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Problem with BJ7 gearbox selector

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BipBip

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Hello,
I would need the help of the forum people. Sorry but I'm from Spain and my english is limited.
I have a BJ7 with a standard gearbox. I had a typical problem with the second synchro, with the time the problem increased and also the problem was increased so also "scarpe" when pass from 3gear to 4 gear. Particularly I realize that when the gearbox was hot the problems increased dramatically at the moment that it was not easy enter any gear, I had to stop to fit one gear!
I decided to rebuilt it and at the same time and to save others problems I have installed a new diaphragm clutch, light flywheel, release bearing, uprated overdrive kit and the most important a new straight cut gear set tulip with new bearings, synchros.... so practically all is new.
I have tried the car today and surprising the problem has been repeated. The gearbox has worked well, only at the beginning has been necessary to make double clutch to reduce from 3 to 4, but right, but when the gearbox is hot he problem appears again. I have practically to stop to fit a gear, and not change is possible.
So the problem isn't in the pinions, clutch... all is new, the problem must be in the selector, perhaps in the interlock balls? I have seen that there is a interlock ball hole plug. Should it be regulated? Perhaps the springs pression change with temperature?
Could somebody help me? Thank you.
Please use simply english in yours answers. Thank you.
 
Your problem may be related to your using the straight cut gears.Fwiw--Keoke
 
I think that no, so the standard gearbox and the new one with the tulip gears work relatively well when cold but bad when hot, both, and I don't change the use when hot.
 
Maybe need to replace the clutch slave cylinder and the hose connecting to it. When hot, it'll swell up and fail not allowing you engage clutch.

easy fix, hope that works.
 
Exactly that was what we thought, a problem with the clutch slave cilinder and we changed it also but the problem continue.
This evening we have found that one of 2 pins that has the lever ball was broken and perhaps the lever didnt't work correctly so it has a little play. I will try tomorrow the car again. I hope that this was he problem, but I don't understand why the problem was only when hot.
 
Could be wear in the hydraulic system that prevents the slave from working the throwout bearing enough to fully release the clutch.

Could also be the pilot bush in the cranckshaft not being lubricated enough or too tight on clearance to the input shaft.

Have seen both these prolems on MGCs.

Would cause the input shaft to spin and the BJ7 gearbox, like all the earlier cars, use brass syncro rings that don't work as well as they could. And they wear quickly, too.

Wouldn't make any difference about the straight-cut Tulip gears, just how well the input shaft is disconnected from the crankshaft when opreating the clutch.

C Ya,
Mark
 
Hello,
the first possibility isn't so all is new and has been checked, so we thouht that also could be the problem.
The second possibility could be: perhaps there is not enough oil! We have introduced in the gearbox the amount of oil indicated in the maintenance book but I remember now that the level of oil was always very hight, perhaps now is lower.
I will try it today. Thank you.
 
I would remove the transmission tunnel ahead of time and then try warm the car and transmission to the point where the problem occurs. Then pull the selector cover and see if I could find where the binding is coming from. Do this with the clutch depressed so there isn't a pre-load from the drive train. The sliding gears should move freely with a slight resistance at mid point from the captured balls and springs. You may need to loosen the selector forks on their shafts. Considering the significant difficulty you are experiencing the cause of the problem should reveal itself.
 
You can see here a video. As you can watch, at the begining - surprising for me - it works well, and this happens some times, but later it's not possible to fit any gear, I have to stop to find the gears again.

https://www.youtube.com/watch?v=YWZPO8k-klg

We have tried to increse the oil level without chance.
Stretch, we have made that, in the garage without the transmission shaft and running the engine... but it's not easy so without the gearbox cover all seems work right but when you install the cover you can't see what is happening inside. It may be some problem in the selectors, perhaps tha captured balls, springs, perhaps the rear plunger selector ... but we don't find it. We will continue looking for. Thank you by help.
 
BipBip said:
... but it's not easy so without the gearbox cover all seems work right but when you install the cover you can't see what is happening inside. It may be some problem in the selectors, perhaps tha captured balls, springs, perhaps the rear plunger selector ... but we don't find it. We will continue looking for. Thank you by help.
Click to expand...

Could the problem be the gearbox cover itself? Others have had problem with the opening not being centered properly, which doesn't allow the shift lever to move freely.
 
Near Johny, we have tried also with different possitions of the cover so it's possible to move it slightly begore tighten the screws cover! we have find that the selector shaft can't move freely in the guide holes when the cover gearbox is hot! this is why the difference when hot or cold. We have repaired and works better, but still some problem.
We have find also that the socket of the speed lever is also deformed and we have changed it. Now the gears are very easy to find, with good fit but the problems hasn't finished:
We have find that when changing from 2 to 3 or from 2 to 4 it grinds, never when reducing, only when the selector pass from the 1-2 gears fork to the 3-4 gearsfork, but never at inverse.
Any idea?
Thank you.
 
Toaday with have tried the gearbox at road, to see if it has the same problem that in the workshop.
At road the problem is reduced to grind when reduce from 4 to 3, and a little grind when pass from 2 to 3, so always when 3 gears.
We will take out de gearbox again to see what happens with the 3 gears synchros... but the synchros are news!
Do you know another reason to make grinding the 3 gear?
Thank you.
 
From what you've said I would guess the problem is with the shifting forks. Are you sure you had them lined up properly on the shift rods, before tightening? When you shift from 3 to 4 your only using one shift fork, and it's going in a straight line, also the same with 1 to 2. Another thought, were the shift forks tightened and "wired" properly, as they also could have come loose.
 
Unfortunately I think the grinding problem is a weakness of the pre-BJ8 gearbox. The BJ8 has a better synchro design. I must shift slowly to prevent grinding with my BJ7 and I have the newer high precision brass synchros. I think it's associated with the high enertia of the heavy gears along with a weak synchro design and maybe some manufacturing quality control issues. That said, when you examine the synchros and shift levers make sure the synchros grip the cone on the mating gear surface in advance of gear engagement. Some poor quality synchros are on the market that have too little interference fit.
 
Thank you, but all the gears are new, they are the stright cut tulip gears with a new BJ8 main shaft, so they aren't compatible with the BJ7 mainshaft. We could say that we have done a conversion to a BJ8 gearbox.
But I think that you are right, so they have sell me the brass BN7-BJ7 synchros so my gearbox was a BJ7
https://www.ahspares.co.uk/products/productdetail.aspx?GUID=GBS140

when the right ones should be the BJ8 ones:
https://www.ahspares.co.uk/products/productdetail.aspx?GUID=7c5cb01d-17e8-4472-b320-548fcde4c5bb

Are this the best ones for a BJ8 gearbox?

I'm going to ask them but I think that the probleme is here.
Thank you.
 
I have no experience with BJ8 transmission parts but a lot of good experience with AH Spares in general. I think they or Denis Welch are likely to have the best parts.
 
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