Grinding when downshifting

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Shane65

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Hi, new to the forum, recently picked up a 65 barracuda 4 speed with 273. Recently got it running, but now i'm noticing some issues with the transmission.

Shifts fine when I'm upshifting thru the gears, but everytime I go to downshift from any gear, I'm getting grinding. Think the synchros are out?

I dont know much about these transmissions, or any transmissions for that matter... If it ends up being a major repair, is there a better transmission to swap in favor, or should I just plan on rebuilding it?
 
Yep synchros going out/worn. How is the fluid? Change the fluid,and try double clutching when downshifting and rev matching.
 
Is it hard to shift into reverse and grinds then? You may need to adjust the clutch. It might not be dis-engaging fully.
 
Yeah, see if it will go into all gears easily at idle and not moving. If so, the clutch is probably ok and either the synchro rings or the whole synchronizers are worn out. Make sure your fluid is some good quality (GL-5 rated) gear oil. I use the 85-140w multi-weight myself but straight 90W will work too. If some knucklehead put 30W engine oil in it, that could cause it too.
 
cudamark said:
Yeah, see if it will go into all gears easily at idle and not moving. If so, the clutch is probably ok and either the synchro rings or the whole synchronizers are worn out. Make sure your fluid is some good quality (GL-5 rated) gear oil. I use the 85-140w multi-weight myself but straight 90W will work too. If some knucklehead put 30W engine oil in it, that could cause it too.
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You mean GL-4,GL-5 is for rear diffs.
 
Yup, same stuff. It works the best unless you're in northern Mn in Feb!
 
GL-5 is fine...lol....

API Category GL-4 designates the type of service characteristic of spiral-bevel and hypoid gears in automotive axles operated under moderate speeds and loads. These oils may be used in selected manual transmission and transaxle applications.
API Category GL-5 designates the type of service characteristic of gears, particularly hypoids in automotive axles under high-speed and/or low-speed, high-torque conditions. Lubricants qualified under U.S. Military specification MIL-L-2105D (formerly MIL-L-2015C), MIL-PRF-2105E and SAE J2360 satisfy the requirements of the API GL-5 service designation.
 
From what I have read the GL5 rated oil has additives that do not play nice with Brass syncro parts. Though some new Gl-4/Gl-5's are being formulated with special additives that would make them compatible in any application.
 
Really? I've been using that stuff since it became available and haven't had an issue with any manual transmission I've ever owned.
 
I have also heard GL-5 can cause premature bearing failure when used in applications that call for GL-4.
 
Thanks for all the help fellas!.. You guys are awesome.

Fingers crossed it's just a fluid change to get me back to normal... The guy I bought it from said it had been sitting in his garage for 3 years, so I'm thinking it's possible the fluid just needs a change... hoping anyway.

So GL4 straight 90W or 85-140W... Or Pennzoil Synchromesh.

This Pennzoil Synchromesh stuff, does it come in different weights or is it one weight? I did a quick search online, it said for GM or Chrysler trannys but I couldn't find any different weights.

To elaborate a bit more... the transmission seems to go into Reverse fairly easy from idle. Just doesn't like downshifting at all when I'm driving.
 
I forget the specs,but yes the synchromesh is only one weight. If you buy from advanced auto,buy it online and check "pick up at store" then use code ES123,it will save you 10 bux when you buy 4. Comes out to 20.76 plus tax,and you can pick it up at the store after an hour.

Also,to save your synchros you really should rev match when downshifting.
 
Red66GT said:
to save your synchros you really should rev match when downshifting.
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This is important and maybe Shane65 you aren't familiar with. Let's say you're downshifting from 4th to 3rd at 50 mph, when you depress the clutch, you gently press the gas pedal to raise the engine revs to approximately what they will be when you're in 3rd, as you downshift. That's 'rev matching' that way you're not putting a strain on your synchros. It takes a bit of practice to get the hang of it. Pretty soon it becomes second nature to do this.
 
goldfish65 said:
This is important and maybe Shane65 you aren't familiar with. Let's say you're downshifting from 4th to 3rd at 50 mph, when you depress the clutch, you gently press the gas pedal to raise the engine revs to approximately what they will be when you're in 3rd, as you downshift. That's 'rev matching' that way you're not putting a strain on your synchros. It takes a bit of practice to get the hang of it. Pretty soon it becomes second nature to do this.
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Well I will admit, I haven't been rev matching when downshifting... I've really only driven modern manual transmissions most of my life and haven't had issues when downshifting... Is this something that older manual transmissions had problems with? Even when they are in perfect working order, they'll grind when not rev matched (downshifting)?
 
No,you should also do it in a modern car. It will save the synchros and clutch. My 87 D100 will downshift without revmatching every time,but I still do it.
 
I rarely downshift. I just let off the gas and let the engine do most of the the braking. Every time you cycle the clutch is one more time closer to replacing it
plus it puts undue stress on the rest of the drivetrain. Brake shoes are cheaper to replace than clutches and transmissions. (don't shoot me, just my personal opinion).
 
on older manual trannys, I double clutch most of the time when downshifting. Clutch in, put in nuteral, clutch back out and rev engine, clutch back in and put it in gear. That brings the input shaft and gear cluster (counter gear?) up to higher speed so it is more closely matched to what it will be when you put it back into the lower gear. Smaller lightweight trannys don't grind as easy as the older bigger ones. Trick trannys, I almost always double clutch when downshifting.
 
69B-Cuda said:
on older manual trannys, I double clutch most of the time when downshifting. Clutch in, put in nuteral, clutch back out and rev engine, clutch back in and put it in gear. That brings the input shaft and gear cluster (counter gear?) up to higher speed so it is more closely matched to what it will be when you put it back into the lower gear. Smaller lightweight trannys don't grind as easy as the older bigger ones. Trick trannys, I almost always double clutch when downshifting.
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Yep, if you have drove an old truck this is the way you shift them.
My 48 Willys shifts up nice, t-90 fresh rebuild. 3-speed.
Down shifting is a art, match the rpms and slide it in from 3 to 2.
From 2 to 1 is a real pain, first has a straight cut gear, so no sycro's, find the rpm and slide it in or the tranny grinds in protest.

My 73 duster does not down shift well without rev matching. Maybe the crappy stock shifter that needs rebuilt, but you can really bang the up-shifts fine.
Use GL-4 fluid in the trans.
 
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