Busted Tranny Housing

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Busted Tranny Housing

April 16, 2019, 08:00:23 pm

Heading west on I-10, our coach (U295) wouldn't move after spending the night at a truck stop about 30 miles east of Los Cruces, NM. After checking things over and finding the tranny roughly one gallon low of fluid, we resumed west. By the time we reached Tucson, we had added about 6 more gallons in order to keep limping along. By the time we reached Phoenix, the transmission gave it up. A truck repair shop found the driveshaft so tightly wedged between the drive axle and the rear housing of the transmission, that is was deemed to be unable to salvage the tranny. We are awaiting a refurbished tranny, but the shop has no ideas regarding why the driveline had jammed between the housing and the axle.

I have my own suspicions, but cannot prove anything. Anyhow, the drive shaft has been the correct length for nearly 25 years (1995 coach). Sure hope the driveshaft doesn't end up trashing the refurbished tranny.

Larry

Re: Busted Tranny Housing

Reply #1 – April 16, 2019, 08:03:54 pm

Possible bulkhead issues, control arm bushings wore out maybe even incorrect ride height. Others can add to the list.
Bulkhead issues eliminated by Larry.

Re: Busted Tranny Housing

Reply #2 – April 16, 2019, 08:10:19 pm

Extreme Graphics recently said our bulkheads were OK.

Re: Busted Tranny Housing

Reply #3 – April 16, 2019, 08:22:24 pm

Check your motor and transmission mounts, short drive shafts require great alignment. Also check your ride height at the rear and that the driveshaft splines are free to move fore and aft, and may have a grease relief hole that is blocked. Ouch.

Re: Busted Tranny Housing

Reply #4 – April 16, 2019, 08:30:55 pm

You have something that has shifted dramatically. What ever it is should become obvious whenever you change out the transmission. Did you notice any vibration or mis handling of the rear of the coach? Good luck with the replacement and diagnosis.

Re: Busted Tranny Housing

Reply #5 – April 16, 2019, 08:35:23 pm

Do all of the above and think about taking the driveshaft to a drive shaft repair shop and make sure they are getting you a trans
with a retarder and get prices ahead of time.

Re: Busted Tranny Housing

Reply #6 – April 16, 2019, 08:38:59 pm

U joints should be checked for binding or just replaced. I've got a car with a 7.75" driveshaft.

Re: Busted Tranny Housing

Reply #7 – April 16, 2019, 09:38:34 pm

Quote from: U295 Owner – April 16, 2019, 08:00:23 pm

but the shop has no ideas regarding why the driveline had jammed between the housing and the axle.
I have my own suspicions, but cannot prove anything. .
Larry

Larry sorry you're having such a expensive repair, I hope you find some answers!
Where did the fluid go?

Re: Busted Tranny Housing

Reply #8 – April 16, 2019, 09:50:13 pm

The only way to tell on the bulkheads it seems is to cut back the fiberglass. Ride hight might be an issue next as the next thing I would look at.

Re: Busted Tranny Housing

Reply #9 – April 16, 2019, 09:58:33 pm

My ? Is with that much wrong how could you not hear something or feel something?

Re: Busted Tranny Housing

Reply #10 – April 16, 2019, 10:05:36 pm

What do you think happened, do
tell. Something has shifted rear axle or engine mounts. Going to be way more to it than a transmission. You sure need to know before installing a new transmission. Shouldn't be too hard to find.

Re: Busted Tranny Housing

Reply #11 – April 16, 2019, 10:13:50 pm

I don't see how incorrect ride height (too high or too low) would "wedge the drive shaft between the axel and the transmission". The drive shaft has sufficient travel in the splines to accommodate any suspension position, full up to full down, without binding.

Incorrect ride height could result in a extreme operating angle in the drive shaft, which could damage the U joints.

Lots of questions to be asked and answered before this failure is fully explained.

Re: Busted Tranny Housing

Reply #12 – April 16, 2019, 10:20:47 pm

Something "Moved" or "Broke" , Engine and transmission should be bolted together, drive shaft would be going forward to the differential, very short drive shaft, the rear axle must have shifted broken center bolt where the axle connects to the "Air Bag" frame?
I would not make any driveline modifications until I checked every part of the rear driveline... Be careful going under this coach, put safety blocks in place to support body.

Re: Busted Tranny Housing

Reply #13 – April 16, 2019, 10:24:41 pm

The easiest one to understand this change is also one of the worst failure modes. Xtreme may have given the bulkhead a pass, but if the bolts are broken under the heads and there is no obvious separation, the bulkhead joint could still be loose. The normal unloaded position of the bulkhead joint even with no fasteners installed (on level ground) will be with the joint closed. It could drive normally and if you weren't sensitive to the feel of it, might go unfelt, and yet the retarder operation could be tugging the torque tubes (AKA trailing arms) with every application which could allow the driveshaft to be pushed against the transmission housing. It seems like that much movement in the bulkhead joint would be obvious just by looking, but... We will all be interested to find the cause!
Don

Re: Busted Tranny Housing

Reply #14 – April 16, 2019, 10:39:42 pm

It's all about the typical diesel pusher short driveshaft length so ride height and alingment is critical, the u joints only have 4 breakover points when the driveshaft angle gets too steep to transmit pure rotary force without excessive vertical loads.. Front wheel drive cars use 6 bearing or more constant velocity joints on both ends. The off roaders with lifted jeeps experience the same issues.

Re: Busted Tranny Housing

Reply #15 – April 16, 2019, 10:53:25 pm

Does rear bulkhead failure during rear braking extend or compress driveshaft, somehow I was under the impression that is what strechted the bottom of the bottom of the coach. IDK exactly as I have an ORED.

Re: Busted Tranny Housing

Reply #16 – April 16, 2019, 11:18:46 pm

Quote from: Old phart phred – April 16, 2019, 10:53:25 pm

Does rear bulkhead failure during rear braking extend or compress driveshaft...

I'm confused also. Since the rear bulkhead is forward of the rear axel, I'm trying to follow Don's comment and understand how the bulkhead joint opening up can decrease the distance between the rear axel and the transmission. I'm not saying he is wrong! He has extensive experience with the rear bulkhead construction and how it ties in to the rest of the coach framework. I just can't get the picture right in my head.

Re: Busted Tranny Housing

Reply #17 – April 16, 2019, 11:45:21 pm

If the bulkhead joint is loose, use of the transmission retarder can apply considerable force trying to pull the bulkhead joint apart via the trailing arms as it tries to slow the coach via the drive wheels. If the bulkhead joint isn't stable, the trailing arms can allow the drive axle to shift to the rear as the bulkhead joint opens. When the axle shits to the rear, the driveshaft could potentially be driven towards the transmission. To a lesser extent, engine braking can do the same thing as the front brakes are not in play unless applies by the service brakes. Conversely, accelerating will try to close the bulkhead joint if it is separated. Similarly, if the airbags behind the drive wheels deflate for some reason, the airbags in front of the drive wheels push down on the front of the 'H' frame that carries axle which would apply a force tending to separate the bulkhead joint. This last only applies to the semi-monocoque Unicoach or Unihome with the eight airbag suspension. The attachment of the control arms, trailing arms, torque tubes... call them what you will, are what locates the drive axle as acceleration or deceleration forces from the drive wheels work to speed up or slow down the coach in motion. The above understanding came to me when I was repairing my bulkhead joint and I was able to separate said joint at will by placing two bottle jacks either behind or infront of the drive wheels. This is of course with no fasteners in place trying to hold it together. Think of a teeter totter with a fat kid only on one end or the other. In this case, the drive axle is the fulcrum and the bottle jack is the fat kid. I hope that I explained it clearly... It is difficult to put into words but would be simple to understand with a diagram.
Don
Edit: for clarity, I hope. I am not trying say that the above is the cause of the OP's issue, just that the dynamic forces of the drive axle through the attachment of the trailing arms to the bulkhead could apply force that might explain what happened. I am pretty convinced that my understanding of the relationships between the drive axle, the trailing arms, and the bulkhead joint is largely correct because I have done thought experiments which proved to be correct as I struggled with rebuilding the bulkhead joint. The use of leverage and mechanical advantage through the bottle jacks, allowed me to open and close the bulkhead joint at will. It was inspiration through sheer desperation.

Quote from: Old phart phred – April 16, 2019, 10:53:25 pm

Does rear bulkhead failure during rear braking extend or compress driveshaft, somehow I was under the impression that is what strechted the bottom of the bottom of the coach. IDK exactly as I have an ORED.

Re: Busted Tranny Housing

Reply #18 – April 17, 2019, 12:38:57 am

Don could be on to something here. I would take a close look at the bulkhead

Changing ride height won't bother the driveshaft. That's what the splines are for. Driveshaft angles at each end should be less than 1 percent and not more than 3 percent for max life. This is the angle out of the pinion gear compared to the input shaft angle on the transmission, not the angle of the driveshaft. Vertical movement of the rear axle should not change this. It would take a failure or something major for angles to exceed this.

Pierce

Re: Busted Tranny Housing

Reply #19 – April 17, 2019, 01:19:38 am

All of that being said, a drive shaft expert can give allowable degrees angular +/- movement- based on driveshaft play length joint to joint before bad stuff starts to happen.

Re: Busted Tranny Housing

Reply #20 – April 17, 2019, 01:26:12 am

Larry, sorry for your problem. I am at a loss why I don't know what model year you are driving, so responding is not targeted.

Many years ago, Foretravel had a recall on our coach for driveline ANGLE.

Measurement were made with an angle measuring device, and adjustments to the angle made by putting a taller rearmost center engine mount that is below the crankshaft pulley, changing the angle of the transmission which is bolted to the engine. Ours had the mount changed to a taller mount

I think out of ANGLE drive shafts were damaging transmission end bearing.

Also, separately and likely not related to the driveline angle, Allison had a modification change for the part that keeps the transmission end bearing in place. I think the original part had one bolt and the revision had two bolts and the revised part came with the specified two bolts.

During an inspection, our end shaft was found to have some upward movement, that led to my Allison knowledge and our transmission end bearing being fixed.

Maybe your end bearing failed taking the seal with it, causing your early tranny fluid leakage. And from your description, if the coach was towed instead of being driven the transmission housing maybe could have been saved.

Also, I wonder why the end of the transmission can't be rebuilt, but maybe a whole rebuilt would be better and less expensive.

After hearing first hand stories of truckers damaging RVs that park in 'their' space, we never park among truckers at truck stops, Walmart, casinos, etc. What could they have done, no idea. We dry camp a lot, just not near truckers.

What Phoenix repair shop are you in? And how did the shop get selected. I think WW Williams is the shop that specializes in Allison.

Good luck.

Re: Busted Tranny Housing

Reply #21 – April 17, 2019, 02:15:01 am

Quote from: Pierce & Gaylie Stewart – April 17, 2019, 12:38:57 am

Don could be on to something here. I would take a close look at the bulkhead

Changing ride height won't bother the driveshaft. That's what the splines are for. Driveshaft angles at each end should be less than 1 percent and not more than 3 percent for max life. This is the angle out of the pinion gear compared to the input shaft angle on the transmission, not the angle of the driveshaft. Vertical movement of the rear axle should not change this. It would take a failure or something major for angles to exceed this.

Pierce

I beg to disagree with your opinion, as u joints roll rover center when not inline, and my coach drive shaft is only about 16" long. So 1% to 3% total from the axle centerline to the to the transmission tailshaft has to be made up as the suspension moves up a down a couple of inches up and down from design ride height. For this reason I believe rear ride is important.

Re: Busted Tranny Housing

Reply #22 – April 17, 2019, 06:11:45 am

Let's wait until owner gets up and gives us more info,we can speculate but never know and we all want to know.Sounds like
whatever was causing the trans fluid to leak may be why they are saying the trans is shot.Were'nt there some posts a few years back
about the seal area on the trans wallowing out and causing a problem?The driveshaft is already out to work on the trans and u-
joint are not hi dollar I would get new ones to go with the tranny.We need to also know if the housing is broken or they are
saying something in the trans cannot be repaired.Think from what I know I would rule out motor mounts and axle movement,the motor mounts are big rubber washers with big bolts thru them and the axle is bolted so there is no front to back movement,unless
Don is right.Remember a few months back when David in Vegas had that torque rod bolt break off,he could have a couple like that
and not know it until now,that would throw things off some,when I redid mine I had to cut some of the bolts in 2 places due to parts
rusting and fusing together and mine did not look that bad,his may be worse.

Re: Busted Tranny Housing

Reply #23 – April 17, 2019, 08:39:25 am

Sorry for your loss.
Keep in the back of your mind that mechanics, for the most part, aren't paid to analyze problems.
I don't know where to start but some quality time spent closely examining everything from the bulkhead back is where I'd start.
It's usually something simple that's gone wrong, so I'd look closely at everything from the stuff that locates the rear axle to the stuff that locates the engine.
Jumping to conclusions is great exercise but it doesn't get the job done.
Take time to think. The best way to kill a fresh idea is to try and force it to the surface.

Re: Busted Tranny Housing

Reply #24 – April 17, 2019, 09:24:30 am

A "root cause analysis" is definitely required. It might be as simple as a failed transmission bearing, or a major suspension failure, or ?? Don't just replace parts without understanding the root cause!

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