ERA wheelhop

cobred · #1 (**permalink**) 07-18-2007, 09:08 PM

Hi Bob, i'm having a wheelhop problem with my car, era698.Trying to do a burnout the hop is so violent the rear wheels come off the ground. Do you know what effect moving the lower trailing arm pivot to the other hole and or changing the length of the heim joint will have? Thanks, Ed

RICK LAKE · #2 (**permalink**) 07-19-2007, 05:06 AM

Cobred Ed your car is not designed for drag racing.

Road racing, autocross, and silverstone. Era sell a watt's link kit that will help fix the wheel hop problem. I would check all the suspension joints and make sure there is no or very little play. Tire pressure also. I would then have the car alignment done by A PRO shop that has the Jag spacers and clips for the adjustments. Have you have the car wieghted with you in it. Have the balance of the car done before the alignment. If you want to keep doing burn outs, you are going to break that rear. Rebuilt or new, Jag rear is good for 500 hp with a locker in it.You want to do burn outs add water to the tires first and rpm the motor to 2,500 and nail it as soon as the clutch grabs. It looks cool, but just plain dumb.

When it breaks and you have to fix it, hope it was worth it.

I hope the people you are trying to impress will help with the repair of the car.

Rick Lake

cobred · #3 (**permalink**) 07-19-2007, 05:40 PM

Who said im trying to impress anyone? I asked a specific question of a specific person on a forum with his name and company name on it. You didnt even answer my question. If you road race your car and blow it up or crash is it worth it? It is if thats what you want to do with your car. If my rear blows I will fix it myself, because I can. Thanks anyway.

WarrenG · #4 (**permalink**) 07-19-2007, 06:19 PM

Quote:

Originally Posted by cobred

Who said im trying to impress anyone? I asked a specific question of a specific person on a forum with his name and company name on it. You didnt even answer my question. If you road race your car and blow it up or crash is it worth it? It is if thats what you want to do with your car. If my rear blows I will fix it myself, because I can. Thanks anyway.

Actually, Rick did mention some possible fixes for your problem.

RICK LAKE · #5 (**permalink**) 07-19-2007, 06:56 PM

Warren G. If Ed had gone back and looked at the old thread that Wayne Decooney had, He would have seen the Watts kit that was made. I believe either ERA or Duanne is selling them. Not to WORRY, Ed can fix it. He Should not even need to ask about wheel hop problem. Bet he doesn't have a rear cradle cover on the rearend to help keep the caps for the carrier in place. A 30 spline rear with chromemoly stub shafts and axles would also take alot more abuse than the 27 spline. But what do I know

Ps If you could understand the info I put in the reply, the reply about roadracing or autocross and crashing and was it's worth. I go to Run and Gun every year since 98. I go for the fun, I drive within my abilities, fix other cars that break and have a good time. Ed needs to look at a couple of suspension books and understand how a 4 link works. Thanks again Warren, Rick

CJ428CJ · #6 (**permalink**) 07-20-2007, 05:50 AM

Cobred,

Check out this link: http://www.erareplicas.com/427man/jagrear/hop.htm

Also, you may want to email or IM ERA626 here on ClubCobra. He tells me that he recently made some changes to his ERA including changing the pinion angle. He said it solved his wheel hop completely.

I have an ERA and I bought one of the watts kits that Decooney developed. It helped but never completely eliminated the wheel hop. After breaking a u-joint that I believe was caused by excessive wheel hop, I bit the bullet and upgraded to the ERA rearend. That solved the problem completely but the upgrade wasn't cheap.

Chris

cobred · #7 (**permalink**) 07-20-2007, 03:19 PM

Thanks Cris. Thats the reason I wrote in the first place, to ask Bob about adjusting the lower arm to change the pinion angle. I will contact 626.

mr0077 · #8 (**permalink**) 07-20-2007, 06:52 PM

Adjusting the lower arm won't change the pinion angle; I believe you'd need to alter/shim the center section or its carrier to change the pinion angle.

hoppy · #9 (**permalink**) 07-20-2007, 09:43 PM

When I first got my car the wheel hop was awful and I got quite a few suggestions from this board but decided to give ERA a call before I started changing anything. Peter referred me to someone (don't remember his name) that did a lot of the set up there. He gave me specific info about ride height, how many threads the control arms should show past the nut, shock absorber adjustments Etc. After following his recommendation the wheel hop was not totally cured but 90% better. That is where I would start. Later had my 4 wheel alignment set up at Tom's Motorsports in Las Vegas and the difference in wheel hop, handling and tracking was amazing. JMHO.

Manowar · #10 (**permalink**) 07-21-2007, 06:10 AM

0077 is correct. The center section to carrier needs to be shimmed not arm adjustments.
Hopefully Bob has a dimension and procedure and will chime in here.

mr0077 · #11 (**permalink**) 07-22-2007, 01:12 PM

Ed, I must correct what I said earlier...I was just under the rear of mine (inspecting brakes, misc. maint., etc.) and realized that because the center section is carried in the ERA cradle that pivots at the top, changing the trailing arm length will pivot the cradle forward or backward and thus WILL change the pinion angle. I couldn't find any info on trailing arm adjustment in the owner's manual, so now I'm off to research this little tidbit of info. I rarely get wheel hop, not sure what triggers it (usually on dry concrete with good traction), but interested in any fixes through adjustment, etc.

Manowar · #12 (**permalink**) 07-22-2007, 04:03 PM

077
Good point but the purpose as I understand it of the trailing arm dimension is to locate the rear wheel centerline squarely in the wheel opening and to get the wheelbase even on left and right sides. Yes the cage pivots at the top but I would prefer to shim the diff solidly at the upper 4-bolt mount so the torque is not taken solely by the arm's forward mounts.

strictlypersonl · #13 (**permalink**) 07-23-2007, 05:38 AM

The differential casting and the subframe are a system to locate the lower control arm pivots. The lower pivot pin passes through the differential bracket and the holes in the subframe. Because the width of the differential casting may not exactly be consistent, shims are used between the casting and the bottom brackets (and at the top of the casting too) so that there is no residual stress between the bracket and the subframe. The bottom line is that the lower control arm is located by the subframe, with the assistance of the differential casting.

Because of the difficulty of measuring the length of the trailing arms on the early cars, the only thing we specify is the thread showing on the rear rod end and the threads showing past the front lock nut.

If you don't have an older manual, I'll have to dig up the specs, since we haven't used the ball/socket system in quite a few years and I will have to go into some very old backups.

RICK LAKE · #14 (**permalink**) 07-23-2007, 05:40 AM

Mr 0077 Here is what I have gone through to get the car to control wheel hop. I have the pinion angle at 3.0 and a shim under the trans to netrualize the angle and have no vibration for the drive shaft. The lower control arm mounts come in 3 different angles, 0,2, and 4 degrees for the control arms. Here is the problem, I have hard plastic bushing in all my joints. The lower arm pivot bolt does not always aline in the 2 lower corner mounts in the cradle. To adjust the rear toe I had to oblong the mounts and install GM shims between the control arm plate and the 2 bolts that bolt to the bottom of the carrier. This was a 3 hour job on the alignment rack. You need to safety wire these 2 bolts after you get the correct toe readings. I talked to a Jag dealer "A" and was told this is what they do on the old cars of the 70'&80's. You have to remember that toe angle and pininion angle is going to change when doing a burnout. If you want to do burn outs you can also raise the rear spring rates and raise the dampeners on the rear shocks. Raise the car in the back an inch will not allow the wieght transfer as much and make the tires easier to spin. A water bar on each rear tires with a 1 quart tank and little pump from a windshield washer kit will also save the drive train from shock when trying to light them up. Rick L.

strictlypersonl · #15 (**permalink**) 07-23-2007, 07:54 AM

Only one side bracket (XJ - 4 degrees) fits the ERA system.

The use of urethane bushings seems to be a primary cause of wheel hop, which is why the assembly manual specifically proscribes them.

RICK LAKE · #16 (**permalink**) 07-23-2007, 08:54 PM

strictlypersonal Bob you are an EXCELLENT ENGINEER and have the paper to go with this. The steady improvement on the ERA car speaks for itself. You know if the rear assembly is not setup with the correct wheel alignment, balance of wieght, a good posi rear, shocks that are too soft, tires that don't have the right pressures or a low rpm, drop the clutch can all cause wheel hop. ERA is not the only cobra company that has wheel hop issues, Watts linkage kit and link kits for the jag rear are being sold on Contemp's cobrafor they when out of business. Some of the other manufactors have added links to control the jag that is only bolted to the top 4 mounting bolts. Will a bearing last longer ( if greased ) in a pivot joint that a poly plastic bushing yes. I am running the white bushing that get grease every race and I see no play or deflection in the joints. You also have to note that doing burnouts is not easy on the drive train and the cobra with a jag rear was not designed for this. You engineered a cobra that is an all around car for doing it all, it also eliminates vibration to the driver and the car. The new graphite bushing coming out are harder than the white ones. How much deflection is there? which point is causing the hopping? It would have to be the outer pivot point on the lower control arm. You have a rod to keep the lower arm in place but the front on that rod has a rubber mount. Is it possible that this mount is compressing? Causing toe to change? Play in the stub shafts in the uprights, Doug at your shop set mine up for the right end play, is it possible that when the car gets up on the tire it pivots in or out and cause the same problem?

Sorry Bob, it is alot more than just those 2 mounting points causing all the problem. Rick L. Ps my car doesn't have wheel hop, it squats and leaves. I don't have my watts linkage on my car either.

cobred · #17 (**permalink**) 07-23-2007, 09:12 PM

I just got off the phone with era626 as cj428cj suggested. He solved his wheel hop problem by moving the front trailing arm mounting bolt to the lower hole and unscrewing the heim joint about 3/4 of an inch, thus bringing the pinion down in the front. It doesn't mean it will work on all cars but ill try it on mine and report back. I wish I had thought of that.