5GTT Gearbox

[Ian S]

Some of the inner workings of the 5GTT's JB3 Gearbox.


Input shaft and output shaft.

The input shaft:
• Is the one that goes into the clutch centre plate splines and is driven by the engine.
• The cogs are a fixed part of the shaft so can't be removed.

The output shaft:
• The gear cogs are free wheeling and not joined to the output shaft though are all permanently engaged with the cogs of the input shaft. In other words, the cogs are spinning all the time and, due to the different cog sizes, at different speeds.
• The selector collars are internally splined to the output shaft and turn with it all the time at it's speed. As they are moved side to side their inner grooves engage with a ring of studs known as Dog Teeth on one side of each gear cog. This transfers the drive from one shaft to the other. These interlocking teeth are an area that wears and might cause the slipping out of gear that many 5GTT owners are familiar with. When engaged, they couple the engine to the wheels and all your impressive torque is going through just them so how do they remain attached to the gear cog? No-one knows!
• In between each is a toothed bronze ring that assists the selector collar synchronise speed with the gear cog and then mesh with the dog teeth. This is known as the baulk ring.
• The 5th gear mechanism, not shown here, fits over the two splined areas on the left (green glove) side of the shafts.
• Also not shown is the third cog required for reverse gear.
• The small chunky cog on the right is part of the final drive and is permanently engaged with a larger cog that turns the differential. It's fixed to the output shaft and not removable.

How the syncromesh works: see the next post.


The input and output shafts:

http://www.rtoc.org/articleimages/5GTT%20gearbox/01%20input%20shaft%20and%20output%20shaft.jpg (http://www.rtoc.org/articleimages/5GTT%20gearbox/01%20input%20shaft%20and%20output%20shaft.jpg)


The output shaft:

http://www.rtoc.org/articleimages/5GTT%20gearbox/02%20output%20shaft.jpg


The selector collar for 1st and 2nd gear:

http://www.rtoc.org/articleimages/5GTT%20gearbox/03%20selector%201st%20and%202nd.jpg


The selector collar for 3rd and 4th gear. This has around it one of the three cogs that comprise reverse gear:

http://www.rtoc.org/articleimages/5GTT%20gearbox/04%20selector%203rd%20and%204th.jpg


1st gear selected:

http://www.rtoc.org/articleimages/5GTT%20gearbox/05%201st%20gear%20selected.jpg


2nd gear selected:

http://www.rtoc.org/articleimages/5GTT%20gearbox/06%202nd%20gear%20selected.jpg


3rd gear selected:

http://www.rtoc.org/articleimages/5GTT%20gearbox/07%203rd%20gear%20selected.jpg


4th gear selected:

http://www.rtoc.org/articleimages/5GTT%20gearbox/08%204th%20gear%20selected.jpg


Looks like worn reverse gear teeth leading edges maybe from all that crunching into reverse:

http://www.rtoc.org/articleimages/5GTT%20gearbox/09%20worn%20reverse%20gear%20teeth.jpg


Mostly pentagon shaped interlocking pentagons aka 'Dog teeth' from 2nd gear. The bronze baulk rings can be replaced as part of a refurbishment:

http://www.rtoc.org/articleimages/5GTT%20gearbox/10%20Penatgon%20shaped%20interlocking%20pentagons, %202ng%20gear.jpg


Mostly non pentagon shaped worn flat sided Dog teeth from 3rd gear. This could be why the gear jumps out when backing off of the power a bit. To withstand 250ft lbs transferring through them yes they're quite small aren't they!:

http://www.rtoc.org/articleimages/5GTT%20gearbox/11%20worn%20flat%20sided%203rd%20gear%20interlocki ng%20pentagons.jpg


Wear on 3rd gear baulk ring:

http://www.rtoc.org/articleimages/5GTT%20gearbox/12%20wear%20on%203rd%20gear%20syncromesh,%20brass% 20coloured%20piece.jpg


Interlocking pentagon shapes inside the 3rd 4th gear selector collar;
note the extra wear on the 3rd gear side facing us
and the cleared area for the detent rollers to sit in:

http://www.rtoc.org/articleimages/5GTT%20gearbox/13%20interlocking%20pentagons%20in%203rd%204th%20s elector,%20note%20extra%20wear%20on%203rd%20gear%2 0side,%20facing%20us.jpg


Smooth inner surface on gear cogs, ie, no splines. This one is 4th gear:

http://www.rtoc.org/articleimages/5GTT%20gearbox/14%20smooth%20inner%20on%20gear%20cogs.jpg


4th gear and baulk ring removed from output shaft:

http://www.rtoc.org/articleimages/5GTT%20gearbox/15%204th%20gear%20and%20syncro%20removed.jpg


3rd 4th gear selector collar removed, showing one of three sprung rollers that are its detent mechanism:

http://www.rtoc.org/articleimages/5GTT%20gearbox/16%203rd%20gear%204th%20gear%20selector%20removed, %20showing%20one%20of%20three%20sprung%20rollers.j pg

IanS27thFeb2011

[Scoff]

The GTT's JB3 is pretty typical in its working to other 4, 5 or 6 speed constant mesh, synchromesh gearboxes.

The gear linkage mechanism controls 3 collars that have splines cut on their inside and live between gears 1&2, 3&4 and a final one for 5th gear. These collars are rotationally connected with the output shaft and are able to slide backwards and forwards to select gears. All of the gear cogs on the output shaft are free-spinning, so they spin on the shaft but are not able to turn it because they are not rotationally connected to it.

Picture for a moment the collar between gears 1 and 2. In the neutral position the collar is mid way between the 2 gears, not connected to either of them. When you select first gear the collar (via the gear change mechanism) is pushed "over" the dog teeth that exist on the face of 1st gear (see pictures). This meshing means that 1st gear is now in rotational connection with the output shaft so power is transferred from the input shaft via the pair of 1st gear cogs and into the output shaft. When you move to select 2nd gear you are pushing that collar away from the 1st gear dog teeth and on to the dog teeth on the 2nd gear cog instead. The 2nd gear cog is now rotationally connected to the shaft and so first gear (along with 3rd, 4th and 5th) is free-spinning and doing nothing again.

You can imagine that if the gearbox worked exactly as described above there would be a lot of grinding and crunching as gears where changed since each gear is spinning at a different speed. To combat this the gearbox is equiped with something called synchromesh. In the JB3's case the synchromesh is made up of bronze rings that sit between the collar and each gear. There is a "syncho ring" for 1st, 2nd, 3rd, 4th and 5th gear. The synchro ring acts a lot like a clutch. On the inside of each synchro ring there is a friction surface that mates with the gear it is protecting. On the outer edge of the synchro ring is a set of teeth that correspond with the dog teeth on the matching gear. The synchro ring is able to rotate a small amount irrespective of the shaft such that it can prevent the collar from meshing with the tog teeth on the gear, BUT it is rotationally connected to the collar and shaft and so it spins constantly. If that description didn't make a lot of sence then imagine that the synchro ring is connected to the shaft but that it can turn backwards and forwards about 10 degree's, enough to either have the teeth in alignment with the collar or not.

Here's how the synchomesh works:
Lets say your in 1st gear. You go to shift into 2nd gear. By doing so you move the gear lever toward the 2nd gear position. This action puts pressure on the collar to move it away from the 1st gear cog and slide it toward the 2nd gear cog. Before the collar can get to the 2nd gear cog to mate with its dog teeth the 2nd gear synchro ring blocks it. This is because as you apply pressure to the collar the collar is in turn puting pressure on the synchro ring. The same pressure is now forcing the synchro ring up against the 2nd gear cog and is slowly getting the cog up to speed while at the same time holding the synchro ring in a state of dis-alignment. The collar is not able to pass the synchro ring because of this dis-aligment until 2nd gear has been brought up to the same speed as the collar and input shaft. Once 2nd gear is up to speed there is no longer any force on the synchro ring holding it in it's "blocking" or dis-aligned position and the effort applied to the collar (by you) is now sufficient to push the synchro teeth into alignment and allow the collar to pass and mate with the dog teeth of 2nd gear. The same system exists on the other gears too. Reverse has no need for a synchomesh since you're generally at a stand still when you select it.

Once you understand how a synchromesh works you can appreciate why a gear lever feels like it does during a gear change. When you go to engage a gear and you feel that little hesitation before the lever pops into position you'll know that is just the synchro bringing the next gear up to speed before it's allowing the collar and gear to mesh.

[Ian S]

Just to be clear, the 'pointed' teeth on the bronze baulk ring ring don't guide the collar onto the dog teeth.

They are there for the collar to press onto so as to then press a baulk ring onto a gear cog so as to match the rotating speed.

This matching also changes the speed of the de-clutched input shaft including the other four cogs it's turning which are free spinning around the output shaft.

The output shaft speed is fixed, via the differential, to the road wheels, so it's rotating speed does not alter.

Once the speed is matched, the collar pushes past the bronze teeth and then pushes into the cog's dog teeth, turning the cog a bit as needed.

While the baulk ring is being pressed it's being pushed back on the collar and gives that resistance that you feel through the gear lever.

[Ian S]

5GTT Ph1 - JB3 014
5GTT Ph2 - JB3 032 (purported to be slightly different ratios).
11 Turbo - JB3 011

From: Cars > 5 GT Turbo > Gearbox choices for Renault 5 GTT http://www.rtoc.org/boards/showthread.php?41219-Re-Gearbox-choices-for-Renault-5-GTT&p=404595 :

Gearbox from a Clio phase 1 172 will fit the C1J engine, it also has the electronic speedo.

Early Clio 172's phase 1 gearbox has slightly taller gear ratio's and phase 2 are shorter.

I believe the ratio's on the 172 phase 1 gearbox will be taller than the R5GTT gearbox. Also, I think you'll need to use the Clio 172 speedo cable/sensor as the speedo cable/sensor on the R5GTT gearbox is different.

Mk2 Clio dci use longer gearing:
a GTT does 70mph at 3250rpm in 5th,
the Clio box does 70mph at 2750rpm in 5th. It's a JC5 box so is a direct fit, but the speedo drive isn't there hence why I started making speedo ring gears to go on the end of a drive shaft instead.


Gear Ratio Speeds: An interactive XLS page that allow you to change some ratios and wheels sizes, etc: http://www.rtoc.org/files/Technical%20Files/Speed%20Calculation/gearbox%20ratio%20speeds.xls


Posted by: francob80
JB3 S04: I've been told that the S denotes a Renault serviced/exchanged box. So my guess would be standard GTT box that was once part of a replacement by a Renault dealer, perhaps a warranty claim.