4-speed manual tranny lock in reverse

City
San Marcos
State
CA
#1
Hi, I'm new here and it's my son's 1985 CJ8 I'm asking about. 4.2L with 4-speed manual. He recently bought it (1500 miles) with "rebuilt engine and transmission". Two weeks ago he went to go into reverse (with grinding noise) and it locked, could not be taken out of gear, so had to be flat-bed towed. The garage where he took it to said "it needs a transmission rebuild" and showed me the oil he had drained which was quite grey, "full of metal bits". 10 days later I pick it up, and when I go into reverse it grinds. I thought I hadn't done the clutch right so I didn't say anything. 50 miles later it locks again: he went into reverse (grinding noise) and bam, locked up again. The mechanic said he'd changed something in the linkages. It's my belief we got hosed: the oil was probably some used junk he had around to show suckers their tran was toast. So now the question is what is the actual problem? Possibly the original "rebuild" was poor, but it seems there must be a part that is vulnerable to breaking, causing this problem. The grinding going into reverse is obviously an issue, don't know what. Since the lockup happened on Saturday he's sending the car back to the mechanic today, and I'd love to have something to say to him... whether we sue him for quackery is another thing.
Thanks very much in advance for any good advice. Bad advice is also tolerated...
Tom
 

spankrjs

Scrambler Junkie
LIFETIME
CJ-8.com Member
SOA Member
City
Biloxi
State
MS
#2
What transmission is in the Jeep?

Most manual transmission, shifting into reverse, will grind some. Try double clutching before shifting into reverse, to get everything to stop spinning.

If it is a T176, the shifter can get sloppy, causing it to lock up.
 
City
San Marcos
State
CA
#3
What transmission is in the Jeep?

Most manual transmission, shifting into reverse, will grind some. Try double clutching before shifting into reverse, to get everything to stop spinning.

If it is a T176, the shifter can get sloppy, causing it to lock up.
I believe it's a T176... if it is sloppy, what can be done to fix it? It's Very Expensive to fix!
Thanks!
Tom
 

93_Fummins

CJ-8 Member
CJ-8.com Member
City
Edmond
State
OK
#4
When you say "locked" do you mean it locked up as in stopped spinning and killed the motor, or do you mean it "locked" itself into reverse and just could not be shifted out?

Most manual transmissions are not synchronized in the reverse gear as it is usually a spur gear on an idler shaft all by itself. If the clutch drags or you are moving at all, unsynchronized gears WILL grind a little. Reverse is even worse in that sense because it's a case where an actual gear is moving and engaging with it's own gear teeth oppose to the smaller dog teeth of a shift collar. Generally, the idler is often located low in the case and the shift fork for the reverse gear can be tricky to line back up with the collar groove on the gear for top loading transmissions. If the "rebuilders" did not line up the fork/pivot correctly on the reverse idler gear, it is totally plausible that the fork just slid the gear back into engagement but is not located in the groove to be able to pull it back out of engagement. I personally have done this with a T-18 I rebuilt, but caught it on the bench test before reinstalling. There is also a possibility that the shift rail is worn, damaged or assembled incorrectly and it is allowing the rail to over-travel thus allowing the pivot or shifter stub to hop out of the groove and float around in no-mans land. I've personally experienced a Getrag 360 do that in 5th gear and it's a bit of a riot hunting around trying to find the groove again as the engine lugs down. The fix for that was a new top cover because a shift rail bore was cracked.

However, if the transmission is legitimately locking up solid and killing the engine only when reverse is selected, that sounds very suspect. Could be that the reverse spur gear is installed wrong and binding on a casting web/boss in the trans, or possibly a piece of trash is stuck in the reverse pocket.... Not an easy explanation for that scenario.
 
City
San Marcos
State
CA
#5
Thanks Fummins...! The engine runs with the clutch down, but we cannot get it out of gear (assume it's reverse). The shifter just goes left-right but nowhere else, across the H I believe. I was wondering if there's a way to get it unlocked without having to go back to the mechanic. Is there a way to take the shifter boot off and get at the linkages and move them around? Is there a fork that might break? (The last mechanic said he had to replace something in the linkages). Sounds like there are many things that could be causing the problem, and you really have to know the box to be able to figure it out. My guess is that the original rebuilder didn't get it right and the latest shop didn't know either. If anybody is reading this in the San Diego area and knows someone who knows their stuff I'd really like to hear from them.
Thanks guys!
Tom
 

spankrjs

Scrambler Junkie
LIFETIME
CJ-8.com Member
SOA Member
City
Biloxi
State
MS
#6
If it is a stock Jeep CJ four speed, and has a straight shifter, it is a T176. The top cover of this transmission contains all the shifter rails. Over time/miles, the two sliding arms that hold the shift lever get wear, and can cause the shifter to lock up. To fix, buy a complete/used top cover off ebay or similar.

For now, pull off the shifter boots and floor cover off. Remove the lower transmission shifter boot. Press down, and twist, on the shifter retaining part. It is spring loaded. Anyway, get the shifter out, then manipulate the shifter parts with a small pry bar. You should be able to get it back into neutral. After this, reinstall the shifter and you should be able to drive. BUT, if you shift into reverse again, it will probably lock up.

I had the same problem on my red Scrambler a long time ago. This shifter felt really sloppy, and eventually got hung up. Pulled it apart, pry bar, back in action.

DO NOT BUY MADE IN CHINA CROWN/OMIX ADA T176 SHIFTER PARTS. THEY SUCK AND WILL NOT WORK. Try to find good/used OEM top cover assembly.
 
City
San Marcos
State
CA
#7
Thanks spankrjs! Nice detailed answer! Do we need to replace all the components or is there one "key" part? Or perhaps it's all-or-nothing?
Thanks again!
Tom
 

spankrjs

Scrambler Junkie
LIFETIME
CJ-8.com Member
SOA Member
City
Biloxi
State
MS
#8
Thanks spankrjs! Nice detailed answer! Do we need to replace all the components or is there one "key" part? Or perhaps it's all-or-nothing?
Thanks again!
Tom
Verify this is your problem first.

If it is, the rails inside the cover are usually OK. There are two parts that go on to rails that hold the bottom of the actual shifter rod. They will wear oblong over time and cause incomplete shift rail engagement, causing the transmission to lock up. This happened on my red Scrambler. I purchased Crown parts, they would not work correctly. I bought a complete, used top cover off of eBay, that was in excellent shape. I installed it, worked perfect.
 

walkerhoundvm

Just trying to stay upright
LIFETIME
CJ-8.com Member
City
Cave Creek
State
AZ
#14
Never had any experience inside a transmission, but the T176 was as easy as it gets. Affordable rebuild kit and some pretty accessible tools - some as cheap as hardware store pvc piping.
 

xatu40

CJ-8 Member
CJ-8.com Member
City
DeBary
State
FL
#15
Thanks spankrjs! Nice detailed answer! Do we need to replace all the components or is there one "key" part? Or perhaps it's all-or-nothing?
Thanks again!
Tom
Just wait, you haven't seen the good stuff yet. Nice detailed answers are his specialty. :)
 
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