A few weeks ago I showed you a broken rear axle after braking with the reverse pedal.
Here is what I found this afternoon as I opened the rear axle.
My opinion is a cracked transmission axle that broke while braking. What is yours? It is surely not the Babbitt trust washers
The part which broke is the driveshaft. By using the reverse pedal instead of the brake, you not only put a strain on the driveshaft by braking, but also the torque of the engine turned the driveshaft in reverse.
This might not be the reason it broke. Look for something internally which would cause the axle to lock up.
Those gears are non stock. They have teeth on an angle. The stock Ford teeth are straight. However, I don't think the angle of the gear teeth is what caused the problem.
Over many years of running forward and in reverse starting out in low gear and braking, the driveshaft finally broke.
Do you have a stock engine in your car? or has it been modified for higher power and speed? The rear axle is a weak link in the Ford drivetrain and when the engine power is increased, there is a greater chance there will be a failure in the axle.
The car came first to in 2012. The owner bought it 25 years ago and could never made it run.
As it came to me there were parts missing and compression was bad so I made it run with a stock ignition and high compression pistons, made the RM brakes working (were mounted left right) and put new spokes in the wheels. I only check the oil in the rear axle, I never opened it. I was told it was overhauled before.
Now it is broken, it was the only thing I didn't put my hand on jet now it will be stock rebuild.
Some interesting parts in there - spiral bevel ring & pinion gears, roller thrust bearing, large ball pinion bearing, hefty bearing sleeves on the inner ends of the axles.
Might be a Chevrolet 490 ring & pinion?
BTW, braking with reverse did not do that. The driveshaft didn't care what was making it stop turning, it just had enough and busted.
The pinion bearing has been changed. Looks like a home made modern replacement bearing unit (they are out there). I DO NOT THINK IT IS ONE OF THE CURRENT MADE ONES. When (if) the drive shaft was modified, maybe there was a score cut in the shaft that acted as a braking point. Other point might be that the bearing used was not allowing enough lube to get in and the bearings seized locking the drive shaft up. You can use an Ford ring and pinion in the early Chevrolet's, so I wonder if someone used a modified Chevrolet unit in the Ford rear end.
What bearing is installed at the other end of the pinion housing, if it's a tapered thrust type which way does it point? Was the U-joint pinned or floating free on the shaft? If it uses a collar with set screw to set the pre-load on the pinon bearing, is it tight on the shaft, loose or show any sign that it has slipped?
I wonder if the drive shaft slipped back and got caught by the differential.
I'm wondering if the spiral-cut gears don't add to the stresses on the end of the drive shaft?
Just a thought, any ideas out there?
I will take the drive shaft apart and show you but the drive shaft broke just before the gear. the breaking point shows a flat part and a part that seems to me as a fresh break surface.
Here a photo close up from the break point.
Looks like the rear axle was rebuilt with modern bearings and a spiral bevel ring and pinion. I wonder if the fit of the pinion on the driveshaft was not quite correct and added a stress raiser which contributed to the driveshaft failure. If the fit were correct the spiral bevel set would be an improvement over the Ford straight bevel gears. Its hard to beat bronze thrust washers and original Hyatt bearings.
Looks like a twist fracture caused by excessive flexing It was probably already cracked when you got the car. I would agree that it is your point of origin of failure.
Now the question is; does the spiral cut gear set increase side loads on the driveshaft to cause this failure?
Weird looking break isn't it? I'd swear it was "pre damaged". Agree with Jerry. Don't think reverse pedal breaking alone is the fault.
Somebody really went to a lot of work on that rear end with different ring and pinion and all kinds of different bearings. It looks like to me that the drive shaft broke right at the pinion and the pinion fell off and bounced around and bound up and broke the case. A grenade in the rear end.
I am no expert, done many rear ends with Ford parts and they have never done that but my guess is a score on the driveshaft that let it break or the pinion bearing seized. First guess is the driveshaft got cut for the bearing and had a little score all around and snapped off...then the pinion was like having a rock bouncing around inside tearing everything up and trying to get out.
The Model T rear axle is not overbuilt or robust in design. It is more than adequate if in good condition and with a driver who respects the fragility of the 100+ year old design.
There have been several companies over the years that offered spiral gear sets for Model T Fords.
At the end of the day it is not possible to know why it blew up like it did. But it could have lasted longer if it was not being abused by using reverse to stop the car more rapidly. The transmission does not stand up well to abuse either.
When I worked in an automotive machine shop my mentor Wallace Rowell used to critique some of the components that came our way with the comment "craftsmanship over engineering".
Many of the modifications or updates I see here look like they would be improvements. The Torrington bearings to handle the side loads of the diff carrier are certainly one of the better ways to update the babbit bearings of the stock design.
That said, I would be want to remove that ball bearing at the extreme end of the driveshaft to see how, if at all, the driveshaft was modified for that bearing. Maybe that particular bearing fit the driveshaft without machining (I doubt it) and the nearly 100 year old driveshaft just gave up. Hard to know without some more forensics.
I would want to attempt to answer that question before I put the rear end back together with the modifications seen in the pics. I do rather doubt the use of a spiral bevel R&P had anything to do with this failure. And yet, that ball bearing which I assume eliminates the Hyatt is not strictly speaking intended to handle the thrust forces that would result from the use of a spiral bevel design. A ball bearing can of course handle some thrust forces but was it capable of handling those introduced by that R&P? I'm no bearing engineer so I will just have to say I don't know.
Until that question is answered I would be inclined to revert to the stock R&P.
I'd get rid of that spiral ring gear and pinion. It creates too much thrust, and it is possible that was the cause of your problem.
I wouldn't even contemplate on using any of the old diff, it's toast!!
But I do feel for the owner for now to find a replacement, England may be the closest and cheapest way for that?
Frank, you are right, nothing of the original rear axle is usable, so when another one is sourced and the rebuild of it commences, it would probably be best to limit the upgrades just to bronze thrust washers to eliminate the babbitted ones. Kind of makes the question about the driveshaft failure moot.
Here is the drive shaft. As you can see the shaft had some heating and punch marks. I don't know how it was set. There no way to set the play right.
The universal joint was repaired in the past and have a lot of play, need to be replaced.
As Toon said, it will be the easiest repair. The only thing that can be reused is the drive shaft tube everything else need to be replaced.
I don't see how using reverse or the brake or even the engine locking up tight suddenly would make any difference to the rear end. All the rear end knows is that the drive shaft quit turning. It doesn't know why, nor does it care. Using Reverse as a brake is bad for the reverse drum, but the rear end won't know the difference. When driving in High, all three drums are turning at the same speed, acting as one assembly with the flywheel and triple gears. NONE of that stuff is moving relative to one another in high gear. It is all just one big flywheel. The maximum amount of stress that can be applied to the entire system is a function of the rear end ratio and how much traction the rear tires have. What happened in the photos above would have happened with just the brake pedal.
I was going to say the same thing. You are 100% correct. Whether braking or using reverse, the driveline (in order, u-joint, driveshaft, R&P, diff carrier, side gears, axle shafts, and last the wheels) experiences a torque reversal. The rear axle/differential can't tell the difference. If it is possible to skid one of the rear wheels on dry concrete in a panic stop with the stock Model T transmission brake then you have maxed out the torque applied to the rear axle. Using reverse would never exceed that. Just a fraction of a second before the point of wheel lock-up that reverse torque peaks. It doesn't matter if it came from the reverse band or the brake band.
Maybe I missed something. Why would the driveshaft have all those punch marks?
Apparently the inner races of the replacement bearings were too loose on the shaft, so somebody put in the punch marks to (temporarily) tighten it up.
Too make it bigger for a better press fit of the bearing, which prevents the race from spinning on the driveshaft.
I don't see how using reverse when braking would help the rear end last longer. It slows the car down more quickly than using the brake alone. That means there has to be increased stress on all parts of the rear axle. That can't be a good thing. In any case, tell the guy to quit doing that.
Ford made millions of rear axle assemblies, with little or no trouble. Why is it necessary to make changes? The above example offers an answer.
In all fairness, I assume the T in question is in Belgium, so parts may not be as readily available there as in the States. I would guess that is why someone rebuilt it using other parts.
Just to be clear, I do NOT condone using reverse to aid in braking. I think the idea was originally put forth by Murray Farhnstock in an attempt to make the brake band last longer, but I think we all know today that reverse drums can be damaged doing that and they cost a lot more than they did in his day. Using reverse to stop will NOT make a rear end last any longer. I'm just saying the use of reverse in braking didn't do anything to that rear end that the brake band wouldn't have done if applied hard enough. As said above, there was likely a crack that was nothing more than a ticking time bomb just waiting on a hard stop to come along.
Here a link to my first post about this rear axle
The drive shaft broke while going down hill and the driver was loosing the car. He made a panic stop by using the reverse pedal ( pedal in the middle as in his all day car) instead of the brake pedal on the right that is connected to the working RM brakes.
I agree to break the drive shaft, as it did, there must be more wrong. Only braking will not do this but I think we will never know for sure.
The reason why the drive train was rebuild that way stay a mystery. Parts are available here in Belgium, you just need to order pay and wait 1 to 3 weeks to get them.
Was the U-joint riveted to the drive shaft? I think the use of two ball bearings might be the wrong way to go. Shouldn't at least one be a tapered bearing? I know that there are ball bearings that handle side thrust, like the one in the Ruckstells, are these that type? The one or two home made setups like this that I have seen had a spacer between the bearings inside the housing, I don't see one in the photos.
The U-joint was riveted to the drive shaft. The ball bearings were just standard bearings and there was no spacer between them. I don't know how the pinion was set. For me it wasn't set at all. It could go backwards and forwards as it likes.
One of the problems I think, specially with this kind of gears.
Ok one more question and then I will leave it up to the experts.
Was the upper a bushing or like the rest of the rear end, needle bearing with or without spacer washers between in the the U-joint?
just the original bushing
The crown gear looks like a model A gear. I don't have one close by me to compare and I have never actually taken a model A gear and a model T gear to see if the bolt pattern is the same though I certainly had the opportunity. I guess I never really thought about doing it. Perhaps one of you gents or ladies that have access to both will take pictures and compare.
The Model A mounting bolts are offset using 9 bolts. One on each side of the spider yoke and one in between each yoke. The holes are not threaded as the same bolts hold the housing together.
According to the numbers on the bearing it is a CONRAD type bearing but its inside diameter is 25.0 mm and 62mm OD with 17 mm width. At 25 mm Inside Diameter then the dimpling of the driveshaft makes no sense if the shaft were good since it would be nominally 1.000 and that is 25.4 mm which means the bearing was undersize at .984 (25 mm) so no way the driveshaft would need to be dimpled to make it larger since if new or nominally correct it would already be .016" oversize. Clearly the end of the driveshaft was turned down and it may be that the dimpling was the previous rear end rebuild and that was done to keep the bearing SLEEVE from slipping. Just guessing but what concerns me that there does not seem to be any provision for any thrust at the pinion bearing. Assuming the bearing itself could deal with the thrust, the bearing would then transfer all of that trust against a very tiny shoulder being the difference between the pinion housing nominal inside diamter (2.375) and the bearing outside diameter that was bored to a shoulder at an ID of 2.441 to have that bearing rest on it. That is not a sufficient shoulder for the main thrust bearing device. It might have gotten lodged sideways. Just a pure guess.
I have seen lots of beautifully put together devices with remarkably nice machining but that is NOT Engineering as someone else already pointed out. This has neither the earmarks of good engineering or good machining.
I am sorry - for those that don't know a CONRAD bearing is a deep groove ball bearing which is able to tolerate at least some side thrust. That assumes that it still is a BEARING when it attempts to do that since this one was turned to crumpled steel before during or after any side thrust was applied.
Thanks for the bearing info John. When I was making modified spools I used a thrust bearing at the rear of the spool, a spacer and then a plain bearing at the front. These were imperial bearings, that is 1" ID on the shaft and the spool was machined to the OD of the bearings.
Your answer is simpler and less costly.
Allan from down under.
I think your guess is right on and explain the reason why the shaft snapped of. On the photo of the housing you can see that the bearing traveled forwards and backwards. It could be as the repair was just done there was a trust setting. After a few miles of use and abuse the trust setting of the drive shaft was gone. The gear was going backwards and forwards giving a lot of stress inside the rear axle and once the most weakest link broke.
Just what I am thinking about this.
It was rebuild to break down.