boese1978

Cruising along a couple weeks ago, city driving, mellow, poof, nothing more than first gear. Limp to a parking lot check fluid etc., limp home in two stages to not overheat / make things worse. Get it to the shop, They do a tear down assessment. The weak point in a TH350 they tell me, is this piece (see pic) with the 8 little rollers, mine have seen better days....although they do look rather decorative laying on the filter The mechanic slammed Monster Trans pretty good too, he showed me some parts that had obviously been there for way more than the 3 years I used it- ( something inside the case they use), he also noted that the Trans I got from Monster also had a couple "rare" pieces( some "one piece"gear set/box that is usually made of multiple components


) - sorry, I am not versed in the various parts and names.He also showed me the holes Monster drills for the shift kit, way to large he noted etc.Anyway, it boils down to me getting it fixed for a good chunk of change and they saying on the receipt- ( This is the reason for the failure in the first place they told me)
"Vehicle has incorrect gearing 2.76 in the rear of the vehicle that will damage the transmission if they are not changed immediately to 3.42 ratio. The vehicle should not be driven until the gearing is corrected. Failure of the transmission due to incorrect gearing will not be covered under warranty"
I am curious what others think? I know some like the highway gears and drive a torquey motor like mine....all good in the long run as getting my rear gears ( another story there!!) is the final step in my build, but did my highway gears lead to my trans failure after only a few years of summer driving? I would get on it a bit but nothing like neutral drops or other silliness

Vistabrat72

The highway gears should not have been a real part of the failure. Oldsmobile - and GM - have been supplying millions of compact, mid-size and full-size vehicles with highway gears such as 2.56 for years. Their statement on their receipt is horsefeathers. Probably to give them an 'out' to refuse warranty. The part which failed is the 2nd gear sprag, which catches hold when the 2nd gear clutches (the big lined plates in your pictures) shift into second gear. Something may have given a hint here. You said the transmission mechanic pointed out to you large holes drilled into the separator plate. This can really raise line hydraulic pressure, and if not done in proper conjunction with valve body spring recalibration and accumulator cushion spring modification at the very least, or a more heavy duty sprag with a torque converter having a higher stall speed to dampen or absorb very harsh shifts, stock parts can break. Was the shift pretty hard even at low speeds before the transmission went piff-paff? This may tell a bit more of the tale. Sorry to see what happened.

matt69olds

The transmission doesn’t care what gear ratio your using. Is there a spring in the accumulator on the side of the transmission? Was it built with the wave plate in the intermediate clutch pack? Lastly, how big are the holes drilled?

I use 3/16 for 2nd and 3rd clutch feed holes for all my high performance builds. As long as the accumulator is still functional and the wave plate is installed the roller clutch seems to be ok.

I haven’t had the best luck with aftermarket roller clutch races. If Monster transmission included a aftermarket part I’d question the quality. To be honest, I’d prefer to use a OEM clutch race over aftermarket. The replacement races seem to be brittle and fail.

boese1978

Thanks for the reply and information / education! The mechanic did say the same thing you state about the large holes and not doing other things to compensate. He addressed the shift kit issue by addressing the combination. I would not say the shift was hard , firm but not hard it was what Monster calls a level 2 shift kit ( should say done with short cuts too). I did as they suggested and have the car elsewhere getting the gears and carrier swapped.Hopefully thie rebuild lasts longer than the first trans....

nicks1966

As stated the transmission doesn't care about the rear gear ratio but the speedometer will, what speedometer gears did they put in the trans. Did they match the tire diameter and 2:56 gear or did they put in the correct gears for the 3:42 and your tire diameter?

Vistabrat72

You are welcome! Simply trying to help with the most honest answers I can through life experiences with these vehicles.

Fun71

Yeah, I agree with the others that the rear gear clause is BS. Back in 1982 I had 3.55 gears under my 1970 Cutlass (originally 2.56 gears) and my rebuilt TH350 failed due to the roller sprag race exploding (I stupidly used the factory original for the rebuild). Rear gear ratio has nothing to do with it.

boese1978

So, what do you guys suspect was the actual cause? poorly done shift kit by monster? I do not beat on the car, do I need to baby it even more??? Mechanic did mention the accumulator and springs and said what he was using were better than what Monster built it with.....my motor is fairly built(SBO 380 stroker with aluminum heads, full roller set up) but the TH 350 should handle it easily, correct?... Speedo gears are set up for my gearing and tires.....not that that matters at all...FYI the shop guy was adamant that having the 2.76 causes more stress on that roller assembly, is that true to any extent?
Thanks!

matt69olds

I can say I have built probably hundreds of 350 trans, the vast majority with stock parts, many going in 11 second cars, and can count on both hand the number of sprag failures I have had. And most of those failures have been aftermarket race replacements.

As for the feed hole size, 3/16 with a 11 inch street converter will knock the dash out of the car at WOT. There will be a noticeable “chirp” at probably 3/4 throttle. If you didn’t have that, chances are the holes aren’t drill too big.

I suggest rebuilding the unit with a throughly inspected direct drum. Throughly inspect the roller clutch race. Make sure your builder installs a wide bushing in the direct drum. Make sure the intermediate accumulator spring is installed, most performances cars used a orange spring. If you can’t find a orange spring, any spring is better than none. Make sure the wavy plate is installed in the intermediate clutch pack. Lastly, don’t give Monster transmission any more money.

matt69olds

I don’t see how rear end ratio can have much effect of transmission durability. A case could be argued that more gear would makes things worse, think about wheel slip on the 1-2 gear change. You might have more “chirp” with the added gear. Who knows?

I think repairing the unit PROPERLY, will go along way towards being able to enjoy the car

Vistabrat72

In theory, this COULD hold merit but in your case it would not. Having tall gears meaning ratios in the 2.whatever, would mean there is not as much leverage to get a mass moving, so more oomph is needed from the rest of the driveline to give heft to get the car going. With a strong engine and sticky tires, more strain is put on moving parts versus 3.73 gears let us say to get that weight moving. Think about the old leverage lessons we learned in school. A length of board 4 feet long pivoted over a pint three feet from one end will have three times the leverage capacity on the short one foot end. I hope I told this all right, I am dyslexic and sometimes have trouble putting thought into print. Again, given the weight of your car, etc, I feel it was calibration setup which led to the demise of your transmission.

matt69olds

Gear ratio can be thought of like leverage or mechanical advantage. No argument there. However, roller clutch/sprag failure is most likely caused by shock loads. Once the roller (roller clutch) or dog-bone elements (sprag) are set and locked, you can put far more torque to it and have it hold than going from a freewheel or overrun condition and then have it lock.

Perfect example, the TH350 was used behind some pretty stout small block engines and last along time. Take that same transmission, put it behind a wheezing 260 Olds, find a big empty parking lot, and do a few neutral slams. It won’t take long before the low roller clutch explodes. It’s not the power that usually kills the roller/sprag, it’s the shock loaf