Pivot Bolt Depth

[PeterBiggerstaff]

This may be a really dumb question, but I have finally got the new Pivot bolt in the bellcrank (what a mission)..

How far do I do this up? do you do it up so that the bolt head is touching the top of the bellcrank, or do you leave room so the bellcrank doesn't wear the bolt head?

Currently I have done it up this far:
39909

[David T]

Tight enough so that there is no play but loose enough that it doesn't bind up. Be sure to clean and lubricate the pivot bolt and beam. If any of the rubber bushings are worn they should be replaced. Keep and extra pivot bolt in the glove box.

[PeterBiggerstaff]

Thanks David,

I can feel though the gearstick that the ball joints are dry, so I'll grease these up, and put some on the shaft of the pivot bolt before I tighten it further.

I'm just stoaked that I can feel gears now, when I first got the car the gearstick was just flopping around and doing nothing.

[Nicholas R]

Tight enough so that there is no play but loose enough that it doesn't bind up. Be sure to clean and lubricate the pivot bolt and beam. If any of the rubber bushings are worn they should be replaced. Keep and extra pivot bolt in the glove box.

This is not correct. If you leave the shoulder bolt loose at all, it will work its way out as the bell crank rotates about it. That will certainly be interesting while driving down the road.

You should be able to tighten the shoulder bolt and draw a full torque on it, with the end of the shank of the shoulder bolt clamped against the frame. This is how shoulder bolts work; you torque the shank against whatever you're bolting to. This way the bolt is rigidly mounted, and creates a shaft for the bushing/bell crank to swivel around, without actually clamping on the bell crank. You can add washers to either side of the crank if necessary to take up any excess space, but if you do, be sure the washers are not so thick that the head of the shoulder bolt actually clamps on the crank. This all depends on the length of the shoulder bolt. I don't know how long the one DMCH sells is because I bought my own last time from McMaster.

Bottom line, there should be NO clamp load on the bellcrank itself. You should essentially be able to spin the bellcrank freely about the shoulder bolt, with the bolt completely tight.

Dave, maybe if you actually tighten your pivot bolt you wont need to keep one in the glove box :wink:

[Bitsyncmaster]

The epoxy was really bad on my car where the pivot bolt would seat. I did not like the bolt did not have much of a seating surface even after I cleaned the epoxy off that area. They should have used a larger diameter bolt or smaller thread to get better seating.

I see your epoxy is also pretty cracked around there so be sure you have the seating area flat. You need to stick a camera up in the hole to see if you have done a good job.

What I did was machine the arm to install a large bronze bushing and made a mating steel bushing for that bearing. That gave me a large seating area and then I could use a standard bolt to hold it in place.

note the fifth photo is the OEM bolt.

[David T]

The epoxy was really bad on my car where the pivot bolt would seat. I did not like the bolt did not have much of a seating surface even after I cleaned the epoxy off that area. They should have used a larger diameter bolt or smaller thread to get better seating.

I see your epoxy is also pretty cracked around there so be sure you have the seating area flat. You need to stick a camera up in the hole to see if you have done a good job.

What I did was machine the arm to install a large bronze bushing and made a mating steel bushing for that bearing. That gave me a large seating area and then I could use a standard bolt to hold it in place.

note the fifth photo is the OEM bolt.

The pivot bolt threads into a nut welded to the frame and once set is locked by another nut effectively double-nutting it in place. The reason I suggest you keep an extra is because the pivot bolts break occasionally and if it breaks you can't drive the car and you won't be able to find a pivot bolt locally.

[PJ Grady Inc.]

This is not correct. If you leave the shoulder bolt loose at all, it will work its way out as the bell crank rotates about it. That will certainly be interesting while driving down the road.

You should be able to tighten the shoulder bolt and draw a full torque on it, with the end of the shank of the shoulder bolt clamped against the frame. This is how shoulder bolts work; you torque the shank against whatever you're bolting to. This way the bolt is rigidly mounted, and creates a shaft for the bushing/bell crank to swivel around, without actually clamping on the bell crank. You can add washers to either side of the crank if necessary to take up any excess space, but if you do, be sure the washers are not so thick that the head of the shoulder bolt actually clamps on the crank. This all depends on the length of the shoulder bolt. I don't know how long the one DMCH sells is because I bought my own last time from McMaster.

Bottom line, there should be NO clamp load on the bellcrank itself. You should essentially be able to spin the bellcrank freely about the shoulder bolt, with the bolt completely tight.

Dave, maybe if you actually tighten your pivot bolt you wont need to keep one in the glove box :wink:

While you are correct in theory Nick, and also about the McMaster bolt you installed in your car, this is not possible with either bolt used by the factory nor the NOS stock sold by DMCH. Both bolts when tightened will completely bind the shifter pivot due to the bolt shoulder being the same length as the bell-crank pivot bushing. The early part #100277 was thus super-ceded by #105844 which has about an extra quarter inch of thread which allows the bolt to be backed off and then locked in place with an extra M8 Nyloc nut. DMCL also added a wavy washer to allow a slight pre-load to the pivot which eliminated a common rattle due to vibrations from the drive line on acceleration . While this fixed the loosening and the rattle problems it leaves the shoulder unloaded hence all the stress is placed on the thinnest (un-threaded) part of the bolt shoulder which is only 6.3 mm thick. Because of this if for any reason shifting forces increase (Most commonly due to a hydraulic fluid leak and the introduction of air into the system) past the norm the bolt has a tendency to be compromised and break....generally at a later unforeseen date.
The best fix would be to make a hardened shoulder bolt from scratch to the correct dimensions but the failure is rare enough that anyone doing so is guaranteed to loose money on that little project. Since no standard shoulder bolt has the correct shoulder height nor the extra thread to allow double nutting to be performed you must have bought an Allen bolt with a longer shoulder and shimmed it with a stack of wavy washers that allows you to tighten it down correctly? If so that is an imperfect solution because an Allen bolt is a pain to install there and it can't be double-nutted in place but it is surely stronger than the stock setup. Unfortunately in the Delorean universe, as well as the one around us, we live in a world of constant compromise...now if only our fearless leaders in Washington could figure that out our world would be a better place. I know I shouldn't mix advice with politics but in this instance does anybody really care?
Rob

[PJ Grady Inc.]

The pivot bolt threads into a nut welded to the frame and once set is locked by another nut effectively double-nutting it in place. The reason I suggest you keep an extra is because the pivot bolts break occasionally and if it breaks you can't drive the car and you won't be able to find a pivot bolt locally.

Sage advice Guru!
Rob

[SS Spoiler]

Sounds like Bitzy should tool up and offer his upgraded pivot bolt to his
list of items for sale.

[Bitsyncmaster]

Sounds like Bitzy should tool up and offer his upgraded pivot bolt to his
list of items for sale.

DPI could probably offer something similar to what I did. I used an O-ring to give a little pre-load.

[Nicholas R]

While you are correct in theory Nick, and also about the McMaster bolt you installed in your car, this is not possible with either bolt used by the factory nor the NOS stock sold by DMCH. Both bolts when tightened will completely bind the shifter pivot due to the bolt shoulder being the same length as the bell-crank pivot bushing. The early part #100277 was thus super-ceded by #105844 which has about an extra quarter inch of thread which allows the bolt to be backed off and then locked in place with an extra M8 Nyloc nut. DMCL also added a wavy washer to allow a slight pre-load to the pivot which eliminated a common rattle due to vibrations from the drive line on acceleration . While this fixed the loosening and the rattle problems it leaves the shoulder unloaded hence all the stress is placed on the thinnest (un-threaded) part of the bolt shoulder which is only 6.3 mm thick. Because of this if for any reason shifting forces increase (Most commonly due to a hydraulic fluid leak and the introduction of air into the system) past the norm the bolt has a tendency to be compromised and break....generally at a later unforeseen date.
The best fix would be to make a hardened shoulder bolt from scratch to the correct dimensions but the failure is rare enough that anyone doing so is guaranteed to loose money on that little project. Since no standard shoulder bolt has the correct shoulder height nor the extra thread to allow double nutting to be performed you must have bought an Allen bolt with a longer shoulder and shimmed it with a stack of wavy washers that allows you to tighten it down correctly? If so that is an imperfect solution because an Allen bolt is a pain to install there and it can't be double-nutted in place but it is surely stronger than the stock setup. Unfortunately in the Delorean universe, as well as the one around us, we live in a world of constant compromise...now if only our fearless leaders in Washington could figure that out our world would be a better place. I know I shouldn't mix advice with politics but in this instance does anybody really care?
Rob

I will certainly concede to you knowledge of the OEM parts. If this is the case, then I assume Rob is correct about how to use the stock bolt. Like Dave said, I cant help but wonder if this is due in some ways to the thickness of the epoxy coating. Such an odd choice by DMC. Seems like this could have been rectified by simply reducing the thickness of the bell crank hub by .5mm. Wouldn't have even needed to change the bolt.

Personally I think any design that allows a component to rotate about a shoulder bolt, where the bolt itself is not completely fixed, is a poor design. The pin of a rotating assembly should always be fixed. It helps prevent uneven wear and scoring, as well as wobble during movement. It has been several years since I changed my bolt out so I do not remember the specific lengths, but I remember being able to draw a full torque on the bolt without issue, and haven't had any issues since. Looking back I cannot remember if it was McMaster or Fastenal that provided the bolt as I was ordering a lot from both during my engine swap, but it was one of the two.

[David T]

I will certainly concede to you knowledge of the OEM parts. If this is the case, then I assume Rob is correct about how to use the stock bolt. Like Dave said, I cant help but wonder if this is due in some ways to the thickness of the epoxy coating. Such an odd choice by DMC. Seems like this could have been rectified by simply reducing the thickness of the bell crank hub by .5mm. Wouldn't have even needed to change the bolt.

Personally I think any design that allows a component to rotate about a shoulder bolt, where the bolt itself is not completely fixed, is a poor design. The pin of a rotating assembly should always be fixed. It helps prevent uneven wear and scoring, as well as wobble during movement. It has been several years since I changed my bolt out so I do not remember the specific lengths, but I remember being able to draw a full torque on the bolt without issue, and haven't had any issues since. Looking back I cannot remember if it was McMaster or Fastenal that provided the bolt as I was ordering a lot from both during my engine swap, but it was one of the two.

It's not so much the design but the way it is used. As you agree the shoulder bolt should be tightened all the way. The problem is, due to variations, most of the time when you do that there is not enough clearance to allow the pivot to move. And when there is enough to allow movement, there is too much and there is play. The proper way to handle this is not to double-nut but to add or remove shims under the shoulder of the bolt. That way you can tighten the bolt and still have the proper clearance. When the shoulder bolt is not bottomed out and fully tightened you are now bending it at it's weakest point, where the shoulder ends, the diameter is reduced, and the threads begin. Add cyclic loading and it's no wonder the bolts break. Ideally there should have been a Service Bulletin explaining the correct procedure to replace the bolt properly.

[Bitsyncmaster]

I seem to remember having the problem with the OEM bolt and tried to use a washer under the shoulder. It would not work because I could not keep that washer centered since the threads were under cut it would not center. There is very little shoulder area where the bolt seats.

[PJ Grady Inc.]

I've decided to fix this issue using the commonly available Allen bolt using proper shims and tightening so the jam-nut is unnecessary. I just tried a shoulder bolt I had laying around but the shoulder is too long. I'll order some the next size longer shoulder than stock and shim to the correct spec. This could be an easier fix than I thought as I was hung up on the idea of double nutting being necessary but it really isn't. I'll get back to you with the results later in the week.
Rob

[Nicholas R]

I've decided to fix this issue using the commonly available Allen bolt using proper shims and tightening so the jam-nut is unnecessary. I just tried a shoulder bolt I had laying around but the shoulder is too long. I'll order some the next size longer shoulder than stock and shim to the correct spec. This could be an easier fix than I thought as I was hung up on the idea of double nutting being necessary but it really isn't. I'll get back to you with the results later in the week.
Rob

:thumbup: Nice! I love design improvements!! ::thumbup2: