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HighRolla
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Sydney
Registered:
January 2004

Re: Sprinter Help - 4th gear pops out when driving

Wed, 28 April 2004 08:06

Check out this website - they're talking about C series gbox, not sure if the same problem for your T50. It's a bit of a tough one.. you outlay on good oil and products when they may not work...then you're down close to 100 bucks and your time. If you buy a box try and get a warranty on it or kow that it's decent.

http://shell.deru.com/~sgn1/AW11/Enginere.htm

Here's the text if you can't be bothered going there (pretty long):

Quote:

Transmission syncro wear and the infamous 5th gear popout

The 85-86 Mr2 had the C-50 transmission while the 87+ NA models had the C-52, which was an upgraded and strengthened version of the C-50. This included stronger input and output shafts with larger diameter bearings on some of the
gears, along with updated syncros. The C-50s are notorious for having what's been described as the 5th gear popout. This is where 5th gear will pop out engagement when the throttle is applied. Some C-52s also have this problem. The trannys will also sometimes have bad 2nd or 3rd gear syncros. While one might think that these trannys are not that great because of all these problems, this is not entirely true. If treated correctly, with a somewhat periodic changing of the tranny oil, a C-50 or C-52 can handle great amounts of power and last a long time. If you have the 5th gear pop out problem, first check your tranny and engine mounts to see if they are worn out and causing too much engine movement. After that, some have been able to stop the problem by replacing the 5th gear and synchro, others have not. John Welch gives the following:

Having rebuilt several C-50/C-52's I think I have a pretty good idea what causes the 5th gear pop-out problem, and how to fix it.
The majority of the problem is the drivers habits, and improper lubrication.

The design on the "C" series of trannys requires that the fluid be kept at the proper level, and be in good condition. It does not have a "pump" to circulate the fluid, it relies upon the movement of the gears in a bath to move the fluid throughout the trans case.

The use of a good quality fluid that is replaced every 20K miles should be considered "standard" for this trans. I use Redline MTL-90 and am VERY happy with it. You may have good results with other brands, or weights, I'm not here to debate them, but I like the Red Line.

The cause of the pop-out is not the syncros, hubs, or gears.... it's from wear on the main input shaft, and output shaft bearings. The output shaft is almost submerged in gear oil, the input shaft however is partially out in the open, This is the one that shows the most wear.

The nature of helical cut gears (used in almost all production manual tran's) is that they run quiet, but the down side is the power that is lost through the axial loads placed on them and the bearings. Helical gears are constantly exerting a liner load down the length of the shaft that they are running on. This translates into a higher bearing load.

The "movement" of the shifter that you observe when changing throttle inputs is actually a display of the movement of the gear shafts inside the transmission, and play in the bearings.

The solution is to replace the main bearings, and make sure that the pre load on them is correct when assembling the trans, and use a good lubricant.

As for the strength of the "C" series of trannys, there are weak one's, and strong ones... Some have additional webbing on the outside of the case and others don't. I have been running a "webbed" C-52 in my 1987 MR-2 for quite awhile now.... and although I only get about 7K-10K miles out of a transmission, I consider that the cost I must pay for pushing 22psi into a 4AGE motor.

P.S. I don't know if we ever fixed our 5th gear popout on the family rolla (I was only about 12 when we sold it..more than 10 years ago) so don't bank on the change of oil/additives I was talking about. We've used slick 50 before and had some good results in terms of smoothness of shifts but a lot of people reckon it does nothing Confused

Good luck with it

[Updated on: Wed, 28 April 2004 08:31]

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