Fourth gear grind

[Sleepergm]

Anyone else have a grinding issue changing from 5th to 4th gear. I have no issues 3rd to 4th and 4th to 5th. But the car seems to grind a little when I do 5th to 4th … 

 

is this a common issue? Had it from the last owner. Bit annoying as I can’t hard shift down. Feels like I have to push a little to the left to get it smoother into gear. 
 

thanks 

[GTSBoy]

Why would you ever need to "hard change down" from 5th to 4th? Any time you're in 5th and need serious accel, you're looking to go down to 3rd or maybe even 2nd, anyway.

Just treat your 30 year old gearbox with some respect.

[The Bogan]

Down shifting = Right gear, right RPM, right road speed!

Try rev matching on the down shift

[joshuaho96]

4 hours ago, Sleepergm said:

Anyone else have a grinding issue changing from 5th to 4th gear. I have no issues 3rd to 4th and 4th to 5th. But the car seems to grind a little when I do 5th to 4th … 

 

is this a common issue? Had it from the last owner. Bit annoying as I can’t hard shift down. Feels like I have to push a little to the left to get it smoother into gear. 
 

thanks 

Change the transmission fluid. I would try Motorcraft XT-M5-QS if you have it in your area for a reasonable price. Also, double check your clutch is fully disengaging. If you are not pushing the clutch pedal to the floor fully for every shift now is the time to start. Make sure the clutch is fully bled. The damper line requires two distinct bleed points to be purged of air or it will not disengage the clutch properly. If either hydraulic cylinders input or output are losing hydraulic pressure in their seals/leaking you can have problems like this.

If you've ruled out everything else then the most likely explanation is the synchros are worn and you need to double clutch the shift or rebuild/replace the transmission. The transfer case is discontinued FYI so you may want to rebuild it while you're in there too. If the chain stretches past spec it can do a ton of damage.

[Sleepergm]

25 minutes ago, joshuaho96 said:

Change the transmission fluid. I would try Motorcraft XT-M5-QS if you have it in your area for a reasonable price. Also, double check your clutch is fully disengaging. If you are not pushing the clutch pedal to the floor fully for every shift now is the time to start. Make sure the clutch is fully bled. The damper line requires two distinct bleed points to be purged of air or it will not disengage the clutch properly. If either hydraulic cylinders input or output are losing hydraulic pressure in their seals/leaking you can have problems like this.

If you've ruled out everything else then the most likely explanation is the synchros are worn and you need to double clutch the shift or rebuild/replace the transmission. The transfer case is discontinued FYI so you may want to rebuild it while you're in there too. If the chain stretches past spec it can do a ton of damage.

Yes I think we changed out the transmission fluid as I had a leak last year so we changed out the seals also. Need to check. 
 

I should have said just change from 5th to 4th gear … down shift. There’s a grind. 
 

I have a new clutch X clutch … but as I said all the changes in other gears are fine. 

[joshuaho96]

35 minutes ago, Sleepergm said:

Yes I think we changed out the transmission fluid as I had a leak last year so we changed out the seals also. Need to check. 
 

I should have said just change from 5th to 4th gear … down shift. There’s a grind. 
 

I have a new clutch X clutch … but as I said all the changes in other gears are fine. 

How fast are you doing the downshift? 4th gear was revised multiple times until 1998 to fix this issue. Synchro clips can fall out, synchros can wear. Most likely you're looking at a new transmission unfortunately. If you need to limp it until then double clutch downshifts into 4th.

[GTSBoy]

Meh. Every single gear in my gearbox will crunch. I've been treating it nicely for >12 years now.

[Duncan]

Most likely the 4th gear synchros (and probably others) are worn. Redline lightweight shockproof gear oil has been the go to for masking that issue a bit, it is very common.

The only real solution is to fit the R33 series 3 gearbox bits in a full rebuild....or accept it is not a new car and shift slower

[joshuaho96]

11 hours ago, GTSBoy said:

Meh. Every single gear in my gearbox will crunch. I've been treating it nicely for >12 years now.

I've worked around a crunchy/grindy gearbox for so long now that track instructors note how I have absolutely awful shifting habits. S L O W shifts and then blipping the throttle even on upshifts out of habit. My vote is R33 series 3 gearbox, those are still readily available and relatively cheap.

Edited November 22, 2024 by joshuaho96

[blind_elk]

The gearbox in my R32 GTS4 (now with RB25DET) has just over 300k on it . Life includes some track time. Has had one change of oil in its lifetime. I rev match on down changes.

I don't have any problems with synchros or gear crunching.

[FRGTN1]

On 22/11/2024 at 10:36 PM, Sleepergm said:

Yes I think we changed out the transmission fluid as I had a leak last year so we changed out the seals also. Need to check. 
 

I should have said just change from 5th to 4th gear … down shift. There’s a grind. 
 

I have a new clutch X clutch … but as I said all the changes in other gears are fine. 

 

Did you manage to fix the problem? I’m having the same issue but everything is new in my gearbox 

 

[joshuaho96]

17 minutes ago, FRGTN1 said:

 

Did you manage to fix the problem? I’m having the same issue but everything is new in my gearbox 

 

Either you specced the wrong fluid or your clutch is not releasing properly for whatever reason.

[Sleepergm]

21 minutes ago, FRGTN1 said:

 

Did you manage to fix the problem? I’m having the same issue but everything is new in my gearbox 

 

My fourth gear is not perfect but I hard shifted it into fourth from fifth and its shifting better now. Not bothering me atleast. 

I think the cheapest option is to replace the whole transmission for a R33 heritage one for like 1500 USD not including the shipping. Thats what I was going to do but its not bothering me anymore. What is bothering me is my idle is weak now after I change my intake to a smaller one so I need a tune again - loves to stall in reverse and when the aircon is on lol ... Love these older cars. WOT is strong though.

[FRGTN1]

10 minutes ago, joshuaho96 said:

Either you specced the wrong fluid or your clutch is not releasing properly for whatever reason.

I was told to put in vmx80 for about 500kms. Then change to Motul 75w90

it goes into all gears smoothly, I do hear a slight hissing noise when release clutch 

[FRGTN1]

2 minutes ago, FRGTN1 said:

I was told to put in vmx80 for about 500kms. Then change to Motul 75w90

it goes into all gears smoothly, I do hear a slight hissing noise when release clutch 

Just the down shift from 5th to 4th is crunching

[joshuaho96]

2 hours ago, FRGTN1 said:

Just the down shift from 5th to 4th is crunching

Downshifts are harder on transmissions than upshifts, the input shaft naturally slows down once disconnected from the engine so the synchros aren't doing all the work. There's no "natural" tendency for an input shaft to increase RPM. Something is not right there, I don't have a great answer on what. You can try a dedicated GL4 75W90, I plan to switch to Motorcraft XT-M5-QS which is supposedly a very good 75W90 for NB Miatas which have a weirdly sensitive transmission from the factory. I would chase down why your clutch is making a hissing noise, that's not normal. It might be no big deal but in the absence of anything else to investigate I would look at that.

[FRGTN1]

1 hour ago, joshuaho96 said:

Downshifts are harder on transmissions than upshifts, the input shaft naturally slows down once disconnected from the engine so the synchros aren't doing all the work. There's no "natural" tendency for an input shaft to increase RPM. Something is not right there, I don't have a great answer on what. You can try a dedicated GL4 75W90, I plan to switch to Motorcraft XT-M5-QS which is supposedly a very good 75W90 for NB Miatas which have a weirdly sensitive transmission from the factory. I would chase down why your clutch is making a hissing noise, that's not normal. It might be no big deal but in the absence of anything else to investigate I would look at that.

I’ll try and see it could be the release bearing. As for the 4th gear grind maybe clutch doesn’t disengage properly cause it is slightly like very slightly hard to go into first could be due to the slab cylinder pin being short uni clutch is a twin plate.

 

Ive attached some assembly photos hopefully you can open the link and see maybe detect what’s wrong

https://share.icloud.com/photos/0dc2YvW__Hl6jl-l2_0jejjpg

https://share.icloud.com/photos/09e0jkWOK-vP48c1cfY6u3ViA

https://share.icloud.com/photos/0b4rDmh5R7pK7fb1VtND73a3g

https://share.icloud.com/photos/05eeUi_6dC4DVi80jOUYDgb0g

https://share.icloud.com/photos/06335TgY1XxyIJal_wkdQLhzw

[silviaz]

On 11/22/2024 at 10:24 PM, GTSBoy said:

Meh. Every single gear in my gearbox will crunch. I've been treating it nicely for >12 years now.

Does your rb gearbox have the common input shaft bearing sound? (One one where it goes away when u push the clutch in or get to higher revs) I heard if you put the wrong oil it can get this sound.

[Duncan]

Pretty sure you are thinking of the throwout bearing there (which you should change when you change your clutch), when they are worn they will get quieter if you put your foot on the clutch. An input shaft bearing is turning/noisy at all times.

[GTSBoy]

10 hours ago, silviaz said:

Does your rb gearbox have the common input shaft bearing sound? (One one where it goes away when u push the clutch in or get to higher revs) I heard if you put the wrong oil it can get this sound.

All RB gearbags, especially the big turbo box, have rollover noise. Mine certainly does. Always has. Sometimes is worse than others - no particular idea why, although it is probably temperature related.

I have smurf jizz in mine and have had to have it in there from the first day the box went into teh car. It simply would not select gears with the engine on, on day one, with normal oil in there. And so, the blue stuff has probably ruined almost everything synchro related in the box. But it has taken 12 or 13 years to get to the point where I simply must replace the box. It has become increasingly baulky of late, which might be symptomatic of the way I've been driving it, as much as anything. I shall have to make some corrections when teh new box goes in.

3 hours ago, Duncan said:

Pretty sure you are thinking of the throwout bearing there (which you should change when you change your clutch), when they are worn they will get quieter if you put your foot on the clutch. An input shaft bearing is turning/noisy at all times.

Input shaft bearing noise will decrease with clutch pedal pressed because the drive is removed. But yes, more often than not noises that work like that are associated with the throwout.

It won't matter either way, new box will mean this one can be relegated to the parts pile.