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MG MGA - Gearbox feels tight after rebuild

I have just finished my first gearbox rebuild. It seems that there is an excessive amount of drag inside the gearbox. Its hard to turn the input shaft. When in neutral the output shaft still spins but i can hold it and still rotate the input shaft. Is this stiffness normal on a new rebuild? Does it just need to be worn in? Its a late 1500 gearbox and i replaced all the bearings and syncros. I fear that one of the input shaft bearings may have slipped causing the problem but i'm not so sure because it all still spins but feels really tight.
Ryan Kew

When you turn the input shaft (in neutral), the output shaft may turn because of friction from oil in the 2nd and 3rd gear bushings. If you hold the output shaft you should still be able to turn the input shaft with your wrist. If you turn fairly slowly it should turn easily. The sticky oil film in the 2nd & 3rd bushings acts like a shock absorber and doesn't want to allow fast motion. Some new ball bearings might be a little stiff at first if they were packed with stiff grease.

If you can't turn the input shaft with your wrist, something is amiss inside. Perhaps the mainshaaft is a tad too far forward in the center main bearing causing endwise interference between the input and ouputput shafts, which might be preloading the ball bearings, or might be causing friction at the back side of the input gear. Be sure the nut on the rear flange is tight to pull the mainshaft to the rear. Tap on the front end of the 1-2 fixed hub to drive the mainshaft back against the center main bearing.
Barney Gaylord

I can definitly turn the input shaft while holding the output shaft, but it isnt easy. To achieve the same effect i can hold the input shaft while rotating the output shaft (in neutral). This is easier because of a larger surface to grab onto but doesnt feel any less stiff while turning overall.
With respect to the mainshaft being too far forward i have had some misalignment issues during reassembly. To get the rear extension on i had to use a press to slide the bearing inside the rear extension onto the mainshaft (the bearing was already inside the rear extension). When i was pushing the two together the entire mainshaft slipped through the mainshaft bearing which also pushed the input shaft and bearing forward about 1/8". At this point the rear extension bearing was firmly seated on the mainshaft so i decided to finsih bolting the two together and have a try at pushing the whole assembly back the other way. I flipped the gearbox up and pressed on the input shaft. It took quite a bit of pressure before the thing budged, probably because i was trying to move the assembly through the two rear bearings (The input bearing was still correctly seated). After the initial jolt of it slipping past the two bearings the whole assembly slid back into place.
This may be where the problem is too, a little binding between the two rear bearings. Or it could be the input shaft is pushed too far against the mainshaft causing the tightness. I just dont want to have to pull this thing apart again considering the difficulty reaching this point.
I may try pulling the mainshaft back using the rear nut and a plate going across the rear extension with the output shaft coming up through a hole in it so i can use the housing for leverage to allow me to pull the mainshaft back a bit. Any other suggestions would be great.

Ryan Kew

Thanks Barney, I wrote the above post before i tried your suggestions. When I tightened the rear bolt for the drive shaft flange it loosened the whole system up. Whew! I was dreading the thought of having to pull this thing apart again. Now all is well. -Ryan
Ryan Kew

When I assembled my transmission, I heated the rear housing slightly with a propane torch to let the bearing slip into the housing easier. It doesn't take much heat, as aluminum expands at a greater rate than steel. It made assembly much easier.
Ed Bell

This thread was discussed on 06/10/2005

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