HP, I have a guy that can build one as nasty as you like and run low 9s.Heres another little write up for you guys. I had never heard about this mod until casper gt mentioned it in a post awhile back so he gets credit for bringing the mod to the table :drink. After wondering what he was talking about I sent him a pm and got some info. “luckly” at the same time the the torque converter in my truck went out so I had just went ahead n’ got a whole new trans and had just finished up putting the new transmission in. So I have an extra 4r70w in the garage to play with and used it for the tailshaft lube mod. I have pics this time too :D
These transmission have a thing with eating up the bushings in the extension/tail housing, and this becomes and even bigger problem with 3.73 and higher gears if you do a lot of high speed driving bc of extra rpms vs the factory gears. This mod allows for some extra and forced lubrication of the bushing.
Just to say this and get it out of the way ive only seen one guide showing how to do this and it says that the line pressure hole in the trans is 3/16”. Slipping a 3/16” tap in this thing was like throwing a hot dog down a hall way. I was able to thread a 5/16 tap into it with ease. I figured id throw this bit of info out there bc im sure someone will post a reply saying “well this other thing says its 3/16”. Maybe they made a typo or something, I donno but when I checked the size with a tap to make sure I was making the hole in the tailshaft housing correctly the 3/16” tap was wayyy to small. You can buy the kits for about $120 with this mod already done to the housing including the fittings and lines but if you have the tools laying around its something you can do to save money.
Youll need the following stuff:
Set of drill bits or a single 5/16” drill bit & a 5/16 x 1/8 tap
Small drill bit, no particular size but 1/8” is a good size
Drill bit that is .050”
BLACK rtv gasket maker – black is the most oil resistant that’s why its in caps
Set of metric sockets & ratchet
New tail shaft bushing
New gasket that goes between the transmission case and tail shaft housing
New tail shaft seal
2 90 degree fittings – Male ends need to be 5/16” with 1/8” threads
18-24” of brake line that will thread into the female ends of the above fittings
a ball penis (I mean ball peen) hammer and a flat head screwdriver and some time or an air hammer/air chisel with a split tip.
Jack up the car and remove the drive shaft, transmission brace, and mount. Support the transmission with a jack or jack stand because when you remove this brace it will want to dip down. Remove the tail shaft housing by removing the 6 13mm bolts in the pic below. The housing will then slip right off. The second pic is of the housing after being removed.
Next remove the black rubber seal on the end (don’t have pics of this) the easiest way to do this is wedge a flathead screwdriver between the lip of the seal and housing and beat it with a hammer. Do this all the way around and it will begin to come out. You can mangle this thing up all you want, youre gonna replace it anyways.
In the above pic that beat up looking ring inside the housing is the bushing you want to remove. Theres a few ways of removing it w/o a press that work pretty good. The first one is a hammer and screw driver. Set the housing on something flat with the bushing side facing up and put the center of the screwdriver head on the bushing where the housing has the little indented slots and knock it with a hammer HARD rotating between the 3 spots. The bushing will probably begin to tear but that’s ok, youre gonna be replace it anyways. The other way to do this which took about 20 seconds if that is take an air chisel/air hammer with a split tip chisel and use it just like you would the screwdriver. The pic below might give you an idea of how im talking about doing this.
After you get the bushing out look on the driver side of the housing and youll see a round circle like the one in the pic below.
In the center of this circle drill you a small hole with the 1/8” (or whatever small size you want to use) drill bit to make a pilot hole for the 5/16” bit. After you drill a pilot hole go back and drill the hole bigger with the 5/16” bit. I recommend drilling it slow and using some sort of lube. The material the housing is made out of is very soft so it doesn’t take much. The pic below is of the pilot hole about half way doing being drilled with the 5/16” bit.
Once you drill the 5/16” hole tap the hole using the tap mentioned in the parts list. Run the tap in a few turns, back it out a turn or two, run it back in farther, and repeat until you have it all the way through. A little lube helps with this as well. Feel the inside of the housing where you drilled/tapped the hole and make sure theres no burrs or rough edges. If so smooth them out with some fine sand paper. Then clean up any metal shavings.
Install your new bushing, lube it up with some vaseline (this is no joke, vaseline is great stuff for transmission work because it mixes well with the fluid) the easiest way to get this thing in there is to press it in or set it in place from the top, put a block of wood on top of it and smack it in with a hammer once its flush with the hosing and the wood will no longer work continue to gradually tap it in with a hammer going around the edges in a circle. After the bushing is in place take the .050” drill bit and drill a hole in the bushing a center as you can of the 5/16” hole you drilled/tapped. Then clean up any burrs/rough edges on the bushing. Clean up any metal shavings that might be in the housing.
Take one of the 90* fittings and put some black rtv on the threads and thread it into the 5/16” hole you drilled/tapped. You can now reinstall your new housing seal, set it in place and gradually tap it into the housing going around the edges using a hammer. You want the female part of the fitting to be facing the front of the trans.
On the side of your transmission case (on the driver side) towards the front youll see a cylindrical bump. Towards the top of this there will be an 11mm plug picture below.
Remove this plug, put some black rtv on the male threads of your other 90* fitting and thread it into this hole with the female part of the fitting facing the rear of the trans.
Reinstall the tail shaft housing using the new tail shaft housing to case gasket. Put some black rtv on the male ends of your brake line and thread your brake line into both female parts of the 90* fittings. Put everything else back together and youre done.
