Lowered with RB springs, running Tokico blues, and springs are about 15 yrs old, so probably sitting lower than the stated 3/4" drop when new. The back end has a habit of swinging around rapidly when cornering quickly which could be a combination of old worn out rear arms and hard tires. Anyway, I'm sure the rear bump stops are getting heavy action because theres a shiny metal ring on both lower spring perches where the bump rubbers hit.

in hopes of removing some of the rebound when I hit a bump, I cut about 3/4" from the bump stops today when I was under there doing rear end gear oil and brake cleanup.

What's the agreed amount of shortening of the rear bump stops to avoid binding up the rear end with my setup? TIA,

 

What bushings?

 

Running 34 year old stock OEM rubber bushings in upper, lower, and locator bar bushings. This car is a nice weather driver that spends about 95% of its time in my 3rd garage bay. That'll all get replaced with NOS Mazda arms with new bushings in the near future. Mazdatrix has all the arms from Mazda for about $700.

 

I did this to my bump stops when I cut down my RB springs by one round with no ill effects.

 

No ill effects, or an improvement in comfort? I took it for a quick drive yesterday and it seems to have lost the ba-BUMP rebound when going over moderate bumps at speed. I had my wife in the car too, just to add a little weight. Much improved and watching for signs of any rubbing at full compression.

 

Yeah ive been there too when i put my RE Speed perches and springs in even though going not much lower than stock. Cut off 3/4 with a big bread knife. It works well, no ill effects.

 

I use GM elastomeric jounce bumbers on both my cars. They give the rear axle a much softer landing and don't upset the car as much. When I bottom out, there's no loud "thunk". Below is a link to a part that can be modified to fit by cutting of the stud and the alignment tab and drilling a hole to accommodate the OEM M10 screw.

 

^ that looks good. What did you use for the fronts? At the time i did my suspension I wanted to use some kind of fancy aftermarket progressive bumpstops but was both over whelmed and underwhelmed at the same time at what was available and what could fit, i ended up just cutting the existing ones front and rear. The stock rears on mine were hard as nails too. I dont know what they are like new but you would be in all sorts of trouble bottoming out hard on them.

 

Also try disconnecting the rear sway bar, it will improve the rear grip. The bar is more designed for reducing sway at stock ride height with stock springs. Once you lower the car and use stiffer shocks it doesn’t help much. Here’s what I found after some track days with different setups.

RB springs, Tokico blues, stock sway bars and cut bump stops: fairly neutral but lots of body roll.

Added front and rear RB sway bars: oversteer like crazy, snap oversteer under any sort of braking.

Disconnected RB rear sway bar and kept front: mild understeer but overall quicker lap times.

RB front and stock rear: just about right but leaning toward understeer.

 

The first setup is perfect for autox, even though it rolls it keeps the car smoothly loading unloading the contact patches of the tires. The last 2 setups using the RB sway bar is a good high speed track setup, you want a bit of understeer to keep it steady under braking.

All depends on what you want. Great info.

 

If I were only doing autox, I might consider using both front and rear RB sway bars. The oversteer is quite manageable in 1st and 2nd gear. It's only those 50 mph 3rd gear turns that I got past my comfort zone. Light steering, very little steering angle, and then all of a sudden it starts coming around on you. You counter steer, but then it suddenly regains grip and whips you back around the other way. I saved it 3 or 4 times but eventually ended up in the gravel...and that was all she wrote for the rear RB bar. Went back to the pits, disconnected the bar, and shaved 2 seconds off my time on the next session, but it just felt pushy. So my next outing I threw the stock bar back on and it was back to carving turns nicely. But if I were doing autox, I'd work with it some more and use that oversteer to get around the cones quicker.

 

I have Racingbeat springs and AGX adjustable shocks. I was looking at my rear suspension yesterday and I noticed the ring under the bump stop. So would I need to trim them down?

 

The ring means you've definitely been hitting them. If you haven't been driving aggressively you may want to trim 1/3 off them. That's what I did when I put my RB springs in.

 

I drive the car pretty aggressive. I plan to start autox after I tune my carb. Then after getting some experience start going to the track. Should I cut half of it? Or still just go with the 1/3?

 

You can't put more on after you cut it off, so I'd start by cutting off 1/2"-3/4" and see what you think. Yours have definitely been rubbing. Once you cut them, spray the lower perch with black spray paint and then take it for a drive. If rubbed shiny again, you may need to cut some more. You can remove springs by lifting the body, lettting the axle hange down, and then lift and twist the springs out of the back.

As a followup, the car got a lot more stable in the rear after replacement of all links and the Watts link and pivot, which had rubber bushing cracking and falling put. Surprisingly, the bushings on the arms didn't look half bad, so keeping as spares. This is after 227k miles of city driving mostly. I was expexting them to be torn to pieces,... the new rubber bushings are definitely softer and more pliable and the car drives much more predictably.

After conflicting reports of Poly bushings i the rear, I stuck with OEM which I know runs well and long,

 

The goal is to get the bump stops to engage around the same time they would from the factory. If you dropped your car 1" to 1.5", you'll be cutting off about the same amount (which is roughly 1/3 the total height). They should not engage under normal driving conditions unless you a) hit a speed bump or rough abrupt patch of pavement or b) you are cornering at racing speeds close to the limit of performance summer tires (ie, not something anyone does on the road unless they're about to hit a telephone pole). The bump stops, contrary to the name, are actually a functional part of the entire suspension system. They serve to increase effective spring rate after the coil spring has a significant load. However, if they engage before the spring is fully loaded, they cause an abrupt change in effective spring rate rather than a gradual one. This can cause an immediate loss of traction sending you *** backwards into a wall (or set of cones). Cut them down too much and they may never engage, you'll suffer from increased body roll and have the general sense of a sloppy suspension. Tuning the bump stops is widely popular in oval racing, as it allows for running softer spring rates that promote a certain amount of body roll and control while still providing the spring rates necessary for max grip.

 

Thanks LongDuck, I am going to take your advice and just trim a little and then go from there.

Thanks chuyler1 for breaking down how the bump stops work. I didn't know how they worked and the effects it had on the rear suspension.

 

Indeed thanks to chuyler1 and LongDuck. I have RB Springs and Tokico Blues and took 5/8" off my stock bump stops today. No more bottoming out...I have a perfect test spot nearby, just the right frost heaves to throw your *** out of the seat as rear axle goes over.

 

It's a simple mod that vastly improves comfort and performance. I'm amazed a lot of guys are still driving around on full-length stops like I did for so many years. Cheap and easy - well worth the time to do it.

 

Yep, I was missing one of mine and while I was cutting a coil from the RB springs all around I took the good one, cut it in half and now have bump stops on both sides but shorter so they only get hit on an extremely hard corner. Very noticable.

 

Have you guys got any pictures of the cut stops? Any mounted ones?

 

Here you go...this is just before I cut mine down. I put chalk marks on the perch to see if I was hitting them. There's a 13mm bolt that holds the stop to the underside of the body. You really do need to remove them to do a nice job cutting them.