Detroit 671 Clutch Update

My buddy has a sixties 4104 Greyhound Bus RV with a 671 Detroit and Spicer 4 speed tranny with a single disk non braking push type clutch. He has had problem for years that gears had to grind bad to put in tranny gear so he just replaced:

Clutch disc and pressure plate with 6 adjustable fingers,,, New Throw out and Pilot Bearings, both fit and work correct,,,,,,,Disk is on right direction and hub fits n slides sweet and smooth on input shaft,,,,,,,,Flywheel turned/machined down smooth,,,,,,,,,,The two side bushings in bell housing (where big bell housing arm pivots when pedal is depressed) are new and tight,,,,,,,Currently the fingers are adjusted so there’s like 1/8 inch between throw out bearing when at rest to the fingers (so throw out don’t turn all the time DUH) ,,,,,,,clutch linkage adjustment set tight so as soon as pedal starts down the throw out tightens up against the fingers,,,,,

BUT WHEN PEDAL IS ALL WAY TO THE FLOOR HE ONLY GETS LIKE ½ INCH OF THROW OUT TRAVEL (1/2 inch of throw out depressing fingers to disengage clutch) Id like to see it move maybe ¾ to 1 inch for more spring depression???

If started in gear with pedal depressed the bus dont move, it releases enough for that, but still grinds bad if put in Neutral then try to get in gear


QUESTIONS: 1) Is ½ inch enough travel so fingers move far enough to disengage clutch?
2)How critical is the 6 fingers adjustment??? We screwed them way
out so theres only 1/8 inch between them and throw out at rest trying to maximize travel when pedal is depressed to push fingers deeper. They were way back from rebuild shop, but as set there
was like ¾ inch before throw out ever contacted them, so we adjusted them more outwards so they will be closer to throw out when its all the way back.

Our plan is to fix any slop or wear in clutch pedal and linkage especially rear where the cross direction pivot is TO TRY AND GET MORE THOW OUT AGAINST FINGERS TRAVEL WHEN CLUTCH PEDAL IS TO FLOOR

PS Today we checked and tightened and adjusted and took up about any and all slack we found in the linkage from pedal all way back to bell housing (after today I no longer think linkage or its wear is the problem) when the pedal starts to move the big bell housing lever arm moves buttttttttt I still don’t believe the throw out travels far enough back to front i.e dont push fingers deep/far enough

PS FINGER ADJUSTMENT: We have them adjusted outwards a bunch so they are closer to the throw out when its all the way back in full retracted rest position. If they are moved farther towards pressure plate all that does is we have to take out more rod linkage slack to bring the throw out up closer to the fingers again. HOWEVER they are alllllllll adjusted equal distance from throw out…….

WHY ISNT IT RELEASING ???? GEARS STILL GRIND BAD,,, PLEASE HELP BEFORE IT DRIVES ME TO DRINK AS I HAVENT ENOUGH HAIR TO PULL OUT LOL

John T

Lets go one thing at a time. First one is: Is this a counter bored flywheel? Also what is the model or who is the clutch manufacture? Let me do a little more thinking. J.

Sounds like you are on the right track looking at the linkage. Something is bent or sloppy enough that you are losing your travel. Could the pedal not be coming up high enough? I recall some real high pedal settings on old rigs to get enough throw in the clutch.

to start with the clutch fingers should be readjusted back to the original position the were in when the clutch was first installed.as the clutch wears the fingers will move rearward toward the throwout bearing and at the same time will reduce tension on the clutch disc.the linkage will have to br readjusted also.you should have 1/16 clearance between the bearing and the fingers.
you stated the cross shaft in the trans has new bushing which are new and snug.
is the throwout finger that is attached to that shaft loose or bent.there is usually a keyway and 1/2 moon key in that shaft.without that key the finger will spin on the shaft

I would be looking and makeing sure that all parts are original, like the throw out arm, linkage parts, clutch pedal. shorter throw out arm could be your problem.

The throw out arm (mounts on bell hsng cross shaft) has 2 washers that fit down into keyways in the cross shaft, its tighter then Dicks Hat Band no slip or loosey goosey whatsoever.

HOWEVER I like your fingers comment, they are wayyyyyyyyy out as from the rebuild shop,,,but thats to bring them back closer to where throw out is at full retracted rest position. If we take then back towards flywheel (as original) they get further from throw out, so then we tighten down side arm linkage slack adjuster star nut to bring throw out closer to fingers buttttttttttttt then the throw out has to come way out on the nose before its pushing the fingers butttttttttt we may try that tomorrow or Monday as it sure dont work as is lol

Thanks, John T

We have the clutch pedal set up as high as possbile (did that today) up into the cab floor already, any higher and it will push upward n out the floorboard lol

Thanks, John T

I have no idea,,,,,the flywheel is like a 2 piece (6 big inner bolts and several out further) and the new pilot fits good and the tranny input shaft fits good into pilot. Disc is correct and hub is also and on right way and fits nice on spline.

No idea who made the clutch, has no labels or name, a rebuild shop in Indianapolis furnished it, the tranny is a 4 speed spicer GM 4104 on a Greyhound Bus

Do different bored flywheels and different manufactured clutches adjust different or require differences to make them release???????? I feel theres not enough travel and/or fingers arent set right (still all are even distance to throw out)

Thanks, John T

Parts are original and 50 years old and worn of course, there are a TON of rods and throws and links and pivots etc etc.....we have taken up all the slack and adjustemtnts so the pedal depression immediately moves throw out regardless of any wear so it should release but the finger adjustment (may be critical)??????????? may not be right and/or insufficient travel but we got rid of any and all slack already today didnt help a bit.

Thanks John T

Hello John,
I am not sure what clutch you have on the bus. most clutches i do on tractors the clutch fingers should be parallel to the clutch disc when bolted on the flywheel. and then the throw out bearing is adjusted to the fingers. 1/2" travel is ok to release the clutch. if the tranny is grinding then there could be something else binding. possibly the pilot bearing or a aliment issue on the clutch shaft. is there dowels on the bellhousing ?
Good Luck Ed
abcrepairparts

WHAT IF YOU ADJUST IT SO THERE IS NO FREE PLAY,EVEN IF IT SLIPS WHEN YOU LET OUT THE CLUTCH,WOULD IT GO SMOOTHLY INTO GEAR THEN? DOES THE PEDAL TRAVEL COMPLETELY TO THE FLOOR?IS SOMETHING RESTRICTING PEDAL TRAVEL? IS THERE ANY ARM IN THE LINKAGE THAT COULD HAVE BEEN INADVERTANTLY REVERSED,CAUSING INSUFFICIENT LINKAGE TRAVEL AT THE THROW OUT BEARING? WHEN YOU PUT IT IN GEAR NOW,WITH THE BRAKE RELEASED,DOES THE BUS TRY TO MOVE FORWARD(OR BACKWARD IF IN REVERSE)WITH THE PEDAL ALL THE WAY ON THE FLOOR? IF IT DOES GRIND THE CLUTCH IS DRAGGING(NOT RELEASING).IF YOU START IT UP IN NEUTRAL,WITH THE CLUTCH DEPRESSED,DOES IT THEN GO INTO GEAR SMOOTHLY OR DOES IT GRIND,OR LURCH FORWARD AS IT GOES INTO GEAR? IF IT GRINDS THE CLUTCH IS DRAGGING.IF IT DOES NOT GRIND THOSE 2 CONDITIONS,THEN MAYBE THE TRANNY FLUID IS TOO LIGHT WEIGHT,OR NOT WAITING LONG ENOUGH TO PUT IT IN GEAR WITHOUT A CLUTCH BRAKE. IF ALL THIS IS OK AND THE CLUTCH IS DRAGGING, I WOULD SET THE FINGERS LIKE THE REBUIDER HAD THEM AND LOOK HARD AT THE LINKAGE.ALSO IS THE THROW OUT BEARING THE THE CORRECT LENGTH OR HEIGHT TO GET PROPER TRAVEL? HAS THE LINKAGE EVER BEEN MODIFIED,OR A PIVOT LINKAGE ARM REVERSED WHERE 1 SIDE IS FOR EXAMPLE 4 INCHES AND THE OTHER 5 INCHES? WHEN IT SHOULD BE OPPOSITE? I HOPE THIS HELPS,GOOD LUCK,MARK.

How heavy is the oil in the tranny? If it is too thin it will cause gear clash. If you can start it in gear, the clutch must be released.

Yes there are several dowels and a ton of 3/8 bolts alllllllll in place and all tight to hold that 400 pound tranny to the engine. Its NOT like its at any angle off the engine I can see or ever imagine

Your finger talk is like twopops advice and from the rebuild shop they were close to paralell but we moved them way out/back to get close to where throw out is in full rest retracted position

Tomorrow or Monday Im gonan set them back to paralell n try her

Thanks John T

WHAT IF YOU ADJUST IT SO THERE IS NO FREE PLAY,EVEN IF IT SLIPS WHEN YOU LET OUT THE CLUTCH,WOULD IT GO SMOOTHLY INTO GEAR THEN?

Havent tried that, I wanted to but my 81 year old (stubborn lol) buddy wouldnt do it


DOES THE PEDAL TRAVEL COMPLETELY TO THE FLOOR?

YEP we did some adjusting and grinding and making clearance today so its almost pushing up thru the floorboard so as to maximize how far it gets pushed down STILL GRINDS

IS SOMETHING RESTRICTING PEDAL TRAVEL? IS THERE ANY ARM IN THE LINKAGE THAT COULD HAVE BEEN INADVERTANTLY REVERSED,CAUSING INSUFFICIENT LINKAGE TRAVEL AT THE THROW OUT BEARING?

No restrictions, even tho theres wear in pins or bushings etc we have alllllllll set up tight n slack free, instant pedal moves, throw out starts its rearward journey to fingers. WE EVEN WELDED A BUSHING IN THROW OUT ARM LOWER DOWN TOWARDS WHERE CROSS SHAFT ENTERS BELL HOUSING TO GIVE US MORE TRAVEL Still she grinds

WHEN YOU PUT IT IN GEAR NOW,WITH THE BRAKE RELEASED,DOES THE BUS TRY TO MOVE FORWARD(OR BACKWARD IF IN REVERSE)WITH THE PEDAL ALL THE WAY ON THE FLOOR?

NO if started in gear with pedal depresed bus dont move buttttttttt hey it weighs tons remember, then if put in Neutral and clutched again to engage tranny she grindssssssssssss


IF IT DOES GRIND THE CLUTCH IS DRAGGINsG(NOT RELEASING).IF YOU START IT UP IN NEUTRAL,WITH THE CLUTCH DEPRESSED,DOES IT THEN GO INTO GEAR SMOOTHLY OR DOES IT GRIND,OR LURCH FORWARD AS IT GOES INTO GEAR?

It grinds to put it in first, butttttttttt once in first (keeps clutch down of course) he can then go to other gears and no more grinding buttttttttttt thats probably because the grinding has stopped the tranny shaft from spinning, it acted as the brake

IF IT GRINDS THE CLUTCH IS DRAGGING.IF IT DOES NOT GRIND THOSE 2 CONDITIONS,THEN MAYBE THE TRANNY FLUID IS TOO LIGHT WEIGHT,OR NOT WAITING LONG ENOUGH TO PUT IT IN GEAR WITHOUT A CLUTCH BRAKE.

has no clutch brake, never had one

IF ALL THIS IS OK AND THE CLUTCH IS DRAGGING, I WOULD SET THE FINGERS LIKE THE REBUIDER HAD THEM AND LOOK HARD AT THE LINKAGE.

Gonna re set fingers paralell with disk tomorrow or Monday as you and two pop and anothe poster suggested


ALSO IS THE THROW OUT BEARING THE THE CORRECT LENGTH OR HEIGHT TO GET PROPER TRAVEL?

No idea, it is new and looks like old one but he had the same problem BEFORE remember. Regardles of its thickness we adjust the slack so tis close to fingers regardless so i DONT see thAT AS THE PROBLEM

HAS THE LINKAGE EVER BEEN MODIFIED,OR A PIVOT LINKAGE ARM REVERSED WHERE 1 SIDE IS FOR EXAMPLE 4 INCHES AND THE OTHER 5 INCHES? WHEN IT SHOULD BE OPPOSITE?

NOT TO MY KNOWLEDGE OR CLOSE OBSERVATION, IT ALL LOOKS RIGHT AND THE ONLY WAY IT CAN BE


Thanks,,,,,, John T

Its released enough (started in gear) so it cant pull a 10 ton bus but still not released enough to prevent it spinning the tranny shaft

No idea what tranny oil he has but it looks n feels n smells n pours like any other big truck or bus tranny oil Ive ever seen. Its heavy NOT 10 weight I can tell you that but sure isnt like 90 or 140 rear end gear oil. I doubt he hAs the wronG oil in it, hes owned the bus for 15 years WITH NEVER ANY TRANNY PROBLEMS

John T

Why not disconnect clutch linkage except for the shaft connected to the bearing fork and use leverage to try to turn shaft beyond the previous range? If you get more travel without breaking anything, tie it in that position. Now "gentlemen start your engine", see if the input shaft is turning and try to put into gear.

One thing is to adjust those bolts on the arms of the pressure plate back to where they were originally from the rebuild shop.Thats not an adjustment you are supposed to mess with,its to adjust the arms so they release the pressure plate evenly.Once you get that done,look for whats wrong from there.One thing that happens a lot is the piece the throwout bearing rides on,or nose piece on the trans that the input shaft goes through wears out or breaks a lot of times.Then its hard or next to impossible to get one like you had.Then after you get one,the throwout bearing piece wont fit it,so that gets changed.It sounds like since you say with the bolts screwed in like they should be the throwout bearing piece is almost off of the nose piece when adjusted up like it should be.Something is probably wrong there.You need an old greyhound mechanic maybe to look at it if possible and see if he agrees.Maybe even see if a parts manual for that bus exists and what the part numbers for those parts are and their measurements.Then measure yours and see if you can figure it out.You might have to make a new nose piece and throwout bearing piece on a lathe to fix it right.There are different length fingers that push the throwout bearing.Somebody could have put the wrong one in because they couldnt find the right one and thought it would work.
Even if you have all of the slack out of the linkage does not mean some parts arent worn to where they arent pushing or pulling enough to move the throwout bearing far enough.You might have to shorten the linkage from just taking out the slack to pushing on the throwout bearing to see if you even can make it work.If you cant make it work then some parts are probably wrong,or bent,or just wont work any more.
Some things are poorly made from the first day.Lots of stuff is slapped together by people who dont care,and especially stuff that companies sell because they dont need it,is slapped together to get it to work long enough to get rid of it.Sometimes they use only what they have on hand and wont spend money on the right parts.Sometimes for old stuff its next to impossible to find the right parts since everything is on a computer now.Some people cant find it if the computer doesnt know they have it.You need to lock up the liquor and duct tape your head real good so you dont pull the few hairs you have and start looking a lot harder for whats wrong with this fine piece of equipment you have.With all the slack out and still grinding gears,thats my best guess,wrong parts to start with.That could be wrong,but its worth looking at.After that I guess it would be alright to hit the nearest bar.

Maybe the flywheel is worn out from the machining and normal wear and tear ,you may need to replace or add shims behind it so travel is restored to specs .

years and years ago,now that my head is in gear!
on the throwout fork attached to the cross shaft,are there 2 arms that come off of it that push the throwout bearing?

I repaired a truck once that the arms were curled back(bent)kinda in a circle.they should be straight with a ball kinda thing on the end.if they are not straight they wont push far enough

I once had the same problem with a car. I fought it for awhile and I finally discovered that the arm in the clutch linkage that was welded to the piviting cross shaft was torn loose where it was welded. It would work some but the crack would spread apart the farther you stepped on the clutch. When you released the clutch the crack would spring back together again. It probably happened from too many speed shifts. )

yeppers, them 2 arms look good and pushhhhhhhh the throw out forward (towards flywheel) as the big lever arm turns the cross shaft and the crosss chaft bushings were replaced

Thanks John T

I threw out a few ideas the other day and it seems like all of that has been covered many times over. Given all of the stuff you"ve tried with no success I"m going to go out on a limb and say, "The problem isn"t in the clutch". If it"s releasing, be it 1/16 of an inch or an inch then it"s released, that"s all it can do. Depending on the model of transmission it may have syncronizers. Whether that one does or not you"d have to call someone that knows more about them than me to find out. That said a syncronizers job is basically to help not necessarily stop the gears from spinning but help them mesh when/if they are turning. Since the gears usually have square cut faces/sides if the syncronizers are worn to the point they aren"t doing their job then the gears are going to grind no matter what you do to the clutch. The transmission in my "78 Jeep J10 got like this once. Like you said it ran find, shifted fine, etc, basically it had no problems beyond gringing gears on the shifts no matter what I did tp try to prevent it. I did a rebuild and replaced the syncronizers, which were worn, and it hasn"t ground a gear now in more than 10 years.

Below is a link to Spicers site. They can probably tell you anything you need to know about the transmission.
Spicer

Wear in pivots etc isn't gonna matter. If you don't have enough travel due to an arm or something not being right you're never gonna get enough travel. This sounds like something I would run into. It sure sounds like an arm or fork etc is incorrect.

I had this problem on a GMC truck and had to use a dial indicator to dial in the bell housing. Check it to see if it is centered to the crankshaft and then to see if it is parallel to the crank axis. I don't know if that is your problem or not but it cured my problem. I think most large truck manuals will explain how to do this.

Two more ?s Is the clutch a single disk or double disk(2 sets of disks)? How far does the clutch pedal come out with it in gear before the bus moves? Just off the floor half way or almost all the way out!!

Too bad you can"t get by a old bus graveyard and do some lookin" and measurin".

A lot of stuff may be different but you never know.

That"s all I had but I tell you what, I am pulling for you John T! Keep us posted, I can"t wait to hear the happy ending/solution!

I am not familier with buses but back in the day on trucks with the 671 and cummins motors, and the big transmissions of this vintage their were clutch brakes that stopped the input shaft when engaging the clutch, these were used with spicer clutches that were adjusted with a spanner in the clutch itself.

I could be all wet here but I was just thinking (and thinking gets me in trouble).

But, does this rig have air brakes? If so maybe there is an air operated brake on the transmission.

I have seen and used them on 10 speeds and I know you said this is a 4 speed but it is a heavy tranny by your comments and would need to be something to stay behind a 671.

The brake I am thinking of was a square plate with an air fitting in the middle. The air pushed a steel pin up against a gear and when the air pressure was up it would drag the tranny to a stop in a few seconds.

RT (definitely a 2 cents worth)

Have seen this 1 time before, are the clutch disk new or new relined ones, relined at times are thicker then new from factory. had a 58 chevy. gave me fits on a relined disk, ended up putting thin washers between flywheel and pressure plate to get enough clearance so it wouldn't grind gears, never did get it wore down enough to take them out. Don c

Years ago I replaced the clutch in a JD 350 dozer. Everything was to spec but when I put it together the clutch was out of adjustment, didn't work propertly. AFter three times pulling it out and replacing, discovered that the small pin that held the linkage to the clutch pedal was almost worn in two! Without taking it apart, you couldn't tell it. That introduced enough slop into the system to throw everything out of wack. Replace the pin and everything was perfect.

John T
Probably not much help, but here goes. Drove bus about 8 years, with some shop experience. Working from memory here,only drove one 4104. 4104 should be a rear engine, right? Does the engine sit crosswise, with an angle drive between clutch & trans? Does the trans sit kittywampus? Or does the engine sit inline, just backwards in the 4104? Thinking because of length, engine sits inline. 8V engine sits crosswise in 47xx models.
Is it an oil-bath clutch? Not sure on the 6 bangers, but 8V models had oil bath. They would rattle, bang, & shake the whole rig when first put in gear. Considered to be normal. Be sure the fast idle is off before trying to shift into gear. They had high speed diff gears, oil clutch allowed lots of slippage to get moving.
Guess I'm not much help after all. To really confuse things, if the engine sits crosswise, it spins backwards too.
Sorry for getting off track.
Willie

Yep its rear engine in line 671,,,,,,,,,sits crosswise,,,,,,,,,runs backwards,,,,,Spicer 4 speed tranny (in line right behind engine) output is at an angle with driveshaft up to rear end,,,,,,,,,NOT oil batt,,,,,,

So now given all that extra info, whys the dern thing grindddddddddd terrible???????????grrrrrrrrr lol

Thanks John T

Its a relined, I dont have the old one to compare but this rebuilt one sure dont look a bit thicker then what Id think is normal or necessary

Thanks John T

Check crankshaft endplay.

Theres no mechanical or air or any kind of tranny brake and it never had one. If it did I bet Id stop that tranny spinning lol


Thanks John T

I think I already posted its only a single clutch, sorry if I missed that. Starts to engage enough to pull bus at maybe mid pedal range. As posted we have the pedal adjustment as high as possible up against floor board bottom to get max travel.

Given this new info, whys it grind grrrrrrrrrrrrrrrrrrrrrrrr lol

Thanks John T

John T, Couldn't tell any difference with the thickness either but there was just enough to make a difference, I would try and get the spec. on new and relined one. Wouldn't surprise me a bit that the reline in thicker.. Don c

Clutch disc bent slightly?

Nope, looked for that, its STRAIGHT, sorry if I missed that in my earlier info

Thanks John T

After reading again what you said,even with wore pins and bushings its adjusted to where there is no slack.Alright that could be the problem.If they are the same size,and should be the least expensive part,buy a bunch of new pins and replace all of the worn ones and see if it works then.Many times I have done that on big trucks to fix a problem like that.That arm that pushes the throwout bearing with the 2 fingers can also be worn and cause you to loose travel.So Especially that pin where it hooks the linkage to that arm needs to have a new pin.If it gets better by replacing pins but still wont work,then see if you can get some new yokes the pins fit in and replace some of them.That might fix it.Even if you take all of the slack out of a linkage,you cant get all of it out,for some reason it wont pull or push something far enough to work sometimes.The only way to be sure you get that little extra is with new parts.Sounds like you are close and just need a little more travel and the pins might do it.

One other thing,and somebody else mentioned it.You might need to check the runout of the flywheel to the belhousing.I remember years ago cutting a bellhousing in the truck using a thick piece of metal bolted to the flywheel with a cutter from a lathe bolted to it.Cranked it with the starter and got it within specs.It was way out on a 318 Detroit.Finally fixed a problem like that the truck had for years.I think there is a Detroit Service manual that tells how to do it.We just made our own piece to bolt to the flywheel that held the cutter.Cur until it was skimming all the way around,put dial indicater on and it wast out enough to worry about any more,bolted trans back in.Might be another thing to think about.

ANOTHER THINGOES THE PEDAL ITSELF HAVE ENOUGH TRAVEL;DOES IT START TOO LOW TO FLOOR(OR NOT CLOSE ENOUGH TO DASH)?IN OTHER WORDS : IF IT STARTS IT'S TRAVEL TOO CLOSE TO FLOOR,THEN IT WON'T TRAVEL ENOUGH TO COMPLETELY RELEASE.BUT IT SOUNDS LIKE TO ME ,SINCE YOU SAID IT DOES NOT TRY TO MOVE ONCE IT IS IN GEAR, AND IT HAS NO BRAKE ,EITHER THE TRANNY FLUID IS TOO THIN,ENGINE IDLE RPM TOO HIGH,OR JUST NOT WAITING LONG ENOUGH TO PUT INTO GEAR AT A STOP.
KEEP POSTING: I WANT TO KNOW WHAT THE FIX IS!GOOD LUCK,MARK