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1979 R20 Overheats/L43 Trans goes South

Old 03-31-2019, 12:52 PM
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1979 R20 Overheats/L43 Trans goes South


Driving up I35 & smelled something like burning plastic - temp started climbing toward max - pulled off and let her cool down - see upper hose in picture (will replace) - waited a bit and backed up to limp home & trans went out when I shifted into first - got a tow - no gears work tho shifting is fine (previously replaced shifter bushings, slave & master cylinder) - fluids good, engine runs fine; MTF fluid checked fine, no coolant leaks - tested thermostat, works fine. Any insights on causes and fixes welcome - would transmission going south spike temperature? Thanks,

Last edited by faber; 03-31-2019 at 01:08 PM.
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Old 04-01-2019, 02:11 PM
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Duplicate removed

Last edited by faber; 04-03-2019 at 08:18 AM.
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Old 04-01-2019, 03:11 PM
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Does your trans cooler run through the radiator. May have boiled the tranny fluid
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Old 04-03-2019, 08:20 AM
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Hi & thanks - AC Condenser is in front of radiator - not familiar w/ a trans cooler (?) tho i noted some aftermarket coolers on the web - And if tranny fluid is "boiled" whats the affect? Btw a friend asked me if I checked the 4WD gears to isolate drivetrain from clutch plate - I didn't check them - currently replacing the original radiator - will check 4WD gears operation after that.

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Old 04-03-2019, 09:32 AM
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Sorry I assumed you had a auto tranny, in my last post. Stupid me.... Spiked temp and tranny problem sounds like unrelated problems and replacing the radiator hopefully will fix one. Does it shift solidly into the gears with engine not running. Grind gears with engine running? First thought was the bushing you already replaced. Can you bump start it with 1st gear engaged and truck moves? Just some ideas
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Old 04-03-2019, 12:19 PM
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How's your clutch pedal feel? Is there any grinding when you go into forward or reverse gear? Has anyone confirmed the new slave is indeed operating when the clutch pedal is pressed?

Just trying to eliminate things to help dissect what's going on.
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Old 04-03-2019, 06:10 PM
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by the bloated fat ass coolant hose i am thinking your thermostat is stuck closed, yes i know you say you tested it or you have blockage elsewhere

transmission- does it only have free play at the pedal? one of the two clips that hold the throw out bearing on may have come off or your 40 year old pivot arm for the throw out bearing broke. Some L43 had cast and some had pressed arms
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Old 04-04-2019, 06:38 AM
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Originally Posted by Lons81 View Post
Sorry I assumed you had a auto tranny, in my last post. Stupid me.... Spiked temp and tranny problem sounds like unrelated problems and replacing the radiator hopefully will fix one. Does it shift solidly into the gears with engine not running. Grind gears with engine running? First thought was the bushing you already replaced. Can you bump start it with 1st gear engaged and truck moves? Just some ideas
Shifts solidly in 2WD - will check 4WD once rad in but so far gears don't engage.
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Old 04-04-2019, 06:46 AM
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Originally Posted by ToyOkie78 View Post
How's your clutch pedal feel? Is there any grinding when you go into forward or reverse gear? Has anyone confirmed the new slave is indeed operating when the clutch pedal is pressed?

Just trying to eliminate things to help dissect what's going on.
Clutch feels fine; no grinding at all - I confirmed slave operation and shifting while under the truck - had to helicoil the two thermostat bolt holes to reinstall thermostat & decided to remove rust/repaint shroud & crossmember - should have radiator installed this pm.
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Old 04-04-2019, 06:58 AM
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Originally Posted by dropzone View Post
by the bloated fat ass coolant hose i am thinking your thermostat is stuck closed, yes i know you say you tested it or you have blockage elsewhere

transmission- does it only have free play at the pedal? one of the two clips that hold the throw out bearing on may have come off or your 40 year old pivot arm for the throw out bearing broke. Some L43 had cast and some had pressed arms
Free play at pedal? Feels like the old normal clutch - Will look into throwout bearing/pivot arm as soon as time permits - Thanks all for the comments & questions -
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Old 04-04-2019, 07:22 AM
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I had a jeep commando once that somehow got the throwout bearing on the back side of the fork like has been suggested, good luck hopefully that's all that happened & let us know what you find

Last edited by ToyOkie78; 04-04-2019 at 03:37 PM. Reason: Spelling error
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Old 04-04-2019, 03:07 PM
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thanks,

I will thanks -
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Old 04-05-2019, 04:49 PM
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more...

So....installed new radiator & hoses - temp good, no issues - engaged clutch in 4WD. No joy... just not engaging...more to look into.

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Old 04-05-2019, 07:48 PM
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The new radiator, cap and new hoses look great!

I think if your old upper radiator hose was that ballooned, the pressure in the system was not being regulated properly by the old radiator cap and allowed the cooling system pressure to keep rising.

I am pretty darn sure the overheating issue and transmission issue are not related.

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Old 04-06-2019, 12:31 PM
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Thanks & agree - got an experienced buddy coming over to look and advise -
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Old 04-12-2019, 03:01 PM
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Update -


Ok...pretend mechanic here...this am I adjusted the slave cylinder clutch release fork/cylinder pushrod and drove off....all gears worked but some engine revving when accelerator is pressed hard - think I screwed up adjustments when installing new slave last Sep - hope I haven't damaged flywheel(?)...so tried different adjustments to mitigate the revving...checked pedal freeplay etc, bled system, and adjusted per pic but unable to pull/move the fork as directed in enclosed pic so I measured the 1/8" pushrod sperical seat separation from fork by pushing the release cylinder in 1/8". Plan to adjust to match old cylinder settings (from pics I took) in the am - Thanks for any insights -

Last edited by faber; 04-12-2019 at 03:03 PM.
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Old 04-13-2019, 05:08 PM
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Update2: Clutch worn out - time to learn how to replace the clutch. (-*
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Old 04-13-2019, 07:09 PM
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There's some pretty good YouTube videos & it's really pretty easy to do, there's couple things I'd suggest.

If your rear main seal leaks even the smallest amount replace it while you're already in there, also easy to replace & It's a cheap part & you'll be glad you did. 2nd there is a good chance your flywheel could either use resurfacing or replaced, you can get a brand new luk flywheel off ebay for $50. Get a good quality clutch kit that comes with a new pilot bearing & you'll be good to go.

I bought the Marlin 1,600lb non ceramic kit for my pickup & when I replace the L45 with the Marlin L52HD I'll be doing all the same.
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Old 04-14-2019, 03:37 AM
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Re:

Originally Posted by ToyOkie78 View Post
There's some pretty good YouTube videos & it's really pretty easy to do, there's couple things I'd suggest.

If your rear main seal leaks even the smallest amount replace it while you're already in there, also easy to replace & It's a cheap part & you'll be glad you did. 2nd there is a good chance your flywheel could either use resurfacing or replaced, you can get a brand new luk flywheel off ebay for $50. Get a good quality clutch kit that comes with a new pilot bearing & you'll be good to go.

I bought the Marlin 1,600lb non ceramic kit for my pickup & when I replace the L45 with the Marlin L52HD I'll be doing all the same.
Thanks for your recommendations! Thinking of picking up that $99 harbor freight trans jack (450lbs/23 extended).
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Old 04-14-2019, 06:32 AM
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Originally Posted by faber View Post
Thanks for your recommendations! Thinking of picking up that $99 harbor freight trans jack (450lbs/23 extended).
I have their regular steel floor jack but an actual trans jack would be nice. The trans alone isn't heavy at all, with the T-case attached that might be a different story

Last edited by ToyOkie78; 04-14-2019 at 06:36 AM.
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