Th400 tailshaft roller bearing

[MadBill]

Does the bushing OD show any signs of having spun and/or the ID any distress?

Assuming that with the press fit, the thermal expansion of the bushing is the same as aluminum (~12 PPM), a 1.4" (for example) ID heated from 70°F. to 300° would expand by 12 x 1.4 x 230 = 0.0038" while the shaft raised to the same temp would expand (~7 PPM) by only just over 0.002" No scope for seizure there!

A shaft/bushing clearance on the high side, say ~ 0.006"- 0.008" or so wouldn't hurt though.

Faced with the same problem a couple of years ago on a magnesium case Trans Am road race car we wondered, as did Smokey about piston pins "Where do those forces come from that push the pin out? Bleeped if I know!", but then we just shrugged and built a really sturdy sleeved retainer that fitted over the seal and carried 3 set screws tightened into dimples drilled in the tailshaft housing. Never had another problem. There are also way stronger products than red Loctite, e.g. Retaining Compound 638, that have bond strengths in the thousands of pounds per square inch, plus handling temperatures up to 300° Perhaps a 'belt & suspenders' approach is called for at this point...

Spiral grooving the bushing and adding a grease fitting works well for chassis Dyno Queen applications...

[jacksoni]

Does the bushing OD show any signs of having spun and/or the ID any distress?

Assuming that with the press fit, the thermal expansion of the bushing is the same as aluminum (~12 PPM), a 1.4" (for example) ID heated from 70°F. to 300° would expand by 12 x 1.4 x 230 = 0.0038" while the shaft raised to the same temp would expand (~7 PPM) by only just over 0.002" No scope for seizure there!

A shaft/bushing clearance on the high side, say ~ 0.006"- 0.008" or so wouldn't hurt though.

Faced with the same problem a couple of years ago on a magnesium case Trans Am road race car we wondered, as did Smokey about piston pins "Where do those forces come from that push the pin out? Bleeped if I know!", but then we just shrugged and built a really sturdy sleeved retainer that fitted over the seal and carried 3 set screws tightened into dimples drilled in the tailshaft housing. Never had another problem. There are also way stronger products than red Loctite, e.g. Retaining Compound 638, that have bond strengths in the thousands of pounds per square inch, plus handling temperatures up to 300° Perhaps a 'belt & suspenders' approach is called for at this point...

Spiral grooving the bushing and adding a grease fitting works well for chassis Dyno Queen applications...

Thanks Bill-
I don't have the trans out of the car yet but in the past both slip yoke and bearing show signs of heat. At the track we didn't have any measuring tools but "relieved" the bearing with some sandpaper on a hole saw of appropriate size to increase the clearance a lot. It does have some spriral grooves stock. Stronger retaining devices/glue really aren't the proper fix I don't think as it is just going to cook it more in place. In your road race car you had lots of G forces perhaps sloshing some lube into the right spots and the retainers worked. On my Salt car there are none really, thus my consideration of a pump, as long as I continue with this trans. Grease fitting would be easy but wonder about adding quantities of that to the trans. Maybe just a bit before each run and frequent oil changes would do it. I recall old time farm machinery ( and wasn't a lube cup being blocked on some Nazi locomotive, thus getting the perpetrator shot having been identified by having a deformed coin in his pocket that just fit, the subject of some movie?) with a cup with screw cap, filled with grease, give it a turn time to time forcing grease to the bearing. I could do that. Locate it in the cockpit and give it a twist time to time.
I wonder if there is some 9500 rpm grease somewhere.

[BrazilianZ28Camaro]

It does have some spiral grooves stock.

Here is you problem. Spiral grooves may do wonders to feed oil into the bushing but may act like a screw, "unscrewing" the bushing out the trans.

I'd fab a graphite impregnated -bronze bushing with about .03 mm interference fit (you can freeze it or heat the trans with hot water to help installation) and two internal 180° straight oil grooves 95% of the bushing lenght ,with the closed end facing the retainer side so the oil wont flow out of the bushing.

I'd set about .04 - .05mm clearance, mirror polish the yoke OD and test again.

My two cents.

[jacksoni]

It does have some spiral grooves stock.

Here is you problem. Spiral grooves may do wonders to feed oil into the bushing but may act like a screw, "unscrewing" the bushing out the trans.

My two cents.

Well, I just checked a new one I have. Has spiral grooves, 2, but they go in opposite directions so the unscrewing theory probably won't work.

[Alan Roehrich]

I'd be willing to bet Rossler has a roller bearing extension housing for a TH400. Rossler puts a roller bearing in most of their drag race units, mostly to reduce friction I suppose. Normally they cut the original bushing and seal section off the housing, and weld a large piece of aluminum in its place to hold a roller bearing and seal.

I've never seen many of those bushings come out, and the few I have seen were always the result of a drive shaft problem of one sort or another. It's far more common for the bushing in the case to spin out. I use red Loctite 271, or green Loctite cylindrical part retainer to hold both bushings, and the rear seal.

We've been looking at making a complete TH 400 case and extension housing, SFI approved, but NHRA told us they wouldn't allow it in Stock Eliminator or Super Stock. That sort of cuts the market by 80%.

[jacksoni]

Thanks, Alan. There are several mfgs of roller tail housing both TH400 and PG.(the latter with a smaller slip yoke that might not work) In the past I had found a bearing that might do the trick but machining the housing alone wouldn't work. Indeed, Just cutting off the offending part and welding in an adapter would be a way to go, or someway reinforcing the current area. I have some time over the winter to see about this. Still have to lube a roller though and there is just not much that gets back there. Again, thanks for the thoughts.

And though this has happened with two different cars, transmissions and driveshafts, (both custom made and balanced) rechecking shaft balance in the plan as well.

[Alan Roehrich]

It shouldn't require that much lube.

Unless you're turning it 10,000 RPM for a really long time, stock lube should be fine. Think how many of those turn 3000 RPM steady state for hours at a time, for years. A regular pickup truck with 3.73 or 4.10 gears will turn 3K for hours at a time, and do that for years.

You could try coating the bushings, H.M. Elliott has a coating we use on bearings and piston skirts that should do the trick.

[jacksoni]

It shouldn't require that much lube.

Unless you're turning it 10,000 RPM for a really long time, stock lube should be fine.
You could try coating the bushings, H.M. Elliott has a coating we use on bearings and piston skirts that should do the trick.

Well, not sure what "a really long time" is here but it is going 9500 for mile and a half and it's not getting enough lube with the current set up. Thus the idea of an oil pump or grease fitting or something. The coating might help. So, whats in the back of your basic Daytona/Talladega trans?

[jacksoni]

Ok some digging shows a PG tailshaft housing with TH400 dimension roller bearing and with Mark Williams making oversize yoke for it.
Allegedly this is the proper bearing ( to be checked): http://www.ebay.com/itm/130654932725?_t ... 97.c0.m619
So, buy the PG housing with bearing in, chop it up, weld to my trans. All fixed.

[jacksoni]

Small update- the bearing # I posted previously id not likely correct. G-Force uses a rna6908 bearing and I suspect is same in Jerico etc. G-Force tells me the roller housing on their GF-5R trans that is based on the Doug Nash/Richmond case architecture and has a roller will not work. I am in process of getting stock tailshaft housing welded to reinforce and will then machine for the bearing above.

Seems Ford big car trans have similar bushing extrusion problems and someone has come up with a pressure lube kit (0r easy make yourself) plumbing from a pressure port somewhere on the auto trans forward with some brake line to a restricted ( .040-.050") port to the bearing. Short time with some drills and taps and about $10 of fittings and tube. Supposedly works well. If interested google "tail shaft forced lubrication".

Again, I appreciate the thoughts of the responders here.

[Warpspeed]

I seem to remember reading something about this many years ago.
This is certainly not a new problem.

I am with Mad Bill, the problem seems not to be the yoke or bushing, but the housing is just not strong enough to hold the thin busing in place with some really serious heat and pounding.

A sturdy steel sleeve pressed over the outside of the housing, and staked in place holds the whole mess rigid, and gives the sleeve a chance.
Even a roller bearing is going to have a hard time if the outer housing is expanding, moving around, and changing shape.

[jacksoni]

Thanks, Warpspeed. I am convinced lack of lube is the issue here. There is no way for any significant lube to get from the back of the trans body, and the bearing on the mainshaft there, to the bushing in the back. I suppose some sort of girdle as you and MadBill suggest could be rigged but not easy and to be honest, just retaining the bushing is not going to do it. See atached photos.
I have two of these housings. They are being weld reinforced and will be machined to put a roller bearing in it same as G Force and other high end transmissions have. The bearing is a double row needle roller with an oiling hole and groove that will be aligned with the hole in the side of the tailshaft housing. I will then rig a small pump that will go from the trans drain plug (my plan anyway) to the bearing and it will be on whenever under way.

[jacksoni]

Just want to show an update and again thanks to all who made suggestions. I got the tail housings welded some to reinforce. This did soften the casting some so maybe not a good trade off but will see. Machined the inside for the bearing which is an RNA6908 double row roller and is what is in most if not all of the roller tailshaft housings for TH400 size shafts/yoke. Mark Williams (and likely others) makes two sizes of slip yoke, one 1.885 and 1.888 diameter for this application. The design internal dimension of this bearing is 1.889+ . The larger diameter is labeled "Nascar". Perhaps the lesser clearance is better for extended high speed. Don't know.
Have attached a couple of photos showing the welding, a tube nipple for the pump and a small pump rigged to the trans drain plug to supply lube to the bearing as needed. Not sure the little cheapie pump will long term do the trick but only has to pump a little lube for a few minutes at a time.

[MadBill]

Slick! And that's an amazing little pump. I'm sure it will do fine; shouldn't take much volume to keep the rollers lubed. You could test fire it for a few minutes hooked to a coffee can of hot* gear oil just to be sure. (Don't use the kitchen stove though, experience has shown such re-purposing is rarely well received.)

[jacksoni]

Supposedly is safe with fuel/oil etc and before assembling it did slowly pump some 40*oil so I think will work. $9.95 including shipping from China/ebay special! (thus my )