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RB25DET gearbox rebuild issue, 4th gear locked

hardsteppa
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hardsteppa Grand Master

hardsteppa

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so have finally finished putting the box back together, but now it's all assembled and housings are back on, I have an issue where it's locked in 4th gear constantly and will only turn by hand in 4th or neutral, but the whole shaft turns in neutral, not just one end. It selects all gears fine but won't turn in any other gear. Before I put the housings back on I confirmed all gears select and shift as they should and all turn accordingly with the gear selected, but once the front housing is back on, it locks up. I stripped it back down to make sure hadn't made any error in reassembly and the syncros bearings etc all sitting as they should, and everything was fine but as soon as the front housing went back on, it locks up again. I haven't filled it with any fluid yet so I'm thinking maybe is there too much friction on the 4th syncro when it's dry? (although I did put a little grease on it on it when reassembling for the 2nd time, hasn't made any difference). 

This box was a 2nd-hander off gumtree so I never actually used it myself to know of any issue with it prior. At a standstill with it now so, ideas are welcome.

BK Grand Master

BK

Posted
Posted

Definitely sounds like 4th synchro is not letting go. Usually some oil squirted there fixes it and sounds like you're onto it being a dry problem. Have seen that happen on our boxes, and have had calls about boxes doing that with new sychros we have supplied.

hardsteppa Grand Master

hardsteppa

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Thank you once again for your help. I was going to give it a part-fill before putting it back in the car and give it a thorough turning over to get oil over everything; hopefull does the trick.

BK Grand Master

BK

Posted
Posted

Hey mate on a more serious note, please tell me you used Threebond 1207C sealant on the bottom three front cover bolts and NOT threadlocker (or even worse nothing) ? Had to pull my dog box out of my 32 on the weekend, after the one box we didn't do ourselves and outsourced pissed oil out of the front cover. Noticed a slight drip under bellhousing and though fcuk, they didn't did they ? Found this as expected...

IMG_1947.jpg

WP_20191012_15_50_48_Pro.jpg

WP_20191012_15_49_22_Pro.jpg

WP_20191012_15_49_12_Pro.jpg

WP_20191012_16_58_53_Pro.jpg

WP_20191012_17_16_51_Pro.jpgPretty annoying to pull a box out to reseal 3 bolts, but said transmission specialist was very apologetic after I showed him the stuff up. We didn't check front cover before install, but why would we ? It was done by a very experienced transmission specialist that knows what they're doing, so it can and does happen to anyone. It is in the Nissan manual after all so no excuse....

Check, check, check

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