Transmission Rebuild for Third Gear Grind

[Stretch]

Here's one to ponder. After one rebuild of my BJ7's transmission already I'm trying again to resolve a grinding problem when selecting third gear. All new "upgraded" synchro rings are being installed and everything else is good. Can anyone provide information about the role of the three detent springs? Fourth gear grinds occasionally when shifting quickly. The springs probably provide a small bump to the synchro ring as the sliding hub transitions from one gear to another but is it significant? Can anyone provide the spring height or tension spec?

 

[Keoke]

HI Stretch, I really can not solve your grinding problem except to say these old BMC Boxes are slow if you are trying to shift them quickly without double clutching too they are going to grind.---Fwiw---Keoke

 

[anthony7777]

STRETCH,recently i began to have a bit of grinding in third and forth for no apparent reason,after several days of a worsening condition,my clutch master cylinder failed completly,went to the floor board with no effect on the clutch,i dont know if this could be your problem as well but how does your clutch pedal feel? /ubbthreads/images/graemlins/cheers.gif

 

[zblu]

Crunching changing down or up?

 

[Stretch]

The grind occurs up or down shifting but is worse downshifting. That makes sense since the gear speed mismatch is the most when downshifting. Clutch operation is normal. I'm pretty sure the grind problem is a combination of the old design, poor quality synchros and possibly, aggravated by modern oils.

 

[zblu]

You didnt also happen to fit a new clutch & pressure plate did you?

 

[wlivesey]

I recently had my transmission rebuilt. I put in a new clutch kit while I had the tranny out. My problem is I have this very same problem - grinding going in to 3rd gear - up shifting or down shifting. There does not seem to be any other problem. I assumed it was a problem with the rebuild. I have spoken to the shop and they have told me to bring the tranny in (and we all know how easy that is!) and they will "fix it." Is it possible it could be something to do with the new clutch. Zblu's message seemed to indicate it might have something to do with the clutch.
I am not looking forward to pulling that 135lb tranny again...
Bill
BT7

 

[wlivesey]

I recently had my transmission rebuilt. I put in a new clutch kit while I had the tranny out. My problem is I have this very same problem - grinding going in to 3rd gear - up shifting or down shifting. There does not seem to be any other problem. I assumed it was a problem with the rebuild. I have spoken to the shop and they have told me to bring the tranny in (and we all know how easy that is!) and they will "fix it." Is it possible it could be something to do with the new clutch. Zblu's message seemed to indicate it might have something to do with the clutch.
I am not looking forward to pulling that tranny again - I do it alone...
Bill

 

[zblu]

The reason I ask is that I put a new pressure plate in along with the rest of the rebuild as well; everything was ok, then after leaving it parked up for a few weeks I had to return it to paint shop, fired up, went to engage gears crunch! like no clutch!, turned off and engaged reverse, fired up and off we went in reverse with clutch fully depressed!, things slowly inproved the more I used it, turns out its a common problem over here with new plates till they bed in, seems they are a bit sticky till run in for a while!, yet for the first couple of thousand miles I had no problems

 

[BT7BN1]

I was going to open a new thread and I read this one, 9 years old, which describes exactly the symptoms on my side-shift BT7: third gear grinding when shifting rapidly for a sporty driving. It grinds from 2nd to 3rd, and also down shifting from 4th to 3rd. It does not grind if I select 3rd below somewhere around 2000 rpm, (driving gently).

I purged the clutch circuit to insure there was no air. The car was a rebuilt, including transmission, when I acquired it in 2015. The crunching 3rd gear was already present at the time, and it still does today after 30,000 km. I thought is was an inherent problem in this old design transmission (which it may be according some answers), but I have since acquired a 100/4 BN1 and fitted a 4 speed BN2 transmission, which is basically the same design of the 3000 Mark I, and the 3rd gear does not grind when up shifted or down shifted.

I have discussed the issue with some specialists in my area (France) and I hear some having fitted steel baulk rings on the side-shift box - to replace the original brass rings - with good results.

I wrote to Denis Welch hoping for confirmation of this, but the answer was that the steel rings are for BJ8 only.

I have open the side cover to inspect the rings, and for as much as I can see, the rings, including 3rd gear, are not "bottoming" to the gear cone, making me think it is not worn out.

I plan to remove the transmission from the car and take it apart for closer inspection of the rings, especially 3rd gear ring.

My question is: are the steel baulk rings a different profile compared to brass rings? This would be a reason for impossible swap.
Are the gear cones of the BJ8 manufactured with a different surface treatment, to withstand the steel baulk ring friction? This would, over time, ruin the surface of the gear cone.

I plan to order a steel baulk ring and mate it to my 3rd gear pinion, using engineer's blue to confirm the surface contact. I think a good practice is to lap the ring to the pinion to obtain a perfect match.

Will appreciate any comment to guide me in this process, especially from persons who fit steel baulk rings in a side-shift transmission, if any.
I can verify the proper mating of the gear cone and baulk, but the surface hardness of the gear will remain a question.

 

[Bob_Spidell]

re: "... are the Steel baulk rings a different profile? ..."

I recall reading this somewhere way back when, but I'm not positive. The switch from brass to steel would have been the time to modify the design.

 

[Randy Forbes]

From memory, and I can be as wrong as I am right, but I'm thinking that the surface finish (or heat-treatment) of the "cone" is different for the gears designed for the steel synchromesh rings than that for the brass ones. While they may be interchangeable dimension-wise, I would expect a higher rate of wear__on the gear__using the harder rings.

If it were mine, I'd prefer to believe that I just got a bad ring, and would just try a new brass one.

 

[BT7BN1]

Thank you for these comments. It makes total sense, and I am going to redirect my initial intention to fit a steel ring and rather look for a quality brass ring. My research on steel vs brass has returned with mixed results, but I prefer not to take the risk to damage the pinion cone, and the primary shaft since I would also replace the 4th ring (direct drive).

 

[BT7BN1]

I have the gearbox on the bench and I dismantled it. The baulk rings look fine, but I will install new brass ones. However i discovered a good reason for the 3rd and 4th gear grinding when shifted quickly.
When I separated the slider ring from the selector hub, two of the bearing balls came free but the 3rd one stayed stuck in its hole. I had to repeatedly push it with a hole punch to finally manage to rotate it on itself and free it up, it was stuck by a chrome shaving that had lodged in the hole.
As a result, the force applied to the baulk ring and consequently on the pinion cone to synchronize speeds was less than normal because the ring unlatched early before the slider geared to the pinion.
The chrome shaving came from the gear lever swivel ball. The gear stick has been re chromed and unfortunately the swivel ball was not protected and was chromed over chrome. I peeled it off without much difficulty. A rather big job for a tiny chrome peeling. I will also replace the springs by new ones and correct the lay shaft end play found over tolerance.

 

[AUSMHLY]

Congrats. What will you set the lay shaft endplay to?

 

[BT7BN1]

Thanks, I am quite satisfied to have found a sign of evidence, not always that easy.
For the laygear end float, my Haynes workshop manual shows 0,012” in the parts examination paragraph, and I found 0,025 on my laygear, twice the recommended end play and I was going to correct accordingly. However, before I answer your question, I verified, and in the same workshop manual in the gearbox specs sheet, I now read a max tolerance of 0,021 (dyslexic printer?)
My TR3 workshop manual indicates 0,06 to 0,010, but this is an aluminum casing so not sure it can be used as a reference.
So your question is still open and maybe someone will answer it. If not, I will reduce it to about 0,015”

 

[AUSMHLY]

The shop manual for my BJ8 states .012
When I was questioning the end float (endplay) plus or minus, on this forum and some articles I read, some target .005.
I guess the less endfloat, the less play the laygear has. Not enough endfloat though will cause a problem too. It must spin freely.
I'm guessing .012 is the max endplay you want.

 

[BT7BN1]

Right, I will use .012 as a max value then, since it is what you see in your BJ8 manual. Mine is a side shift, but the design is very similar.
i would think that aluminum casing gear boxes require a tighter end float as the casing expansion will be higher than cast iron casings. I just see on a table that aluminum alloys expansion coefficient is around 13 (10-6 in/ F increase) as compared to 5,8 for cast iron (our gearboxes casings). I will try to target somewhere between .009 and .011 end play.