front driveline vibes

How common is this with 6-8 inch lifts. is getting a longer DL the only real fix.

guarantee with that much lft an you will need at the bare minimum a sye.

Well my prob. is that i just called RE with some final q's before i order everything and they kinda scared me. My plan is to run RE7.5 with stock isolator with their 4.5 leafs 1.25 shackles and 1.5block. I have an AA SYE and custom LA kit and ARB's front and rear. I will also be installing their adjustable etreme duty TB and bracket brake lines etc. They said that i will have issues with the front DL and that these coils actually give like 10" of lift. what is going on here. is my plan a good one or is there something im not aware of or thinking about. this will be my DD. thankx

dellstopjeep said:

guarantee with that much lft an you will need at the bare minimum a sye.

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You don't need a SYE for the front driveline - it already has a fixed yoke. You also should not need a new driveshaft unless you are moving the front axle forward. I have 8" of lift with the stock driveshaft.

The issue with the front end is simple: as you lift, you either have to create angle at the u-joint, which will cause vibes even in 2wd unless you have lockout hubs, or you have to sacrifice caster. At 6" of lift, a perfectly aligned front driveshaft equals ~0 degrees caster. This won't be driveable on the highway. You can run some angle in the driveshaft, but not more than about 2 degrees. At 8" of lift, forget about finding a caster/driveshaft angle balance.

This is the big problem with the D30 in my opinon if you ever use 4wd at any speed. Lockout hubs are fine for 2wd, but do nothing for 4wd.

The best solution is to have both lockouts and a front axle with cut and turned knuckles, allowing proper caster for your lift with a vibration free front driveshaft for 4wd use, and lock it out entirely for 2wd use to save wear and tear and quiet things down considerably.

I have 8" of lift, and I can run full time 4wd at 65 mph smooth as silk. I live in a snowy climate, and I would not sacrifice this capability. The cost was a custom built front D44.

Nay

wannabe said:

Well my prob. is that i just called RE with some final q's before i order everything and they kinda scared me. My plan is to run RE7.5 with stock isolator with their 4.5 leafs 1.25 shackles and 1.5block. I have an AA SYE and custom LA kit. I will also be installing their adjustable etreme duty TB and bracket brake lines etc. They said that i will have issues with the front DL and that these coils actually give like 10" of lift. what is going on here. is my plan a good one or is there something im not aware of or thinking about.

Click to expand...

The 7.5" coils do not give 10" of lift. They give 7.5" of lift, maybe a hair less. Read my other post about the front driveshaft. They are correct - it is going to vibrate if you are keeping the D30, and at a minimum you should be looking at a set of 5 on 4.5 Warn lockout hubs.

Oh, if this will be your daily driver, why are you thinking about an 8" lift? That's no fun unless your daily drive is short. I daily drive mine, but it's only a mile to work and I ride a bike the rest of the time. A longer commute would be painful, and the wear and tear adds up. Get an old Honda for the daily drive, trust me.

Nay

Disagree, i had 8" lift in my DD with no driveline vibes. Lengthened the front driveshaft and caster was about 3°, no probs with my 30 mile commute daily. You will more likely have to fight death wobble issues than front driveshaft vibes. SYE rear is mandatory with that lift height.

XJoachim said:

Disagree, i had 8" lift in my DD with no driveline vibes. Lengthened the front driveshaft and caster was about 3°, no probs with my 30 mile commute daily. You will more likely have to fight death wobble issues than front driveshaft vibes. SYE rear is mandatory with that lift height.

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Well, that is my point. Caster goes too low and you end up with shimmy and tracking problems, and too high and you have driveline vibes. You are more likely to deal with which ever issue you choose. It is nothing more than how you set the pinion angle. Fix the driveline angle so there are no vibes and you get caster problems, fix the caster (by increasing u-joint angle) and you will get vibes.

My XJ would not track straight (it zig-zagged from side to side) at anything over 55 mph when caster was below 4 degrees, and it shimmied really badly over any bump at speed (I had enough dampening to prevent death wobble). When I raised caster the front driveshaft vibrated. Even at 6" of lift I couldn't find a balance, and I tried everything including a $500 driveshaft with double cardans on both ends (vibrated worse than the stock setup).

I'll give you one caveat: now that I have radius arms (long arms) on a front D44, my rig tracks very nicely with good steering return to center at about 3 degrees of caster.

But the point RE was making remains the same: at 8" of lift it is only luck if you can lower caster just enough to prevent front driveline vibrations. Basically you lose one degree of caster for every inch of lift if you keep a zero degree pinion angle in relation to the driveshaft (as is optimal for a CV (double cardan) driveshaft such as on the front of your XJ).

If stock was seven degrees of caster, then at 8" of lift you are at zero caster, maybe slightly negative, if you keep the pinion in line. Now, you can get away with about three degrees of pinion angle and no vibes in 2wd, but that is typically a maximum. So drop the pinion three degrees and pick up three degrees of caster. Now you have between 2 and 3 degrees of caster and a driveshaft that is on the edge.

Will your XJ drive well with this amount of caster? I don't know and neither does anybody else. I wouldn't count on it, personally. You can install the two degrees caster correction ball joints, and that would probably be enough. I did that, and one of them rotated in the press joint and I had to do it all over again. Locktite those babies with the really serious stuff if you plan that mod, otherwise your caster correction can quickly become a camber problem as the balljoint shifts.

Anyway, here is the simple part. Plan a front D44 if you are going to 8" of lift. There are a few D30 diehards out there, and that's great, but most people at this height get rid of the D30 eventually simply because they get tired of polishing the turd.

Joachim has a 60 up front now, if I'm not mistaken. That's a far cry from an occasionally shimmying D30 .

Nay