?-clutch slipping-2H with clutch boost/5-speed

[LCDiesel60]

When we purchased the rig no clutch problems.
Now that we are nearing end of 15 year restoration and doing shakedown test drives-have had slipping issues to the point of being towed home-even after field adjusting to minimum.

The clutch is such a simple system-I’ve done many clutch replacements over the past 40 plus years on other rigs…studied the FM many times-and even pulled the transmission/clutch system awhile back and could find nothing…

Details:
1-LC was upgraded with a turbo; currently about 11 psi boost.
2-during restoration: removed-inspected clutch master boost; looked excellent, very clean. Installed new clutch slave cylinder and bled-bled again recently just in case and today; clean, no air in fluid.
3-when clutch installed added new disc and pressure plate: fly wheel looked great but still scuffed it up with sand paper—all clean no oil leaks, previously replaced rear seal.
4-pilot bearing and clutch throw out bearing replaced.

Setting:
Test drove up and down hills for 4 hours and no issues. Another day for an hour-fine. Another day one hill, slower and slipped some…another day just coming up the driveway it slipped.
Checked adjustment per book and backed off on setting to more slacking in piston-worked fine till second time climbing hill-then began slipping ( was setting fuel and boost: boost 8psi at that time).
So-pulled transmission and clutch assembly having doubts I put the clutch plate in backwards-was in exactly per FM with protrusion to front. Reassembled and test drove a few times on hills-no issues: relief but no idea why…test drove same hills yesterday to finish using fuel/boost and it started slipping-1/2 hour drive time. Checked adjustment-backed off more-continued to slip-getting worse till driveway: so used super duty to pull it up to shop.

I’ve a new clutch disc coming from SOR-been wondering if whomever sold us the new pressure plat sold is an FJ version-wondering if so if insufficient hard pressure for diesel torque?

I still have original pressure plate; cleaned it up and looking at using that with new clutch disc…

BUT, before reassembly I would really like some fresh ideas to look into so that this really is the last time….being retired and older this is getting pretty hard to do…

Thankyou for your inputs!!

 

[duncanrm]

I have seen this on the vacuum assisted clutch masters when there's a vaccum booster fault or there is insufficient clearance on the push rod into the master cylinder from the booster. The FSM describes the adjustment process for the booster to clutch master rod. The clutch boosters are available brand new (at least Australia they are eg: EBay AU).

Confirmation could be had this is the issue by ensuring the slave cylinder to clutch fork rod has a tiny bit of play.. and then observing that there's none when the fault occurs (indicating there is hydraulic pressure without any foot on the clutch pedal).

The adjustment nut shown below on the booster output rod (into the master) provides for adjustment. I have screenshotted the FSM page for the booster to master adjustment below and extracted the relevant pages of the manual here -> HJ60 Clutch Booster - manual pages from 36262E

You won't have the SST but a set of calipers (used in depth mode) maybe? Or you could even just shim out the master as a diagnostic step.

From the Chassis/Body manual.. (36262E - Repair Manual for Chassis and Body)

 

[LCDiesel60]

Duncan-good to hear from you again!
Wow-your LC knowledge is sure broad and detailed!

I’ve read through all your notes and posting-that was a ‘full meal’—I think I understand most of it…yesterday I actually studied the FM on the clutch boost and performed the tests and inspected the vacuum line one way valve and all seemed good.

Before seeing your post I had thought back to the prior installations and the CB problem I had with installing the slave cylinder—the rod firmed up against the clutch fork about 3/16” before I could get the 2-bolts in—I didn’t think much of it at the time thinking it was hydraulic pressure that would balance out with use or when I adjusted the rod on the clutch pedal.

Your photo caught my attention-I don’t recall that adjustment during clutch master install-but I may not have noticed or forgot—

Your comment about having tension on slave cylinder rod matches my observation..but obviously I didn’t understand the concern it indicated.
prior to your comments I had considered pulling the slave rod and grinding down the length about 3/16” as noted above so there wasn’t that preload on the fork…..

The manual instructions regarding the booster rod setup before install confused me—there is no depth specifications since they appear to be built into the SST—as such I feel like I would do all that RR work only guessing as to adjustment changes…..plus bleeding the system..ugh.

Do you think modifying the slave rod would accomplish the same affect-removing pressure on the clutch fork?

I’ve a few days or more before new clutch disc arrives-have all removed, cleaned up most: hand sanded friction surfaces for a fresh surface-no heat checking.

 

[duncanrm]

Your clutch rod should have a threaded adjustment.. When you installed the new clutch slave did you re-use your old rod or install a new one? I really like to feel the clutch fork have just a tiny bit of play in it when there's no clutch activation and I adjust the threaded rod to achieve this. If you dont have a threaded rod then grinding may be an option but I'm no expert in this field.

Once you have a bit of play in the fork you'll be able to verify if the booster is causing issues next time your clutch slips - you'd want to see the same amount of play evident to indicate no hydraulic pressure is being applied.

The SST doesn't have a built in measurement.. its merely a glorified depth caliper to verify the rod is poking out JUST enough to touch the head of the master cylinder piston.

 

[LCDiesel60]

Your clutch rod should have a threaded adjustment.. When you installed the new clutch slave did you re-use your old rod or install a new one? I really like to feel the clutch fork have just a tiny bit of play in it when there's no clutch activation and I adjust the threaded rod to achieve this. If you dont have a threaded rod then grinding may be an option but I'm no expert in this field.

Once you have a bit of play in the fork you'll be able to verify if the booster is causing issues next time your clutch slips - you'd want to see the same amount of play evident to indicate no hydraulic pressure is being applied.

The SST doesn't have a built in measurement.. its merely a glorified depth caliper to verify the rod is poking out JUST enough to touch the head of the master cylinder piston.

The new slave cylinder is just an aluminum rod with no adjustment: I don’t recall the old one-will look to see if I have it still…..I agree on your comment regarding just slight play-otherwise pressure wears out the throw out bearing early too.
Our family had a ford bronco II with a hydraulic clutch and that slave cylinder had no adjustment so didn’t think anything of this LC unit not having any-it pains me dearly (work and $$) when I make a mistake …even when I’m trying so hard to do excellent work each step of the way—but, it’s life as much as I try….

If I don’t find the old slave cylinder then with slowly grind with multiple test fits what I have to get the results needed. May be end of week-first of next week before disc arrives for install and the modification can be completed.

Duncan-glad to hear your humility-but, I think we can all agree your as close as they come to ‘Senior Skilled LC Guru’ as they come.

Thankyou greatly for your detailed info that cleared the fog in my head-showed what concerned me was a greater issue so I didn’t ignore it again!

…it’s so ‘fun’ putting the trans-transfer case by myself-done it twice before, so hopefully easier/smarter this time.

Take care

 

[LCDiesel60]

Hello Duncan-Easter Sunday for you-likely evening or later….

Saturday afternoon here and have finished stalling the new clutch disc from SOR-

Started up and shifted-total clutch slip, backed off pedal/piston adjustment: crawled under and slave cylinder rod that was loose was now tight…backed off the slave rod adjustment-still clutch slipping:

Took slave rod out and started in low range reverse-very solid clutch grab even against brakes.

Shortened slave rod and inserted: started up and able to shift with no grinding of gears and no noticeable slippage.

Doesn’t feel right though as clutch release is close to floor-adjust somewhat as per book but seems to tighten slave cylinder into clutch fork tighter than we discussed.

Maybe I’m so used to it feeling like I needed almost the full leg stroke to release that this set up is uncomfortable,,,? But, on other manual transmissions I’ve drive close to the floor release was never correct ——

Seems like whenever I adjust the pedal/ piston it changes the slave rod tighter-so feels like a bounce back and forth and I don’t want to over adjust and ruin the new clutch disc.

Maybe I’m tired and need to look at it fresh Monday.

Any thoughts would be appreciated.

Take care

 

[duncanrm]

Hello Duncan-Easter Sunday for you-likely evening or later….

Saturday afternoon here and have finished stalling the new clutch disc from SOR-

Started up and shifted-total clutch slip, backed off pedal/piston adjustment: crawled under and slave cylinder rod that was loose was now tight…backed off the slave rod adjustment-still clutch slipping:

Took slave rod out and started in low range reverse-very solid clutch grab even against brakes.

Shortened slave rod and inserted: started up and able to shift with no grinding of gears and no noticeable slippage.

Doesn’t feel right though as clutch release is close to floor-adjust somewhat as per book but seems to tighten slave cylinder into clutch fork tighter than we discussed.

Maybe I’m so used to it feeling like I needed almost the full leg stroke to release that this set up is uncomfortable,,,? But, on other manual transmissions I’ve drive close to the floor release was never correct ——

Seems like whenever I adjust the pedal/ piston it changes the slave rod tighter-so feels like a bounce back and forth and I don’t want to over adjust and ruin the new clutch disc.

Maybe I’m tired and need to look at it fresh Monday.

Any thoughts would be appreciated.

Take care

Pull the clutch pedal forwards the drivers seat so it’s at a nice resting position and tie it up with a piece of rope.. gravity bleed the system and close it up before adjusting the clevis at the top of the clutch pedal to suit..

 

[LCDiesel60]

Pull the clutch pedal forwards the drivers seat so it’s at a nice resting position and tie it up with a piece of rope.. gravity bleed the system and close it up before adjusting the clevis at the top of the clutch pedal to suit..

Hi Duncan-interesting…trying to think through what this does differently than I have so far?—does holding the pedal up then slight drain prevent the bounce between the adjustment of pedal area and slave cylinder rod I told you about?

Will give it a try Monday afternoon after my errands.

 

[duncanrm]

Hi Duncan-interesting…trying to think through what this does differently than I have so far?—does holding the pedal up then slight drain prevent the bounce between the adjustment of pedal area and slave cylinder rod I told you about?

Holding the pedal up in the correct position with the clevis at the top of the pedal adjusted appropriately when bleeding ensures the full hydraulic volume is delivered when the pedal is pressed. I have found even with just gravity and a poorly adjusted clevis at the top of the pedal you end up with an insufficient stroke/volume being delivered and the clutch dis-engagement is only experienced at the end of the pedal travel.

 

[LCDiesel60]

Holding the pedal up in the correct position with the clevis at the top of the pedal adjusted appropriately ensures the full hydraulic volume is delivered when the pedal is pressed. I have found even with just gravity and a poorly adjusted clevis at the top of the pedal you end up with an insufficient stroke/volume being delivered and the clutch engagement is only experienced at the end of the pedal travel.

Duncan-thankyou!-clutch master cylinder ‘full volume’ at adjustment helped my mind to grasp this process.
Tomorrow I’ll be doing that.
Take care

 

[LCDiesel60]

Good morning Duncan,
Just finished performing the bleed and adjustment as discussed above-no fluid drained out of slave cylinder until I pushed back on clutch fork-closed it up and then large slack (over 1”) between clutch fork and rod.
Adjusted inside cab and went for test drive; clutch started slipping a bit on hill at 10psi so pulled over and adjusted-pedal now lower—didn’t notice any slipping this time on next bigger hill.

The pre I think about it the slave cylinder will always find its full position till it has pressure against it on clutch for-the nature of a fluid system that can’t utilize a check valve.

So, I think I see why Toyota had a fixed length rod-all adjusting in the pedal.

So I’ll extend the slave adjustable bolt rod closer to stock rod -bleed again as you noted above: then work more on the pedal adjustment-and as you noted your correct about small adjustments.

Will do all that plus test runs later this week—family in town for a few days: spend time with them then fine tune these adjustments, defaulting to less than book adjustment to avoid clutch slip.

Hopefully a few more test runs should wrap this up d as o I can do some 1/2 day trips in the Rocky Mountains nearby for final shakedown.

Dauncan-with all your amazing help on multiple issues the past couple months-I think we are about done..and a bit wiser for the ‘wear and tear’.

Thankyou Sir so very much!!

 

[LCDiesel60]

Just did a secondary bleed per your technique Duncan and while slave cylinder was retracted adjusted he push rod out about 1/4”-3/8” then readjusted pedal-made the pedal “feel” like it as in a better location.

I’ve done 2- test drives on hills full power since then and was GREAT with no slips-did one final adjust less than book setting to er’ on less clutch pressure-still shifts well.

So I believe we are finally finished —turbo pressure still 2-3 psi low so will adjust more otherwise time for some more serious test drives (longer/bigger hills and more drive time) to finish the shake down process-then we can stock the rig and do a ‘walk about’ through Idaho and Montana.

Duncan-thankyou again so much!!

 

[duncanrm]

Just did a secondary bleed per your technique Duncan and while slave cylinder was retracted adjusted he push rod out about 1/4”-3/8” then readjusted pedal-made the pedal “feel” like it as in a better location.

Super! Glad to hear its all sorted.

Bring on the Idaho and Montana road trip!