Tranny Reinforcement Q’s

[99Super]

Ok, so what percentage of tranny failures are from blowing out the pass side of the trans due to diff deflection?
I see pictures of folks welding on stiffening plates, filling in w/ added material, the steel diff covers etc.
Does any of this stuff work?
I just got access to a bunch of heavy aluminum channel. 8” wide w/ 3” legs. 5/16” thick and I was thinking about making a plate that would bolt to the bearing cap and connect to the side cover. That way, some of the case deflection load around the bearing cap could be transferred to 4 or 5 of the bolts in the side cover. I suppose I could even tie it in to the diff cover too.
Is this too much work for a failure that only occurs a few % of the time?
What do the engineers here (Seth?) think?


john

[Crazyswede]

23%


There is a good deal of side load to the passenger side. The diff wants to walk right out the side of the transmission and is limited by the case and the bearings. There is also the torsional force that you get between the two wheels spinning and locking at different speeds. I am a little rusty with all this...Geoff seems to be more on top of these things lately....my mind has been focused on the material side of things a bit more lately.

[99Super]

23%.
Really? I'd love to know where you got that number

I'll try to figure out what grade aluminum I've got and let you know.

Thanks!

john

[squaab99t]

23%.
Really? I'd love to know where you got that number

I'll try to figure out what grade aluminum I've got and let you know.

Thanks!

john

He might be dorking with you . Lately the failures I've seen are the spring coming off the 3rd gear syncro and getting tangled up in the gear set. I've only seen one picture of the busted case. I did see the shot were someone had welded the living crap out a case. I would think you would have to re-machine all the bearing and gasket surfaces to account for the warping the would occur.
I'm thinking a smartly designed girdle that reaches from driver's bearing to the passenger side. Maybe it wraps around the diff cover or around the bottom?

[Neil_G]

squaab99t

Lately the failures I've seen are the spring coming off the 3rd gear syncro and getting tangled up in the gear set.

Is there any way to prevent this happening then?

The solution for longer gearbox life (as gleaned from the many online forums) that I plan to apply is:

1. Steel Differential Cover (to help strengthen the gearbox casing a bit)
2. Fitment of LSD (to balance forces more evenly between the driven wheels)
3. Fitment of Gearbox / Differential oil cooler system.
4. Gearbox simpathy !!!! - treat it with repect.

regards
Neil

[Crazyswede]

squaab99t

Lately the failures I've seen are the spring coming off the 3rd gear syncro and getting tangled up in the gear set.

Is there any way to prevent this happening then?

The solution for longer gearbox life (as gleaned from the many online forums) that I plan to apply is:

1. Steel Differential Cover (to help strengthen the gearbox casing a bit)
2. Fitment of LSD (to balance forces more evenly between the driven wheels)
3. Fitment of Gearbox / Differential oil cooler system.
4. Gearbox simpathy !!!! - treat it with repect.

regards
Neil

I agree with #1,3, and especially #4. However fitting a LSD will put a lot more strain on your gearbox then the stock open diff. Dropping the hammer in first gear with an open diff will likely result in one wheel spin. Dropping the hammer in first with an LSD fitted will result in lock up of both wheels and a lot of extra stress on the transmission case and innards. The other way to think about this is to say that with a Limited slip under full lock up...its like welding the pinion gear so it cannot move...now where does all the force go?

But in most cases if you liberally apply Rule #4 even a stock gearbox will last a long time.

[99Super]

94.3% of Statistics are made up on the spot

I've been racing my current box for almost 10 years of 12-15/yr AutoXs (4-8 runs ea.) and 2/yr Hillclimbs (8-12 runs ea.), plus a couple of track day events. Oh, and a few drag races. Box still feels solid. Over the years it's had BG Synchro-Shift, Motul, Diesel dino and Redline.

#4 is spot on. I discussed this w/ Rob at ScanWest a while back and we agreed that clutches are waaaayyyyy cheaper than trannies so slip the clutch, not the tires. That said, when I have lit them up on purpose, both tires spin when in a straight line, but the inner spins on corners as expected. THAT is what I'm hoping to cure w/ the LSD.

The plan for the new box is LSD, Steel rear cover, side saddle and lastly, the cooler. Most of my events are very short, but when I installed the second engine oil cooler, I noticed a sharp drop in engine temps. I would have to think it is keeping the trans cool as well.

This "saddle" I'm working on will tie the diff bearing cap to the side access plate and perhaps the steel diff cover. I'll try to have some pics of the prototype ready by Monday.

Perhaps a discussion of preventing the 3rd gear self-destruct would be another good topic?
I'd really like to know what the failure mode is on that one...

john

[Crazyswede]

The path of destruction is sort of like the escalation of military force during the Cold War. I have become very aware of this since my getting involved with Land Rovers. What I am referring to is the path of component failure that tends to follow after each successive component is upgraded. So for instance: Many of the old Land Rovers came with a 2.25 litre inline 4 cylinder engine. The high compression version of this engine is 8:1 and it makes about 80 or 90 HP. It also makes about 120 ft-lbs of torque...not a rocket by any means. So the stock axles have been known to break with the stock engine. A lot of people convert to a turbo diesel. Now you really start snapping rear axles. So you put in heavier duty rear axles...now you start breaking diff carriers...so you beef up the whole axle, differential etc...now your drive shafts start to suffer...fix that...now the gearbox is behind the curve.

So same principal in the Saab. Put on the steel diff cover, the carrier clamp, the LSD....the power is better contained but now has to go somewhere.....either you start snapping axles, blowing up CV joints, or your shafts start spreading more under full power which in turn reduces gear contact area and leads to tooth chipping and failure...or the shaft bearings start to wear...more heat...on and on.

[99Super]

Nicely put.

I don't know what kind of HP my old motor ran, but I've haven't broken a gearbox...yet. I really try to baby them, maybe I've just been lucky

I'd like it to be 220hp +/- w/ a chassis weight of 2400lbs w/ cage. W/ the LSD and slicks, I suppose a failure of some sort is inevitable.

[Geoff]

94.3% of Statistics are made up on the spot

You must have typed that 5 mins after I started my response to this thread last night, I was going to say the same thing!

What is happening at the diff is that the pinion gear is transferring rotational energy into linear energy. The component of the linear energy that we want is pointed directly upward or downward (depending if you're driving forward or backward). That energy is transferred to the gear teeth on the ring gear, the energy is then transferred back into rotational energy (and out to the wheels). Of course, there are other force components other than those of which that turn the ring gear. Due to the shape of the gears there are also force components pointing outward from the the pinion gears, one towards the right side driver and one towards the rear of the transmission. The design of the gears allows most of the force to be translated in the way we want (moving the ring gear) but some of the force causes the gears to separate. Now don't forget Newton, "For each action there is an equal and opposite reaction". So if the diff is pushing to the right, the pinion is pushing to the left, and if the diff is pushing to the rear the pinion is pushing to the front.

This happens at other gears, including 3rd gear (the amount of force going in unwanted directions is dictated by the shape of the gear teeth, helical, straight cut, etc.). By adding the steel diff cover you can lessen the amount of flex that the case endures from the R&P pushing apart from each other. It probably also helps with 3rd gear a bit and I presume that when the case flexes from the R&P pushing apart it also adds to the amount of separation at 3rd gear (which causes failure).

I've seen a few cracked cases at the rear. The most memorable was one that came into the shop I worked at in 1998, the day I started. It was cracked 360° all the way through the case. I could grab the drivers and shake the rear of the box around. I don't think we bothered to tear down that one but my boss told me it was from a failed pinion bearing ("they said it was whining and then it wouldn't move.") Cases cracking there are due to bad bearings and more likely, weak bearing housings (of which there is some suitable info on the interweb). The weak bearing housings are probably being broken by the R&P pushing apart causing the housing to break. And as Mongo points out, you fix that and you come up with another issue. In this case you fix the weak bearing housing and then maybe the case flexes and allows 3rd gear to separate and the teeth to pop off.

In my opinion, strengthening the case by adding a girdle to it is a good idea.

[DeLorean]

The diff housing snapping off the trans entirely is NOT that uncommon of a failure. I know of 2 cars that relatively recently did this. Typically, it seems to be caused by the pinion bearing locking up at speed. Over about 20 MPH, the rotating mass is too great, so Rather than the wheels locking up, the transmission housing can't take the shock load, and snaps the whole shit off, and the ring gear just slips by the pinion gear.

My brothers 900 had the pinion bearing lock up in a parking lot with his 86 900, and thankfully he was doing about 15, and the wheels locked but the trans case was undamaged. Any faster, and the diff hosuing probably would have snapped off the case like they tend to do....

Also, this sort of failure seems to be most typical on cars with a pinion bearing that had been making noise for months before the detonation, not typically something that happened very unexpectedly.

[Rallyho]

the first rally I ran with the lsd installed ended with what I guess you could call a "cracked" case...some dumbshit (me) had not lock-tighted the little screws holding the spinny parts inside of the diff.

About 50 stage miles later, deeeep into Parmacheeny land, I tach-er' up and dumped-er at the start line...big loud bang...box full of neutrals...big puddle of Redline in the dirt and we were done.

during the post-mortem the entire ass-end of the box fell into my hands when I backed the rear cover bolts out. The diff ramps did their thing, pushing against the inside of the diff, which in turn pushed against the case...and right out into the dirt.

I still have some of those BIG pieces.

Oh, and we got flat towed like 30 miles back out, with all that mess bouncing around in there. The pinion chowed big chunks out of the ring gear..that was a fun sound to listen to....:)

[Geoff]

About 50 stage miles later, deeeep into Parmacheeny land, I tach-er' up and dumped-er at the start line...big loud bang...box full of neutrals...big puddle of Redline in the dirt and we were done.

Chris told me that the guy working the start said "Hey, a SAAB with a working transmission!" 45 seconds later... BAM!

[99Super]

Ouch.

[DeLorean]

Dang, ain't that a kick in the teeth