O/T, catastrophic trans failure redux.December 2 2017 at 2:29 PM
6667fan (Login 6667fan)
I heard back from the guy I contracted to build a toploader for me. We had to wait for the builder to return to the area to take apart and inspect the trans. I was informed that first gear is “welded” to the mainshaft and that only two likely scenarios could have caused that to happen.
One is there was little or no oil in the trans and two I must have wound the engine up to 7K in first gear. Neither of those things happened. So I’m back to looking for suggestions from you guys as to what likely happened. I got less than ten miles of easy driving around town before the trans blew. It had two quarts of Driven 80/90 GL-4 oil in it. The main case split at about 4500 rpms in third. I managed to get it into first as I was trying to get the car into my yard.
Could first gear be stuck on the mainshaft due to the time the trans ran dry before I got the car in the yard? The total distance from the explosion to my yard was less than 1800 ft.
Every second counts
|December 2 2017, 3:18 PM |
There is another reason why some of these transmissions fail like this is not enough gear end clearance. Those who builds these need to put proper end clearance in all the gears for oil to inter and to escape to keep the gear lubed and cool. I have found many that do not have this in 1st, 2nd and 3rd. The 1st gear seizing is usually the rear bearing being pressed on and then not being pushed back towards the rear of the trans once the snap ring is installed. Learned this from hands on experience. I have found some even when this is done is marginal clearance. I keep an array of different thickness thrust shims for 1st and 2nd and then machine the 3-4 slider block for 3rd gear clearance as needed. Hope this helps on the rebuild.
|December 2 2017, 3:28 PM |
Just like engine survival oil in & out. All clearances must be checked.
Inside gear diameter & mainshaft outside diameter & end clearance are all critical to transmission survival. Oil has to circulate in & out.
Toploader 1st gear to rear thrust and to 1&2 synchronizer were always on the tight side of end clearance. Many need custom a ground thrust washer plus extra oil slots on synchronizer & thrust are a plus.
Minimum.010” end play is needed between gears / thrusts / synchronizer hubs.
Gears to mainshaft .003” minimum.
All parts need to be checked , the tolerances can add up to catastrophic failure.
1963 1/2 Galaxie 500 390 Z code 4 spd.
|December 2 2017, 3:32 PM |
Did not see Andy’s response....slow typer......He is 100% correct.
1963 1/2 Galaxie 500 390 Z code 4 spd.
|December 2 2017, 4:07 PM |
Went back and took closer look at your parts. Is the 1st gear blued in the front that would ride against the slider block? If so not enough clearance but it also a possibility that the aftermarket mainshaft could be at fault as to not enough clearance between it and the gear as Mike explained. The main shafts with only a single groove around it such as yours need to be ground on to enhance the oil to be spread across the inner face of the gear.
Re: O/T, catastrophic trans failure redux.
|December 2 2017, 4:37 PM |
I agree with Mike and Andrew, but might add due to the quick failure, the builder may not have pre-lubed the bearings adequately. Bones
|December 3 2017, 2:04 PM |
A few thoughts on your trans from a guy whose built more than a few...
1st, spinning the trans to 7K in first gear wouldn't cause first gear to seize on the mainshaft, because when the shifter is in 1st, first gear is already locked to the mainshaft by the sliding ring.
2nd, I've used a lot of the currently produced parts, and never had a clearance issue where I had to modify anything due to out of tolerance parts.
My thoughts on what went wrong?
It's hard to tell without having the trans in front of me, but I'd look real close at what's left of the blocking ring and the syncro assembly. If the 1-2 syncro assembly is assembled or installed wrong, you can have a situation where the blocking ring is constantly forced against the cone on 1st gear. From the looks of your 1st gear it looks like the synchronizer cone got real hot, which could cause either the lubricant film to break down or the gear to bite the shaft and gall, then seize. Once 1st welds itself to the mainshaft, If the trans is in any other gear it will lock up and push the cluster sideways, splitting the case just as yours broke.
If the failure was caused by out of tolerance parts (another possibility) I would expect the whole gear to show some heat discoloration , not just the syncro cone.
If the gear wasn't lubed properly on assembly, you could also cause damage to the gear or mainshaft bearing surfaces the first time you moved the car( before enough gear oil got between the parts). Once there was surface damage, the trans would fail in short order.
I've seen gears weld themselves to the mainshaft before, but it's usually second, and it's usually in endurance applications(road racing) where you can be in second under power extensively. Gears that are bronze bushed are available for these applications, in fact, I think the 67 Shelby transmissions (RUG-S) boxes were built with a bushed second gear from Ford.
I guess what I'm saying is that I can't imagine what you could do as an operator (driver) to cause a properly assembled toploader to fail like this. Generally, driver abuse results in beat up syncro teeth, a broken mainshaft (about 6" past the rear bearing), or a twisted input shaft.
JMHO (as always,)
|This message has been edited by jetstuff on Dec 3, 2017 2:06 PM|
Thanks much for all the ideas guys
|December 4 2017, 4:52 AM |
Of course the builder wants to put it on me but I did not do anything wrong as far as I know. After I filled the trans with the Gl-4 I rolled the shafts around many times to get everything swimming in oil. This was before trans install. The guy I contracted with says $900 in parts are now needed and is offering that we split that cost. Sigh.
Every second counts
|December 4 2017, 6:35 PM |
Like I said above, I can't imagine what you could have done to cause this, but the flip side is that to fix this box right (actually , build another transmission using what little is left of your box) 900.00 is a steal assuming you would trust this builder to build you another box. You couldn't pick up a decent used trans for the 450.00 you'd have to lay out again. I'm guessing you can't give the guy 450.00 and get the parts, and have someone else build the box. Judging from your pic's, I'd reuse the input shaft and bearing retainer, the synchronizer assemblies, second gear,the tail shaft housing, and the shift forks/rails/interlock parts. That leaves you a lot of parts you'd need to buy for 900.00.....
John, the tail housing is not healthy
|December 5 2017, 4:28 AM |
I'll assume that makes your opinion that 450 to get me a trans back is an even better deal.
I don't know how much of a deal it is to follow the $1800 investment up with another 450 but on the other hand I don't have a lot of choices here.
I don't know how I could prove it was the builders fault. We know it was not mine but getting the builder to acknowledge it is his fault is unlikely. Thanks again for your thoughts. They are much appreciated. JB
Every second counts
If you have the piece...
|December 5 2017, 5:49 AM |
and know someone with a MIG welder you could weld it back on.
I've fixed a few things at work that were cast iron using 309 wire in a MIG welder. Here is a video that I followed when I wanted to try it.
I agree with Andrews assessment of the failure. With the end of the gear all burnt, it was definitely rubbing hard and caused the lock up/failure.
If the person that did the rebuild was only familiar with late model transmissions, I could see them not realizing that the gear was too tight(no side clearance). These boxes need SLOP to allow the grease to get in all the nooks/crannies. The new stuff is all run with ATF and is built TIGHT on clearances.
2006/2009 UMTR Points Champion