Chevota Clutch Slipping (1 Viewer)

[NikP]

I have '75 with SBC and a stock Chevy low profile clutch setup. For the most part, it's worked just fine in normal driving over the last 20K Miles.

This year, I've started to do a bit more serious off-roading on steep slick rock (Moab, Farmington NM). I have an issue if I'm trying to feather the clutch and slowly start up a feature. I get to a point where I have RPM's in a decent range (just enough to now kill the engine) but my clutch slips and I go no where. No wheel, spin, engine running good RPM's. but the clutch just slips until I can smell it. I even have my foot totally off the pedal when this happens.

I've read a lot about the Chevota clutches on the forum and the all seem to focus on throw and getting the clutch to engage. I seem to have an issue where it just doesn't seem to have enough clamping force.

Looking for advice or thoughts.

I'm curious if I ought to get the Advance Adapters recommended Centerforce. I want to spend money with some feeling the it solves the problem.

 

[B y r o n]

When I dropped a 350 SBC in my FJ40 I had an issue of dropping the clutch and just smelling the burn of the clutch. I was running 33x12.5-15 tires. My original clutch install was a Mcleod. After contacting them they recommended the WorkHorse clutch which was actually double sprung for more grip. If you need more grip then look at a clutch with more spring pressure.

 

[pb4ugo]

1st i hope you were in low range. Make sure the throw out bearing is not in contact with the pressure plate springs when the clutch is released. I'd go thru Toyota's adjustment procedure, adjust pedal height, then pedal freeplay, then adjust the slave rod for freeplay. The return spring seats the piston in the back of the slave. Adjusting pedal freeplay is not when you feel resistance, its when the slave rod starts to move. My slave is on the drivers side, so I was able to check pedal free play by watching the slave initially move while pushing on the pedal with my hand. These adjustments insure full stroke from the master and the throw out bearing is not touching the pp. You should get more than 20k on a clutch disc.

 

[3_puppies]

@Downey

 

[archie73]

What tranny are you running? Toy or Chevy?

I’ve had good results with a stock Chevy clutch and toyota master/slave. I have a Chevy transmission tho.

 

[NikP]

1st i hope you were in low range. Make sure the throw out bearing is not in contact with the pressure plate springs when the clutch is released. I'd go thru Toyota's adjustment procedure

Yes, in low range. I've been through the adjustment procedure a couple of times just to validate. The throw out bearing has no contact with the diaphragm and has a couple mm space.

What tranny are you running? Toy or Chevy?

Toyota 4 speed and 33x12.50x15 tires.


I really think this is an issue of pressure and not any issue with hydraulics and slave/master travel. I can shift just fine and for the most part it gets me down the road. I just can't crawl worth crap.

they recommended the WorkHorse clutch

I think that's probably my answer since it seems to be a pressure or contact surface issue. You wouldn't happen to have part numbers or specifics on this would you?

 

[lcwizard]

when you replace it, make sure to use the 12" clutch rather than the 11 or 10.5. A stock 12 2400lb holds better than a 4500lb 10.5 McCleod
with a much easier pedal pressure, hence longer slave life. If you compare the plates side by side all the surface area added to a 12" is on the outer circumference.
The ID of the friction area is the same on both. the 12 adds an 1 1/2" material on the outer ring compared to 10.5

 

[NikP]

make sure to use the 12" clutch

Do you have part numbers of this configuration?

I've read most of the clutch threads 15 years ago when I put mine together and this topic is so confusing without proven configurations and part numbers. (many say stock configurations work, many say you need Downey or AA configurations). Downey is no longer selling his so what's a guy to believe? I believed the stock chevy clutch crowd last time.

Is the 12-inch configuration just the disc or does that include the pressure plate? I understand more surface area on the disc helps with grip but there is also a point where the pressure plate torque capacity is the real determining factor. I want to get the best of both figured out before I start spending money.

 

[B y r o n]

When I dropped the 350 SBC in my FJ-40 it was back in the mid 80's. McLeod at that time was still build the 3 arm pressure plates like the factory Toyota pressure plates. My first setup would slip if I dumped the clutch on dry ground with 33x12.5-15's. I contacted McLeod and talked to there support staff. It was suggested that I try the WorkHorse pressure plate which was supposedly double sprung for twice the grip. I already had a 12" clutch disc with 10 spline count which worked with the factory 3 speed.

In looking at their website it appears that McLeod no longer builds the 3 arm pressure plates or the WorkHorse pressure plate. Technology has improved since the 80's and it looks like their Street Pro line is what you want to look at. It's a diaphragm pressure plate and disc combination that they say will handle up to 400 HP. Here is the part number and spec's:

75128

Street Pro: Kit:1959-90 GM 12" x 1-1/8x10​

1

$295.00

If you are unsure then I would suggest you contact their customer support.

 

[Pierps]

I have 9/75, a sbc, and a Toyota 4-speed. I used this clutch:

RAM Clutches 88762 RAM Premium Replacement Clutch Kits | Summit Racing

Free Shipping - RAM Premium Replacement Clutch Kits with qualifying orders of $109. Shop Clutch Kits at Summit Racing.

www.summitracing.com

I used a kit from specter off road for the master and slave. Item #330-918. Their site appears to be down or I'd send a link.

It's for the Chevy swap. If I recall correctly, it uses an early model master cylinder and a later model slave. Or maybe the other way around. It's been awhile.

Everything works just fine!

Hope that's helpful.

 

[Pierps]

Here's a thread I posted a while back in case it helps.

Using Earlier Clutch master for more throw/travel

Hi All, I have a small block chevy 350, a chevy bellhousing, and Advance Adapters ranger overdrive unit which also acts as an adapter to the stock toyota 4 speed. i'm using the OEM clutch master and slave for my 9/75 US-spec fj40. I'm 75% through a restoration (ahem, "restomod" for the...

forum.ih8mud.com

 

[NikP]

@Pierps I appreciate the links. I've studied the hydraulics and I know with a small bore slave and a larger bare master you can get a bit more travel. That's not my problem as I can shift just fine.

Since I'm analytic guy, I want to be able to understand the torque ratings of the clutches people are recommending. Without that, I'm not sure if I'm fixing my issue. Like I said earlier, mine does just fine going down the road with a stock-type low profile pressure plate. It's worked for me for 15 years.

But the first time I placed my FJ40 on a slick-rock trail at Moab and tried to ease up over an obstacle, I sat there with the clutch slipping. Most people's installations will never encounter the Moab scenario therefore their solution "works" just like fine.

I'm going to call McCleod this week and ask about torque specs. The problem is most parts stores don't have a clue on this spec. Since I'm running a standard pressure plate it may only hold 275ft. lbs. of torque but I don't really know.

The Centerforce CF265473S indicates 479 ft. lbs. The McCleod Street Pro site says theirs is good up to 400HP but that doesn't help me compare the two for clamping performance.

The other thing I'm planning to do after studying is to replace my flywheel with a Nodular Iron Flywheel for better grip and less glazing. Billet is likely overkill.

 

[pb4ugo]

I had the same problem as bryon with a 3 finger in the 80's. I was running a 450+hp sbc. I went to a local clutch mfg and picked up a ceramic disc with individual pads on the disc. It was grippy using the same pp. I used the same disc and pp with a bbc. Many yrs later I put in an organic/ceramic disc with pads with good results. I don't recall its diameter. Later i put in a low profile pp along with an sm420 and used the same disc. That was probably 15yrs ago and still works great. The 40 is mostly a trail rig any more.

 

[NikP]

Updating information for future reference:

Ram Cutches responded to email questions on clamping force and recommended a different model (go figure). They recommend model 92762 which has roughly 2800 pounds clamp force. The 88762 has roughly 2300 pounds of clamp.


McLeod Racing recommended the their Super Street Pro Series. 2400 pounds of clamp and about 550 ft.lbs. torque. The 11 inch kit part number looks like 75224. After an email correspondence they say the following: The 75224 is not considered a low-profile pressure plate. It has an operating height from the flywheel surface to the fingers of 2.100.” We can piece together the parts you need as individual components that would have a low finger height pressure plate, 1.690”

P/P – 361928 (This pressure plate is unlisted on most websites.)
Disc – 260541

Centerforce look like in has a higher clamp option. The Advanced Adapter recommends a CF165473S pressure plate and in looks like there's a kit that has a bit more clamping pressure. Their email response:
That DF735473S should work with your application.
The main difference with these covers is the overall height.
This pressure plate is considered a shallow mount cover.

 

[pb4ugo]

You say you were getting into more serious wheeling, were you slipping the clutch a lot? This may be why the clutch started slipping. You may have glazed or over heated the disc, flywheel and pp. A stronger pp will create a stiffer clutch pedal. You may end up with the same results later down the road/trail. You might ask about different materials on the clutch disc. It may be harder to slip to start, but wont slip once your foot is off the clutch. If your running the stk trans/tcase and diff gears, you may want to consider some form of lower gearing through out the driveline if your going to dive into harder trails. 28- 29:1 in 1st gear low range is not really crawling. I ran a sbc with stk gears for many many yrs and struggled at 1st and eventually I got better with it and tried to limit my use of the clutch if I could. Then I went to 4.88's in the diffs, 34:1 was noticeably better for someone who was running stk gearing for 10 yrs or more. In hind sight the reduction was minimal. Once I got serious and installed a SM420 and lower tcase gearing things became a lot easier, like butter. You might consider a different trans like a H41 trans or something else with better gearing.

 

[NikP]

You might consider a different trans

I agree. The current ratios are not too conducive to serious off-roading. I'm already on the hunt for an Orion so I can get 4:1 at the transfer case in low-gear. I want to make sure when I do all this work, I have the clutch issues all sorted out as well.

 

[NikP]

were you slipping the clutch a lot

No not by most standards. I eased up to the first obstacle and idled the front wheels up until the back wheel hit the ledge then I raised my RPMS slightly and engaged the clutch. No go, just slipping. If I hit the incline moving with some momentum and have enough RPM to carry me, I can go up inclines with no slipping. It's that tight engagement window where it either slips or it catches. That's why I think it's a clamping force issue and not a glazing issue. (I might be wrong).