Bucking / surging when starting from a dead stop.....clutch?

[whiteboyslo]

I have what I THINK is a clutch issue, but I wanted to run it by you guys.

When taking off from a dead stop, the truck is giving me a bucking/surging sensation. It's more pronounced in reverse or if I have a load in the back (like a couple of sportbikes), and especially bad if I try to take off in 2nd (not that I regularly do that. Just trying to diagnose). I can mask it a bit by giving it more revs and slipping the clutch a bit, but obviously that isn't ideal. It shifts fine, goes into gear just fine, and doesn't slip at all. It does have a new slave cylinder (from O'Reilly) because the last one developed a bit of a leak, but the bucking has been around since before that. No leaks anywhere that I can tell. Miles on the truck are low, but I know the previous owners used it to tow horse trailers and boats, so who knows?

Is this a clutch problem, or should I be looking elsewhere? If I am looking at a new clutch, I think I'd join the masses and go for a SMF conversion. Bit confused there, too. Do I have 11" or 12"? Can I upgrade from 11" to 12"? Should I? What parts are needed? I know LUK is the preferred brand, but I see several options from places like South Bend Clutch. I just need a basic clutch since the truck barely gets worked and isn't putting out a TON more power than stock, but I do want quality. Recommendations?

Only problem is that a clutch job would likely take me the better part of the weekend, and jobs like that are frowned upon by my HOA, so I'd likely have to get a shop to do it (ugh). Anyone know a good shop in SoCal?

Mike

 

[gdhillon]

Mine bucks/tries to die when I start in second to. I thought that its normal for the truck to do that specially with added weight, but I could be wrong.

 

[smokinpipes]

Quick question to aid in diagnosis, you say revving it a little bit more takes the edge off; so you slip the clutch a bit more..
What happens if you just idle, and say put into a low gear (1st or second) and slowly let the clutch out.. does feel like it is grabbing and releasing? or does it feel like the motor is sputtering?

If it feels like there is a grab-release from the clutch causing the 'bucking" of the whole truck when taking off, your pressure plate is bad. (It will almost remind you of a warped brake rotor in time with the engine) (a.k.a. new clutch time)... if it is your engine surging, bucking, etc., it's, well, not drive train related.

I had an 84 with these symptoms, some days it felt like I was taking off from "rumble speed bumps" ... heck even the change in the ashtray clinked around a bit lol... I figured I would just do a complete clutch job, bought a new flywheel, and entire clutch assembly. never put it on though, ended up throwing a connecting rod. Still have the parts in the basement come to think of it.

 

[whiteboyslo]

Quick question to aid in diagnosis, you say revving it a little bit more takes the edge off; so you slip the clutch a bit more..
What happens if you just idle, and say put into a low gear (1st or second) and slowly let the clutch out.. does feel like it is grabbing and releasing? or does it feel like the motor is sputtering?

I'll try it at lunch today and report back. My guess would be the former. Knock on wood, the truck runs GREAT. Assuming it is the pressure plate, I'd assume that it'd be a stupid thing to only have that replaced rather than the entire clutch while someone is in there, correct?

Mike

 

[smokinpipes]

I'll try it at lunch today and report back. My guess would be the former. Knock on wood, the truck runs GREAT. Assuming it is the pressure plate, I'd assume that it'd be a stupid thing to only have that replaced rather than the entire clutch while someone is in there, correct?

Mike

Yeah pretty much. It entails the exact same amount of work to not change the clutch disc as it has to come out to remove the pressure plate, and so does the throwout bearing, and it is an extra 10 seconds to pull and replace the pilot bearing as well. A clutch kit from say Oreillys or autozone should have one for (depending on your existing clutch size) ~$110 for the 11" to ~$180 for the 12" clutch. (without the dual-mass flywheel)

 

[laserjock]

I would guess a weak pressure plate from what you have posted. The spring fingers get weak and the "bucking" is the pressure plate diaphram trying to "decide" if it is in or out and not just holding tight to the slave. The increased revs provide more slipage and some centripetal force increasing the effective spring pressure. I have seen Centerforce clutches which are weighted to give more spring pressure at high RPM's engage engough with the pedal in to make the truck lunge.

 

[whiteboyslo]

Thanks for all the responses, guys. Took it out for a bit of a jaunt at lunch. Of course, it behaved perfectly normal, which is another characteristic I forgot to mention. The problem seems to be intermittent, and I haven't really been able to draw any conclusions as to when or why it starts to act up. For reference, I let it idle into movement going both forward and backwards at lunch. No hesitation, no no jerking, nothing.

But it sounds like at least one clutch component is on its way out or at least needs attention, which is what I was figuring. Can anyone help me out re: the 11" vs 12" and SMF vs DMF questions I had?

Mike

 

[laserjock]

Might want to check your rear main seal. I had a gasser that leaked from the rear main when it got hot at first and caused a "slip-stick" condition that is pretty similar to what you are talking about. As it got older and the leak rate increased, the problem got worse. Might add temp and drive time to your list of things you are tracking anyway for your troubleshooting matrix. Did I just say that???

 

[whiteboyslo]

Might want to check your rear main seal. I had a gasser that leaked from the rear main when it got hot at first and caused a "slip-stick" condition that is pretty similar to what you are talking about. As it got older and the leak rate increased, the problem got worse. Might add temp and drive time to your list of things you are tracking anyway for your troubleshooting matrix. Did I just say that???

I've never seen a leak or puddle (oil at least) under the truck, but I'll take a look. Thanks! I'm assuming a quick glance with the inspection plate off will tell me everything I need to know, yes?

Mike

 

[laserjock]

I would think so. Just need to see if there's oil on things there shouldn't be. Would also be a good time to check that the slave is traveling correctly. Maybe bleed it? It's been a really long time since I did one so maybe someone else will pipe up.

 

[smokinpipes]

Thanks for all the responses, guys. Took it out for a bit of a jaunt at lunch. Of course, it behaved perfectly normal, which is another characteristic I forgot to mention. The problem seems to be intermittent, and I haven't really been able to draw any conclusions as to when or why it starts to act up. For reference, I let it idle into movement going both forward and backwards at lunch. No hesitation, no no jerking, nothing.

Mike

On my '84 ... I noticed the same symptoms; it mostly always shuddered; some days, it was REALLY bad, other days it was there, but not super pronounced.
I wish I could be your one-stop shop for answers on the SM vs. the dual mass... but I only have my experience with the one manual truck.

I was just happy as all get out when I had the 11" clutch and not the 12". lol At the time, it was nearly a 150 dollar difference between the two.

---EDIT---
The 11" vs. 12" is the 12" clutch has a little more surface area to grab with, and will provide more grip and the ability to handle more torque. However with my 11" clutch I was able to stall the truck out right, and I didn't need the additional clutch size. Granted I had a granny gear to aid in heavy take offs. So if you are like me, and use your truck, but not all day everyday; and you aren't trying to haul a 15k trailer up hill, shifting all the time, etc., I think you'll be fine with a simple parts store clutch.

As it turns out, my '84 had a single mass flywheel; so that is why I was a bit unsure of the difference between the two. When I checked out autozone's website, they had a single mass conversion kit for $700 and some change and it included the flywheel, and all the clutch hardware for your truck. LUK is very decent, however, I've not had bad luck with the 'Duralast' clutch setups either.

 

[whiteboyslo]

AZ's site is a little cryptic in their descriptions, but I THINK this is their kit to convert FROM DMF to SMF: http://www.autozone.com/autozone/pa...tu0cZ6o243?itemIdentifier=570707_448877_4121_

Reasonable price, but don't know the brand. The other option is the LUK setup for my truck. Looks like Carolina Clutch is a popular shop from what I've read. Price is about $200 more: http://carolinaclutch.com/ShowItem/108870.aspx

Don't mind spending the extra $$$ to not have to do the job again anytime soon. But I think the real challenge is to find a shop that'll a) do the work and b) either use the parts I specify or let me supply my own.

Mike

 

[whiteboyslo]

Would also be a good time to check that the slave is traveling correctly. Maybe bleed it? It's been a really long time since I did one so maybe someone else will pipe up.

Thought about that. Could be related, but not sure. Everything I've ever read about the slave says if you can get it to operate, it'll bleed itself over time. Like I said, the problem's been around since before it was replaced, but that doesn't necessarily mean anything....

Mike

 

[Kevin 007]

My 84 does it to. some days worse then others and if I increase the revs (which I normally never do) upon take-off; it calms it down a bit.. Its not getting worse and im not worried about it. When time permits, I will put a clutch in it. hopefully a ZF-5 at the same time.

 

[McGIDI]

just replaced my pressure plate and it doesnt do that anymore... i had the same problem