break a typical high power built four speed (like a T-10, Muncie, or A833 -- not stock but built for drag racing) before you break the GV unit. The GV unit is stronger than the Laycock-DeNormanville unit AMC used... at least the current ones are. GV got their start by buying left over LD units from AMC after AMC stopped using them in the late 70s. GV converted them to divorced units at first, then started making adapters. Not long after they purchased manufacturing rights and started making a stronger unit. I wouldn't be surprised if any divorced unit you found in a truck or bus was actually manufactured by GV.
	Frank Swygert

farna Members Profile Send Private Message Find Members Posts Add to Buddy List Supporter of TheAMCForum Moderator Lost Dealership Project Joined: Jul/08/2007 Location: South Carolina Status: Offline Points: 19686	Post Options Post Reply Quote farna Report Post Thanks(0) Quote Reply Posted: Sep/17/2018 at 5:38am
	Rambler Mexicano -- The Laycock-DeNormanville unit AMC used replaced the output shaft and housing, like all factory OD units (except for some heavy trucks with a divorced unit). A special short input shaft is used so that the total length of the transmission is just a bit longer (6-10") than the standard transmission without OD. Back in the days of the torque tube the standard transmission (without OD) had a longer than usual output shaft and housing so the same torque tube could be used with or without OD. A manual trans with OD is just a few inches longer than most automatic transmissions. A divorced OD is the same OD unit, but with a cover plate on front that has a bearing and a short shaft extending from the front. A coupler is then used to attach that shaft to the output shaft of a standard length manual transmission. The coupler can be a simple tube that is splined to match the transmission output and OD input shafts, or two yokes joined by a single u-joint. That type of installation is the length of the OD unit (15-18") + the distance between the standard trans and OD unit (3-6"). So you're looking at an additional 18-24" of length instead of 6-10" with a factory OD. There is usually a crossmember supporting the divorced unit with rubber mounts similar to transmission or motor mounts also. The GV unit uses the adapter to rigidly attach itself to the transmission, so no seal or support bearing or additional support for the unit itself is needed. Gear vendors appear to use a coupling as well, just no support bearing or cover on front. The GV unit is 12.25" long, and the shaft extends an inch (maybe a bit more) from the front, so even it will add about 13.5" to overall length. Converted to a divorced unit it would be a couple inches longer, as you would need room for the cover plate with a bearing and seal to support the coupler and input shaft.
	Frank Swygert

vinny Members Profile Send Private Message Find Members Posts Add to Buddy List Supporter of TheAMCForum Joined: Jan/05/2012 Location: Calgary Status: Offline Points: 2837	Post Options Post Reply Quote vinny Report Post Thanks(0) Quote Reply Posted: Sep/16/2018 at 6:01pm
	6 1/2 kms per L (15.4L per 100km?) is pretty bad IMO even with what you have. I'd try to get it tuned better because I don't think just an overdrive would improve it that much. What octane fuel are you using? I can remember a trip we did through Mexico in the early 70's with a 64 Impala that it used to ping more than usual and we figured that maybe the fuel had lower octane. It could have also been that we were in higher altitudes than at sea level where the car was from. With these old cars I strive for 10kms per L, or 10L per 100kms, or 28 MPG Imp, or 22.4 MPG US. With my 64 Classic 232 2 barrel auto 3.15 axle I can get that on the highway if the speed is kept under 50 MPH.

Rambler Mexicano Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Mar/05/2011 Location: Guadalajara Status: Offline Points: 977	Post Options Post Reply Quote Rambler Mexicano Report Post Thanks(0) Quote Reply Posted: Sep/16/2018 at 4:03pm
	AMC did have a divorced overdrive available as an option in 1975 and 1976, it was used in Gremlins, Pacers and Hornets with three speed manual transmissions and column shift. Here it is, from 1975 Popular Mechanics. The gear ratio of it is specified as 0.714:1
	Mauricio Jordán Cuando no se es una empresa famosa se deben hacer mejores automóviles. - Vehículos Automotores Mexicanos S. A. de C. V.

purple72Gremlin Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Charter Member Joined: Jul/01/2007 Location: Illinois Status: Offline Points: 16614	Post Options Post Reply Quote purple72Gremlin Report Post Thanks(0) Quote Reply Posted: Sep/16/2018 at 3:06am
	AMC did not have a divorced OD. Divorce means separate, meaning a drive shaft to OD then driveshaft from OD to rear end. IRS---- Independent Rear Suspension.

Rambler Mexicano Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Mar/05/2011 Location: Guadalajara Status: Offline Points: 977	Post Options Post Reply Quote Rambler Mexicano Report Post Thanks(0) Quote Reply Posted: Sep/16/2018 at 2:02am
	Thanks a lot jpnjim, 304-dude, Trader and purple72Gremlin. After all you're telling me, I find it strange that AMC actually offered a divorced overdrive in the Gremlin for 1975 and 1976 as a factory option (the Laycock-de-Normanville one), having the same short wheelbase as the Spirit. Unless that unit was very short in length and had rear suspension mods to avoid what you mentioned. 304-dude, what does IRS stand for?
	Mauricio Jordán Cuando no se es una empresa famosa se deben hacer mejores automóviles. - Vehículos Automotores Mexicanos S. A. de C. V.

purple72Gremlin Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Charter Member Joined: Jul/01/2007 Location: Illinois Status: Offline Points: 16614	Post Options Post Reply Quote purple72Gremlin Report Post Thanks(0) Quote Reply Posted: Sep/15/2018 at 11:36pm
	And if you do find a divorced OD, [out of a truck/bus]....its going to be big and heavy. You are wasting your time. Either live with what you have, or T5.

Trader Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: May/15/2018 Location: Ontario Status: Offline Points: 6909	Post Options Post Reply Quote Trader Report Post Thanks(0) Quote Reply Posted: Sep/15/2018 at 9:35pm
	Front wheel drives have short drive shafts with loads of angle variation. It takes fabrication mine you, but a CV joint and Tripod Joint can take a lot of HP and not care about excessive drive angle. Just outside the box option. Many high lift off road vehicles are going this route.

304-dude Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9082	Post Options Post Reply Quote 304-dude Report Post Thanks(0) Quote Reply Posted: Sep/15/2018 at 8:49pm
	Farna could get away with a short shaft, using his Jag rear setup. Since the center is stationary, and pinion angle is statically set for proper angle. IMO small wheel based cars do much better with IRS than long wheel based cars. So a spirit body may be a fun conversion if inclined.
	71 Javelin SST body 390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker

jpnjim Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Nov/25/2007 Location: New England Status: Offline Points: 2752	Post Options Post Reply Quote jpnjim Report Post Thanks(0) Quote Reply Posted: Sep/15/2018 at 8:35pm
	Short rear driveshaft can cause steep u-joint angles, or a mismatch between front and rear joint angles. That can lead to vibration, wear, breakage depending on your setup and use. Short wheelbase Jeeps have a high ride height and a very short rear driveshafts, so it can be managable, it's just one more thing to be aware of and deal with. If I were building a Spirit with an add on rear OD unit I would want to see just how short the driveshaft would be before collecting parts, there are limits to how short a shaft can be, and still allow suspension travel (especially with a leaf spring suspension). Edited by jpnjim - Sep/15/2018 at 8:40pm
	71 P-code 4spd Javelin/AMX some Jeeps and some Fords