13 replies to this topic

[Pickwah]

Evening all

 

Just fully rebuilt my engine after having the block bored, head work and crank ground.

 

Whilst it was away at the machine shop I felt best to strip and build the gearbox to make sure I wasn't bolting £2k worth of engine onto a box that wasn't up to scratch.

 

Before the box was stripped it ran fine with no crunching and no odd noises of any sort.

 

I completely disassembled the main shaft, cleaned everything spotless and reassembled.

 

The only parts replaced in the box were the third motion bearing (as a matter of caution) with a genuine RHP bearing, center oil pickup and x-pin diff.

 

The baulk rings seemed to have plenty of *grab* and the gears had plenty of friction with the rings not riding all the way up to the gears, so these weren't replaced.

 

Idler gear end float was set at 4 thou and primary gear was also set to 4 thou.

 

So here's the thing..

 

Now the engine/box is back in the car ive noticed that there is a slight *clunk* as the car is put into 4th gear. The noise isn't a grind and the gear does go in, but it can be *felt* through the gear stick only from 3rd to 4th. I have noticed this seems to be at higher revs as a slow change into 4th while cruising is silent.

 

If anyone can shed some light as to what could be causing this I would be hugely grateful as I really don't want to have to strip the lot down again.

 

Thanks in advance!

 

Matt

[Spider]

The 'clunk' you describe here, I know these can be difficult to put in to words, but is it like it goes in to 4th very 'suddenly', like putting pressure on the stick, moving it, moving it and then suddenly 'clunk' and it's in?   Kinda like 'off then on'?

Also, what gearbox case is it?

 

When you checked the baulk rings for wear / fit, did you measure the clearance between the baulk ring and the dog teeth on the gear?  (lower wear limit here is 0.030").

 

Did you replace the Synchro Hub Springs?

[Pickwah]

It doesn't struggle to go into gear at all, but like I say there is a clunking noise before with slight resistance on the gearstick. It's a standard 4 synchro box, all gears were in good condition.

Would a mix up of baulk rings cause this? Although I didn't measure the gap between the rings to the gears there looked plenty of clearance. The springs are the same but never had a problem before the box came apart?

Really don't want to have to take it all to bits again!

[Spider]

Sorry to say, but based upon what we've uncovered so far, it does sound to me like 4th Gear isn't synchronising ie, it's an internal issue and will have to come out to fix it.

 

There can be a number or combination of problems that's causing this.

 

The first is of course that the baulk ring is worn beyond service limits. It can still have clearance between it and the gear, but be worn out. The inside of the baulk ring has grooves cut in to it, these work much in the same way as a treaded tyre does on a wet road, clearing oil off the synchro cone off the gear, to create friction and synchronise the speed of the gear as it's being selected. When these groove wear, their ability to clear the oil out of the way is reduced.

 

The Springs in the Syncho Hubs do loose tension and in doing so, reduce the force exerted on to the baulk ring when shifting, so will act in a similar way to a worn baulk ring, however, I'm inclided to include here that if the springs are indeed week, then you'd usually have troubles with 3rd gear too.

 

The Syncho Hub itself can be worn, though I'd suspect you'd also find to crunching in to 3rd on down shifting, similar to that above.

 

I've found the odd 1st Motion shaft on which the Sychro Cone is worn or chipped and this can be a cause.

 

What gearbox case do you have ? Tthis maybe an issue too

[Pickwah]

I understand where your coming from but all baulk rings looked in good condition with no blunt edges. The gearbox is A+ and I'm sure it's a DAM casing!

[Spider]

DAM 5262?  There were a few different DAM boxes (eg 2886, 4818 etc).

 

Do you recall how many bolts were holding in the Mainshaft Bearing Retainer?  (be 3 or 4)

[Pickwah]

Wouldn't know without looking, 3rd motion retainer was held in by 3 bolts.

[Spider]

Wouldn't know without looking, 3rd motion retainer was held in by 3 bolts.

 

Ah, OK. A DAM 5262.

 

I'll post some info on these tomorrow (our time).

[Spider]

I acknowledge that it apparently worked OK prior. I've found in many DAM 5262 Cases a machining error (I can't explain it any other way).

 

For 1st, 2nd and 3rd gears, the distance between these is set by the Mainshaft on to which they are mounted, however for 4th gear, being a separate shaft, it relies on being mounted in the correct location. 

 

What I have found on many of these late cases is that the registers machined in to the cases for the Mainshaft and the 1st Motion shaft are 0.020" too close together when compared with a great number of other gearbox cases measured, with the Mainshaft Bearing Tunnel being in error. When assembled, this puts the 1st Motion Shaft too close by 0.020" to the 3 / 4 Synchro Hub. This usually results in 3rd or 4th Gear Baulk Ring 'dragging' or indeed locking up more often than not and on some boxes - relevant here - can drag on 4th gear, or 3rd and 4th at the same time (resulting in the lock up I've mentioned)

 

It also results in serve overshoot of the synchro hub when selecting 4th gear to the point were the detent balls almost come out when everything is new. It will only take a bit of wear in the selector and these will come out and either lock it in 4th gear (this happened to my brother) or the balls will come completely out and you’ll have no sychromesh on 3rd or 4the gears.

 

I’ve tried various methods to rectify this, all successful, none easy though, but IMO worthwhile.

 

Given your description, there is a possibility that this could also be a cause for the issue you are having

[Rorf]

When reassembling the synchro hubs you might have put the inner part in the wrong way around. I do not recall any manual saying which way they should be, but if I recall the inner part protrusion should face towards the clutch side. 

 

Thanks to Guessworks for the pic

Attached Files

•  4th synchro hub.jpg   16.91K   0 downloads

Edited by Rorf, 04 May 2018 - 12:00 PM.

[Spider]

When reassembling the synchro hubs you might have put the inner part in the wrong way around. I do not recall any manual saying which way they should be, but if I recall the inner part protrusion should face towards the clutch side. 

 

Thanks to Guessworks for the pic

 

Fair point Rolf, and quite true that there no decent illustration I've come across which shows them decently, however, while the outer tacks can be put on the wrong way around and fitted to the box this way, if the inner was the wrong way around, you can't get the 1st motion shaft in.

 

When the outer track on either is the wrong way around, you can't get the gearbox in to neutral.

[Rorf]

Thanks Moke, one would be surprised at how many people put a box together without testing that everything turns and clicks and it goes into various gears etc, before attaching it to engine ha ha 

 

And of course using the BFH to hit the main shafts and bearings back in.

Edited by Rorf, 05 May 2018 - 05:27 AM.

[Spider]

 

And of course using the BFH to hit the main shafts and bearings back in.

 

OH ,,,,,,, OH,,,,,,,

 

That to me is like running your finger nails down a chalk board ,,,,,,,,, NOOOOOOOOOOOOOOOOOOOOOOOO !!!!!!!!!!!!!!!!!!!

 

I like the 'squawk,,, squawk,,,,,squawk' of my press thanks  

 

Many years ago, I used to be able to easily 'knock' together 2 and sometimes 3 gearboxes in a day,,,,,, these days, well,,,,, I just spent a solid week blue printing one gearbox,,,,,,,,,,,, I think I need my head read,,,,,,,,

[Pickwah]

Hi guys

Many thanks on the replies, I did notice the protrusion on the inner part of the hub on assembly and funnily enough I used that very picture to see which way it went.

I'm going to try a couple of things before I do anything drastic. I'm going to lengthen the top engine steady a few mm as it's adjustable and was shortened, tilting the engine backward to stop the exhaust rattling in the tunnel. I am also going to fit a new verto clutch arm as the one I currently have doesn't have much of a "ball" shape to it anymore.

I'll get the basics right first and let you know how I get on!