Grinding into Reverse... grrrr

[Joopin]

91 YJ - 4.0 5spd...
Grinding when I put it in reverse... 75% of the time.
all the rest of the gears are fine.

? ?

[hi_c]

You're not rolling when you do it are you? I find that by putting it in 4th, then going immediately to Reverse it goes without grinding. Could prolly use any gear, but 4th is easy to find. Try it.

c

[Bounty__Hunter]

Probably bad synchonizers, just double clutch.

I know you're running the proper gear oil in there after all the discussion we've had about it, right?

[odjeep]

Could be ur clutch going out. Try this When ur standing still in neutral with the clutch pedal up and the engine running push in on the clutch and try to put it in reverse a second or so after, if it grinds its a sign that ur clutch is going bad. Or try this, while setting still and the engine is running, put the e-brake on, and put it in 5th gear. Then give it just a lil bit of throttle and dump the clutch. If it stall right out the clutch is still good, if it boggs down and starts to buck b4 stalling the clutch prolly needs replaced. Of course if the clutch is on its last legs the dumping of the clutch in that last test might just be the straw to break the camels back so its up to u if u try it or not :) . Hope u figure it out.

od

[Joopin]

Hey, I always heard the term "double clutch" but I never really knew what it meant.... maybe someone can help me out on that so I can take bountys advice. And bounty, I don't know what discussion your reffering to... was it a recent post that I missed?

I'll try the other ideas tomorrow... I hope the clutch isn't going! How much is that gonna cost me? Damn, good thing I got a deal on the winch I just got.

[odjeep]

Double clutching is what is done on transmissions without synchronizers like a rig or dumptruck. It is basically the act of getting the drive gear in the transmission to go the same speed as the next higher or lower driven gear. On upshifting you: 1) push in the clutch. 2) pull into neutral. 3) release the clutch. 4) let the rpms fall to where they would be in the next higher gear at ur current speed. 5) push in clutch. 6) put in next higher gear. It may sound difficult but it happens so quickly that u dont think about it. Its essentially shifting the same way that u do except u pump the clutch twice while doing it. Downshifting is practically the same with the acception that in step 4 instead of letting the rpms drop u want to ''spike'' the rpms with the throttle so that the rpms raise to the point, or higher, where they would be in the next lower gear and then go on to steps 5 and 6. It sounds complicated so i hope this makes :) . It did when I was thinkin it. .
The thing is, double clutching works in the foreward gears when the synchros are failing. Reverse has no synchronizer and therefore does not need double clutching. I hope this helps ya out.

od

[XJNick]

Hi,

Reverse is not syncronized. If you are grinding in reverse with the clutch pedal pushed in and the vehicle stopped, it'd be a problem in the bellhousing (clutch) or the clutch hydraulic system.

-Nick

[avyoung]

Clutch kits are usually around $130+ or so depending on quality. They are not that bad to install but can be really frustrating when you can not get stuff to line up.

[Bounty__Hunter]

I thought reverse was synchronized in the Aisin-Warner jeep trannies?

The 'other' discussions I referred to is all the times we've recommended taking out the factory recommended GL5 gear oil and putting in Redline MT90 or Penzoil Synchromesh. The GL5 eats the soft brass synchronizers in the AX5 and AX15. Just figured you caught one of those many threads.

[88Wrangles]

You might want to first check and see if it has enough clutch fluid. I've seen some people who think that they need a new clutch, but it turns out they are just out of fluid. Usually, though, when I tell them to check the fluid, they never believe that that could be the problem!!

[Snitty]

Believe it or not... grinding into reverse is a very very very very common thing... and is not really a bad deal... There is no synchronizer for the reverse gear so there is nothing in the transmission to get the shafts at corresponding speeds...

first i'll explain the shafts of a transmission... the input shaft connects directly to the clutch, or the flywheel when engaged... the input shaft is always directly geared to the layshaft.... the layshaft spins gears which are always engaged to gears which spin FREELY AROUND the output shaft... and there are "dogs" (gears with teeth on the sides) connected to the output shaft which slide back and forth and connect to teeth on the sides of the various, constantly spinning gearsets, to finally connect all three shafts

as the transmission sits in neutral, clutch petal out.. the input and layshaft of the transmission are always spinning, but are not connected to the output shaft by any selected gear.. when you press the clutch, the two shafts remain in motion because of their momentum... and even possibly from a minor viscous wind friction in the clutch from the flywheel... when you move into a forward gear, synchronizers on the dogs allow you to match the layshaft to the output shaft to their corresponding speeds...

If you are moving forward, you will NOT get into reverse, i'm sure you already know that... And like said before, the layshaft may be spinning from viscous friction or from previous momentum... because the reverse gear has no way to synchronize the layshaft to the speed of the output shaft, you WILL experience a grind if your layshaft is still spinning... also, if you are moving, and the layshaft is not, you will grind as well.... a synchronizer corrects that in the other gears by making the shafts catch up to speed before the gears engage...

another reason you may grind... is because reverse doesn't engage the same way as the other gears.... like said, all forward gearsets are always engaged to the input shaft, and will spin according to the engine/clutch... and are connected to the layshaft through the dogs which are always connected to the output shaft and are selectively connected to the forward gearsets which are constantly spinning in their corresponding speeds... BUT... the reverse gearset is NOT always connected, and has no dog to connect it... instead... there is one gear always connected to the output... one gear always connected to the layshaft... but the two gears are not connected to each other... there is a third gear in this gearset... it is called an idler gear.. instead of a synchronized dog transferring the torque to the shaft... the idler gear is slid in between the two gears on the layshaft and the output shaft... if there is ANY movement in the layshaft while you are stopped.. you WILL hear that gear grind as it tries to mesh between the gears... that is also why a reverse grind sounds different from a forward gear grind... one is a gear physically grinding... one is a dog coming in from the side.... this third "idler" gear is also how the rotation of the shaft is reversed.. each gear in series of a gearset spins in the opposite direction of the previous... all forward gearsets have 2 gears connected... the reverse gear, having 3 gears, obviously spins the output in a direction opposite of the others

one last thing... that is also why it is common to hear a "whirring" noise while in reverse... the forward gears are helical cut, therefore called helical gears... the teeth are cut at an angle, so there is always more surface area of more teeth connected at all times... the reverse gear, in order to slide in to engage, has to be straight cut, called spur gears... a helical gear will smoothly make gradual tooth contact as each tooth comes in and out of contact... a spur gear will "slap" teeth into and out of contact...

So... again... it is very common, and expected for reverse to grind.. it doesn't mean anything is going wrong.. it just means that it is getting old, but still working... every manual vehicle i've ever had ground into reverse... i ALWAYS go into a forward gear before going into reverse... when you are going into reverse, you should be stopped, which means the output shaft is not spinning... no matter what ratio a gearset is, if you synchronize the layshaft to the 0 rpm output shaft, the layshaft will stop spinning... this is utilizing other synchronizers to allow the reverse gear to shift in smoothly, because both gears that the idler has to slip into will be stopped

did i make any sort of sense? i hope i helped...

here are some helpful pics to show you...


here you can see the input shaft (top left), layshaft (bottom), and the output shaft (top right)... you can tell the reverse gear by its spur cut rather than the forward gears which are helical cut... you can also see the idler gear on its own shaft which will slide left to mesh into the two other spur gears to engage reverse...

http://static.howstuffworks.com/flash/transmission.swf
or you can click here to see how it all works... you can shift through the gears to watch how they all engage

[TwistedCopper]

Originally Posted by hi_c

You're not rolling when you do it are you? I find that by putting it in 4th, then going immediately to Reverse it goes without grinding. Could prolly use any gear, but 4th is easy to find. Try it.

c

I used 1st gear then reverse. worked for me, too!

[XJNick]

Snitty, Good info! makes sense to me.

I usually go into 2nd before going into reverse to prevent any possible grinding. After changing my clutch, reverse rarely ever grinds anymore. With the old crappy clutch I had, it was another story...

-Nick

[Snitty]

i always use 2nd gear... even if driving a vehicle that doesn't grind into reverse... just habit... and better on the idler gear to have everything stopped

[graewulf]

now that is cool... i always had the concept but never actually saw it...

[jps4jeep]

I as well go into second prior to reverse.

Snitty, thanks, I have never had the chance to see a (jeep) tranny that close and personal. Sweet info!!
Joop I figured out what is wrong, the solution is.... Don't use reverse! hehe