901 Transmission shifting issue

[tdavies]

Hi,

I'm looking for some advice on a 901 shifting issue on 2nd gear. When driving the car, shifts from 3rd to 2nd would grind and blipping the throttle made it worse. When shifting from 1st to 2nd, I would double clutch to avoid grinding gears.

When I tore apart the transmission, I expected to see a worn 2nd gear syncro ring and damage to the 2nd gear and sliding sleeve engagement teeth. To my surprise, there was no excessive wear on any of the parts.

Does anyone have any ideas on what the issue is?

Thanks,

Trevor

[HawgRyder]

First thing...type of fluid?
Second...adjustment of shift assembly.
Third...clutch action...disengaging properly?
Bob

[DRACO A5OG]

Originally Posted by HawgRyder

First thing...type of fluid?
Second...adjustment of shift assembly.
Third...clutch action...disengaging properly?
Bob

+1

year too

[tdavies]

The gear oil is Red Line synthetic 75W90 high performance gear oil.

I believe the shift linkage is in proper adjustment. I replace all the shift linkage bushings and it shifts fine in all other gears with no issues.

Yes, the clutch is new and adjusted correctly.

It is a 1968 911.

[HawgRyder]

I am not familiar with the Redline product.
The two things the gear oil needs to have....lubrication of course..and then some stickyness ( my brain fart for this morning) so that the syncro rings will have a little friction to work.
If the gear lube is too thin or maybe too effective in cutting down friction...then the syncros will not work as they should.
The fact that you see no damage to the ring...leads me to think more in the direction of the lube.
Did the previous owner use the same lube?
How long have you had the car?
If you made a change...then the last thing you did is probably the cause.
If the clutch is new...was the pilot bearing changed and lubed?
An old pilot bearing will keep the gears spinning even though the clutch is disengaged...and if it has enough drag...it will overcome the syncros.
Things to think about...good luck.
Bob

[tdavies]

What gear oil do you recommend? I don't know what was in it when I purchased the car, but the issue existed before I put the Red Line in it. I put about 20K miles on the car with Red Line. I just never down shifted into second and always double clutched from first to second.

The pilot bearing was replaced and lubed when the clutch was replaced.

Here are some pictures of the 2nd gear dog gear, slider and syncro. I plan to replace the syncro, but I'm concerned that it will not fix the issue. If you think the wear is excessive, and just replacing the parts will fix the problem, that would put my mind at ease.

[Rob R]

I have a 1970 911T with a 911/01 transmission with the exact same symptoms. I have only had the car a few months so I don't know what gear oil is in it. I checked the level when I first got it and it was full and yellow.
I replaced all the shift rod bushings and used the "coupler whisperer" coupler bushings. Still no better. I think I will try some Kendal gear lube and see if it helps.
I was planning to take it all apart in the next few weeks but will try the kendal first.
My first post I have been lurking for a while.
Rob

[HawgRyder]

Unless there are teeth missing on the slider...it looks useable.
The dog teeth appear to be pointy and not worn much...so OK too.
The fluid everyone recommends is Swepco 201...I haven't used it myself...(bought 85W-140W when I did mine...generic brand).
I only used the car in the summer...so the heavier lube was OK.
I suspect that the previous owner may have put some sort of friction reducing addative in yours...would explain a lot of your symtoms.
As long as everything looks good inside...and there are no glaring faults..(check the bearings carefully)...and you check the input shaft bearings for lateral play (can do some wierd things)...you should be on the right track.
Bob

[tdavies]

Thanks for the advice!

[Peter Zimmermann]

Originally Posted by tdavies

Hi,

I'm looking for some advice on a 901 shifting issue on 2nd gear. When driving the car, shifts from 3rd to 2nd would grind and blipping the throttle made it worse. When shifting from 1st to 2nd, I would double clutch to avoid grinding gears.

When I tore apart the transmission, I expected to see a worn 2nd gear syncro ring and damage to the 2nd gear and sliding sleeve engagement teeth. To my surprise, there was no excessive wear on any of the parts.

Does anyone have any ideas on what the issue is? Thanks,Trevor

Are you sure, while downshifting from 3rd to 2nd, that your linkage wasn't out of adjustment just enough that you were actually nicking reverse? This would explain why a throttle blip made the problem worse. Remove your shifter, turn it upside down, and examine the plate that the shift lever fits into, I'm pretty sure that's where you'll find your problem - wear on the plate, wear on the shifter, or both.

[Cal MX5]

I have recently purchased a car with a 901 box and have the exact same issue. I have replaced the coupler bush and also the 2 bushes in the gear lever. I have played around with the adjustment of the coupler clamp, but am still not convinced I have it right. Yesterday I purchased some Swepco 201, as the previous owner couldn't tell when when the gear oil was last changed.

One question re the adjustment, what effect does moving the rod coupler clamp fore and aft have? I have only been adjusting it's rotation.

[gamin]

The common wisdom on this board is to only use synthetic gear oil on G50 and newer trans due to type of syncros. Non-syn only in 901/911/915 swepco or kendall. I have used swepco for years and just switched to kendall due to availability and price. All is well. Proper adjustment of the clutch and a new shift coupler helps. My shifts to second are smooth as butter and the trans has never been opened, the 911 on the 70.

[Cal MX5]

Thanks. Any comment on moving the rod back and forward, as apposed to rotating it to get the adjustment perfect?

[Cal MX5]

I changed the gear oil to Swepco 201. Still having issues with the shift. Any further tips on adjusting the coupler?

[gsjohnson]

As Peter stated previously, the grind you feel when shifting to 2nd gear is that your catching reverse just for a moment as you pass by the reverse gear and it grinds as a result. That's why you didn't find any second gear damage when you pulled the trans apart. The damage is occurring to the reverse gear...probably minimumly. This is usually a result of a misadjusted shifter coupler. A common symptom with 901 transmissions. Remove the coupler plate. Place your shifter in the neutral position, loosen the coupler clamp bolt, and move the shifter towards the driver all the way while still in the neutral position. Then move the shifter all the way to the right while still in neutral. Tighten the coupler clamp bolt and then go thru all the gears while standing still. If everything feels like it should, road test your vehicle and see if you have eliminated the grinding noise. Take your wrenches with you on the road test, so you can fine tune it with the coupler while your on the road. It took me three tries and 10 minutes before I got mine just right. Hope this helps.

[911kiwi]

Hi CalMX5,

The adjustment fore & aft is primarily for driver reach, that is positoning the gear lever to suit your seating position/arm length - which indirectly assists smooth gear shifts.

Are your engine/transmission mounts in good condition?

Check your clutch cable adjustment for correct end play.

Also remember that these older gearboxes don't like "lightning fast" gear changes. Try slowing down your shifts, pause momentarily in neutral, making a 2 stage shift action and see if this eliminates the problem.

Good luck. Patience and lots of fiddling usually pays off in the end. I have a 5-sp 901 in the 912 - long throw but smooth as silk.

Cheers
Gary

[chris_seven]

Motul Motylgear 75W90 - Technosynthese - API GL-4 / GL-5

Recommended for transmissions which are hard to shift or noisy.

Semi-synthetic.

Motul MOTYLGEAR 75W90 - TechnosyntheseŽ - API GL-4 / GL-5

We have used it successfully for about 6 years and everyone we have supplied has found an improvement is shift quality on both 901 and 915 transmissions.

When used with a plate type LSD it does need a small amount of friction modifier.

I used the Redline 75/90NS and also found it good but when we switched to the MOTUL we did see a shift improvement.

I would never use Swepco in a 901.

[Cal MX5]

Originally Posted by gsjohnson

As Peter stated previously, the grind you feel when shifting to 2nd gear is that your catching reverse just for a moment as you pass by the reverse gear and it grinds as a result. That's why you didn't find any second gear damage when you pulled the trans apart. The damage is occurring to the reverse gear...probably minimumly. This is usually a result of a misadjusted shifter coupler. A common symptom with 901 transmissions. Remove the coupler plate. Place your shifter in the neutral position, loosen the coupler clamp bolt, and move the shifter towards the driver all the way while still in the neutral position. Then move the shifter all the way to the right while still in neutral. Tighten the coupler clamp bolt and then go thru all the gears while standing still. If everything feels like it should, road test your vehicle and see if you have eliminated the grinding noise. Take your wrenches with you on the road test, so you can fine tune it with the coupler while your on the road. It took me three tries and 10 minutes before I got mine just right. Hope this helps.

Thanks very much. I figured it's still a coupler adjustment issue. That would make perfect sense as this morning it did it bad on a 1st to 2nd up change. It sounded like it was grinding against a gear travelling at a vastly different speed. If I am indeed snagging reverse gear, I suppose that would indicate the clamp is adjusted too far towards reverse (the drivers side) yeah?

I've done the drive around with the spanners making adjustments, but I've been stabbing in the dark to a degree. I did have trouble engaging 4th and 5th, but I seem to have fixed that. I'd say I must be close.

If I change really really slowly (like you would in a car with no syncro), I can usually engage 2nd on the up and down change.

Originally Posted by 911kiwi

The adjustment fore & aft is primarily for driver reach, that is positoning the gear lever to suit your seating position/arm length - which indirectly assists smooth gear shifts.

Are your engine/transmission mounts in good condition?

Check your clutch cable adjustment for correct end play.

Thanks, I'm glad I don't have to worry about that, just the rotation.

Engine and trans mounts appear fine.

I've yet to check the clutch, but will.

[gsjohnson]

Before you go thru the adjustment procedure and road test, play around with the adjustment to better understand what the movement change of the coupler actually does. Just sit inside the car without the motor running and move the coupler around to get a feel how much movement has what effect...Once you understand it, then go for the procedure and road test. Just take your time and plot your way forward...Good luck.

[Cal MX5]

Am I correct in the assumption that it's possibly adjusted too far "left" towards reverse?